Mecanisms of variability of dense water formation and export in the subpolar North Atlantic
Julie DeshayesIFREMER, Brest
Wednesday, February 23rd, CERFACS Conference Room - 14h00
Abstract.
The oceanic poleward heat transport and the meridional overturning circulation (MOC) are strongly influenced by what happens in the subpolar North Atlantic, where convection forms dense water that is exported southward. In a convective basin, variability in the formation and export of dense water is due to changes in the two drivers: local buoyancy fluxes and the convergence of buoyancy.
We first investigate the relative contribution of local heat fluxes and the convergence of heat by the remotely-forced circulation using a conceptual model of a convective basin. When applied to the Labrador Sea, the model suggests that variability in the formation of Labrador Sea Water simply integrates the local atmospheric forcing on decadal timescale, whereas variability in the export of water as dense as Labrador Sea Water is directly related to the subpolar gyre variability. Analysis of dense water formation and export in a realistic hindcast simulation of the North Atlantic, supports this result.
The hindcast simulation also allows to explore the role of salinity fluctuations in the subpolar variability during the last 4-5 decades. Salinity is found to act as a passive tracer, ie it has no active influence on dense water formation nor the MOC.
Finally, the conceptual model suggests that eddies influence interannual variability in dense water formation and export. This motivated our current research projects that attempt to fully resolve meso-scale processes in realistic hindcast simulations of the subpolar North Atlantic.
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