Estimates of air-sea feedbacks on sea surface temperature anomalies in the Southern Ocean

Abstract

Sea surface temperature (SST) air-sea feedback strengths and associated decay time scales in the Southern Ocean (SO) are estimated from observations and reanalysis datasets of SST, air-sea heat fluxes, and ocean mixed layer depths. The spatial, seasonal, and scale dependence of the air-sea heat flux feedbacks is mapped in circumpolar bands and implications for SST persistence times are explored. It is found that the damping effect of turbulent heat fluxes dominates over that due to radiative heat fluxes. The turbulent heat flux feedback acts to damp SSTs in all bands and spatial scales and in all seasons, at rates varying between 5 and 25Wm-2K-1, while the radiative heat flux feedback has a more uniform spatial distribution with a magnitude rarely exceeding 5Wm-2K-1. In particular, the implied net air-sea feedback (turbulent1radiative) on SST south of the polar front, and in the region of seasonal sea ice, is as weak as 5-10Wm-2K-1 in the summertime on large spatial scales. Air-sea interaction alone thus allows SST signals induced around Antarctica in the summertime to persist for several seasons. The damping effect of mixed layer entrainment on SST anomalies averages to approximately 20Wm-2K-1 across the ACC bands in the summer-to-winter entraining season and thereby reduces summertime SST persistence to less than half of that predicted by air- sea interaction alone (i.e., 3-6 months).