The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current

Abstract

The date of inception of the Antarctic Circumpolar Current is debated due to uncertainty in the relative opening times of Drake Passage and the Tasman Seaway. Using an idealized eddy‐resolving numerical ocean model, we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current. We find that overlapping continental barriers do not impede a circumpolar transport in excess of 50Sv, as long as a circumpolar path can be traced around the barriers. However, the presence of overlapping barriers does lead to an increased sensitivity of the current's volume transport to changes in wind stress. This change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress. Specifically, when the pressure drop across continents is the main balancing sink of momentum, the zonal volume transport is sensitive to changes in wind stress. Changes in zonal volume transport take place via altering the depth‐independent part of the circumpolar transport rather than that arising from thermal wind shear. In such a scenario, isopycnals continue to slope steeply across the model Southern Ocean, implying a strong connection between the deep and surface oceans. This may have consequences for the meridional overturning circulation and its sensitivity to wind stress.

Eddy saturation and frictional control of the Antarctic Circumpolar Current

“…The numerical model is an idealized eddy‐resolving (10 km grid spacing) configuration of the MITgcm [ Marshall et al ., ], previously used to study the impact of the Drake Passage and Tasman Gateway on the ACC [ Munday et al ., ], to which the reader is referred for full model details and parameters. The configuration used in this study is that with a single topographic obstacle in the form of a 1.5 km high topographic ridge; the channel is otherwise 3 km deep, 9600 km long, and 2000 km wide.…”

New Paleomagnetic and 40Ar/39Ar Geochronological Results for the South Shetland Islands, West Antarctica, and Their Tectonic Implications

“…The breakup of Gondwana around Antarctica commenced in two stages (Chen et al, 2008;König & Jokat, 2006). The opening of the Drake Passage and Tasman Seaway resulted in the formation of the Antarctic Circumpolar Current (ACC) (Barker, 2001;Eagles et al, 2006;Livermore et al, 2005Livermore et al, , 2007Munday et al, 2015). As a consequence of the final breakup event of Gondwana, the Antarctic Peninsula and the South American Plate were finally separated, forming the Drake Passage.…”

The onset of modern‐like Atlantic meridional overturning circulation at the Eocene‐Oligocene transition: Evidence, causes, and possible implications for global cooling

“…The development of the ACC is controlled by the history of two critical oceanic gateways, the Drake Passage and the Tasman Gateway [e.g., Toggweiler and Bjornsson , ; Stickley et al ., ; Exon et al ., ; Lagabrielle et al ., ; Sijp et al ., ]. The ambiguity about the ACC during the late Paleogene is about its depth that drives a full interhemispheric AMOC, and its route while the Tasman Gateway was closed [ Munday et al ., ]. There are three principal events in the history of the ACC during the late Eocene and the Oligocene.…”

“…Geochemistry, Geophysics, Geosystems 10.1002/2017GC006826 Lagabrielle et al, 2009;Sijp et al, 2011]. The ambiguity about the ACC during the late Paleogene is about its depth that drives a full interhemispheric AMOC, and its route while the Tasman Gateway was closed [Munday et al, 2015]. There are three principal events in the history of the ACC during the late Eocene and the Oligocene.…”