Sea ice modulated convection processes in the Nordic Seas

Friday, December 14, 2018 - 08:00
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Lower North Atlantic Deep Water (NADW) primarily forms in key locations of the Nordic Seas, where convection is believed to occur as a combination of strong heat losses to the atmosphere and brine rejection from sea-ice formation. A recent study (Moore et al. 2015) has suggested that the northwestward retreat of sea ice in the Greenland and Iceland Seas over the past several decades could substantially impact NADW formation because of reduced turbulent heat flux exchanges with the atmosphere. The idea is that, while surface heat fluxes are highest over the oceanic regions next to the ice edge, convection also needs preconditioning of the upper ocean stratification to occur, and would be reduced if surface heat exchanges were to take place away from the Greenland and Icelandic gyre centers. Here, we investigate these hypotheses in a high-resolution, fully-coupled Earth System Model simulation: the Energy Exascale Earth System Model (E3SM) v0.1 pre-industrial simulation, featuring a 1/10deg horizontal resolution in the ocean/sea ice components and a 1/4deg resolution in the atmosphere/land components. Since greenhouse gases are fixed at pre-industrial levels, the simulated sea-ice changes and impact on convection are solely due to internal variability within the model, and their investigation will allow us to infer on possible mechanisms in a changing climate. Preliminary results show that the deepest (~3500m depth) convection sites are found next to the ice edge that is closer to the continental slope, rather than near the center of the Greenland and Icelandic gyres. Convection is mostly correlated with a high surface heat flux tongue found near the continental slope, which is more extensive during years when sea ice coverage is limited to the shelf area rather than extended to the Greenland gyre interior. These results and a preliminary investigation of the possible mechanisms for these correlations will be presented here.

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