WHOI PO

Title: Observing the multi-scale processes linked to high-latitude ocean ventilation 
Abstract: At high latitudes, cold surface waters sink and spread through the abyss. This “ventilation” of the deep ocean creates a vast sink for anthropogenic carbon and replenishes oxygen to marine organisms at depth. Predictions of how ocean ventilation will respond to rising global temperatures and glacial melt remain uncertain, in part due to the sparsity of observations in the polar and subpolar regions.

Here, I leverage moored observations to examine the formation of two crucial water masses tied to ocean ventilation: Labrador Sea Water (LSW), which feeds into the lower limb of Atlantic Meridional Overturning Circulation, and High Salinity Shelf Water (HSSW), a precursor to Antarctic Bottom Water, a water mass that fills the lowest kilometer of the global ocean. Using a moored array of dissolved oxygen time series, I quantify the net export of oxygen from the Labrador Sea and show that LSW formation is a key contributor to North Atlantic ventilation. As LSW formation is partially decoupled from overturning across the broader subpolar North Atlantic region, a crucial implication is that the future of North Atlantic ventilation will not necessarily follow projected declines in the strength of AMOC. Turning to smaller scales, I use moored turbulence and salinity measurements to examine turbulent mixing of brine in the Terra Nova Bay Polynya, Ross Sea, Antarctica that facilitates the formation of HSSW. I find that Law of the Wall, a simple boundary layer scaling based on wind stress, sufficiently predicts the measurements of turbulence and yields a mixing time scale consistent with observed changes in salinity over depth. This holds despite pervasive Langmuir Circulation in the polynya, which is often thought to invalidate Law of the Wall due to its lack of terms accounting for wave-generated turbulence. Law of the Wall forms the basis for widely-used vertical mixing schemes in ocean models, and these results suggest that its use may not be a dominant source of error when simulating vertical upper ocean fluxes in the polynya, and possibly the upper ocean more broadly. Together, my findings highlight the multi-scale physical processes governing high-latitude ocean ventilation and inform efforts to improve predictions of a changing ocean-climate system.