P06 The Southern Ocean: where Ocean, Ice and Atmosphere Meet

IAPSO (Physical Oceanography)

30-Jun-2015, 10:30 - 12:00

Abstract content:

Cryospheric drivers of recent changes in Southern Ocean stratification, circulation, and carbon uptake

In recent decades, Southern Ocean surface waters freshened and stratified. Our prior work shows that the freshening of the surface and intermediate waters can mostly be attributed to an increased northward freshwater transport by sea ice. The freshening of the shelf and bottom waters is largely driven by increased glacial melt water fluxes from Antarctica. Here, we investigate the effects of these observed changes in the cryospheric buoyancy forcing on the water mass structure, circulation, and air-sea carbon flux of the Southern Ocean using an eddy-resolving regional ocean model (ROMS). At the surface, we drive the model with newly derived buoyancy and momentum fluxes, which are a combination of an observation based sea-ice mass budget, melt flux estimates from ice shelves and ice bergs, and ERA-Interim atmospheric reanalysis data. With this forcing, the model reproduces the spatial and temporal complexity of the Southern Ocean water mass structure and circulation very well. First results, from factorial simulations show that changes in surface buoyancy fluxes from sea ice and land ice can explain most of the recent stabilization of the Southern Ocean surface waters, especially in the Pacific sector. Initial results from performing simulations with an embedded ecological/biogeochemical model support the hypothesis that this stabilization of the surface waters reduces the upwelling of carbon-rich waters, and thus increases the uptake of CO2 from the atmosphere. Consequently, this mechanism may be crucial in explaining the recent reinvigoration of the Southern Ocean carbon sink, i.e., its recovery from a period of saturation.

A. Haumann1,2, M. M├╝nnich1, N. Gruber1,2, S. Eberenz1, C. Nissen1, P. Landsch├╝tzer1.
1ETH Zurich, Environmental Physics / Institute of Biogeochemistry and Pollutant Dynamics, Zurich, Switzerland.


Southern Ocean     freshening     stratification     upwelling     buoyancy forcing     sea ice     ice shelf     carbon sink