Wechselwirkungen zwischen Eis und Ozean im Weddellmeer Studien mit einem gekoppelten Eis-Ozean-Modell des Su?dpolarmeeres

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In the framework of the Bremerhaven Regional Ice Ocean Simulations (BRIOS) a coupled sea ice-ocean model of the Southern Ocean was developed. The model is called “BRIOS-2” and is based on the S-Coordinate Primitive Equation Model (SPEM) and a dynamic-thermodynamic sea ice-model. The model is run on a circumpolar grid which is focussed on the Weddell Sea. It includes the Antarctic ice shelves; shelf ice-ocean interaction is described by the sea ice-model’s thermodynamic component. Numerical simulations are initalized using data from the Hydrographic Atlas of the Southern Ocean and forced with 6-hourly data of the ECMWF-reanalysis. The model is validated against observations of water mass structure and vertically integrated transport as well as sea ice extent, thickness and drift. Quantitatively, a good agreement with observations is achieved. Investigations of sea ice-ocean interaction on the continental shelf in the southwestern Weddell Sea feature a strong correlation between fluctuations of atmospheric forcing and the variability of sea ice formation. Anomalies of meridional wind stress in the inner Weddell Sea are consistent with the phase of the Antarctic Circumpolar Wave (ACW). Positive anomalies of northward wind stress cause an increase of sea ice export in the same and of sea ice formation in the following year leading to an increased production of High Salinity Shelf Water. Driven by a varying density distribution over the continental shelf, the circulation in the Filchner-Ronne ice shelf cavity fluctuates between two modes, each of which features a characteristic distribution of basal freezing and melting regions. Thus, signals of interannual atmospheric variability propagate into the deep ocean and the sub-ice shelf cavities. The simulated Weddell Gyre features a pronounced double cell structure which is caused by the topographic effects of Maud Rise and Astrid Ridge. Flow around and across these elevations causes anomalies of vertical heat flux which affect the sea ice distribution only locally. The spring polynya in the region of Maud Rise appears as a wind-induced phenomenon which is not affected by regional topography. Deep convection in this region may be caused by modifications of the surface fresh water balance and does not depend on the existence of Maud Rise. Inhaltsverzeichnis 1 Einführung 4 2 Modellbeschreibung 11 2.1 Ozeanmodell