Sea state and boundary layer physics of the emerging arctic ocean

Abstract

We present a large collaborative program investigating surface processes over the Arctic Ocean during the early autumn ice advance. With recent observed and predicted declines in summer minimum sea ice extent, the nature and role of air-ice-waves-ocean interactions driving autumn ice advance are expected to change. Central to these changes, the greatly increased open water fetch permits the generation of waves that may propagate far into the ice pack. Wave-ice interactions lead to wave attenuation and scattering while simultaneously fracturing ice into ever changing floe size and thickness distributions. Thus, the processes of wave generation and wave Dissipation are complicated by the marginal ice zone (MIZ). During the ice advance, waves can enhance ice formation rates through frazil/pancake generation. Further complicating these processes are forcing by winds and surface fluxes from the ocean to the atmosphere, which are episodically driven by storms. These processes moderate the release of heat from enhanced summer warming of the upper ocean, which may in turn impact the rate of ice advance. We apply a combination of numerical modeling, in situ observations, and remote sensing, with a focus on arctic conditions during the seasonal ice advance in early autumn. In preparation for a six-week cruise in the autumn of 2015, we have assessed emerging trends for the annual freeze-up of the Beaufort and Chukchi seas. Waves are clearly controlled by the extent of open water (i.e., fetch limitation) and strongly damped in newly forming ice. Winds are significantly affected by ice cover and reduced by increased atmospheric stability over the ice. The ice advance rate is nearly constant, despite extreme interannual variations of sea-ice extent in recent years, which suggests that large-scale thermodynamics are the dominant process.