Surface Turbulence in the Presence of Pancake Ice in the Autumn Arctic Ocean

In open water, the input from wind to waves is assumed to be locally balanced by dissipation due to wave breaking. The dissipation due to breaking primarily takes the form of turbulent kinetic energy (TKE) near the ocean's surface, altering the exchange of heat and gases at the air-sea interface. In the Arctic Ocean, the direct transfer of energy from wind to the ocean surface is reduced by the presence of sea ice. Although we expect a diminished net exchange of momentum at the air-sea interface, this is not well documented by field measurements as measurements of waves and near-surface turbulence in ice-covered regions are difficult to obtain and have been sparse. Determining the pathways for momentum and energy is a key component in improving the physics of coupled models.

Recent measurements in the summer 2014 Arctic Marginal Ice Zone have suggested that reductions in waves by ice lead to reductions in turbulence such that the wind-wave equilibrium is maintained (Zippel and Thomson, Elementa, 2016). Here, we present new measurements of near-surface turbulent dissipation from SWIFT drifters deployed during the 2015 Arctic fall freeze-up period. Observations were made as part of the Sea State DRI in the Beaufort Sea in a variety of wind, wave, and ice conditions. In particular, we compare the changes in the wave field and TKE surface dissipation over a range of ice covers. Our observations confirm that turbulent dissipation is generally diminished in the presence of partial ice cover, coincident with the reduction of wind energy input to waves. This effect is particularly evident during the growth of thin pancake ice, where we observe a rapid decline in turbulent dissipation with the formation of ice. However, we also observe that this effect may be counteracted by increased near-surface turbulence in the presence of ice due to increased drag at the ice-ocean interface. We use these measurements to determine the overall dependence of surface turbulence on wind, wave, and ice conditions.