On the role of the Antarctic Slope Front on the occurrence of the Weddell Sea polynya under climate change

Polynyas, which are large holes in sea ice, are believed to have a signicant impact on the climate

through feedback with the atmosphere and modication of the global ocean circulation. A study by de

Lavergne et al. (2014) found that CMIP5 models predict a slow down or even cessation of these events

into the future due to ocean freshening. Here we revisit the conclusion of a cessation of the Weddell Sea

Polynya (WSP) under climate change. We hypothesis that, because of their relatively coarse resolutions

in the ocean, CMIP5 models are unable to capture important processes involved in the formation of the

polynyas and in their response to climate change. To invesitigate that hypothesis, we use pre-industrial

control and 1%CO2 rise/year simulations of the high resolution GFDL CM2.6 and of the CMIP5 models

that form polynyas in the Weddell Sea to investigate the response of the polynya to climate change. We

find that, under climate change, CM2.6 forms WSP at the same time and with the same duration as

under preindustrial forcing. In contrast, the CMIP5 models show either a cessation or slowdown of these

events under climate change due to open ocean surface freshening. Furthermore, we find that CMIP5

models cannot accurately capture the shelf Antarctic Slope Current and Antarctic Slope Front, which

when resolved in CM2.6, constrains freshening driven by sea ice melt and enhanced runoff to remain on

the shelf region. Open ocean stratication is then enhanced by freshening in CMIP5 models, resulting in

a slow down of these WSP events. These results point to the need to improve simulations of shelf ocean

circulation used in climate change projections.