Abstract
AbstractThe 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.
Highlights
IntroductionIt is common to describe the Antarctic Circumpolar Current (ACC) as existing due to the belt of open latitudes that are not intersected by land within the latitude band of Drake Passage, the Southern Ocean’s narrowest constriction [see, e.g., Thompson, 2008]
The Southern Ocean and Antarctic Circumpolar Current (ACC), with a zonal volume transport of 137 ± 7 Sv (1 Sv = 106 m3 s−1), are important to the Earth’s climate in providing the major interbasin connection between the Atlantic and Indo-Pacific Ocean [Meredith et al, 2011]
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
Summary
It is common to describe the ACC as existing due to the belt of open latitudes that are not intersected by land within the latitude band of Drake Passage, the Southern Ocean’s narrowest constriction [see, e.g., Thompson, 2008]. The date of the inception of the ACC remains controversial, with estimates spanning those of the opening of Drake Passage [Wei and Wise, 1992; Scher and Martin, 2006]. The opening of these gateways may have played a significant role in the general cooling of the Cenozoic [Sijp et al, 2014]
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