| Summary: | The Arctic has arguably undergone the most rapid environmental changes in the world in recent decades due to climate change. Climate change in the Arctic has a large range of climatic and societal impacts, such as sea level rise and large-scale changes in the oceanic circulation, which affect the global climate as a whole. The deeper water masses of the Arctic Ocean have similarly undergone large structural changes in recent decades, however the lack of observational data makes it difficult to understand the role of the deep ocean for the global climate. Through the use of global climate model output and observational data collected in field campaigns as part of this project, the work in this dissertation sets out to improve the understanding of the deep Arctic Ocean, a rapidly evolving and simultaneously poorly understood part of the climate system. Through analyses of global climate models, a number of biases were found in the central Arctic Ocean, which were related to poor sea ice-ocean coupling and inaccurate properties introduced further upstream in the adjacent Nordic Seas. Using observational data, the significance of small-scale sea ice-ocean processes was highlighted. Additionally, new circulation pathways were discovered, and it was found that eddies likely have an important role for setting deep oceanic properties over large spatial scales. Finally, it was found that the deep waters of the Greenland Sea are now a heat source for the central Arctic Ocean, due to a strong warming trend that occurred as a result of the cessation of deep convection in the 1980's. The biases found in the models, and the importance these processes were found to have in observations, suggest that these processes need to be better considered in future iterations of global climate models. This dissertation therefore provides another step towards understanding the Arctic.
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