Freshwater processes and water mass transformation in the Arctic Ocean

This thesis explores freshwater-related processes and water mass transformation in the Arctic Ocean. Knowledge of these processes is important from both a local and a global perspective. Globally, because the export of cold and low saline water and sea ice might influence the North Atlantic and global meridional overturning circulation. Locally, because freshwater processes affect the vertical stratification and permit favorable conditions for the ice cover. Models of different complexity are the main tools of the present work. A part of the material considers how these models can be used to examine the key processes governing freshwater balance. Additionally, the freshwater budgets amongst 10 different ocean general circulation models (OGCMs) are compared and robust features and weaknesses identified. A large part considers the freshwater processes governing the stratification with an emphasis on the low saline upper parts. The interactions between freshwater sources and sinks are studied in an OGCM using passive tracers. It is found that the composition, pathways and shelf-basin exchange of low saline water primarily involve processes linked to Siberian runoff, Pacific water and sea-ice melting and formation. Motivated by observed changes and paleorecords the sensitivity of the stratification is further explored in freshwater perturbation experiments with an OGCM. The response yields a deeper halocline for decreasing freshwater input, in line with a theoretical model. The final part focuses on a new framework for analyzing water mass transformations. In the framework volume, heat and salt budgets are computed in salinity-temperature space. Using different OGCMs it is shown how surface and interior processes transform inflowing waters towards colder and fresher waters and how the halocline renewal rate can be estimated. Limiting cases for the water mass transformation balance are identified by separating contributions from surface, internal and boundary fluxes.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.