Projected change in the carbon budget of the Southern Ocean due to altered large-scale ocean circulation patterns in a warming climate.

Climate model simulations over the historical period (1861 to 2005) suggest that the Southern Ocean (SO) accounts for ~43% of the anthropogenic CO₂ uptake (Frölicher et al. 2015). As the climate continues to warm throughout the 21^st century, climate and Earth System Models contributed to the fifth phase of the coupled model intercomparison project (CMIP5) project a continued uptake and storage of carbon in the SO. The effects of increased greenhouse gas concentrations include alterations in the wind stress forcing at the ocean surface and increased surface freshwater and heat fluxes, which directly impact the ocean density structure. Such changes alter ocean mixing, reduce deep water formation at high latitudes, and lead to the reorganization of large-scale ocean circulation patterns. The ability to represent physical processes and properties in the SO relative to historical observations differs remarkably across CMIP5 models (Beadling et al. 2019). Thus, we expect their response under increased radiative forcing to differ accordingly, with particular differences in their temporal and spatial patterns of carbon storage and transport. This study evaluates changes in the SO carbon budget in a suite of CMIP5 models at a basin-scale, with a focus on quantifying the changes in carbon fluxes under the RCP8.5 scenario associated with altered water mass formation, meridional transport across 30°S, horizontal transport between basins, and vertical transport from the deep ocean to the intermediate and surface layers. Such an analysis aids in understanding the inter-model differences in projected changes in SO carbon storage and mechanisms controlling the model’s response.

Frölicher, T.L., et al., J.L. Sarmiento, D.J. Paynter, J.P. Dunne, J.P. Krasting, and M. Winton, 2015: Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models. J. Climate, 28, 862–886.

Beadling, R.L., J.L. Russell, R.J. Stouffer, P.J. Goodman, and M. Mazloff, 2019: Assessing the Quality of Southern Ocean Circulation in CMIP5 AOGCM and Earth System Model Simulations. J. Climate, 32, 5915–5940.