| Summary: | Thesis: Ph. D. in Physical Oceanography, Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019 Cataloged from PDF version of thesis. Includes bibliographical references (pages 121-133). Global patterns of ocean salinity arise from the exchange of freshwater between the sea surface and the atmosphere. For a quasi-steady state system, these surface fluxes are balanced by compensating transports of salt in the ocean interior. In a warming climate, the atmosphere holds additional water vapor which acts to intensify the global water cycle. Amplified freshwater fluxes are then absorbed at the surface and propagate along ocean circulation pathways. Here, we use coupled model results from the CMIP5 experiment to identify coherent responses in the atmospheric water cycle and in ocean salinity patterns. Some aspects of the response are consistent across models, while other regions show large inter-model spread. In particular, the salinity response in the North Atlantic subpolar gyre, where the mean salinity plays a role in maintaining high surface density for deep-water formation, has low confidence in CMIP5 models. To understand how differences in ocean circulation may affect this response, we use two techniques to diagnose the role of salt transports in the present-day climate. The first is a salt budget within the surface mixed layer, which identifies major transport processes. The second is a Lagrangian particle tracking tool, used to understand the regional connectivity of water masses. From this analysis, we find that anomalous freshwater signals become well mixed within the ocean gyres, but can be isolated on larger scales. The subpolar Atlantic salinity response generally shows freshening at the surface, but is sensitive to the transport of anomalously salty water from the subtropics, a largely eddy-driven process. As CMIP5 models use a range of ...
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