Trends in water mass properties in the Weddell Sea from assimilation of float data in a regional ocean model

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Climate change is strongly conditioned by variations in key areas of the ocean. The Weddell Sea is such a key area, where a major amount of Antarctic Bottom Water (AABW) is formed as an essential contribution to the Meridional Overturning Circulation (MOC). Up to now, hydrographic observations were strongly biased in time toward summer season and spatially toward two repeated WOCE-sections. Within this project all available observational data will be combined with a numerical ocean model with the help of dynamical consistent data assimilation into a complete stateestimate of the Weddell Sea. The main emphasis is placed on collecting and using temperature- and salinity profiles of newly developed ice compatible Argo floats which remove the aforementioned biases. The resulting estimate and the complete phase-space trajectory of the Weddell Sea will enable us to answer the following questions: • How do water mass properties change in the Weddell Gyre, in particular to what extent are the sparse hydrographic observations characteristic for the entire Weddell Sea? • What causes the changes in water mass properties within the Weddell Sea? • To what extent are water mass properties and inflow of Circumpolar Deep Water (CDW) subject of short- and intermediate term variations? Is it possible to detect long-term trends? • How do variations in the WDW-range affect deep and bottom water formation within the Weddell Sea? Further, this work will provide a dynamically consistent time series of the water mass properties of the Weddell Gyre and will be an essential contribution to the project bundle “The role of the Atlantic sector of the Southern Ocean in the climate system”.