Speaker

Daniel Watkins, Ph.D., Senior Research Associate, Brown University

Observing air-ice-ocean coupled dynamics: Results from the MOSAiC expedition and beyond

Abstract

Sea ice mediates the exchange of momentum, heat, and moisture between the atmosphere and the ocean. During the year-long MOSAiC expedition, an array of drifting buoys surrounding the R/V Polarstern enabled the characterization of sea ice motion and deformation across a range of spatial scales. In addition, autonomous sensors at a subset of sites measured the atmospheric and oceanic structure and vertical fluxes. These observations provide a rare window into the spatial and temporal variability of coupled air-ice-ocean processes in the sparsely observed central Arctic. In this talk, I focus on two main topics: key processes for air-ice-ocean momentum transfer during a winter storm, and the evolving, scale-dependent roles of wind and ocean currents for ice dynamics in the marginal ice zone. First, I share results of a case study from the central Arctic, where the MOSAiC observatory sampled a strong winter cyclone with unprecedented detail. We find that the formation of strong low-level jets behind the fronts is responsible for the strongest coupled ice-ocean response. A sharp increase in air-ice and ice-ocean stress resulted in the initiation of inertial oscillations in the upper ocean, prolonging the storm effects and impacting the ice dynamics. The results suggest an important role for cyclone-forced ocean mixing in pack ice during the Arctic winter. Next, I show how the sea ice dynamics evolve as the observatory drifts through the Fram Strait and enters the East Greenland marginal ice zone. Sharp transitions in the characteristics of the ice dynamics can be directly attributed to changes in ocean currents as the ice drifts across abrupt changes in ocean bathymetry, while changes in the state of the sea ice affect the relationship between ice and wind. I close by describing current work deriving floe-scale sea ice motion from optical satellite imagery.