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The Cold Transit of Southern Ocean Upwelling
Author(s) -
Evans Dafydd Gwyn,
Zika Jan D.,
Naveira Garabato Alberto C.,
Nurser A. J. George
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl079986
Subject(s) - upwelling , downwelling , circumpolar deep water , thermohaline circulation , oceanography , climatology , north atlantic deep water , antarctic intermediate water , water mass , environmental science , deep ocean water , geology , ocean general circulation model , deep water , surface water , atmospheric sciences , general circulation model , climate change , environmental engineering
The upwelling of deep waters in the Southern Ocean is a critical component of the climate system. The time and zonal mean dynamics of this circulation describe the upwelling of Circumpolar Deep Water and the downwelling of Antarctic Intermediate Water. The thermodynamic drivers of the circulation and their seasonal cycle play a potentially key regulatory role. Here an observationally constrained ocean model and an observation‐based seasonal climatology are analyzed from a thermodynamic perspective, to assess the diabatic processes controlling overturning in the Southern Ocean. This reveals a seasonal two‐stage cold transit in the formation of intermediate water from upwelled deep water. First, relatively warm and saline deep water is transformed into colder and fresher near‐surface winter water via wintertime mixing. Second, winter water warms to form intermediate water through summertime surface heat fluxes. The mixing‐driven pathway from deep water to winter water follows mixing lines in thermohaline coordinates indicative of nonlinear processes.