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I. Intermediate and surface circulation and transformation. Ultimately provide a three-dimensional picture, based primarily on hydrographic data, of the transports and transformations between layers in the North and South Pacific. Contribute to picture of overall transformation, top to bottom.
I.1. Antarctic Intermediate Water layer. Global maps of AAIW properties and intermediate isopycnals using WOCE and hydrographic historical data show that AAIW originates in two locations: the southeastern Pacific and the southwestern Atlantic. In the southeastern Pacific, it is identical to the local Subantarctic Mode Water (based on P19) and enters the subtropical gyre through subduction. It is swept around the gyre and enters the tropical South Pacific in the west. Major fronts exist near 15°-20° latitude on each side of the equator; salinity is highest in the equatorial zone, implying vertical diffusion from above. From properties on the detailed WOCE sections crossing the ACC and circling Antarctica, the direction of transfer of the intermediate, deep and bottom water properties across the front can be distinguished, as can the regions where most transfer occurs. What are the cross-frontal transfers? Can we quantify the complete overturning circulation including upwelling, from the subtropical front southwards? Combination of hydrographic, tracer and float data for further study.
I.2. North Pacific Intermediate Water layer. Using CTD and bottle data from pre-WOCE cruises, it was possible to show that the principal source of freshening for the NPIW layer is in the Okhotsk Sea; the mechanism is brine rejection through ice formation. The amount of newly ventilated water exiting the Okhotsk Sea and entering the subpolar and subtropical gyres has been roughly quantified. The effects of double diffusion and cabelling when the newly-ventilated and freshened intermediate waters meet the much more saline waters of the subtropical gyre may be important. Continue this work from the WOCE data using better methods for quantifying the transports, as well as in situ process studies in the Okhotsk Sea. How is the overturning cell closed - where does the water that feeds the NPIW production come from and how is the loop closed? Is it restricted to the North Pacific or must a larger region be considered? Combination of hydrographic (WOCE and historical), tracer, and float data.
I.3. South Pacific subtropical gyre variability. Using the ongoing quarterly high resolution PX50/PX34 XBT sections at about 30°S we are investigating variations in transport and structure of the upper 800 meters of the subtropical gyre. We have already detected very large-scale disturbances with lifetimes of several months. Useful for understanding representativeness of the P6 WOCE section. With Sprintall, Stammer and Roemmich. Combination with floats, hydrography, altimetry, and wind data for maximum usefulness.
II. Tropical and abyssal circulation. Describe features of the tropical and abyssal circulation which appear to be common.
II.1. Deep tropical circulation. In the tropics from intermediate to abyssal depths, the flows are primarily zonal and vertical and horizontal mixing appear to be enhanced relative to higher latitudes. Properties in the circumpolar water layer (1500-3000 meters) suggest a large-scale, simple circulation pattern, with eastward flow close to but slightly south of the equator, and westward flow 5° to 10° north and south of the equator. The driving mechanism for these flows has not yet been determined, but they resemble a Rossby wave pattern. With Johnson. The deep jets within 2° of the equator are now being described, quantifying their vertical structure using BVF profiles and the LADCP data; this is a global study encompassing all three oceans. With Firing/Hacker/Donohue. There is a well-defined bottom boundary layer on all of the cross-equatorial sections as well. Combination of hydrography, float and LADCP data, also modeling.
II.2. Bottom boundary layers and effects of topography. In all ocean basins, away from strong western boundary currents and the ACC, the bottom-most layers "puddle" in the center of the basins. This yields cyclonic flow around the basins relative to the bottom (and anticyclonic flow around the ridges). I am describing this effect globally. Hydrographic data (LADCP if available).
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