Süßwasserschwankungen im arktisch-nordatlantischen Raum

In the past decades, observations in the upper Arctic Ocean and subpolar North Atlantic have shown signicant freshwater changes that were in each region mainly attributed to independent processes. Both regions are sensitive to changes in the density stratication with possible implications for the ocean/atmsophere heat exchange and the deep convection. Thus changes in the freshwater content of the Arctic Ocean and subpolar North Atlantic have the potential to impact the climate locally and globally. The objectives of the present study are to investigate the freshwater content (co)variability of the upper Arctic Ocean and subpolar North Atlantic, to identify the processes causing the observed changes in freshwater content and to analyse possible drivers of these processes. To investigate the freshwater content variability I used objectively mapped salinity fields for the subpolar North Atlantic and Nordic Seas, and objectively mapped liquid freshwater inventories and sea ice volume estimates from the Pan-Arctic Ice Ocean Modeling and Assimilation product for the upper Arctic Ocean. To explore possible links, I compared the liquid freshwater content of the subarctic North Atlantic (SANA; combination of subpolar North Atlantic and Nordic Seas) with the sum of liquid and solid freshwater content of the upper Arctic Ocean from the observational and assimilation products. I found a distinct anti-correlation of the freshwater anomalies in these two regions between 1992 and 2013 with anomalies of the same magnitude. An analysis of freshwater fluxes from the global Finite Element Sea ice Ocean Model and the Common Ocean-ice Reference Experiment version 2 atmospheric forcing data set suggested that the observed freshwater variations resulted from changing freshwater transports. Variations in the Arctic freshwater export to the North Atlantic are found to be most important for the total freshwater content variability of the upper Arctic Ocean and for the liquid freshwater content variability of the western SANA. The eastern SANA freshwater content seems to be mainly influenced by the exchange with the subtropical North Atlantic. Furthermore, this study reveals that the observed freshwater changes are correlated with the Arctic and North Atlantic Oscillation indices. Therefore I suggest that a changing freshwater export from the Arctic Ocean to the SANA responds to decadal alternations of the dominant large-scale atmospheric variability. Thereby the export through the Canadian Arctic Archipelago is associated to different patterns of the atmospheric and oceanic pressure and circulation than the export through the Fram Strait and Barents Sea Opening. I propose, that the recently observed rapid changes in the SANA and upper Arctic Ocean freshwater content resulted from an interplay of these different driving patterns causing parallel changes in the freshwater export on both sides of Greenland. According to the present phase of the decadal alternations of the atmospheric variability and the final years in my freshwater content time series, the fresh water accumulated in the Arctic Ocean during the previous decades started to be released into the SANA. This release might continue in the following years and could have the potential to impact the Atlantic Meridional Overturning Circulation and the oceanic heat release to the Arctic atmosphere and sea ice.

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