The Reponse of the Southern Ocean to Variable Wind Forcing and the Role of Sea Ice

The roles of winds and sea ice in subsurface Southern Ocean warming have been discussed, but it is not known if these mechanisms are independent of each other. This question is addressed in this study through a set of wind-forced sensitivity experiments in the Community Climate System Model version 3 (CCSM3). These experiments force the ocean with spatially varying and linearly trending anomalous wind stress derived from National Centers for Environmental Prediction (NCEP) reanalysis data from 1948--2007, multiplying the derived pattern by -1x, +1x, or +2x. An experiment with a wind multiplier of +1x and enhanced CO2 was also performed.;After 40 years of forcing, the positively forced Antarctic Circumpolar Current (ACC) generally cools due to wind-driven turbulent mixing and isopycnal eddy mixing, while to the north, mode waters have warmed due to Eulerian heat transport convergence. South of the ACC, the Weddell Sea cools strongly between 500--3000m depth. A mechanism linking wind-forcing and sea ice changes to the deep Weddell Sea changes is proposed: enhanced wind stress accelerates the Weddell Gyre, increasing sea ice export from the east coast of the Antarctic Peninsula. This thins the coastal sea, increasing the sea ice growth rate and salt rejection to the ocean. This in turn drives enhanced deep water production and more rapidly ventilates the deep ocean. Most wind forced changes to the ocean are shown to be fairly linearly related to the strength of the forcing. The addition of CO2 tends to not only strongly warm the near surface atmosphere, the ACC, and mode waters, but also largely negates the deep Weddell Sea wind-forced cooling by opposing the mechanism described above. A set of eddy permitting ozone forced experiments CCSM4 was also examined. They indicated a potential underestimate in the eddy response to forcing in the CCSM3 experiments, though direct comparison with the CCSM3 experiments was difficult due to differences in forcing and forcing strength.