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Seminar talk: A Conceptual Model of Polar Overturning Circulations

Thomas Haine from Johns Hopkins University will give a seminar talk on November 9, 2020.

Portrait Thomas Haine
Thomas Haine

Short biography:

Thomas Haine is a Professor at the Department of Earth & Planetary Sciences at Johns Hopkins University. His research interests are in ocean circulation and dynamics, and the ocean’s role in climate. He is involved in improving estimates of the geophysical state of the ocean circulation through analysis of field data and circulation model results. He is particularly interested in the high latitude oceans, including the subpolar North Atlantic, Arctic, and Southern Oceans. He studies watermass ventilation processes (rates, pathways, variability, and mechanisms), three-dimensional circulation, and geophysical fluid dynamics. He also investigates key physical processes that maintain the state of the extra-tropical upper ocean focusing on fluid dynamics and thermodynamics and their role in controlling sea surface temperature variability over years to decades.


The global ocean overturning circulation carries warm, salty water to high latitudes, both in the Arctic and Antarctic. Interaction with the atmosphere transforms this inflow into three distinct products: sea ice, surface Polar Water, and deep Overflow Water. The Polar Water and Overflow Water form estuarine and thermal overturning cells, stratified by salinity and temperature, respectively. A conceptual model specifies the characteristics of these water masses and cells given the inflow and air/sea/land fluxes of heat and freshwater. The model includes budgets of mass, salt, and heat, and parametrizations of Polar Water and Overflow Water formation, which include exchange with continental shelves. Model solutions are mainly controlled by a linear combination of air/sea/ice heat and freshwater fluxes and inflow heat flux. The model shows that for the Arctic, the thermal overturning is likely robust, but the estuarine cell appears vulnerable to collapse via a so-called heat crisis that violates the budget equations. The system is pushed towards this crisis by increasing Atlantic Water inflow heat flux, increasing meteoric freshwater flux, and/or decreasing heat loss to the atmosphere. The Antarctic appears close to a so-called Overflow Water emergency with weak constraints on the strengths of the estuarine and thermal cells, uncertain sensitivity to parameters, and possibility of collapse of the thermal cell.


Arranged date for the seminar talk: Nov 09, 2020 at 14:15