Impacts of Climate Change on Mode and Intermediate Water Masses in the Southern Ocean

• Published in: Journal of Climate
• Main Authors: Downes, S, Bindoff, NL, Rintoul, SR
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2009
• Subjects: Earth Sciences; Oceanography; Biological Oceanography; Indian; Southern Ocean; Antarc*
• Online Access: https://doi.org/10.1175/2008JCLI2653.1; http://www.ncbi.nlm.nih.gov/pubmed/8948755; http://ecite.utas.edu.au/62715

Changes in the temperature, salinity, and subduction of Subantarctic Mode Water (SAMW) and AntarcticIntermediate Water (AAIW) between the 1950s and 2090s are diagnosed using the CSIRO Mark version 3.5(Mk3.5) climate system model Caps under a CO2 forcing that reaches 860 ppm by the year 2100. TheseSouthern Ocean upper-limb water masses ventilate the ocean interior, and changes in their properties havebeen related to climate change in numerous studies. Over time, the authors follow the low potential vorticityand salinity minimum layers describing SAMW and AAIW and find that the water column in the 2090s shiftsto lighter densities by approximately 0.2 kg m23. The model projects a reduction in the SAMW and AAIWannual mean subduction rates as a result of a combination of a shallower mixed layer, increased potentialvorticity at the base of the mixed layer, and a net buoyancy gain. There is little change in the projected totalvolume of SAMW transported into the ocean interior via the subduction process; however, the authors find asignificant decrease in the subduction of AAIW. The authors find overall that increases in the airsea surfaceheat and freshwater fluxes mainly control the reduction in the mean loss of the SAMW and AAIW surfacebuoyancy flux when compared with the effect of changes supplied by Ekman transport because of increasedzonal wind stress. In the A2 scenario, there are cooling and freshening on neutral density surfaces less than27.3 kg m23 in response to the warming and freshening observed at the oceans surface. The model projectsdeepening of density surfaces due to southward shifts in the outcrop regions and the downward displacementof these surfaces north of 458S. The volume transport across 328S is predicted to decrease in all three basins,with southward transport of SAMW and AAIW decreasing by up to 1.2 and 2.0 Sv (1 Sv [ 106 m3 s21),respectively, in the Indian Ocean. These projected reductions in the subduction and transport of mode andintermediate water masses in the CSIRO Mk3.5 model could potentially decrease the absorption and storageof CO2 in the Southern Ocean.