The Transfer of Antarctic Circumpolar Waters to the Western South Atlantic Ocean

Open Access

Abstract

22 pages, 17 figures, 6 tables, supporting information https://doi.org/10.1029/2020JC017025.-- Data Availability Statement: Argo float casts and positions are available from http://www.coriolis.eu.org, the float metadata and parking depths come from https://www.usgodae.org/cgi-bin/argo_select.pl and the NOAA and L.M. Gould SADCP data sets are obtained from https://accession.nodc.noaa.gov/NCEI-UH-JASADCP and http://adcp.ucsd.edu/lmgould/, respectively ; Southern 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 ; This work has been funded by the Spanish Government through project SAGA (Ministerio de Ciencia, Innovación y Universidades, ref. no. RTI2018-100844-B-C33). AOA is grateful to the FPU program, funded by the Spanish Government (Ministerio de Educación, Cultura y Deporte, reference FPU17/03796). [.] The authors also recognize the institutional support of the Spanish Government through the Severo Ochoa Center of Excellence accreditation (CEX2019-000928-S) ; Peer reviewed