Evolution of an Arctic Ice-Ocean Boundary Layer across a developing Thermodynamically Forced Marginal Ice Zone

Shawn Glenn Gallaher1, Timothy P Stanton2, William J Shaw3, Sylvia T Cole4, John Merrill Toole5, Jeremy Wilkinson6, Ted Maksym4 and Phil Byongjun Hwang7, (1)United States Naval Academy, Oceanography, Annapolis, MD, United States, (2)Naval Postgraduate School, Oceanography, Monterey, CA, United States, (3)Naval Postgraduate School, Monterey, CA, United States, (4)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (5)WHOI, Woods Hole, MA, United States, (6)British Anarctic Survey, Cambridge, United Kingdom, (7)Scottish Association for Marine Science, Oban, United Kingdom
Abstract:
As part of the 2014 ONR Marginal Ice Zone (MIZ) Experiment in the Beaufort Sea, summer observations of temperature, salinity, turbulent fluxes and sea ice conditions show that the ice-ocean boundary layer (IOBL) responds directly to the evolution of sea ice albedo, and associated melt pond development, and can be divided into three distinct stages: Stage I – Melt Pond Development and a Neutral IOBL; Stage II – Melt Pond Drainage and IOBL Freshening and Warming, and; Stage III – Enhanced Ice-Ocean Albedo Feedback. In Stage I, radiative input on topographically-smooth, low-albedo seasonal ice, as compared to perennial ice, facilitates meltwater production. In Stage II, this melt water drains into the ocean mixed layer contributing 40% (34 MJ m-2) of the total stored heat content and 70% (ΔSml = -1 psu) of the total freshening at MIZ cluster 2 through largely non-turbulent vertical advection processes. Under calm conditions, drained meltwater develops thin fresh mixing layers, and underlying ephemeral pycnoclines, resulting in episodic heat flux events at the ice-ocean interface and large differences between observed basal ice melt and ice-ocean heat fluxes at 4.5 m. As surface forcing increases overcoming the ephemeral pycnocline buoyancy, a seasonal pycnocline and near surface temperature maximum develop. Comparisons to other MIZ assets show that IOBL freshening and timing of seasonal pycnocline development have very little geographic variability across the Beaufort Sea. During Stage III, open water fractions range from 30-70% increasing ocean radiative fluxes and fully engaging the ice-ocean albedo feedback mechanism, resulting in large basal melt rates. Sea ice and ocean heat budgets suggest the late season ice-ocean system in the Beaufort Sea responds primarily to changes in the absorption of summertime shortwave irradiance and ocean turbulent exchanges within the ice pack as part of a “thermodynamically forced MIZ” and not the result of edge forcing.
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