Observations of Sea Ice Melt and Ice-Ocean Boundary Layer Heat Fluxes in the Marginal Ice Zone North of Fram Strait

Given the prospect of a merely seasonally ice-covered Arctic Ocean in the future and a consequential new quality of atmosphere-ocean coupling, understanding and quantifying oceanic processes that contribute to sea ice melt is of particular relevance.

A region of intense melting is the marginal ice zone (MIZ) north of Fram Strait, where inflowing warm Atlantic Water meets sea ice advected southward by the Transpolar Drift. We present observations of the ice-ocean boundary layer (IOBL) from a cruise of German research vessel Polarstern to that region in summer 2022, where we gathered continuous-in-time hydrographic observations from autonomous drifting stations on three separate ice floes, supplemented by intense observation periods of vertical microstructure profiles and ice cores from crewed stations during three revisits per floe throughout the drifting period.

The three occupied floes were oriented on a line approximately perpendicular to the ice edge, initially about 25 km apart from each other, with the southernmost floe located 75 km away from the edge. The drifting instrument platforms cover a common time period of approximately two weeks, under relatively quiescent atmospheric conditions. First results show that, while the floes exhibited similar drift trajectories dominated by superimposed diurnal and semidiurnal oscillations, the evolution of key IOBL variables, such as stratification, melt rates, friction velocity, and turbulent fluxes, varied considerably – both in time and among the occupied floes.

We plan to assess how this observed variability relates to other measured properties of sea ice (e.g., ice roughness, ice thickness distribution, floe size distribution) and of the upper ocean (e.g., ice-ocean velocity shear, turbulence, surface waves, internal waves and tides) and their interaction, in order to put our preliminary findings into the broader context: ocean controls on sea ice melt in the marginal ice zone north of Fram Strait.