UC San Diego

Oceanic uptake of atmospheric heat as well as incorporation of freshwater occurs across a vast range of spatial scales. Subsequently, these buoyant water masses are transported and modified within the ocean interior. Several physical processes relevant to the transport and mixing of heat and freshwater at an array of coastal scales, ranging from 1000s of km at the continental shelf slope to m within estuaries, are the topic of this dissertation. Analysis of a mix of data assimilative and idealized numerical models and field observations has yielded several impactful results that have direct relevance to coastal societies and ecosystems. At the largest scale, a mechanism that delivers warm water within the Antarctic Circumpolar Current to the continental shelf slope where it crosses into the Amundsen Sea outer shelf has been identified. Vorticity input by wind-stress curl results in the poleward motion of heat that has potential to contribute to Antarctic Ice Sheet mass loss and consequently, global sea level rise. At the much smaller scales of the inner-shelf to surf zone, surface gravity wave induced onshore currents and mixing drastically modify low inflow estuarine freshwater outflows by reducing offshore transport and elongating alongshore and vertical extent within the surf zone. Because the freshwater distribution can be thought of as a proxy for tracers such as pollution, nutrients, or other plume constituents, these results have strong implications for beach contamination among other concerns that frequently arise due to the presence of buoyant outflows in the nearshore region. Within the estuary, lateral circulation moves channelized waters to regions of enhanced productivity over bathymetric shoals. In San Diego Bay, a low inflow estuary that lies in a unique parameter space among estuaries, this process is, at least in part, due to differential advection. Field data suggest that this process is sensitive to seasonal variation in buoyancy inputs and that circulation patterns may be altered in future climate change scenarios, thus impacting the wildlife that utilize the bay for breeding, habitat, and foraging. As such, the findings of this dissertation advance the fundamental science necessary to contribute to many societally relevant coastal management issues.