Ocean Sciences 2010

An Argo global mixed layer depth climatology
J. Holte; J. Gilson; L. D. Talley; D. H. Roemmich
1. Scripps Institution of Oceanography, La Jolla, CA, United States.

The Argo profiling float array is currently producing the most comprehensive data set of the upper ocean, including the mixed layer. A global monthly climatology of mixed layer properties has been computed from more than 430,000 quality-controlled Argo profiles. This climatology is intended for use with pCO2 observations, estimation of upper ocean heat budgets, and examination of mode and intermediate water formation regions. The climatology is calculated with a new hybrid algorithm (Holte and Talley, JAOT 2009) for detecting the mixed layer depth (MLD). The algorithm can be used with either density or temperature profiles, and represents a significant improvement over threshold methods when only temperature is available. (XBT data sets, which currently constitute about 25% of ongoing profiling, will be included in future work.) The new monthly climatology is compared with previously published climatologies based mainly on threshold criteria. Improvements are especially large in regions of intermediate water formation, where deep winter mixed layers blend into deeper waters and threshold methods are not robust. In the Labrador Sea, the new climatology's average MLDs are more than 100 m shallower than the threshold climatologies. Subantarctic Mode Water mixed layers in the Southern Ocean are typically 40 m shallower in the new climatology. The temperature threshold climatology also features anomalously deep mixed layers in regions where salinity contributes significantly to the upper ocean density structure. The new algorithm climatology provides accurate information about the depth, area extent, and seasonal patterns of global mixed layers. The individual profile results are also easily retained and can be used to construct time series of mixed layer properties in specific regions of interest.