Abstract
AbstractThe 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 parameterizations 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 that approximates the meteoric freshwater flux plus the sea ice export 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 toward 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.
Highlights
The global ocean overturning circulation is transformed in the high latitudes of both hemispheres
The shelf circulation is relatively weak and most Overflow Water (OW) is formed by Atlantic Water (AW) being entrained into the overflowing SW
Overflow plume model requires as input parameters the ambient water (aW) properties and SW properties and flux, so it is not closed
Summary
The global ocean overturning circulation is transformed in the high latitudes of both hemispheres. The transformation is achieved by extraction of heat to the atmosphere, addition of meteoric freshwater (from precipitation minus evaporation, river runoff, and iceberg calving), and interaction with ice. Understanding how warm salty inflows to polar oceans partition into different outflow components is primitive, and this question is important for oceanography and climate science. The Arctic Ocean and Nordic Seas are separated from the global ocean by relatively shallow ridges between Greenland and Scotland. The flow across these ridges consists of surfaceintensified warm salty water from the North Atlantic Current flowing north (Hansen et al 2008). There is overflow water, which spills into the North Atlantic Ocean through gaps in the ridges. There is a cold fresh surface outflow in the East
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