Collaborative Research: Gas Transfer through Polar Sea Ice (GAPS) - Mechanisms of Turbulence Production in the Seasonal Ice Zone and its Control of Mixed Layer Ventilation

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AbstractHigh latitude ocean and sea ice surface fluxes of heat, momentum, fresh water and radiatively important gases such as carbon dioxide are critical to understanding polar, and thus global, climate processes. Field observations of these fluxes, and the physics and biogeochemistry that control them is hampered alternately by both the high winds and sea states typical of polar seas, and the complex potentially non-linear transport pathways between water, ice and air during conditions of active freezing and partial sea-ice cover. This project will study, in a unique controlled laboratory facility, the relative contribution of the physical processes that regulate gas exchange through sea ice.A seasonal evolution cycle of different sea-ice types found in the ice pack, namely 1) pancake ice, 2) complete ice cover, but with leads (openings), and 3) melted ice floes with a freshwater lens, will be simulated in a well controlled laboratory setting. Additionally, different turbulence regimes of wind, wave effects, convection and ice-water current shear at various levels of freezing will be studied in the CRREL sea ice pond facility (New Hampshire). Potentially transformative nature of this research The physics, and biogeochemistry of air-sea flux exchanges in heterogeneous and multi featured environment such as sea-ice is extremely challenging for any existing theory or computational approach. The observational approach that the investigators are using, introduction of chemically inert gases as deliberate tracers, has the ability to account for several different limiting steps encountered in gas exchange through sea ice. A multi-tracer (e.g. SF6, He, Ar, CO2...) mass balance approach has been used and refined by these investigators over the course of prior field campaigns at less challenging and more conventional air-sea boundaries. Preliminary results used to investigate the ice pond experimental approach have indicated that gas exchange through sea-ice does not scale with the amount of open water, negating what otherwise appeared to be a reasonable approximation. The resulting parameterization to be revealed by such studies may suggest redirection as to what really are the rate limiting steps of sea-ice flux transfers. These processes are important for accurate coupled Earth System Models of climate change.