Variability of the Ross Gyre, Southern Ocean: Drivers and Responses Revealed by Satellite Altimetry

Tiago S Dotto,Michael P Meredith,Sheldon Bacon,Eleanor Frajka‐Williams,Alberto Naveira Garabato,Paul R Holland,Andy Ridout,Jack Hooley,Michel Tsamados

doi:10.1029/2018gl078607

Abstract

AbstractYear‐round variability in the Ross Gyre (RG), Antarctica, during 2011–2015, is derived using radar altimetry. The RG is characterized by a bounded recirculating component and a westward throughflow to the south. Two modes of variability of the sea surface height and ocean surface stress curl are revealed. The first represents a large‐scale sea surface height change forced by the Antarctic Oscillation. The second represents semiannual variability in gyre area and strength, driven by fluctuations in sea level pressure associated with the Amundsen Sea Low. Variability in the throughflow is also linked to the Amundsen Sea Low. An adequate description of the oceanic circulation is achieved only when sea ice drag is accounted for in the ocean surface stress. The drivers of RG variability elucidated here have significant implications for our understanding of the oceanic forcing of Antarctic Ice Sheet melting and for the downstream propagation of its ocean freshening footprint.

Highlights

The Ross Sea (RS; Figure 1a), Antarctica, is a region where mixing of distinct water masses and complex interactions with the cryosphere lead to the production and export of dense water, with global-scale impacts (Orsi & Wiederwohl, 2009)
The largest area is observed in May (~2.20 ± 0.22 × 106 km2) and November (~2.30 ± 0.14 × 106 km2), and the smallest at the end of winter and, most prominently, in summer
Our findings suggest that the Ross Gyre (RG) responds to the Amundsen Sea Low (ASL) forcing, and a future deepening of this feature might expand and intensify the gyre, in accord with climate models (Meijers et al, 2012) and sea ice drift trends (Holland & Kwok, 2012)

Summary

Introduction

The Ross Sea (RS; Figure 1a), Antarctica, is a region where mixing of distinct water masses and complex interactions with the cryosphere lead to the production and export of dense water, with global-scale impacts (Orsi & Wiederwohl, 2009) This region is sensitive to climatic changes, and perturbations in the water mass transformations that it hosts influence the properties and quantity of Antarctic Bottom Water exported to the global thermohaline circulation (Jacobs & Giulivi, 2010; Schmidtko et al, 2014). Kwok and Morison (2015) demonstrated the potential use of radar altimetry to study the ice-covered Southern Ocean, with Armitage et al (2018) showing that the large-scale wind curl modulates nonseasonal variability of austral SSH, including within the subpolar (Ross and Weddell) gyres

Results

Discussion

Conclusion