Topographic Control of Southern Ocean Gyres and the Antarctic Circumpolar Current: A Barotropic Perspective

Ryan D Patmore,Michael P Meredith,Paul R Holland,David R Munday,Alberto C Naveira Garabato,David P Stevens

doi:10.1175/jpo-d-19-0083.1

Ryan D Patmore, Michael P Meredith + Show 4 more

Open Access

https://doi.org/10.1175/jpo-d-19-0083.1

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Abstract

AbstractIn the Southern Ocean the Antarctic Circumpolar Current is significantly steered by large topographic features, and subpolar gyres form in their lee. The geometry of topographic features in the Southern Ocean is highly variable, but the influence of this variation on the large-scale flow is poorly understood. Using idealized barotropic simulations of a zonal channel with a meridional ridge, it is found that the ridge geometry is important for determining the net zonal volume transport. A relationship is observed between ridge width and volume transport that is determined by the form stress generated by the ridge. Gyre formation is also highly reliant on the ridge geometry. A steep ridge allows gyres to form within regions of unblocked geostrophic (f/H) contours, with an increase in gyre strength as the ridge width is reduced. These relationships among ridge width, gyre strength, and net zonal volume transport emerge to simultaneously satisfy the conservation of momentum and vorticity.

Highlights

The Antarctic Circumpolar Current (ACC) and Southern Ocean gyres are key components of the global climate system
A series of experiments are carried out exploring the response of Southern Ocean gyres and the ACC to variations in the width of a meridionally aligned ridge
The results show that the volume transport of a barotropic circumpolar current is highly sensitive to ridge width variations

Summary

Introduction

The Antarctic Circumpolar Current (ACC) and Southern Ocean gyres are key components of the global climate system. Heat, salt, and other important tracers are transported zonally between these ocean basins around Antarctica via the ACC (Talley 2013), which has an estimated total volume transport of 173.3 6 10.7 Sv (1 Sv [ 106 m3 s21) (Donohue et al 2016). The Southern Ocean has numerous topographic features with scales similar to terrestrial mountain ranges, spanning distances of O(1000) km. Large-scale topographic features are of particular importance in the Southern Ocean (Hughes and Killworth 1995) and are known to have a significant effect on steering the path of the ACC (Gordon et al 1978; Killworth 1992)

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