Frontal Circulation and Submesoscale Variability during the Formation of a Southern Ocean Mesoscale Eddy

Megan Stamper,Philip Hosegood,Katherine A. Adams,Jean-Baptiste Sallée,John R. Taylor,Ricardo Torres,Scott Bachman

doi:10.1175/jpo-d-16-0266.1

Abstract

AbstractObservations made in the Scotia Sea during the May 2015 Surface Mixed Layer Evolution at Submesoscales (SMILES) research cruise captured submesoscale, O(1–10) km, variability along the periphery of a mesoscale O(10–100) km meander precisely as it separated from the Antarctic Circumpolar Current (ACC) and formed a cyclonic eddy ~120 km in diameter. The meander developed in the Scotia Sea, an eddy-rich region east of the Drake Passage where the Subantarctic and Polar Fronts converge and modifications of Subantarctic Mode Water (SAMW) occur. In situ measurements reveal a rich submesoscale structure of temperature and salinity and a loss of frontal integrity along the newly formed southern sector of the eddy. A mathematical framework is developed to estimate vertical velocity from collocated drifter and horizontal water velocity time series, under certain simplifying assumptions appropriate for the current dataset. Upwelling (downwelling) rates of O(100) m day−1 are found in the northern (southern) eddy sector. Favorable conditions for submesoscale instabilities are found in the mixed layer, particularly at the beginning of the survey in the vicinity of density fronts. Shallower mixed layer depths and increased stratification are observed later in the survey on the inner edge of the front. Evolution in temperature–salinity (T–S) space indicates modification of water mass properties in the upper 200 m over 2 days. Modifications along σθ = 27–27.2 kg m−3 have climate-related implications for mode and intermediate water transformation in the Scotia Sea on finer spatiotemporal scales than observed previously.

Highlights

The Southern Ocean hosts the most energetic current in the world, the Antarctic Circumpolar Current (ACC)
At the time of the drifter release, 18 days after the sea surface temperature (SST) and sea surface height (SSH) observations presented in Figure 2, the meander had sharpened yet remained tethered to the ACC as observed by SST and SSH fields, Figure 4a
We have presented high-resolution observations across the ACC as a cyclonic eddy formed in the Scotia Sea

Summary

Introduction

The Southern Ocean hosts the most energetic current in the world, the Antarctic Circumpolar Current (ACC). Results from the drifter-following survey are presented as follows in Section 3: a) eddy formation, b) frontal circulation, c) cross-frontal variability, and d) water mass modification.

Results

Conclusion