UC San Diego

The Arctic Ocean is characterized by a halocline rather than a thermocline, so that fresh water is found at the surface, with saltier (and often warmer) water beneath. In the western Arctic, the Pacific and Atlantic Oceans provide sources of oceanic heat. The year-round Pacific Summer Water (PSW) temperature maximum is found 40-80 m beneath the sea surface, while Atlantic Water (AW) is generally found deeper than 200 m. Both the Atlantic and Pacific source waters are warming, and the heat content of PSW has nearly doubled over the last three decades.

The broad goals of this disseration are to identify the processes that regulate the release of heat out of these two water masses, to quantify the heat transported upwards where it may affect sea ice, and to understand how these processes may evolve in a changing Arctic Ocean. Microstructure data collected during the 2015 ArcticMix and 2018 Stratified Ocean Dynamics of the Arctic (SODA) process cruises provide a unique opportunity to observe the small-scale mixing associated with subsurface heat in the Canada Basin.

Multiple processes play a role in setting turbulence rates in the western Arctic. Widespread double diffusive convection results in small upwards heat fluxes out of the AW. We investigate the possible influence of observed wind-generated near-inertial internal waves on AW turbulent heat fluxes and find that the impact is minimal, with AW heat fluxes consistently low due to a number of factors inhibiting the creation and vertical propagation of internal waves. We additionally investigate the relative importance of mixing processes associated with anomalously warm PSW intrusions. We find double diffusive convection results in high upwards heat fluxes out of two separate warm intrusions, one warm-core eddy observed in the 2015, and one slope current intrusion observed in 2018. We document a relationship between the vertical complexity of warm intrusions and the total heat flux out of them, with more complex vertical structure corresponding to increased overall mixing. This relationship is supported by 12 microstructure surveys that sampled PSW conducted across both 2015 and 2018.