Modeling the variability of the liquid freshwater export from the Arctic Ocean

In this thesis an analysis of the variability of the liquid freshwater (FW) export from the Arctic Ocean on annual and seasonal timescales is presented. Due to missing long-term observations, the variability of the liquid FW export is not well known or understood. Model simulations are therefore currently the only way to study the variability of the FW export from the Arctic.;In order to better understand the differences between the mechanisms driving the export variability through Fram Strait and the CAA, passive dye tracers are added to the ocean module of a state-of-the-art global general circulation model, the Community Climate System Model Version 3 (CCSM3). These tracers allow the identification of FW from different sources, and therefore the individual investigation of the export variability of FW from individual sources. It is shown that the Fram Strait FW export is made up mainly of Eurasian runoff and Pacific FW, whereas the FW exported through the CAA comes primarily from Pacific FW and North American runoff. The variability of the FW exports from individual sources is largely in phase in the CAA, as the CAA FW export is mainly driven by velocity anomalies, not FW concentration anomalies. In Fram Strait on the other hand, FW concentration anomalies contribute as much to the FW export variability as velocity anomalies. The variability of the Fram Strait FW concentrations from the two main FW sources is not in phase, as Pacific FW and Eurasian runoff have different pathways to Fram Strait and their variability is governed by different mechanisms. Whereas the Eurasian runoff export depends strongly on the release of FW from the Eurasian shelf during years with an anticyclonic circulation anomaly (negative Vorticity index), the variability of the Pacific export is mainly controlled by changes in the Pacific FW stored in the Beaufort Gyre, with increased export during years with a cyclonic circulation anomaly (positive Vorticity index). A high vertical resolution of the ocean model is found to be important to resolve the role of FW concentration changes for the Fram Strait FW export variability.;The model simulation also shows that in contrast to the interannual variability, the seasonal variability of the Fram Strait FW export is driven almost entirely by the seasonal cycle of sea-ice melt, with a smaller influence of velocity changes or advected FW concentration changes. The disappearance of the summer sea-ice cover in the Arctic during the 21st century might therefore affect the seasonal cycle of the Fram Strait FW export.;To investigate the role of the atmospheric forcing for the variability of the liquid FW export, a model simulation for 1950--2007 from the University of Victoria Earth System Climate Model (UVic ESCM) is analyzed. It is shown that large-scale atmospheric circulation changes generally control the variability of the FWexport through changes in the FW storage in the Beaufort Gyre. These changes have a large influence on the variability of the FW export through the Canadian Arctic Archipelago (CAA), whereas the Fram Strait FW export is also influenced by changes in the FW storage in the Eurasian basin.