Abstract
AbstractSouthern Ocean waters enter the South Atlantic Ocean through the Scotia Sea along pathways constrained by the bathymetry of the northern Scotia Sea passages. We use the Argo profiling‐float data set to calculate the water transports in and out of the region, focusing on the water balances down to the deepest isoneutral sampled in all passages (γn = 28.0 kg m−3, located between about 500 and 2,000 m in the Drake Passage and even shallower in the Northern Passages). Down to this reference level, the water inflow through the Drake Passage is 140.8 ± 7.4 Sv and the water outflow through the deeper portions of the Northern Passages is 115.9 ± 8.3 Sv, implying a leakage of about 25 ± 11.1 Sv over topography shallower than 1,000 m. Below the reference isoneutral and down to 2,000 m, an additional 23.4 Sv enter through the Drake Passage; when added to reported inputs of about 20 Sv through the South Scotia Ridge, this accounts well for the observed 43.4 Sv outflow–from 28.0 kg m−3 to 2,000 m–through the Northern Passages. Relative to the 2,000 m reference level, the mean barotropic contribution always represents over half the total transports. We also observe substantial seasonal and moderate interannual variations in the water transports and composition (peak differences occur seasonally in the Drake Passage, with a range of 111–174 Sv), associated with changes in water exchange across the frontal systems. Two independent measures set the water mean‐residence time in the Scotia Sea at about 6–8 months.
Highlights
The Antarctic Circumpolar Current (ACC) constitutes the skeleton of the global overturning circulation, as it exchanges heat, mass, and freshwater between the Pacific, Atlantic, and Indian oceans (Rintoul & Naveira Garabato, 2013)
The first one comes from the Drake Passage section between 64°W and 62°W (1979–2013) while the second one comes from the Laurence Gould Platform
We have estimated the errors in the 1,000 m reference velocities to be always well below 0.01 m s−1, in good agreement with the velocity errors for these same passages according to the ANDRO database (Lebedev et al, 2007; Ollitrault & Rannou, 2013)
Summary
The Antarctic Circumpolar Current (ACC) constitutes the skeleton of the global overturning circulation, as it exchanges heat, mass, and freshwater between the Pacific, Atlantic, and Indian oceans (Rintoul & Naveira Garabato, 2013). The ACC does not flow as a single barotropic jet; instead, it exhibits a complex structure of frontal systems that merge and diverge along the circumpolar path, as reflected from the three-dimensional distribution of temperature, salinity, and dissolved oxygen (Kim & Orsi, 2014; Meredith et al, 2003; Orsi et al, 1995; Sokolov & Rintoul, 2007). As part of the intensive measurements performed in the 1970s and 1980s during the International Southern Ocean Studies program, Whitworth and Peterson (1985) obtained the first ACC transport estimate, 134 Sv (1 Sv ≡ 106 m3 s−1). More recent studies have found transports to be as large as 173 Sv (Chidichimo et al, 2014; Donohue et al, 2016) and 175 Sv (Colin de Verdière & Ollitrault, 2016)
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