Long Term Observations of Thermal Diffusivity in the Arctic Pycnocline

Despite high levels of heat contained within the strongly salinity stratified Arctic pycnocline, the contribution of this heat to ice melt is typically small compared with solar radiation entering the upper ocean during the summer. As the flux of heat from both Pacific and Atlantic inflows at depth into the Arctic system increase, it is important to correctly estimate the turbulent thermal diffusivity of the pycnocline at depths near the base of the mixed layer. Observations of vertical turbulent heat fluxes and local diffusivity are being made with sensor systems suspended at 50m depth below ice-deployed Autonomous Ocean Flux Buoys (AOFBs) drifting in the Beaufort Sea and Central Arctic Basin as part of the ONR SODA project and the NSF MOSAiC program. These instrument systems measure thermal microstructure and finescale vertical thermal gradients over seasonal timescales resolving the highly episodic turbulent mixing events that move heat vertically through the pycnocline. Concurrent measurements of the local stratification and current shear identify processes contributing to the mixing events. Pycnocline heat fluxes will be compared with winter ocean/ice heat fluxes measured at the top of the ocean mixed layer by the AOFB.