Hydrographic measurements in support of Japan/East Sea circulation, ventilation and frontal process studies

Mark Warner
University of Washington
School of Oceanography
Box 357940
Seattle, WA 98195-7940
(206) 543-0765; mwarner@ocean.washington.edu

Vyacheslav Lobanov, Pavel Tishchenko and Vladimir Ponamarev
Pacific Oceanological Institute, Far Eastern Branch
Russian Academy of Sciences
43, Baltiyskaya Street
Vladivostok, Russia 690041
poi@stv.iasnet.ru; lobanov%dana1@poi.marine.su

2. Technical information.

Large-scale hydrographic/CTD work is proposed as support for the components of the ONR Japan/East Sea DRI. Our scientific objectives are:

(1) determining the full vertical structure of the major components of the circulation, including the Liman Current, East Korea Warm Current and Tsushima Current, as well as a possible deep western boundary current and the other portions of the deep circulation which likely are coupled with the near-surface circulation;

(2) understanding the origin and maintenance of the subpolar front in the central JES, and the potential for topographic control;

(3) obtaining a complete synoptic view of the vertically-layered structure of the JES;

(4) using chemical tracers including nutrients, oxygen, and chlorofluorocarbons to discern the major circulation paths and relative importance of the northwestern versus the northern (Tatar Strait) regions for intermediate and deep overturn;

(5) characterizing the vertical structure of at least one eddy in the subpolar convective region or subpolar front and one in the East Korean Warm Current south of the subpolar front.

We propose that there be two surveys of the JES: one in summer to comprehensively map the major features in the horizontal and vertical, and one in winter with sparse large-scale coverage concentrated in the northern JES and with attention to local features - the subpolar front, the Liman Current and carefully chosen eddies.

Observations include full-column CTD profiles, salinity, oxygen, nutrient and chlorofluorocarbons. Discrete sampling by other groups for other tracers would be easily accommodated. Our data sets would be available to all JES participants immediately following each cruise. Our experience is that our fully integrated preliminary data sets are, in quality and ease of use, nearly comparable to our final data sets which will be of the highest achievable standards.

Various tools, including a box inverse model, will be used to analyze the circulation. Analysis of existing data sets, including the long-term routine hydrographic and concurrent surveys by Japanese agencies, will augment the new data collection.

2.b. How the proposed research effort will respond to the objectives of ONR.

The proposed research will support the Japan/East Sea DRI through provision of new information on the large-scale circulation, forcing and eddy field of the JES, and synoptic in situ information on the temperature/salinity structure useful for calibration and context for the major profiling observational programs. Specific attention will be paid to the relation between topography and the circulation, subpolar front and quasi-permanent eddies. The proposed analysis will benefit ONR modeling for this region through provision of a synoptic, complete coverage of the full water mass structure and estimate of circulation strength, and through differentiation between the variously proposed sites for strong winter buoyancy forcing.

2.c. Statement of work (list of tasks, responsible investigators and cost).

Analysis of both the new hydrographic data collected through the Japan/East Sea (JES) initiative and of historical and routine Japanese survey data is proposed to fulfill a number of scientific objectives for JES circulation, prominent eddies, subpolar front structure, and ventilation. This list of objectives is broad and explored in depth in section 2.d, reflecting the diverse uses of hydrographic data for:

- highly accurate surveys of the whole of the JES
- detailed surveys of the full water column structure of eddies and the subpolar front,
- in situ interpretation of surface information including that from satellites and drifters
- calibration of other profiling in situ instruments.

A very brief outline of the tasks is given here with costs. Rationale is given in section 2.d.

2.c.1. Summer 1999 hydrographic survey ( Fig. 1a).

30 days at sea to collect CTDO, salinity, oxygen, nutrient and CFC data is proposed. Lynne Talley will have overall responsibility for collection of all but the CFC data; Mark Warner is responsible for the CFC's. The normal size of the party required for this work, assuming two 12-hour shifts is: 6 to 7 technicians from the Oceanographic Data Facility, 4 in the principal investigator's group for deck, console and salinity analysis work, and 2 chemists for CFC's. The group of 6 "ODF" technicians and 4 from the PI's group will be made up of: 3 actual ODF technicians, 3 chemists from POI to assist them (Pavel Tishchenko and 2 co-workers), 3 from Scripps (Talley, a programmer and a graduate student), and 1 from POI (Vladimir Ponamarev). Both CFC chemists will be from U. Washington (Warner and assistant).

ODF will supply all equipment, calibration and processing necessary for production and integration of high quality data set at sea. At-sea data processing, calibration and processing capabilities allow serious use of data in near real-time, and availability of the complete data set to all investigators by the end of the cruise.

The 30 day estimate is based on an actual need for 24 days to complete the cruise track shown in Fig. 1a with about 150 stations to the bottom, assuming use of Pusan as port, plus 6 days for tasks carried out by other investigators. If the track in Fig. 1a is occupied by 2 ships rather than 1, then more time is available for other tasks or the cruise length can be reduced.

Pre-cruise tasks: Lobanov, Talley and Ponamarev pursue AVHRR image analysis, and communicate with D.-K. Lee and P. Niiler on drifter tracks and AVHRR, to provide guidance for adjustment of the final cruise track and the limited special studies of eddies and the subpolar front. POI AVHRR analysis and travel to meetings will be proposed separately to NICOP and so is not included here.

Post-cruise tasks: Talley finalizes data quality assessment and makes data available to all JES investigators through a password-protected website. Warner finalizes CFC data processing and quality assessment.

Cost breakdown including salaries, travel, supplies and equipment and indirect costs:

CTD/O2, salinity, oxygen and nutrient analyses for 30-day cruise.

$226,879 (SIO/ODF - 3 people, all equipment, supplies)
$47,246 (SIO/Talley - 4 people for cruise including Ponamarev, excluding student salary/tuition)
$27,276 (POI/Tishchenko - 3 people for cruise)

$92,622 (U. Washington/Warner - 2 people, all equipment, supplies)

2.c.2. Winter 2000 hydrographic survey ( Fig. 1b).

30 days at sea to collect CTDO, salinity, oxygen, and nutrient data is proposed. (CFC data collection could be shifted to this cruise, but only one CFC cruise is proposed.)

Other than for CFC's, the tasks and cost assumptions are the same, but costs are slightly higher for the next year. Cost breakdown including salaries, travel, supplies and equipment and indirect costs:

CTD/O2, salinity and oxygen analyses for 30-day cruise

$231,721 (SIO/ODF - 3 people, all equipment, supplies)
$50,059 (SIO/Talley - 4 people for cruise including Ponamarev)
$28,270 (POI/Tishchenko - 3 people for cruise)

2.c.3. Data analysis.

Analysis of the newly-collected and historical data sets is assumed in all three years. Talley's own analysis in years 1 and 2 can proceed with the computer and office maintenance included in the cruise costs. The graduate student salary and tuition are separated out and indicated here.

Talley, Ponamarev, Warner and the graduate student will be principally responsible for initial circulation and water mass analysis, including developing an inverse box model using the new hydrographic data. Talley and student will pursue historical NODC data study especially for characterization of the subpolar front and the relation of circulation features to topography, and collaboration with Japanese groups collecting hydrographic/CTD data along routine survey sections, and contact with Japanese groups monitoring the three principal straits.

Warner and Ponamarev will study ventilation using the hydrographic and CFC data.

Lobanov and Talley will pursue the eddy evolution and subpolar front study, using the new hydrographic data and AVHRR analysis. Analysis of altimeter data should also be included in this, perhaps through collaboration with another JES DRI investigator. A proposal to NICOP to fund Lobanov's group's work will be made.

Year 1:

$29,378 - SIO graduate student salary and tuition

$30,190 - SIO graduate student salary and tuition
$28,468 - U. Washington - Warner

$66,992 - SIO - Talley and graduate student

2.d. Description.

2.d.1. Introduction and summary of needs for hydrographic data collection

The proposed hydrographic surveys and hydrographic data analysis, undertaken in conjunction with analysis of other data sets, are aimed at the specific objectives outlined in each of the science sections below. The overall goal is to obtain a quantitative description of the Japan/East Sea circulation and a coherent picture of its water mass distributions. Highlighted are the roles of the energetic eddy field of the JES and of topographic control.

Because all of the central to bottom water in the JES is manufactured within the sea, the overall gradients in properties are very small, requiring highly accurate measurements. CTD and salinity profiles collected by highly qualified groups with careful calibration will provide the basic density field for dynamic calculations, and for mapping properties on isopycnals. Tracers such as oxygen, nutrients and CFC's will provide needed additional information on sources of waters in isopycnal layers, given that the salinity signal is very weak.

The hydrographic surveys will not in themselves provide sufficient resolution of the small-scale features which may contribute greatly to mass flux within the JES - the eddies associated with the boundary currents and with the subpolar front. Nor will they provide direct velocity measurements or continuous highly-resolved covereage of the sea surface. On the other hand, these other programs cannot provide the highly accurate subsurface information, from top to bottom, which is required for a complete mapping of the circulation and which is provided by hydrography. The hydrographic measurements will also provide the required level of calibration of the other instruments. Thus integration of the hydrographic measurements with the other JES programs is central to the success of the whole of the DRI.

In the following three sections, we examine particular elements of the JES circulation, eddies and ventilation for which our proposed hydrographic work will be well suited - these are clearly the scientific issues which interest us the most. They should also give a flavor of the range of projects which can benefit from hydrographic data collection in the JES.

2.d.2. Japan/East Sea circulation and subpolar front

The following discussion proceeds from the largest, all-Pacific scale to the Japan Sea circulation, to the subpolar front, in order to provide a logical development. Highest priority in research will be placed on Japan Sea processes.

2.d.2.1. The JES relative to North Pacific circulation and ventilation. The Japan/East Sea is a marginal sea at the western boundary of the North Pacific, connected by two straits (Tsushima and Tsugaru) to the North Pacific and by two straits to the Okhotsk Sea (Soya and Tatar), all of which have sill depths less than 130 m. Thus with a maximum depth of 3725 m and a mean depth of 1350 m, much of the volume of the JES is isolated from exchange with the adjoining North Pacific. On average, inflow occurs in the south at Tsushima Strait and outflow at the other three straits.

The Japan/East Sea's role in conveying saline water from the latitude of the Kuroshio up to the much fresher subpolar regions of the North Pacific is central to the latter's ventilation and overturn. Inflowing water at Tsushima Strait is warm and saline - warmer than 10 to 14°C, salinity of about 34.5-34.7 psu, and density less than about 26.0 sigma theta (Lim and Chang, 1969; Isobe et al., 1994; Kim et al., 1991). The water which exits the JES through Tsugaru and Soya Straits is considerably fresher than the inflow, but is nevertheless much more saline than the fresh waters found in the North Pacific between Honshu and Hokkaido, and in the Okhotsk Sea. The saline JES water between Honshu and Hokkaido preconditions this region to have the highest surface density in winter of any other location in the North Pacific (Talley, 1991). The effect of the saline JES outflow on maximum surface density in this region is clear in Fig. 3 from Talley (1991), showing maximum surface density based on all available NODC hydrographic data. Thus the JES is a major factor in setting the density and properties of the North Pacific's main salinity minimum (maximum directly ventilated depth).

Outflow from the JES through Soya Strait is even fresher than that through Tsugaru Strait, but still retains high enough salinity that it is the major source of salt for the Okhotsk Sea. This is a major factor in making the dense water formation in the Okhotsk Sea considerably denser than that in the Bering Sea, which lies at a higher latitude but which has no saline water source. Both the Okhotsk and Bering Seas are connected to the North Pacific through much deeper straits than is the JES, and so their dense water production has a direct effect on the North Pacific. The densest water in the Okhotsk and Bering Seas is created through brine rejection during ice formation on the shelves. The ambient water in the Okhotsk Sea into which the brine mixes is more saline than in the Bering Sea. Hence the Okhotsk Sea produces the densest water in the whole of the North Pacific, excepting only the JES (Talley, 1991; Talley and Nagata, 1995).

Of course within the JES, the overturn in the north is fed much more directly from the saline inflow, and so the densest water created in the JES (up to 27.4 sigma theta) is much denser than in the open North Pacific or Okhotsk Sea, as is apparent in Fig. 3 from Talley (1991). The maximum density water which flows out is 26.4-26.7 sigma theta through Tsugaru Strait (Talley et al, 1995) and 27.0 sigma theta through Soya Strait (Talley, 1991). (The latter mixes with fresher water in the Okhotsk Sea, and so by the time it contributes itself to dense water formation in the Okhotsk, it is considerably fresher. After cooling to the freezing point, it reaches a density of only 26.7 to 26.8 sigma theta.) Thus the very dense overturn in the JES does not directly flow out into the North Pacific. All of the water in the JES denser than about 27.0 sigma theta must upwell. This and the existence of the two major methods for dense water production - ice formation and open ocean convection - make the JES an interesting sea for studying most aspects of the overturning circulation, which otherwise require data sets and models for much larger basins, or indeed the globe.

The overall circulation of the JES is relevant to the North Pacific mainly through this advection of saline water northward, to re-enter the North Pacific where the latter is much fresher.

Objective:

To quantitatively and simply determine factors setting the maximum density in the JES, Okhotsk Sea and North Pacific

Approach. The maximum density of overturn in the JES and Okhotsk Sea is likely set mainly by the surface salinity in the areas of ice formation, where surface water reaches the freezing point. Maximum density in the North Pacific just south of Hokkaido is more complex as ice formation does not occur there, so there is no obvious choice of minimum surface temperature. However, salinity appears to be a controlling factor for maximum surface density here too.

The simplest approach is to quantify the bulk salt balances in the JES - a very simple calculation is of the maximum possible overturn density given the inflow salinity (such as was done for the Okhotsk Sea using Soya Current characteristics in Talley, 1991). The surface layer salinity presented to atmospheric forcing in the overturn regions (whether by convection or plume formation under ice) depends on local fresh water inputs as well. A calculation of the average freshwater balances in the JES will be based on the new hydrographic data collected in a closed grid ( Fig. 1) which is amenable to making the necessary mass balances. The freshwater balances will yield a prediction of fresh water input whether by precipitation or runoff, and insight into what sets the surface layer salinity in the northwestern and northern JES, and the salinity of the outflows into the Okhotsk through Soya Strait and into the North Pacific through Tsugaru Strait. Historical NODC data will be central to the overall analysis.

2.d.2.2. JES processes in comparison with other marginal seas; forcing of the JES circulation. It is often remarked that the JES is much like a small North Pacific, with an anticyclonic, warm, saline subtropical circulation and cyclonic, cold, fresh subpolar circulation, separated by a subpolar front. In miniature it represents a number of important buoyancy forcing processes: open ocean convection especially in a region of very strong, winter continental winds which demonstrably produces a 500-meter thick mode water, and which may produce deep or sometimes bottom water; ice formation with polynyas which results in brine rejection and dense water formation; intense mixing across fronts. No other marginal sea has this suite of processes, which are hence easily studied with a relatively small commitment of resources compared with say the full North Pacific.

The JES is typical of the other two North Pacific marginal seas - the Okhotsk and Bering - in the relative importance of eddies to mean flow compared with the open North Pacific. (See AVHRR images in Fig. 2 for examples of the eddy field evident in SST.) It is possible that due to the small size of the marginal seas, reflection of energy from boundaries is a stronger process than in the open ocean. Major change in strength and even reversal of the western boundary currents in the JES has been noted, and is likely due to the short east-west scale of the sea relative to the wind forcing, much as in the Arabian Sea.

The JES also has its own peculiar characteristic - throughflow of water originating in the East China and Yellow Seas, perhaps containing some portion of Kuroshio water, with exit at the Tsugaru and Soya Straits, of much modified water. This throughflow affects the circulation of the JES: the subpolar front appears to be more the northern edge of this throughflow, which attempts to move westward upon entry to the JES, rather than the typical subpolar front found near an annual mean zero wind stress curl location. The latter type of subpolar front (North Pacific) likely originates from separation of a subpolar gyre western boundary current and seasonal wind stress convergence (e.g. Yuan and Talley, 1995).

A number of numerical modeling studies have looked at the throughflow in the JES (for instance Minato and Kimura, 1982; Nof, 1993; Ohshima, 1994), with emphasis on the sea level differences which cause a portion of the North Pacific's western boundary current to enter and flow through the JES. These studies produce reasonable estimates of the magnitude of transport through Tsushima Strait (order 1 to 3 Sv). In the simplest terms, they show the Tsushima Current as a shelf-wave type flow (Kelvin-wave if vertical boundary) which proceeds northward along the boundary. Dispersion westward by Rossby waves broadens the current. The East Korea Warm Current may be the extreme result of the latter.

Wind stress and wind stress curl should also create circulation within the JES, which should be superimposed on the throughflow. The cyclonic circulation of the north (Liman Current) is not created by the throughflow, but must be forced by local winds and buoyancy forcing. Lee and Niiler (personal communication) have used NSCAT winds to show that the very strong winter atmospheric jet which penetrates the JES at Peter the Great Bay has an associated wind stress curl which is negative to its west and positive to its east. Even the Hellerman and Rosenstein (1983) winds show this winter pattern very coarsely. In the summer, the much weaker monsoon winds have associated positive wind stress curl. These may be related to the reversal of flow at the western boundary, the occurrence and strength of eddies important to mixing and circulation (such as eddy D in Fig. 2), and seasonal shift in the average latitude of the subpolar front (section 2.d.2.4 below).

Objective.

To study seasonal variations in the circulation of the JES, and determine how they relate to changes in wind stress, wind stress curl and buoyancy forcing. By studying the changes, differences between local forcing and remote (Kuroshio) forcing on the circulation might be clarified. To help determine if possible which portions of the circulation respond to local forcing and which respond to external forcing.

Approach. We would document the seasonal changes through analysis of hydrography, AVHRR, ECMWF winds and surface fluxes and possibly altimetry data. We would work with those making surface drifter measurements (Niiler and Lee; others?). We would work with JES modelers to help discern the effect of local forcing on the circulation north of the subpolar front versus that of the Tsushima Current and EKWC.

2.d.2.3. JES circulation and relation to topography.

The basics of the JES surface circulation have been presented in many other works; we have chosen the cartoon from Tomczak and Godfrey (1994) (Fig. 4). Depicted are the Tsushima Current and its branches, the East Korea Warm Current, flow along the subpolar front, and the Liman Current in the north. The simplicity of this cartoon belies the major discussion around the precise sources of the Tsushima Current (e.g. Beardsley et al., 1992), the nature of its branching, the role of eddies in the subpolar front (which appears in AVHRR - Fig. 2 - to be just a series of eddies and mushrooms) and seasonality in the Liman Current. Nevertheless, it is a useful large-scale view.

The Tsushima Current "branches" have been linked to topography. Katoh (1994) shows that the "first branch" remains close to the 100 meter isobath along Japan, and that the faster and more variable "second branch" tends to fall somewhat inshore of the 200 meter isobath. There is some evidence for such topographic steering also in the surface drifter tracks in the Tsushima Current (Lee et al., 1997), which are also strongly affected by the shape of the Japanese coastline (bays, peninsulas and islands). The "third branch", which is also essentially the East Korea Warm Current (EKWC), is depicted as separating to flow eastward from the Korean Coast at about the location of Ulleung Island, which is also where the bathymetry bends eastward around the Ulleung Basin (e.g. Fig. 1). Thus topographic steering of the shallow Tsushima Current branches appears to be important, as it must be if the Tsushima Current is functioning in a sort of rectified shelf-wave mode with the beta effect spreading its influence westward through Rossby waves.

Kim et al. (1996) have suggested that the separation of the EKWC is affected by the influx of cold water from the north in the North Korea Cold Current (NKCC). This cold, fresh water ("East Sea Intermediate Water" salinity minimum) is often found inshore and as far south as the western channel of Tsushima (Korea) Strait.

The intermediate and abyssal depth circulations are much less well studied as a whole than the near-surface circulation. The simple reason is that the intermediate (salinity minimum) to bottom waters are all formed within the JES; the deeper water masses have very little contrast in salinity and temperature, with the deep layer being nearly adiabatic. Thus observational programs have concentrated on the upper part of the JES, and almost no observations in the right regions (deep straits, across boundaries and rises, deep basins) and with the right station resolution have been made to study the deep geostrophic shear.

Some work has been accomplished on deep water mass structure using sparsely-distributed station profiles which show the interrelation of deep waters in the three deep basins (Ulleung, Yamato and Japan). Gamo et al (1986) show, with 9 CTD stations in the Japan and Yamato Basins, that the adiabatic bottom water layer is warmer and has lower oxygen in the Yamato Basin than in the Japan Basin, indicating that the Yamato Basin is, understandably, farther removed from the JES deep ventilation source. Interestingly, the profiles they show in the deep passage connecting the two basins do not have the adiabatic bottom layer - it is not clear whether greater station resolution across the deep passage would find adiabatic layers which connect between the basins. However, one might speculate that mixing in the passage is rather vigorous, and disturbs the adiabatic deep layer, which is restored but at a higher temperature once the water has been advected southward into the Yamato Basin. Our new survey would provide sufficient coverage to determine this, and allow some estimates of deep diffusivities based on estimates of flow through the deep passage, much as we have done recently for a deep passage in the Indian Ocean (McCarthy et al., 1997), following work such as that for Vema Channel (Hogg et al., 1982) and for the Samoan Passage (Roemmich et al., 1996).

Kim et al. (1991) analyze one of the few closely-spaced surveys of a JES deep basin - the Ulleung - and speculate on the strength of the current through the passage entering this basin from the northeast, based on the clear records in the sediments of the passage of a strong flow.

Otherwise, little has been shown of the actual circulation or dynamic calculations relevant to the deep waters. The intermediate depth smoothed dynamic height shown in the ONR workshop report on the JES (Riser and Ramp, 1996) is one depiction of the intermediate depth flow (Fig. 5). The map shows a remarkably coherent western boundary current feature, which is anticylonic at 1500 relative to 2500 dbar. Min et al. (1996) and Min, Weiss and Kim (manuscript in preparation) show evidence in CFC's at the deepest levels in the JES of flow from north to south along the western boundary - evidence of a deep western boundary current carrying newly ventilated water from the northern JES to the Ulleung Basin without as direct a connection into the interior of the Japan Basin. This is consistent with the Riser and Ramp figure if flow at the bottom is stronger than at 1500 dbar, which is normally the case with deep western boundary currents. Kim et al. (1991) speculate on the existence of such a deep western boundary current based on deep properties in the Ulleung Basin.

Hurlburt et al. (1996) make a very strong case for the importance of bottom topography and the barotropic mode on the overall circulation including the upper layer and its boundary currents and separated boundary currents and fronts. They show through their numerical modeling that the mean abyssal currents are related strongly to bottom topography (through the f/h contours), and that baroclinic instability associated with the abyssal flows affects the upper flows. A barotropic mode is central to obtaining realistic solutions, as is very realistic bottom topography, along with other non-topographic issues (nonlinearity, horizontal resolution, good forcing). Hurlburt et al.'s (1996) model is of the whole of the North Pacific including the JES, with emphasis on results in the Kuroshio/Oyashio. However, it is reasonable to assume that their conclusions apply equally well to the JES.

Based on the model results, it would seem reasonable to conclude that the circulation in the JES from top to bottom is important for the surface circulation. (We assume that determining the paths and variability of the surface circulation is a main objective of the ONR DRI.) It is only reasonable then to suggest that the actual circulation from top to bottom should be mapped and quantified. Because of the weakness of the deep salinity signal, this simply has not been done - knowledge of the top-to-bottom circulation in the JES lags significantly behind what was known of the Kuroshio/Oyashio region even before the recent ONR initiative KERE, which concentrated on measuring the Kuroshio Extension including the deep western boundary current (Hallock and Teague, 1996), and even behind what is known about abyssal circulation in the overall North Pacific. It is eminently possible to measure the deep properties in the JES properly, assuming careful calibration of salinity, to the standards set by WOCE. Such standards appear to achieved by the CREAMS group (Kim et al., 1996), but thus far their station coverage and strategy has not been adequate for determining the deep and bottom layer circulations. Shiller et al. (1996) showed clearly how important station resolution is for observing the deep western boundary current in the Kuroshio Extension region. A DWBC in the JES might well be more vigorous due to its nearby ventilation source, but would likewise be quite narrow.

Objectives:

Map the deep and bottom circulation of the JES and relate these to the surface circulation, to identify pathways and quantify abyssal flow, examine the existence of a deep western boundary current, and allow budgets for calculating upwelling rates and vertical diffusivities. Specific attention should be paid to the narrow passages connecting the three major basins, as well as to obtaining profiles within the basins sufficient for dynamical calculations. Specific attention should be paid to the western boundary region all the way north into the Tatar Strait. Compare these results with numerical model results.

Measure the baroclinic structure of several eddies which recur prominently, to determine whether their shear signatures reach to the ocean bottom. Coordinate hydrographic observations with direct velocity observations in the same to determine the full vertical structure. Determine if the more permanent eddies have any relation to topography.

Study the subpolar front location relative to the Yamato Rise (see section 2.d.2.4 below on subpolar front), to determine if the Rise affects it.

Approach:

1. Obtain a quasi-synoptic hydrographic data set covering the whole of the JES in one season, to the bottom at all stations, and with highly resolved sections across important passages and boundary regions, and combine with direct velocity observations. Use chemical measurements, such as CFC's, oxygen, nutrients, to aid in determining flow paths. Use a box inverse model, constrained by topography and by any available simultaneous direct velocity observations, to map the deep circulation. Calculate average upwelling and diffusivity rates in confined deep layers (as in a number of recent publications - our own contribution is McCarthy et al., 1997).
2. Obtain several cross-sections of a few regularly-occurring eddies and combine with any direct velocity observations. Use AVHRR and possibly altimetry to track eddies and determine if topography is a factor in their location.
3. The same for the subpolar front (see next section).

2.d.2.4. Subpolar Front characteristics/topographic constraints.

A major front across the JES at about 40°N is tantalizingly similar in location and properties to the subpolar front crossing the North Pacific at about 40-42°N. Frontal analyses from the Naval Oceanographic Office show clearly the subpolar front in the JES (Fig. 6 from Hurlburt et al., 1996), with a possible dual location, remarked on below. Both are temperature and salinity fronts, separating warm, saline subtropical waters from cold, fresh subpolar waters. Analogous fronts are found in the North Atlantic and as part of the Antarctic Circumpolar Current (the subantarctic front). Understanding the creation, dynamics and maintenance of at least one of these fronts should add considerably to understanding of all of them.

The JES subpolar front is a very useful for this study because of the limited size of the JES and hence the ability to better observe all of the possible mechanisms.

It is our opinion that the North Pacific's subpolar front originates as the separated Oyashio front, and hence that its initial location is set by the large-scale Sverdrup transport of the North Pacific with the front occurring at the zero Sverdrup transport (Yuan and Talley, 1996). (The Kuroshio separation point is more at at the zero wind stress curl at the western boundary.) Advection eastward is accompanied by horizontal diffusion which would spread this front to a width which is comparable to the actual frontal zone width in the eastern Pacific. However, sharp fronts are found within the frontal zone - usually two or three in the eastern Pacific. We attribute these mainly to seasonal Ekman convergence acting on the larger-scale meridional gradient created when the Oyashio separated from the coast and formed a front - despite the co-location of the subpolar front in the eastern Pacific with the annual mean zero wind stress curl, every summer the wind pattern migrates northward and a maximum convergence caused by its curl is found at the subpolar front latitude (Yuan, 1994).

Local buoyancy forcing (precipitation gradient) and a gradient in the energy of storms (large number of storms north of the front) likely also contribute to the maintenance of the North Pacific's subpolar front, but the exact interplay of these is not yet understood. Kazmin and Rienecker (1996) indicate that very high resolution wind, heat flux and SST gradient data sets will be required to adequately discern between various mechanisms of frontogenesis - the rate of frontogenesis is greater than that calculated from the various forcings.

In the JES, the subpolar front appears in high resolution AVHRR images to be the northern side of the separated East Korea Warm Current (Figs. 2 and 7). This may be somewhat different from the frontal source in the North Pacific - the separated Oyashio. However, in the surface temperature gradients constructed from coarser grid data in the JES ( Fig. 8a , Fig. 8b , Fig. 8c , ), the subpolar front appears to originate farther north than the main separation of the EKWC near Ulleung Island, and may rather be the interaction between the North Korea Cold Current and a northward-advected filament of the EKWC (eddy D in Fig. 2).

Two coarse views of the JES subpolar front SST gradient shown in Fig. 8a , Fig. 8b are representative of most of the winter and most of the summer realizations. There appears to be a marked seasonal cycle in location of the subpolar front, based on five years of NCEP sea surface temperature analysis. In summer, the subpolar front appears along the northern flank of the Yamato Rise. In winter, it appears along the southern flank. East of Yamato Rise, the front swings northward and is subject to the same direction of seasonal oscillation (farther north in summer). The question is whether this is due to change in local wind forcing, or to change in the strength of the NKCC versus the EKWC (which would also likely be related to wind forcing, as well as seasonality of flow through Tsushima Strait).

Also intriguing in this is the potential role of the Yamato Rise in steering the subpolar front - lying along either the northern or southern flank of the rise. The dynamics of eastward flow lying over topography deepening to the north versus deepening to the south must be different (sustaining standing waves when on the southern flank versus eastward advection of eddies when on the northern flank). It would be interesting to investigate seasonal differences in eddy population and advection associated with the front and its mean latitude at the Yamato Rise.

The actual subpolar front in detail is composed of many eddies and mushroom vortices (Fig. 7). Finding the mean front location in such a high resolution image appears nearly futile, and yet the mean gradient has a recognizable pattern ( Fig. 8a , Fig. 8b , Fig. 8c ). This larger-scale field is what is observed from coarse sampling such as was used in the North Pacific subpolar front analyses of Yuan and Talley (1996) and Kazmin and Rienecker (1996). Some of the ambiguity in understanding frontogenesis in the latter might be resolved through the finescale sampling that will be possible in the JES. Most of this should be done through towed profiling instruments. We also suggest that detailed hydrographic sampling be accomplished in at least one small portion of the subpolar front to determine the vertical structure of the surface features. Salinity measurements are necessary since the front is well-defined in salinity and the deep Japan Sea is nearly adiabatic. Since deep salinity gradients are tiny, highly accurate salinity measurements are required.

Objectives:

Observe the vertical structure of the subpolar front in the JES, and determine how the front is associated with bathymetry. This association may well be seasonal. Observe in detail one of the subpolar front structures, including hydrographic stations with salinity and temperature to the bottom, in order to attempt to resolve some of the ambiguity in frontogenesis calculations based on large-scale fields.

2.d.3 Japan/East Sea eddy characteristics

Recent observations and modeling suggest that mesoscale eddies are an essential component of the Japan Sea circulation (e.g. Ichiye and Takano, 1988). Mesoscale eddies are found distributed over much of the basin, suggesting a connection both in origin and through interactions and water mass exchange. The eddy streets or compact eddy systems caused by intrusions between closely located eddies have been found to advect water and biological species through the basin much faster than the "mean flow". We hypothesize a mesoscale/synoptic scale mode for the Japan Sea circulation and fluxes and the existence of a whole-basin eddy system.

Lee and Niiler (personal communication) show that eddy energy based on surface drifters is not uniform, but is high in several regions, including each of the major currents and the subpolar front. Previous studies focused on the anticyclonic warm eddies located in the Tsushima Warm Current (eddy F in Fig. 2 and others not visible in this figure) (Isoda and Nishihara, 1992; Isoda, 1994), the East Korean Warm Current (eddies D and G) (e.g. Isoda and Saitoh, 1993; An et al.,1994) and over the Yamato Rise (eddies E and at 40°N, 135°E) (Isoda et al., 1992).

A prominent warm streamer is apparent in the January and April, 1997 images, at 39-40°N and 134°E, where the EKWC finally retroflects completely (Fig. 2 - eddy D and Fig. 7). Kim et al. (1996) show an anticyclonic eddy in a drifter track at this location, obviously at an earlier time. This is the region over the Korean Plateau where Ryabov (1994) observed from historical data (especially from oxygen) that "young" deep water is regularly found, even more regularly than off Peter the Great Bay. It is possible that the juxtaposition of saline water from the EKWC and very cold water drifting southward in the North Korea Cold Current, and surface buoyancy forcing, can create a dense water in this region. This has not been proven or disproven in the literature at this point, owing to the lack of data.

Eddy E in Fig. 2 lies over the western bump in the Yamato Rise, and is a regularly occurring feature. An anticyclonic eddy again was observed here with a drifter at a much different time (Kim et al., 1996). It appears from the AVHRR image that the streamer which feeds the eddy may be steered northward by the north-south portion of the Yamato Rise (from 38 to 40°N). This streamer is essentially the subpolar front in this region. Again, if this eddy is present at the time of the JES surveys, it should be criss-crossed by stations to the bottom as well as receiving a Seasoar survey.

Satellite observations show additional mesoscale eddies in the area to the north of subpolar front (Huh and Shim, 1987; Sugimoto and Tameishi, 1992; Goncharenko, 1994; Ostrovskii and Hiroe, 1994). The locations of these eddies is reasonably predictable - eddies A and C in Fig. 2 are often found. Much less attention has been paid to these eddies than to those in the more southern areas. Recent observations in the northwestern JES (Danchenkov, Lobanov and Nikitin, 1997) demonstrated the existence of stable eddies of 50-100 km radius and a probable life time from a few months up to more than a year. Preliminary examination of hydrographic, drifter and mooring data show that the northwestern eddies have a relatively warm and low saline (<34.0%o) core, anticyclonic rotation with tangential velocity of 20-30 cm/s, and a strong barotropic component. They are most likely the cause of the high velocity events at the Takematsu moorings at the CREAMS site M3 (41° 30'N, 134° 21'E) at 1000, 2000 and 3000 m depth - this location is similar to that of eddy C in Fig. 2. If any part of this eddy lies within the region which can be sampled at the time of the JES surveys, then it should clearly be profiled to the bottom.

In the winter-spring period of both 1996 and 1997 the northern eddies moved southward along the western border of the deep Japan Basin. Hydrographic data of spring 1988 demonstrated a relatively warm and low saline core in the eddies. Thus drifting south from the area of 41-42°N to 39-40°N the eddies supply fresh water into the subtropical low salinity layer. Recent observations made by V. Lobanov suggest that the northwestern eddies can drift southward to 38-39°N.

Interaction between the eddies were observed as a partial water exchange by intruding filament or streamers. There is some evidence which suggests a complete merging. Streamers evolving between the eddies are a likely mechanism of fast transport of warm subtropical water through the array of closely-spaced eddies up to the northwestern coast of the JES. Likewise, southward advection along the eastern edge of anticyclonic eddies maintains a permanent intrusion of cold water into the subpolar front along 132-133°E.

As the eddy cores are well mixed in density, they are a possible site for deep convection and for ventilation. However their cores are fresh and so dense water production is unlikely.

The eddies' movement seems to be controlled by topography. They move clockwise from north to south and then to the east-north east parallel to the slope of the Japan deep basin. Other mesoscale areas related to topography which might be responsible for mixing and ventilation are described in section 2.d.4 below.

Objectives:

To study dynamics and water mass structure of mesoscale eddies in the northern part of Japan Sea and the subpolar front area using both physical and hydrochemical characteristics; their origin, evolution, connection with bottom topography, winter air-sea interaction, and the eddies to the south of the subpolar front; their role in basin scale water transport and fluxes of matter and biological species; physical and biological processes inside the eddy, water mass modification, formation of chemical anomalies and evolution of biological communities; eddy influence on coastal waters.

A combination of satellite, in situ hydrographic station and Seasoar-type data analysis and numerical modeling is suggested. The satellite data analysis will be proposed by the Russian investigator group to the NICOP program, and is central to the investigation. As a first stage of the study historical satellite (NOAA AVHRR IR) and hydrographic data will be examined for geographical distribution of the eddies, typical size, trajectories, relation to topographic features, life span and other aspects of their behavior. Satellite monitoring of the JES based on daily AVHRR images should be started well before the first CTD cruise.

Slightly in advance of the first proposed hydrographic survey (summer, 1999), one eddy in the northern region should be selected based on daily AVHRR images and up-to-date drifter tracks (the latter courtesy of Lee and Niiler - see collaborations in sections 2.d.5 and 2.d.6). If the EKWC eddy located at 39N is present and has enough cross-section outside North Korean waters, then it should be targeted. Otherwise a similar type of streamer farther east in the subpolar front should be selected.

During the first cruise more highly-resolved CTD, chemical and biological sampling of the two eddies should be carried out augmenting the larger scale survey. The eddies should be followed continuously thereafter. If they are still present at the time of the winter survey, they should again be sampled in situ to trace the evolution of their water mass structure and changes of dynamical (velocity, potential vorticity) and biological parameters.

Just prior to the large-scale summer survey, several other eddies observed at that time in the AVHRR and drifter data to lie near the proposed survey tracks could be selected, and the tracks modified to cross them. These might be eddies in the central area of the subpolar front and Tsushima current.

Numerical simulations with a multilayer circulation model will be used to interpret observations and to examine the eddies' role in general circulation; this would be carried out by Ponomarev, Trousenkova and Martynov and will be proposed separately to NICOP. ADEOS and SeaWiFS satellite data on SST and ocean color would be also examined.

2.d.4. Japan/East Sea water mass structure and ventilation

Inflow to the Japan/East Sea occurs through Tsushima Strait, and is shallow, warm and saline. Outflow occurs through similarly shallow straits. Thus much of the volume of the JES is isolated from exchange with the adjoining North Pacific. The deep water is denser than any water which could conceivably flow over the sill, and thus must be formed by processes within the JES. Dissolved oxygen values in the deep JES are much higher than waters at the same depth in the North Pacific, suggesting that the ventilation processes are occurring on fairly short time scales. Several recent studies have included transient tracers (Gamo and Horibe, 1983; Watanabe et al., 1991; Tsunogai et al., 1993; Kim, 1997; Riser and Warner, 1997) to derive better estimates of the ventilation rates. However, the processes by which the JES is ventilated are poorly understood because of the lack of nearly synoptic data sets with good horizontal and vertical coverage, as well as due to the relative lack of chemical measurements, and because of the lack of detailed regional observations where ventilation is expected to occur.

Below 200 m, the waters of the JES are remarkably uniform. Historically, this single water mass has been referred to as Japan Sea Proper Water (Yasui et al., 1967) defined as having salinities between 33.96 and 34.14 and potential temperature between 0° and 1°C. Other researchers have subdivided the JES waters below 1000m into Deep and Bottom Waters with the boundary between these two being a discontinuity of potential temperature, silicate, and dissolved oxygen near 2000 m (Gamo and Horibe, 1983). These studies were based on traditional hydrocasts. Recent CTD surveys of the JES have revealed further details of the fine structure of the Proper Water, including a weak but marked deep salinity minimum (Kim et al., 1996). Takematsu et al (1996) have proposed that the waters below 200 m be classified as:

- East Sea Intermediate Water - 200-300 m - characterized by a salinity minimum as low as 34.00, also a maximum in dissolved oxygen (Kim and Chung, 1984)
- East Sea Central Water - a layer of relatively high salinity and dissolved oxygen between the two Intermediate Waters
- East Sea Deep Intermediate Water - a salinity minimum near 1500 m (note that the minimum is only 0.002 lower than the surrounding water), theta near 0.1 deg. C
- East Sea Deep Water - a minimum in dissolved oxygen below ESDIW
- East Sea Bottom Water - an adiabatic layer below 2500 m, potential temperature between 0.06 to 0.07°C

Additional water masses are identified in the southern JES: the Tsushima Warm Water which is characterized by a salinity maximum greater than 34.5 at 13°C and lying at a depth of about 50 m (Kim et al., 1991) and a seasonally-occurring thin fresh layer above this due to runoff in the East China Sea (Lee et al., 1997).

The water masses below 200 m can be seen in profiles of the properties from a CREAMS station in the western Japan Basin (Fig. 9, Kim and Kim, 1996). Note that the salinity below 500 m varies over a range of .005 from 34.060 to 34.065, while dissolved oxygen varies by 30 umol/kg. Although there are property extrema in the vertical profiles, the variations are small and may reflect temporal and/or spatial variations in the ventilation of the JES water column and not be water masses in the classical sense.

The sources, circulation, and processes responsible for the distributions of properties in the JES are poorly understood. The hydrographic surveys are not synoptic or of high horizontal resolution. There are very few hydrographic surveys in the winter to regions where the ventilation processes are suspected to occur. Since the range of values for salinity and potential temperature is very small, very accurate, well-calibrated measurements are required to infer the circulation and ventilation from non-winter hydrographic cruises. Dissolved oxygen concentrations, because of their larger range of values, have been used to determine much of what is known about the ventilation processes and the temporal variations. Oxygen is generally highest at or just below the surface and decreases rapidly below 500 m. Between 500 m and the minimum of ESDW, there are often isostads of dissolved oxygen which reflect remnants of the ventilation processes. Nutrient concentrations in the historical data show a great deal of scatter, probably due to analytical difficulties. Tsunogai et al. (1993) is one of the few studies of the nutrients of the JES. The vertical profiles of the nutrients (dissolved silica, nitrate, and phosphate) are quite similar. There are very low concentrations of these compounds in the surface waters due to their role in biological processes. There is a nutricline at depths between 100 and 200 m. The concentrations increase with depth with evidence of various layers (isostads) to approximately 1000 m. A weak maximum in nitrate and phosphate is associated with the oxygen minimum of ESDW. Silicate concentrations continue to increase to the seafloor. Recently, measurements of transient tracers (carbon-14, tritium, and CFCs) have been used to derive further information on the ventilation of the JES.

The source of the deep and bottom waters in the JES must be modification of the inflowing Pacific surface waters within the basin. In general, there are two possible mechanisms for deep water formation - open ocean convection and brine rejection associated with formation of sea ice - both of which can occur within the JES. The northern areas of the sea are ice-covered in the winter and the winds are favorable in Peter the Great Bay and Tatarskiya Straits for continual renewal of ice (Martin et al., 1992). This process leads to an increase in salinity, and therefore density, such that dense water can be produced. The vertical increase of dissolved oxygen from ESDW to ESBW is often cited as evidence that this process has occurred (e.g. Gamo and Horibe, 1983). Conditions within the JES are also favorable for open ocean convection. The Tsushima Current transports warm, saline water into the sea from the south. This water is separated from the colder, fresher surface waters of the northern JES by a sharp polar frontal zone. The transport of this warm water across the polar front in the form of eddies, or along the western boundary is essential for the production of deep convection. Wintertime cooling of the relatively saline water produces a marked mode water in the region of Peter the Great Bay, easily reaching a depth of 500 meters (Sudo, 1986; Senjyu and Sudo, 1993 who studied the mode water production process using an analysis similar to that of McCartney and Talley, 1982; Ryabov, 1994). It is important to note that these processes can easily produce waters which would ventilate shallower portions of the water column.

Sudo (1986) attempted to determine where the bottom water was being formed by averaging properties below 2250 m over areas and layers. From this analysis, he concludes that the deep water has formed in the north of 43°N in the JES and spreads southward and southwestward. The carbon-14 distributions at 4 stations in the JES reported by Gamo and Horibe (1983) are consistent with this conclusion. A box model which assumes a direct input of surface water to the bottom water is used to calculate a residence time, based on carbon-14, of 300 years for water below 2000 m. Gamo et al. (1986) concluded that the bottom waters were formed in only very cold winters on the northwestern JES where it sinks into the Japan Basin. The abyssal circulation transports this water into the Yamato Basin where topography permits. This bottom water layer must also be upwelling to conserve mass. These conclusions are based on the potential temperature and dissolved oxygen distributions at 6 CTD stations. Gamo et al. (1986) also noted that between 1969-1984 that the both the thickness and the dissolved oxygen content of the bottom water layer were decreasing. They infer that this is the result of a slowdown or stoppage of bottom water production in the JES. In their study of Tatarskiya Strait as a possible location of bottom water formation, Martin et al. (1992) found that the frequency of severe storms in the northern strait had also decreased during a similar time period, suggesting that the storms play a role in bottom water formation. Ponamarev et al. (1996) report that the highest dissolved oxygen measured in the bottom waters during a severe winter (1949-1950) were found in the southern and central Japan Basin. They hypothesize that ventilation occurs in the convergence areas associated with anticyclonic eddies located in the northwestern JES adjacent to the polar frontal zone, over topographic rises.

Ventilation of the upper portion of the water column in the JES occurs is believed to occur near the Siberian coast west of 136°E between 40° and 43°N (Sudo, 1986; Senjyu and Sudo, 1993). These authors use a discontinuity in vertical profiles of dissolved oxygen and potential temperatures at depths near 1000 m to divide JSPW into Upper and Lower components (UJSPW is defined as water between 32.00 and 32.05 sigma-1.) North of 40°N, there is a strong seasonal cycle in the dissolved oxygen concentration of UJSPW, and the oxygen is always greater than that of UJSPW south of 40°N. Senjyu and Sudo (1993) plot horizontal distributions of the thickness of the UJSPW layer to determine its formation region and its circulation. They assume that the layer thickness approximates the potential vorticity. Their results show similarities to the subpolar mode water production process of the North Atlantic (McCartney and Talley, 1982). The UJSPW leaves the formation region and is advected southward to southwestward along the continental slope. It then enters the Yamato Basin by flowing anticyclonically around the Yamato Rise.

As in the North Atlantic, net heat flux from the surface calculated from bulk formulae appears to be largest where the warmest water is advected northward - that is, in the Tsushima Current (Hirose et al., 1996), and minimal in the region where the deepest convection is thought to occur off Peter the Great Bay (Vladivostok region). This result obtains even though winter winds which are thought to be responsible for this convection are channeled by inland valleys and very strong coming southeastward out of Peter the Great Bay. It would be very useful to check the surface heat balance against an in situ estimate based on geostrophic and direct velocity measurements and in situ temperatures. A box model of the overturns, along the lines of McCartney and Talley (1984) would then be useful, to quantify the production rates of the UJSPW and the deeper portion of the JS Proper Water.

ESIW, the salinity minimum, is found south of the polar front of the JES. Kim and Chung (1984) report that the properties of this water mass are essentially the same as those of the mid-depth water north of the polar front. Senjyu et al. (1994) hypothesize that the Intermediate Water is formed south of 40°N and west of 132°E. It mixes rapidly with the underlying waters, becoming colder and more saline, until it reaches the density of 27.28 sigma theta. It then spreads isopycnally towards the Japanese coast. They also conclude that ESIW is a separate water mass from waters north of 40°N. Ponamarev et al. (1996) hypothesized that ESIW is ventilated every winter in the northwestern polar frontal zone. The distributions of tracers have not been applied to this problem yet.

Measurements of tritium in the JES during 1987 are discussed by Watanabe et al. (1991). Tritium was produced and supplied to the surface ocean by the atmospheric testing of nuclear weapons during the 1960s. Tritium has a half-life of 12.43 y and decays to helium-3. This makes tritium a useful tracer for the study of water movements on the timescale of decades (e. g. Fine et al., 1981). The tritium levels generally decrease from the surface to depths greater than 1500 m. Only one sample was analyzed at depths below 2000 m. It still showed tritium concentrations greater than the analytical detection limit (0.3 TU) at 2700 m in the southern Japan Basin. These researchers believe that this is the result of relatively rapid vertical mixing in the JES. When the tritium is fit to a simple three-box model of the JES with two surface boxes and a deep box, the residence time of the deep box is calculated to be between decades and 200 years. They attribute the difference between their result and that obtained for carbon-14 using the same model to slower gas exchange for carbon dioxide. Tsunogai et al. (1993) added another layer to the box model to represent water between 200 m to 1000 m, and they included all of the tracer data - CFCs, carbon-14, tritium, and radium-226. Again, the data set is rather sparse - CFCs are only measured at a few depths at a few locations. In this case the residence times for the deep and intermediate layers are 100 and 110 y, respectively. However, this model underestimates the amount of CFCs in the deep water by 50%.

Kim (1997) and Kim and Kim (1996) expand this box model to 5 boxes - 2 surface water boxes, and boxes for central, deep, and bottom waters. The model permits the volumes of the lower three boxes to change, as long as the sum of their volumes remains constant, to explain the longterm trends first pointed out by Gamo et al. (1986). Riser and Warner (1997) attempt to model the change in bottom water properties over time by fitting a model to the salinity and dissolved oxygen. This model includes both direct ventilation of the bottom water and vertical mixing with the overlying deep water layer. Direct ventilation ceases in the early 1970s in this model.

In 1995-1996, CFCs were measured in the JES during two separate expeditions. M. J. Warner measured CFC-11 and CFC-12 during an expedition to the Sea of Okhotsk which transited through the JES. Min et al. (1996) also measured the CFCs during the CREAMS 1996 Summer expedition. In the following discussion, data collected during 1995 is discussed. Seven stations were occupied in the central JES, and two short sections were taken - one with 13 stations at 46°N across Tatarskiya Strait and the other with seven stations extending 140 km southeastward from the Russian coast at 45°N.

The CFCs, which have only been produced since the 1930s, are found throughout the water column. The CFCs are found much deeper in the JES than in the adjacent North Pacific ( Fig. 10). During early April, the CFCs decrease from the surface where they are in equilibrium with the atmospheric CFCs to the bottom water. In May, surface waters have warmed, decreasing the solubility of the CFCs, which results in a subsurface CFC concentration maximum. Beneath the surface waters, the CFC concentrations decrease towards the bottom. Several stations show inflections in the vertical profiles, but the depths of these features varies between 500 m and 1500 m. Unlike the dissolved oxygen distributions, CFC concentrations do not increase towards from ESDW to ESBW. The water below 2500 m is fairly homogeneous with mean CFC-11 and CFC-12 concentrations of 0.15 pmol/kg and 0.08 pmol/kg respectively. These values correspond to a CFC "ratio age" (see Warner et al., 1996, for a discussion of ratio ages) of 24 +/- 2 years with a 13-fold dilution with CFC-free water. It is clear from the vertical distributions and the ratio age that bottom water production has not occurred in the past two decades. CFC concentrations have increased by a factor of 3 to 4 in the past 25 years while the atmospheric ratio has remained nearly constant for the past 20 years. Any recent input of CFCs due to bottom water formation would strongly bias the CFC ratio to the modern value.

Although the CFCs in the bottom water at first glance appear to be well-mixed, there do appear to be differences from station to station. There also is fine structure in the vertical profiles which is greater than the analytical precision. It is difficult to understand these features with both the limited number of samples and the very homogeneous distributions of salinity and dissolved oxygen. The CFC distributions may result from enhanced vertical turbulent mixing near topography.

The CFC concentrations in the upper 2000 m are generally higher at the central JES stations than at either of the two short sections in the northern JES. Between 200 and 1500 m, the CFC concentrations at Station 184 (40°44.5'N, 132°38.7'E) are significantly higher than were measured elsewhere. This is in the region where open ocean convection is believed to occur (Sudo, 1986; Senjyu and Sudo, 1993; Ryabov, 1994). Between 1500 m and 2000 m, the highest CFC concentrations were measured at Station 5 (42°20.9'N, 137°01.2'E) There is a isostad of CFC concentration associated with a slight increase in salinity between 1370 m and 1660 m

There is no evidence in the CFCs across Tatarskiya Strait that bottom water had formed during the previous winter; however there is one sample with relatively high CFC concentrations at 800 m. The Tatarskiya Strait CFC-11 section ( Fig. 11) shows the effect of this high value at Station 171. Dissolved oxygen concentrations are similarly high in this sample, and show a slight local vertical maximum a depth near 800 m across Tatarskiya Strait. There is a weak dissolved oxygen maximum (1 to 3 umol/kg) at this depth along the western boundary however the CFC distributions are characterized by an isostad. This mid-depth feature may result from brine rejection beneath the sea ice in Tatarskiya Strait. For some reason, this process is now producing a less dense water mass which ventilates the intermediate depths of the JES.

Samples were also collected during the 1995 expedition for tritium/helium-3 analyses at WHOI (W. Jenkins, PI). Only the helium-3 samples have been analyzed currently. Jenkins (personal communication) reports a helium-3 minimum at 3000 m, indicating a "younger" water mass. If the historical tritium data are used to calculate an age, the result is 25 y. Again this age is the age of the bottom water component added to the abyss, not the average age of the bottom water. According to Jenkins, the helium-3 distributions support the hypothesis that Tatarskiya is the source of these bottom waters. Once the tritium results are available, detailed interpretation will be carried out.

Objectives:

To document the sources of the principal water mass structures of the JES.
To discern the sources of ventilation in the subpolar region, including formation of mode water - upper Japan Sea Proper Water - and likely sources of deep water (northwestern versus Tatar Strait verus Korean Plateau).
To quantify heat and freshwater fluxes using in situ observations sufficient to distinguish between regions of large heat loss versus small heat gain, and between regions of freshwater gain through precipitation versus ice melt.
To quantify deep upwelling rates by basin and hence to determine if there is any geographical pattern to upwelling and diffusion rates, perhaps associated with topography or strong currents.

2.d.5. Proposed new hydrographic observations - philosophy and practicalities We propose that there be two hydrographic surveys of the JES, one in summer 1999 (July) with careful attention to full coverage of the JES horizontally and vertically, and one in the following winter (February or March, 2000), with concentration on the region north of the subpolar front and the front and commonly- occurring eddies. Station tracks and study areas for the two surveys were shown in Fig. 1.

2.d.5.1. Summer survey. The station tracks were chosen with consideration given to the boundary currents, the subpolar front, the regularly-occurring eddies, coverage of the straits, and major topographic features - the deep passages into the Ulleung and Yamato Basins, and the Yamato Rise. In particular, the tracks:

1. cross each boundary current (Tsushima, East Korea Warm, Liman) in several places, and work to resolve the existence of a deep western boundary current.
2. provide stations down the axes of the Ulleung and Yamato Basins, and doing so parallel the subpolar front, which will be useful for other project's continuous profiling, backed by our calibration information. Coverage along the axis of the Japan Basin is adequate, and can be increased with some extra stations on the return steam to Pusan from the Tatar Strait.
3. box off the inflow at Tsushima and outflow at Tsugaru and Soya Straits, and generally consist of closed boxes for circulation calculations (useful for mass/heat/freshwater budgets and inverse box model)
4. cross the deep sills into the Ulleung and Yamato Basins
5. follow portions of several routine Japanese sections along which there are decades of data in the upper ocean, crossing the Tsushima Current up to the subpolar front
6. cross the Yamato Rise - to examine topographic steering by this dominant topographic feature

The surface temperature and velocity structures will likely be better resolved with other measurements (AVHRR, surface drifters, Seasoar - which will require calibration from standard hydrography). The straits' transports must and will be measured with long time series, but the hydrography will provide synoptic chemistry information which is important for tracking water structures. The hydrographic data set is the only one which can provide information on the complete vertical structure of major features. Hydrography is the only way to provide the chemical information (oxygen, nutrients, chlorofluorocarbons) which is so important to tracking circulation and ventilation given the very small signal in temperature and salinity below about 500 meters. Highly accurate salinity measurements are a necessity for this same reason, and we will provide such.

A synoptic view of the entire circulation of the JES would be invaluable for modeling purposes, and for budgets of heat and freshwater. The clear changes in the deep structure of the JES - the cessation of bottom water formation - mean that the boundaries between definable layers have been migrating significantly (Gamo et al., 1986; Kim and Kim, 1996). Moreover, the range of salinity which must be measurable for the deep JES is very small - on the order of 0.005 and less - and has not been achieved until very recently, by the CREAMS group (Kim et al., 1996). The total vertical structure of dynamical features such as the subpolar front, boundary currents and eddies has not been systematically studied, although it is clear that topographic steering is important (e.g. Hurlburt et al., 1996; Katoh, 1994).

Despite the many hydrographic stations collected over the years, mostly by Japan, it is next to impossible to construct from existing data a synoptic picture of the JES from top to bottom and including at a minimum oxygen measurements to discern deep water masses. A deep circulation scheme is non-existent due to the lack of current-resolving station spacing - most treatments show just individual station profiles and say that the water must have come from over there, somehow.

The summer survey is therefore designed to address the need for complete coverage of the JES. Because we also intend overall to adequately survey some of the quasi-permanent eddies which are associated with the subpolar front and northwestern ventilation, we also include survey of several eddies at locations where eddies have often been found, depending on their existence at the time of the survey. This intensity of sampling is feasible at a reasonable cost because of the small lateral extent and general shallowness of the JES compared with other open ocean basins.

We assume for planning purposes that there will also be extensive additional use of the research ship(s) during the summer cruise, including Seasoar profiling of the subpolar front or its eddies, and possibly deployment of moorings.

Clearance issues will guide the actual structure of the survey. It is unlikely that a single country's vessel will be able to complete all of the stations shown in Fig. 1a. We assume that the northern portion will be covered by a Russian ship, and the southern/eastern by a U.S. or Japanese ship. Chemical tracer measurements, such as the chlorofluorocarbons which we propose here (U. Washington proposal), are intended mainly for discerning ventilation. If a choice has to be made, then they should be done on the northern cruise. However, the other hydrographic measurements which are proposed here (UCSD proposal) could equally well be done on the southern/eastern vessel.

2.d.5.2. Winter survey. The proposed winter cruise is concentrated in the northern JES and subpolar front, and so should avoid the clearance problems of the full summer survey. The winter survey focuses on "study areas" rather than complete JES coverage. The special areas are the expected convection region off the ice formation and strong winter wind region of Peter the Great Bay, the Liman Current flow from the Tatar Strait, and eddies associated with the subpolar front and more northern ones associated with ventilation.

It is assumed that routine data collected in the Japanese region, while not reaching the bottom, will suffice for filling in the synoptic winter survey. (Of course, it might again be useful to operate two ships in the winter thus covering the entire region.)

We have a strong group interest in the structure, development and maintenance of the eddies in the northern JES, which may be closely associated with winter ventilation, in addition to not having been studied closely in the past. Therefore our great preference is to work in the north in the winter.

2.d.5.3. Shiptime requirements and disposition of data Because of the uncertainty at this time for the scope of the whole ONR JES DRI, we can only crudely guess at the shiptime requirements. The summer survey shown in Fig. 1a can consist of 100 to 170 stations. All stations are to the bottom. The latter, maximum value, can be accomplished along the cruise track of Fig. 1a in 24 days, assuming a steaming speed of 12 knots, and normal wire speed. (If stations are all truncated at 1200 meters, 3 days less are required - we feel that such truncation would be very inadvisable due to the questions about topographic constraints on flow and front location.) We also assume that other programs will be using the vessel and so assume a total cruise length of 30 days. The same length of time is assumed for the winter cruise, which would allow weather days and time to thoroughly and opportunistically sample convection/eddy features. Of course, if a synoptic survey is carried out by two ships, the length of cruises could be less.

As stated before, our data sets are in a form which is usable during and at the completion of a cruise. Final calibrations, which can take more than one year, rarely affect results deduced from the preliminary data set, except perhaps for CTD oxygen profiles which require a great deal of processing. Talley routinely makes the complete data sets, including CTD profiles available to all associated investigators at the earliest possible time - on the ship, just after the cruise. Her own data sets are available online through her own webserver, and amalgamated data sets and databases are made available through the nemo.ucsd.edu webserver, for which she has partial responsibility.

2.d.5.4. Measurements and expected accuracies, investigator responsibilities

CTDO. Responsible principal investigator - Lynne Talley. CTD and continuous oxygen profiles will be collected at each station, and calibrated with the discrete salinity and oxygen samples collected at each station. Final calibration of temperature relies on laboratory calibration following the cruise, but use of dual thermistors during the cruise allows much of this calibration to proceed prior to the end of the cruise. The salinity signal in the deep Japan Basin is very weak (0.002 psu), but necessary to measure. As described in section 2.d below, Scripps' Oceanographic Data Facility routinely works at this level of accuracy and precision. Talley, Lobanov and Ponamarev will make use of the CTD profiles in their circulation and eddy analyses.

Salinity - discrete. Responsible principal investigator - Lynne Talley. Discrete salinity samples from rosette water samples are required for calibration of the CTD salinity profile, at a minimum of 12 levels at each station. It is also our philosophy to provide coverage in discrete salinity which is comparable to a full oxygen and nutrient profile so that the data set composed of discrete samples is complete and stand-alone. Salinity analyses are run at sea, by two members of Talley's group, under the close supervision of Scripps' Oceanographic Data Facility, as has been the usual practice on WOCE one-time survey cruises. The accuracy of our salinity analyses is determined by that of the standard sea water, which is now routinely better than 0.002.

Oxygen - discrete. Responsible principal investigator - Lynne Talley. Pavel Tishchenko and his group will work with the ODF group in making the shipboard analyses. Oxygen content has been shown to be a reliable means of discerning intermediate to deep water mass structure in the JES, especially given the very small salinity signal (Sudo, 1986; Gamo et al., 1986; Ryabov, 1994). CTD oxygen profiles require a large amount of calibration, and in fact discrete oxygen is normally much more precise and accurate. We propose a maximum of 24 samples on the deepest stations (3000 meters), reducing to about 15 samples on the many stations of about 1000-1500 meter depth, and to fewer on the many shallower stations. It would be very beneficial to compare the automated Winkler titration observations which Scripps' ODF provides, and which are of sufficient accuracy and precision for the JES, with the new system being used by Prof. Kyung-Ryul Kim, which promise to be more easily carried out and which may be more accurate. All discrete observations will be made available to K-R Kim for comparison with his CREAMS results and any analyses he makes during the JES initiative. Talley, Tishchenko, Warner and Ponamarev will make extensive use of the oxygen results in their analyses.

Nutrients. Responsible principal investigator - Lynne Talley. Pavel Tishchenko and his group will work with the ODF group in making the shipboard analyses. Gamo and Horibe (1983) and especially Kyung-Ryul Kim (Kim et al., 1991; Kim et al., 1992; Kim and Kim, 1996) have made excellent use of nutrient information as tracers of the water masses. Kim et al (1992) developed an expression for pre-formed phosphate and nitrate in the JES based on his nutrient and oxygen measurements. These are essentially the values that the nutrients would have had at their surface origin. They showed that sufficient variation exists in the surface nutrient distributions to allow pre-formed phosphate and nitrate to be useful tracers of water mass origins and deep mixing. The total nutrient data set for the JES is remarkably limited, and especially in winter. Therefore, we propose full sampling for nutrients in both the summer survey (full survey of JES) and also in the winter survey (northern area), to produce a water mass description of the whole of the JES and the surface winter boundary condition for the preformed nutrients. We will share the data freely with K-R Kim, and hope that he will be a major user and synthesizer of the results.

Chlorofluorocarbons. Responsible principal investigator - Mark Warner. To properly study the ventilation processes in the JES, a large-scale synoptic survey of the regions where the processes are thought to occur will be necessary. It is clear that the transient tracers and other chemical species (i.e. Dissolved oxygen, nutrient) contribute information on the timescales of these processes which cannot be resolved by CTD casts alone. With two technicians, each working twelve hour watches, we are capable of analyzing 60-70 samples for dissolved CFCs per day. We have the advantage of producing preliminary data soon after sample collection, which allows us to devise our sampling strategies for the upcoming stations. Based upon our experience with previous expeditions, the preliminary CFC data can be easily merged with the hydrographic data at sea.

Carbonate systems. Responsible principal investigator - Pavel Tishchenko. Observations of carbonate parameters in the Japan Sea in summer (Chen et al., 1995) demonstrated that deep waters have low normalized concentrations of alkalinity (NTA) and total nonorganic carbon (NTCO2) in comparison with the Pacific Ocean. High concentrations of oxygen were found deeper than 1500 m. which implies good ventilation and renewal of deep waters.

Observations for late fall period along the section crossing the sea from Vladovostok to Niigata in the POI and Environmental Agency of Japan 1995 November cruise of R/V Akademik M.A.Lavrentyev confirmed this and demonstrated very uniform parameters of water below 2300 m in different regions of the sea (normalized concentration of total alkalinity NTA = 2.355+- 0.003 mg-eq/kg; normalized total carbon dioxide NTCO2 = 2.310+-0.003 mmol/kg; pH using electrode pair standardized by SWS scale and (T=25C) pHsws(25) = 7.446+-0.010; partial carbon pCO2 = 600 matm) (Tischenko et al., submitted).

Deep maxima of NTA and NTCO2 found in the North Pacific were absent in the Japan Sea. Waters of surface mixed layer were undersaturated of both oxygen and CO2 for the whole sea. To explain this correctly a method to separate biochemical effects (photosyntesis and destruction of organic matter) and physical effects (air-sea gas exchange, variations of water temperature) were developed and used. It was found that both of these effects work in subtropic and subarctic areas of the sea in the period of cruise observations (2 Nov - 8 Dec). Input of O2 from photosyntesis was important ins pite of beginning of winter cooling and mixing. This corresponds with previous data on the fall plankton bloom in the Japan Sea (Hong et al., 1996). Because of undersaturation of its surface layer the Japan Sea may be considered as a sink of atmospheric CO2 in fall.

Other tracers. Responsible principal investigators - outside our group. Water from the 10 liter rosette bottles will be made available to any other funded projects that require it. At this time, these could include argon/neon (Jenkins, WHOI), delta O18 (K.-R. Kim, Seoul National Univ.) and AMS carbon-14 (also K.-R. Kim).

2.d.5.5. Analysis.

Analysis of the complete hydrographic data sets will be carried out by all of the principal investigators. Our scientific objectives and proposed analysis methods were described above. It is assumed that most of these analyses will be carried out jointly with other scientists, including ONR JES investigators and Japanese, Korean and other Russian investigators as described in sections 2.d.6 and 2.d.7. Within the scope of our proposal, Lobanov and Talley will focus on analysis of the subpolar front and eddies, using the new data set, satellite information and historical data. Talley and the graduate student will lead description of the complete circulation and water mass structure. Warner, Ponamarev and Talley will study the ventilation signatures.

2.d.5.6. Scripps Oceanographic Data Facility support for hydrographic data collection

The Scripps Institution of Oceanography Oceanographic Data Facility (ODF) will provide a team of three ODF technicians, assisted by three chemists from the Pacific Oceanological Institute in Vladivostok, to carry out full depth CTDO profiling, up to 24-level rosette sampling, and sampling and analyses for salinity, oxygen, and nutrients. Water samples will be collected in 10-liter ODF/Bullister bottles which will provide water for other measurements. The ODF work will meet WOCE Hydrographic Program data quality standards in data collection, processing and reporting; this is important for the ONR Japan/East Sea program, due to the high accuracy required to discern important signals in the deep and bottom waters, High priority is placed not only on the quality of the work, but also in the documentation of performance, including for example an annotated list of every questionable result.

Dr. James Swift and Mr. Woody Sutherland of SIO are responsible for the technical aspects of the ODF work. However, all data will be reported directly to Dr. Talley, who subsequently forwards data to all cruise participants, program offices, and national archive. SIO retains no special scientific control over the data or the research program.

CTD and water sampling will be carried out along the expedition track as directed by the principal investigators. At each station the water column will be profiled with an ODF-modified Neil Brown Mark III CTD probe (or superior device if available). A single device will be used for all CTD casts unless there is an instrument failure or loss. Rosette bottles will be closed on up casts by the CTD operator at depths chosen after consideration of the down cast profiles. Final deep CTD data will be accurate in absolute terms to about 2-3 dbar, 0.002 degC, and 0.002 psu, with real precision about one-half the accuracy in each case.

ODF plans to supply the at least the following major equipment: 2 24-place rosette systems and pylons, 24 10-liter ODF-modified Bullister style bottles, 2 ODF "WOCE" NBIS CTDs, 2 altimeters, 2 pingers, 2 Autosal salinometers with salt bottles, 1 oxygen autotitrator with flasks, nutrient AA system, Barnstead E-pure water purification system, 2 Sun SPARCStation data acquisition & processing systems, plus numerous terminals, PCs (for the analytical equipment), spare parts, and tools.

Most ODF technicians are "cross trained" and so a statement that there will be "one nutrient analyst, two marine technicians," etc. would be misleading. We know from past experience and Dr. Talley's past contributions to the seagoing team that an ODF party of 6 is required for this work and must include the following skills at the appropriate level of expertise: CTD/electronic technician, CTD data analyst, bottle data analyst, salinometer operator, oxygen technician, nutrient technician, and marine technician. The Russian chemistry group of 3 under Pavel Tishchenko has extensive experience working as part of the ODF group, and hence the actual number of ODF technicians is reduced to 3.

Assistance is required from the principal investigator's party, including all CTD console operations, salinity/nutrient sample drawing and most of the autosalinometer operation, under strict supervision from ODF personnel. The PI's group also examines the CTD and bottle data on a daily basis and interacts as needed with the ODF processing technicians during underway data processing. A minimum of two persons to run CTD console operations, and two persons for salinity analyses is required. The PI's group will consist of Talley, Vladimir Ponamarev (POI), David Newton and an SIO graduate student.

ODF data will be reported only to the Dr. Talley unless directed otherwise. ODF expects to deliver preliminary CTD and bottle data at sea. The schedule for final data processing is dependent upon competition from other cruises. Our expectation is that following CTD recalibration at the laboratory the technicians can soon complete final processing. However, final documentation requires significant time, and CTD oxygen probe data processing to high quality standards - near the last of the data processing activities - requires additional technical oversight from senior ODF staff, who may or may not be away on an expedition. Hence final data availability will likely stretch to 12 months from the end of the expedition.

Notes on ODF Support

The ODF/NBIS Mk IIIb CTDs include dual platinum resistance thermometers (as a temperature channel stability self-check) and oxygen probe, and are capable of supporting additional measurement channels. ODF will carry out pre- and post-cruise pressure and temperature calibrations which will not only cover static offsets but will also include evaluation of overall instrument stability and dynamic response. ODF will supply an altimeter for bottom approach monitoring. An underwater CTD data logger and rosette controller should be available. This device is contained in a separate pressure case and used with existing CTD systems both to improve CTD performance when signals are disturbed by line and slip ring noise, and also to allow full data return in the occurrence of partial or total conductor failure. The device also allows pre-programmed operation, including rosette sample closure, with non-conducting cables. This unique device, constructed by ODF with NSF support, is a valuable back-up.

The ODF CTDO acquisition and processing system is capable of real-time processing including application of best-estimate sensor models and corrections, block averaging, and statistical analysis and sorting, plus can present multiple simultaneous real-time multi-parameter screen plots, completely definable by the user, which may be changed, updated, and interrogated at any time, either during or after any cast. The system also permits a host of user interactions regarding cast observation and control, plus a variety of recording, plotting, and printing options and data back-ups. The system also supports active data porting to of from a variety of instruments and other computers, plus multi-user support for remote terminals.

2.d.6. Relation to other proposed projects

SeaSoar and other profiling instruments. We look forward to discussions of the best way to support continuous profiling observations in regions such as the subpolar front, and the more randomly-spaced ALACE profiling in the gyres. The strength of the more traditional CTD/rosette profiling is its high accuracy, and ability to meaningfully sample the full water column. The large-scale hydrographic data which we collect, and which will be of the highest possible accuracy including especially salinity and temperature, will be made available in near-real time during the cruise(s) to other investigators aboard. At the conclusion of the cruise they will be made available to all JES investigators through our website. The calibrated CTD profiles and the more basic discrete salinity samples will be of basic use if there is be calibration of sensors on other profilers, including the SeaSoar (Craig Lee) and profiling ALACE floats (Steve Riser). In the subpolar front region, we are especially interested in seeing how the surface structures which will be well resolved by, say, SeaSoar, extend to the bottom.

Optical measurements. Our equipment will easily accommodate other profiling instruments, such as a transmissometer (G. Mitchell, Flatau and Stramski). We have discussed joint operations with Mitchell et al., and are interested in seeing how the optical properties can add to water mass detection. Our CTD equipment and software is configured to easily incorporate a transmissometer, which can be reported as part of the immediate output.

LADCP. Although we have not reached an arrangement with Beardsley regarding collaboration, we note that we are very experienced in transmitting CTD time series data nearly immediately after a station to the LADCP operator, who requires it for processing. The LADCP information can sometimes be useful in assisting with reference velocity choices for geostrophic calculations.

Chemical tracers. The equipment which we will be using will easily accommodate sampling by other chemistry programs. In particular, Bill Jenkins of WHOI has expressed keen interest in collaboration should we be sampling in the northern and northwestern Japan/East Sea. He would be collecting samples for argon and neon to distinguish between waters ventilated through ice formation versus those ventilated through open ocean convection. He has a number of deep helium stations from the 1995 cruise on the Lavryentev, which he has published in an informal note, and made available to us. The tritium samples from that cruise are not yet ready to process.

We are also very interested in the possibilities of underway pCO2 measurements. K.-R. Kim has indicated that there is a strong correlation between pCO2 and mixed layer depth, and so the pCO2 can aid in finding relatively narrow convection cells.

Other hydrographic data collection. As indicated above, we are of the opinion that a sensible strategy for the summer 1999 survey would be simultaneous operation of two ships, one which can work easily in Russian waters (Russian ship) with the other operating in Japanese waters (U.S. ship). This requires two separate hydrographic groups at sea at the same time. The Seoul National University group (Kuh Kim and Kyung-Ryul Kim) are proposing with Bob Beardsley to work on a Russian ship. We suggest that this be supported and that the basic CTD/O2/S/nutrient work on the U.S. ship be done by us, to produce a complete coverage of the Japan/East Sea, to the bottom.

CFC measurements will be most valuable in the northern and northwestern Japan Sea. Therefore, we propose that if the Beardsley/Kim/Kim group is working in the northern JES on a Russian ship, that Mark Warner make his measurements on that vessel, even though the SIO/ODF group might be on a different vessel. Dr. Kyung-Ryul Kim has offered him use of a portion of his nutrient van for this purpose.

In the event of joint work, we would like to have a thorough discussion of and agreement on the station sampling strategy, as we believe that rather dense coverage to the bottom is required, as argued in section 2.d.2 above. Our complete data set would be made available immediately following the cruise to the Beardsley/Kim/Kim group. Dr. Kyung-Ryul Kim has expressed interest in comparison measurements with us, which would be easily accommodated if two ships are operating at the same time with a small spatial overlap in sampling.

Synthesis of integrated data sets. The newly-collected hydrographic data will be incorporated initially in a box inverse model of the Japan Sea circulation. Successful exercises are underway now on incorporating subsurface float, surface drifter and ADCP velocities in such box models, as well as altimetry information (e.g. Gille and Donohue, 1997). The strong topographic constraints afforded by the various basins could help to provide robust transport estimates, such as were possible in Bingham and Talley (1991) for the Kuroshio. Talley is a member of a new joint effort for WOCE Pacific data analysis which will combine similar information. Therefore strong collaboration with the groups measuring velocity directly (Riser - floats; Niiler and Lee - drifters; any ADCP measurements) would be beneficial, as well as the international collaborations described below for incorporating transport information from the straits.

Model comparisons. Our data set as well as the work we do in assembling time series of hydrography from the historical data set and potentially directly from Japanese agencies (including CTD data) will be made available to JES modelers, along with our interest and direct involvement in such comparisons. We believe that our new information on the relation between surface and deep circulation, synoptic mapping of the layer interfaces, contributions to discerning the sites and strengths of strongest buoyancy forcing, and detailed observations of the structure of eddies in some key areas will make a good observational basis for choice of model parameters and comparison with model results. We will also use our circulation information to calculate deep and near-surface diffusivities, which should assist also in model parameterizations (as in McCarthy et al., 1997; Zhang and Talley, 1997).

Data assimilation into models is a rapidly maturing area. We have not had experience ourselves with assimilation, but expect to do so as part of WOCE analysis teams in the next few years.

2.d.7. International collaborations

Substantial international collaboration is central to this proposal, as is extensive collaboration with the other US ONR investigators. Specific contacts which have been made as of the proposal deadline include:

Drs. Yuri Volkov and Alexander Tkalin, Far Eastern Regional Hydrometeorological Research Institute (FERHRI) in Vladivostok, Russia. Dr. Volkov is the Director and Dr. Tkalin the head of the department of oceanography. They have been involved in the CREAMS program through use of their ship the Khromov for most of the surveys. They indicate interest in general scientific collaboration. (see attached email 1 and shiptime cost quote in section 2.g.1)

Dr. Kunio Rikiishi, Hirosaki University, Aomori, Japan - Tsugaru Strait and eastern Tsushima Current transport measurements using seabed cables (see attached email 3)

Dr. Kyung-Ryul Kim, Seoul National University, Seoul, Korea - well-developed chemistry laboratory and expert on the East Sea chemistry and circulation. He has offered use of a portion of his van to Mark Warner for the cruise(s) on the Russian ship, where isolation from shipboard systems is required for accurate CFC work. He will also collaborate with us in intercomparison of chemical measurements between his group and SIO/ODF in areas where stations overlap should there be a two-ship survey. We anticipate that he will take the lead in analysis of nutrient measurements collected overall.

Dr. Dong-Kyu Lee, Pusan National University, Pusan, Korea - satellite-tracked drifter tracks and associated AVHRR and wind analysis, analysis of hydrographic time series in the East Korea Warm Current and Tsushima Strait. We will collaborate intensely with him in final planning of regional studies, for knowledge of surface current and temperature conditions at the beginning and possibly during the survey(s). We will deploy drifters for his and Peter Niiler's project, in the cold water region north of the subpolar front and along Korea and Japan.

Collaborations are being pursued with (1) the Maizuru Marine Observatory and with (2) Dr. Akifumi Nakata. The Maizuru Marine Observatory has collected hydrographic data along a principal section crossing the Japan/East Sea for many decades, from the vessel Seifu Maru. Present measurements along this section are restricted to the Japanese EEZ, but the overall time series and subsurface information especially concerning the subpolar front structure would be invaluable. Dr. Nakata is responsible for the submarine cable transport measurements in Soya Strait, in a joint project with Dr. Kantakov of Sakhalin.

Dr. Emil Herbeck, Institute for Automation and Control Processes, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia - receiving and processing of the AVHRR data in LAC (high resolution) format [LAC - Local Area Coverage, resolution is about 1 km - this is only possible to obtain at local satellite acquisition stations (in a radius of direct vision to satellite - about 2000 km) or using onboard satellite memory which is limited; other option is GAC - Global Area Coverage (4 km)].

Mr. Aleksandr Nikitin, Pacific Research Institute of Fisheries and Oceanography (TINRO), Vladivostok, Russia - collaboration on AVHRR data analysis, coordination of additional hydrographic surveys of eddies and northern area by TINRO ships, historical satellite and hydrographic data of TINRO.

Mr. Andrey Martynov, Computing Center, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia - scientific collaboration on assimilation to numerical modeling, comparison with model results.

Dr. Mikhail Danchenkov, FERHRI, - scientific collaboration on eddies and their role in general circulation (using FERHRI current and historical data).

Dr. Igor Zhabin, POI, - scientific collaboration on deep convection and dense water formation.

A new Russian federal program named The World Ocean is supposed to begin in 1998. The Pacific Oceanological Institute submitted several proposals on the Japan Sea physical oceanography and biogeochemical cycles including mesoscale eddies. However their status as well as the status of the whole of the World Ocean Program is not yet decided.

For the seasonal tracking of eddies, and construction of field observation time series, cooperation could be pursued with other programs operating in the area. Annual cruises under the Joint Study of Marine Environment of the Japan Sea by POI and the Environment Agency of Japan, biannual CREAMS field observations and routine observations in the Japan Sea by Russian State Committee on Fisheries allow cooperation with the proposed project.

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Minato, S. and R. Kimura, 1980. Volume transport of the western boundary current penetrating into a marginal sea. J. Oceanogr. Soc. Jap., 36, 185-195.

Moriyasu, S., 1972. The Tsushima Current. In: Kuroshio: Physical Aspects of the Japan Current, H. Stommel and K. Yoshida, eds., 353-369.

Nof, D., 1993. The penetration of Kuroshio water into the Sea of Japan. J. Phys. Oceanogr., 23, 797-807.

Ohshima, K.I., 1994. The flow system in the Japan Sea caused by a sea level difference through shallow straits. J. Geophys. Res., 99,C5, 9,925-9,940.

Ostrovskii A. and Y.Hiroe (1994): The Japan Sea circulation as seen in satellite infrared imagery in autumn 1993. Proc. CREAMS'94 Int. Symp., 75-88.

Ponomarev V.I., A.N. Salyuk, and A.S. Bychkov (1996) The Japan Sea water variability and ventilation processes. Fourth CREAMS Workshop , Vladivostok, February 12-13, 1996, Proceedings, 63-69.

Riser, S.C. and S. R. Ramp, 1996. The oceanography of the Japan/East Sea. Report of a workshop held in Honolulu, Hawaii 25-27 June, 1996. Sponsored by the Office of Naval Research.

Riser, S. and M. Warner, 1997. Long-term changes in the deep ventilation of the Japan Sea. J. Phys. Oceanog., to be submitted.

Roemmich, R., S. Hautala and D. Rudnick, 1996. Northward abyssal transport through the Samoan passage and adjacent regions. J. Geophys. Res., 101, 14039-14055.

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Senjyu, T., H. Sudo, and M. Matsuyama (1994) On salinity minima in the Japan Sea. Abstracts of the Japan Oceanographic Society 1994 Fall Meeting, p. 209-211.

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Talley, L.D., 1991. An Okhotsk Sea water anomaly: implications for sub-thermocline ventilation in the North Pacific. Deep-Sea Res., 38, S171-190.

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Yuan, X., 1994. Characteristics and frontogenesis of the subarctic front in the North Pacific, Ph.D. thesis, 172 pp., Scripps Institution of Oceanography, UCSD, La Jolla.

Yuan, X. and L.D. Talley, 1996. The subarctic frontal zone in the North Pacific: Characteristics of frontal structure from climatological data and synoptic surveys. J. Geophys. Res., 101, 16,491-16,508.

Zhang, H.-M. and L. D. Talley, 1997. Heat and buoyancy budgets and mixing rates in the upper thermocline. Submitted to J. Geophys. Res.

2.e. Biographical information

The key personnel are Lynne D. Talley (Scripps Institution of Oceanography, Professor), Mark D. Warner (University of Washington, Assistant Professor), Vyacheslav Lobanov (Pacific Oceanological Institute, Associate Director), Pavel Tishchenko (Pacific Oceanological Institute, Senior Scientist), Vladimir Ponamarev (Pacific Oceanological Institute, Senior Scientist).

Brief biographical information appears in section 2.h below with the bibliographies.

2.f. Requested support of facilities, equipment or materials

2.f.1. Russian shiptime. Shiptime on a Russian ship will be required for both the summer and winter surveys. It is assumed here that a Russian ship will be necessary for work in the northwestern and northern JES. It is also assumed here that for the summer survey, Russian shiptime is incorporated in Korean plans. We have discussed our own needs for the winter survey through email with Dr. Yuri Volkov, Director, Far Eastern Regional Hydrometeorological Research Institute (FERHRI), and a letter from Dr. Alexander Tkalin, his spokesman, is included as section 2.g.1. An arrangement with FERHRI has been made by Korea (Kuh Kim) for the past several years for CREAMS, with very satisfactory results.

Shiptime can also be provided by the Pacific Oceanological Institute (POI), although procurement of such was discouraged by ONR in the DRI planning letter phase. However, POI has a certified vessel, the Bogorov, which could be operated at a cost of $3200 to $4000/day, and which afford much the same facilities as the Khromov.

2.f.2. Other. No new equipment or material purchases other than normal expendable supplies for the hydrographic work are included. The latter include sample bottles and chemicals, and are detailed in the budget section 3.c.

2.g. General and special facilities available for performing the proposed work.

2.g.1. Specifications for the FERHRI ship, R/V Khromov. Specifications for two FERHRI ships, the R/V Khromov and the R/V Pavel Gordienko, have been communicated by email from Dr. Tkalin, and are included here. It is assumed that the larger Khromov is the appropriate vessel for the proposed work.

From hydromet@online.ru Wed Aug 27 19:58:49 1997
To: "'ltalley@ucsd.edu'"
MIME-Version: 1.0
Content-Type: text/plain; CHARSET=koi8-r
Content-Transfer-Encoding: 7bit
Status: R

ltalley@ucsd.edu

Attn: Dr. Lynne Talley, SIO
From: Dr. A.V.Tkalin, FERHRI

August 28, 1997

Dear Dr. Talley:

(1 paragraph deleted)

The cost of our R/V "Professor Khromov" is 6,000 USD per day. There is smaller ship, R/V "Pavel Gordienko", for 4,000 USD per day. You can contact Prof. Riser regarding both ships: he and some Japanese specialists just have inspected these R/Vs (I've said "Good bye" to all of them this morning).

Some technical details about "Khromov": built in Finland in 1983, 2,140 tons, 72 m length, 4.5 m draught, research staff about 30. Two CTD winches (up to 8,000 m of single conductor cable of about 10 mm diameter, max. load about 2 tons). These winches have been already successfully used with three different CTD systems: GO, FSI and SBE when this ship participated in CREAMS activities. There are four wire winches as well (for moorings and other kinds of fieldwork including sediment sampling), two A-frames and two cranes. There are "Navstar" GPS and two echosounders available. No ADCP, you were right. There is an automatic meteorological station "MIDAS" (Finland) with sea surface temperature and some meteorological parameters available at any time. There is also seawater supply available for CO2 measurements. Nevertheless, before preparation of real cruise plan, the ship should be inspected and all these details discussed. May be something should be modified or changed.

"Pavel Gordienko" is about 930 tons, built in Finland in 1987, 50 m length, 3.6 m draught, research staff about 15. Three winches (including CTD winch) with maximum load of about 3 t, crane, MIDAS meteorological station, GPS, echosounders, etc. No ADCP too. This ship was used for winter CREAMS cruises and other international expeditions.

I hope it's enough to submit proposal. If not, please contact me or Prof. Riser: he has "fresh" experience. Hope to be in touch.

Thank you for your attention, sincerely yours,
Dr. Alexander V. Tkalin,
Head, Department of Oceanography and Marine Ecology,
Far Eastern Regional Hydrometeorological
Research Institute, 24 Fontannaya Street,
Vladivostok 690600 RUSSIA.
Phone: 7-(423)-2224887
Fax: 7-(423)-2227754
E-mail: hydromet@online.ru

2.g.2. Scripps Institution of Oceanography, Oceanographic Data Facility.

Laboratory: The Scripps Oceanographic Data Facility (ODF) includes a chemistry laboratory outfitted for support of high-precision analyses of nutrients and dissolved oxygen in water samples. All relevant support equipment, including water purification system, balances, sinks, hood, etc. are in place and operational. The laboratory also prepares equipment, reagents, supplies, and standards for seagoing analytical work involving thousands of sample analyses per year.

The ODF electronic laboratory provides full diagnostic and repair facilities for CTDs, salinometers, altimeters, pingers, and other electronic devices used for shore and sea support of ODF activities. All principal equipment required is in place and functional. Support is also provided for ongoing electronic design and fabrication activities for ODF operations.

The ODF calibration laboratory is a state-of-the-art pressure and temperature facility with large and small temperature baths, reversing thermometer bath, Ruska pressure bench, automatic thermometer bridge, and a wide assortment of standards, references, etc.

Computer: ODF maintains local-area networks connected to the UCSD campus-wide network and the internet. The core computers for STS administrative, ODF data processing, and WHP Office use are now a 4-cpu, single I/O bus Sun SPARCStation 10 and a 2-cpu, dual I/O bus Sun E3000 enterprise server. Seven other Sun SPARCStations of various types and capabilities are also used - when not at sea - in ODF shorebased processing to relieve some cpu load. Other ODF and STS computer-related facilities include 80 GBytes of on-line disk storage, 2 Zeta plotters, 3 HP1200C color plotters, 2 laser printers, 8mm Exabyte and 4mm DAT tape drives, PCs, Apple Macintoshes, and X terminals.

Other: Major ODF seagoing equipment includes six ODF-modified NBIS MkIIIb CTDs (4 have provision for dual PRTs for temperature stability self-check); 3 "WOCE" 36-place single ring rosettes each with 36-position pylons plus 40+ 10 liter ODF or "Bullister" bottles; numerous rosettes based on the older GO pylon design with capacities including 12-24 2-liter bottles, 12-36 10-liter bottles (or up to 48 bottles if half are 2-liter bottles), or 12 30-liter bottles; 3 24-place GO pylons and 3 12-place GO pylons; a large inventory of Niskin type bottles (some from GO and most constructed at SIO) with nominal 2, 2.5, 3, 5, 10, and 30-liter capacities; seven 270-liter "Gerard" water samplers (the remaining US inventory); 4 CTD altimeters; 4 12kHz pingers; 2 ODF-constructed CTD data logger / rosette controllers which enable CTD data logging at full bandwidth plus rosette control (at preset levels) in absence of or supplement to a conducting cable; 350+ reversing thermometers; six Guildline 8500 or 8500A salinometers (modified by ODF for improved performance; some have automatic data logging); three ODF-constructed oxygen autotitrators; three Technicon AAII nutrient autoanalyzers (one is 5-channel), two with automated data logging, plus one Flow Systems autoanalyzer; 3 Barnstead E-Pure water purification systems; cart, track, and air tuggers for large rosettes; plus numerous other items for expedition outfitting.

ODF also operates warehouse and staging facilities, a Niskin bottle repair and test shop, a small machine & carpentry shop, and a logistics office.

Other SIO resources: These include the Marine Science Development Shop (which constructs ODF's rosette frames and bottles and has drafting facilities), the Nimitz Marine Facility (ship support and UNOLS cable inventory), carpentry shop, photography laboratory, MLRG graphics and illustration support facility, large format plotters, and SIO library.

2.g.3. University of Washington, Chlorofluorocarbon Laboratory

The CFC analytical laboratory at the University of Washington has all of the necessary equipment to measure the dissolved CFCs aboard a ship. A seawater extraction system with calibrated seawater volume, automated valves, temperature-controlled valve bodies, and sample loops with calibrated volumes which can be filled with standard gases in the pressure range of 0.02 atm to 3.0 atm has been assembled during the past 3 years. This system has been successfully utilized on two previous expeditions. A Hewlett-Packard 5890II gas chromatograph with an electron capture detector is used to detect the CFCs after they have been extracted from a seawater sample. The chromatographic signal is converted from analog (voltage) to digital using a Hewlett-Packard 35900E analog-digital converter. The digital signal is analyzed using a software package developed at SIO by P. Salameh. This software package runs under the Solaris operating system, currently running on a Sun SparcStation LX. With this package, the CFC data can be processed to near completion at sea. A minimal amount of data processing then needs to be done upon returning from the expedition. The UW CFC laboratory has spares of all of the major components.

A major concern when working aboard any vessel is contamination of the shipboard laboratory by leaky refrigeration/cooling units. On foreign vessels there is also the problem of voltage difference - Russian ships usually supply 220V/50Hz as opposed to 110V/60Hz. Both of these potential problem are solved using a portable laboratory. The UW laboratory has converted a 20-ft. container into a laboratory with an isolation step-down transformer. The container can be secured to the deck and connected to the ship's power to provide a clean working environment. Professor K.-R. Kim has a similar, although smaller, portable laboratory which we plan to utilize.

2.g.4. Principal investigators' facilities

Lynne Talley has provided funding and direction for the nemo.ucsd.edu website, which is our principal hydrographic and float database webserver at SIO. The latter can easily be extended to provide password-protected web support for the ONR JES initiative, at no cost other than the minimal programmer support already contained in the proposal. The address is http://nemo.ucsd.edu. David Newton created and maintains this website.

Talley also maintains a personal website (sam.ucsd.edu) containing some of her own public hydrographic data sets, personally-produced hydrographic atlas materials, and communications regarding cruises while they are being planned or after completion.

No new computer equipment is required. Talley will be upgrading to a Sun Sparc Ultra workstation in October, 1997, as part of WOCE hydrographic data analysis work, which will include extensive inverse modeling. Therefore no new equipment is required in the current proposal.

2.h. Pertinent bibliography of the investigators (attached)

3. Cost information

This three-year proposal includes costs in the first two years which are primarily for collection and processing of new hydrographic data. The third year contains a modest amount for joint analysis of the data set in collaboration with other JES investigators. Cruise costs include support for the Scripps Institution of Oceanography's Oceanographic Data Facility team of 3 and all of their required equipment, materials, shipping and travel. Their budget is described in more detail below in section 3.c. The ODF group is purposely undersized and requires the support of 3 chemists from POI (Tishchenko - co-investigator, Andreev and Sadhakova). Also, as explained in section 2.d.5.d of the project description, a group of 4 additional people is required for CTD console operations, salinity analyses and daily data checking - this group is myself, Ponamarev (POI), D. Newton (programmer - SIO), and a graduate student (SIO). All will be working 12-hour watches at sea; Newton requires associated remote location compensation. Travel to the cruises is budgeted at the same rate as for the ODF group (see below).

Beyond the cruise-specific costs only the following are requested in the first two years - 2 weeks for Newton for cruise preparation, 2 weeks for an administrative assistant, and full support for the graduate student, plus minimal computer maintenance and project specific costs. Programmer support is expanded slightly in the third, analysis, year, which also includes foreign travel to one JES meeting. Publication costs for two manuscripts is included in the third year.

Supply and expense items categorized as project specific are for expenses that specifically benefit this project, are reasonable and necessary for the performance of this project, and can be readily allocable to this project.

Salaries for the Research Project Assistant are for tasks that will specifically benefit and relate only to this project, will be assigned by the PI and charged on a time reported basis, and will not exceed the percent of effort requested. These tasks will include extensive data accumulation, analysis and entry, surveying, tabulation, searching literature, technical typing and editing, and coordination of efforts between project participants.

3.b. University of Washington (Warner) budget

This two-year proposal has a cost of approximately $121,000 for the University of Washington CFC analysis group. During the first year, three months of support are requested for both Mark Warner and a technician to participate in a month-long hydrographic expedition in the Japan/East Sea. The extra months are for preparing the analytical system for shipment and for post-cruise data processing. Foreign travel is requested to and from Pusan, South Korea from where the expedition will be staged. Shipping costs for both air and sea transport are requested. Most of the equipment will be shipped to SIO to be placed in a cargo container for sea freight. The rest will be flown directly to Pusan. A wide variety of expendable supplies are necessary for the shipboard analysis of CFCs. Two thousand dollars are requested for communications, xeroxing, and other miscellaneous expenses associated with this project.

In the second year, analysis and interpretation of this data set will be carried out. Two months of salary for Mark Warner are requested for this purpose. Domestic travel is requested to present results at a national meeting and/or discuss collaborations. Publication charges for a manuscript summarizing our results are included in the second year's budget.

3.c. Scripps Institution of Oceanography/Oceanographic Data Facility

The ODF costs are itemized in the manner which has been used for other ODF proposals. Funds are requested for all of the expendable supplies used before, during, and after the expedition, plus services required in overhauling equipment, processing data, maintaining the calibration laboratory, and distributing the final data. Insofar as possible, costs are charged on a per-cast basis. These include digital and audio tapes, connectors, cabling, data forms, normal wear, maintenance costs, and calibration supplies. Standard seawater for the expedition is here charged at the actual use rate considered proper for "WOCE-quality" expeditions. While this is not a WOCE expedition, the very small but important signal in the deep Japan Sea requires WOCE quality measurements.

The ODF CTD/rosette equipment suite, spare parts, tools, standards, and chemicals will weigh about 12,000 pounds. We have placed the funds for round-trip shipping in this proposal, utilizing ground/sea freight, but also air freight for certain critical items which experience has shown will fare better that way.

The ODF shore support required for a major expedition is substantial. Approximately two months of technician time are spent for shore activities for each technician-month at sea, and additional support beyond that is required for shop services, logistics arrangements, calibrations, and final data reporting. The production of 'final' quality data for each expedition involves support for the specialized calibration and processing services required to extract deep ocean data of the highest reliability. SIO technicians are paid on an 8 hour day, 40 hour week basis. The State of California requires that any weekly time above 40 hours is compensated as overtime. In this case we know from our experience on other sections that the ODF technicians will average 12-hour days and 7-day weeks at sea, and so overtime compensation must be provided.

ODF air travel to and from the cruise is shown at standard or reduced coach rates, but not at "super-APEX" fares. This is required to retain flexibility in re-ticketing as needed to meet expedition contingencies.

4. Supporting information

4.b. Institution participation and support.

The University of California supports the academic year salary of Lynne Talley. The University of California supports the contributions of James Swift as Scientific Director of the Oceanographic Data Facility (ODF) and Woody Sutherland as manager of ODF. Due to the off-campus nature of seagoing research, an off-campus indirect cost rate of 26% is allowed for the University of California budget items other than ODF costs. UCSD allows ODF a very favorable overhead rate of 13%, recognizing the unique off-campus nature of its work as opposed to on-campus laboratory work.

4.c. Other agencies receiving the proposal. No other agencies have received this proposal.

4.d. Coordination of work with Navy and industrial counterparts.

No specific coordination has been planned in this proposal stage. Our assumption is that the new data sets which are gathered will be made immediately available to the Navy and that joint work with Navy modelers in analyzing the new and historical data sets and comparing them with model results will be an integral part of the analysis.