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Séminaire

Titre : Antarctic Sea Ice Control on the Depth of the North Atlantic Deep Water
Nom du conférencier : Louis-Philippe Nadeau
Son affiliation : Institut des Sciences de la Mer de Rimouski
Laboratoire organisateur : LMD
Date et heure : 01-12-2017 16h15
Lieu : Ecole Normale Supérieure, 24 rue Lhomond, salle L369
Résumé :

Changes in deep ocean circulation and stratification have been argued to contribute to climatic shifts between glacial and interglacial climates by affecting the atmospheric carbon dioxide concentrations. Recently, two hypotheses have suggested that changes in deep ocean circulation and stratification during glacial times are linked to changes in Antarctic sea ice: an increased latitudinal extent of Antarctic sea ice (Ferrari et. al., 2014) and an increased rate of Antarctic sea ice formation (Jansen and Nadeau, 2016). Both mechanisms rely on the upward shift of the Atlantic Meridional Overturning Circulation (AMOC) above depths where diapycnal mixing is strong (above 2000 m), thus decoupling the AMOC from the abyssal overturning circulation. Here, these two hypotheses are tested using a series of OGCM simulations in an idealized configuration using two basins connected by a channel to the south. In order to investigate independently the effect of an increased latitudinal ice extent from the effect of an increased ice formation rate, sea ice is parameterized as a latitude strip over which the buoyancy flux is negative. The results suggest that both mechanisms can effectively decouple the two cells of the MOC, and that their effects are additive. In order to illustrate the role of Antarctic sea ice in decoupling the AMOC and the abyssal overturning cell, the age of deep water masses are estimated. Both an increased latitudinal ice extent and increased sea ice formation rate yield a dramatic increase in water mass age at depth. Implications for a global warming scenario are also discussed.

Contact :

bruno.deremble@ens.fr