Causal Interactions Between Southern Ocean Polynyas and High-Latitude Atmosphere-Ocean Variability

The Weddell Sea open-ocean polynya has appeared only once in the observational satellite record, while the smaller Maud Rise polynya has occurred more frequently. Yet, many standard resolution models represent these features poorly, if at all. We analyze a synoptic-scale Earth system model simulation to investigate the impact of open-ocean polynyas on high-latitude atmosphere-ocean variability. Consecutive annual appearances of a polynya in austral winter are associated with a poleward shift in turbulent air-sea heat fluxes and increased ocean heat loss from the Weddell Sea. We conduct a novel statistical analysis of cause-effect relationships to diagnose the local and remote interactions with this heat loss on interannual time scales. First, we find that polynya heat loss causes a persistent increase in surface air temperature poleward of 55˚ S, reducing the meridional temperature gradient and poleward atmospheric heat transport in the Southern Hemisphere mid-latitudes. A second response is found in the pattern of zonal wind over the Weddell Sea, which exhibits strengthened subpolar westerlies in response to polynya heat loss. Surprisingly, the buildup of high-latitude ocean heat content, which supplies polynya heat loss, is driven by reduced surface heat flux during periods of full ice cover. Ocean heat transport variability opposes this buildup of heat, but surface processes dominate. These results underscore the potential for open-ocean polynyas to appear periodically, yielding significant impacts on high-latitude climate and highlighting the challenge of representing these highly episodic features correctly in climate models.