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Seminar

Title : Antarctic Sea Ice Control on the Depth of the North Atlantic Deep Water
Name of the speaker : Louis-Philippe Nadeau
Affiliation : Institut des Sciences de la Mer de Rimouski
Laboratory organizer : LMD
Date and time : 01-12-2017 16h15
Location : Ecole Normale Supérieure, 24 rue Lhomond, salle L369
Summary :

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