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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, C06013, doi:10.1029/2006JC004051, 2008

Southern Ocean mixed-layer depth from Argo float profiles

Shenfu Dong

CIMAS/RSMAS, University of Miami, Miami, Florida, USA


Janet Sprintall

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Sarah T. Gille

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Lynne Talley

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Abstract

Argo float profiles of temperature, salinity, and pressure are used to derive the mixed-layer depth (MLD) in the Southern Ocean. MLD is determined from individual profiles using both potential density and potential temperature criteria, and a monthly climatology is derived from individual MLDs using an objective mapping method. Quantitative data are available in the auxiliary material. The spatial structures of MLDs are similar in each month, with deep mixed layers within and just north of the Antarctic Circumpolar Current (ACC) in the Pacific and Indian oceans. The deepest mixed layers are found from June to October and are located just north of the ACC where Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are formed. Examination of individual MLDs indicates that deep mixed layers (MLD ≥ 400 m) from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of SAMW. The surface salinity for these deep mixed layers associated with the SAMW formation are slightly fresher compared to historical estimates. Differences in air-sea heat exchanges, wind stress, and wind stress curl in the Pacific and Indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes. Wind mixing and Ekman transport of cold water from the south may assist the SAMW formation in the Indian Ocean. In the eastern Pacific, the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling.

Received 9 December 2006; accepted 26 February 2008; published 13 June 2008.

Keywords: mixed-layer depth; Southern Ocean; mode water.

Index Terms: 4572 Oceanography: Physical: Upper ocean and mixed layer processes; 4207 Oceanography: General: Arctic and Antarctic oceanography (9310, 9315); 4283 Oceanography: General: Water masses; 4504 Oceanography: Physical: Air/sea interactions (0312, 3339); 4262 Oceanography: General: Ocean observing systems.

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Citation: Dong, S., J. Sprintall, S. T. Gille, and L. Talley (2008), Southern Ocean mixed-layer depth from Argo float profiles, J. Geophys. Res., 113, C06013, doi:10.1029/2006JC004051.