Abstract
Abstract. We study the variability of hydrographic preconditioning defined as the heat and salt contents in the Ligurian Sea before convection. The stratification is found to reach a maximum in the intermediate layer in December, whose causes and consequences for the interannual variability of convection are investigated. Further study of the interannual variability and correlation tests between the properties of the deep water formed and the winter surface fluxes support the description of convection as a process that transfers the heat and salt contents from the top and intermediate layers to the deep layer. A proxy for the rate of transfer is given by the final convective mixed layer depth, that is shown to depend equally on the surface fluxes and on the preconditioning. In particular, it is found that deep convection in winter 2004–2005 would have happened even with normal winter conditions, due to low pre-winter stratification.
Highlights
Deep convection occurs in regions of the ocean where a high buoyancy loss from a weakly stratified ocean to the atmosphere leads to very intense mixing and deep water formation
The stratification in the intermediate layer is found to reach a maximum in December, likely due to the Tyrrhenian Current crossing the Corsica Strait only in winter
The interannual variability of this maximum is shown to be closely linked to the density in the intermediate layer
Summary
Deep convection occurs in regions of the ocean where a high buoyancy loss from a weakly stratified ocean to the atmosphere leads to very intense mixing and deep water formation. Deep water formation by convection has been observed in the Labrador (Marshall et al, 1998) and Greenland (Schott et al, 1993) Seas and is traditionally thought to be driving the thermohaline circulation (Marshall and Schott, 1999). It has been observed in the Gulf of Lion, western Mediterranean Sea (MEDOC-Group, 1970) where the Western Mediterranean Deep Water (WMDW) is formed and exported to the Atlantic through the Strait of Gibraltar (Stommel et al, 1973; Bryden and Stommel, 1984; Kinder and Bryden, 1990), its potential impact on the oceanic thermohaline circulation. We will characterise the variability of deep convection by using proxies such as the maximum winter mixed layer depth and the properties of the WMDW formed
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