Changes in the Subduction of Southern Ocean Water Masses at the End of the Twenty-First Century in Eight IPCC Models

• Published in: Journal of Climate
• Main Authors: Downes, S, Bindoff, NL, Rintoul, SR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2010
• Subjects: Earth Sciences; Oceanography; Physical Oceanography; Antarctic; Southern Ocean; Antarc*
• Online Access: http://www.ametsoc.org; https://doi.org/10.1175/2010JCLI3620.1; http://ecite.utas.edu.au/68291

A multimodel comparison method is used to assess the sensitivity of Subantarctic Mode Water (SAMW)and Antarctic Intermediate Water (AAIW) formation to climate change. For the Intergovernmental Panel onClimate Change A2 emissions scenario (where atmospheric CO2 is 860 ppm at 2100), the models showcooling and freshening on density surfaces less than about 27.4 kg m23, a pattern that has been observed inthe late twentieth century. SAMW (defined by the low potential vorticity layer) and AAIW (defined by thesalinity minimum layer) warm and freshen as they shift to lighter density classes. Heat and freshwater fluxes atthe ocean surface dominate the projected buoyancy gain at outcrop regions of SAMW and AAIW, whereasthe net increase in the Ekman flux of heat and freshwater contributes to a lesser extent. This buoyancy gain,combined with shoaling of the winter mixed layer, reduces the volume of SAMW subducted into the oceaninterior by a mean of 8 Sv (12%), and the subduction of AAIW decreases by a mean of 14 Sv (23%; 1 Sv [106 m3 s21). Decreases in the projected subduction of the key Southern Ocean upper-water masses implya slow down in the Southern Ocean circulation in the future, driven by surface warming and freshening. Areduction in the subduction of intermediate waters implies a likely future decrease in the capacity of theSouthern Ocean to sequester CO2.