Role of Ice Rheology in Modulating Surface Stress and Sea-Ice Drift in the Beaufort Gyre

The Beaufort Gyre is a prominent feature of Arctic Ocean circulation and a focal point for studies of Ekman dynamics. Midlatitude gyres are primarily forced by atmospheric winds, and Ekman pumping can be directly estimated from the atmosphere–ocean stress. However, in polar regions, the presence of sea ice modifies and mediates momentum transfer from the atmosphere to the ocean. In this context, the surface stress can be expressed as a weighted sum of atmosphere–ocean stress and ice–ocean stress, with the weighting determined by sea ice concentration. In regions of open water, the surface stress is dominated by direct atmospheric forcing, whereas in areas of high ice concentration it is largely controlled by the ice–ocean stress. Under these conditions, internal rheological stresses within the ice pack also play a role in redistributing the stress applied by the atmosphere before it is transmitted to the ocean. The combined action of surface and internal stresses determines the effective forcing felt by the ocean and has direct implications for Ekman pumping and the resulting circulation. To investigate the roles and influence of these stresses, we use output from the MIT general circulation model (MITgcm).

We begin with the free drift regime, in which internal rheological stresses are neglected, and assess the ability for this regime to produce sea ice drift. Observational data in the Arctic are limited, so we attempt to recover sea ice drift using readily available measurements, such as wind speed and altimeter derived sea surface height. Sea ice drift is first inferred from the balance between atmospheric and oceanic stresses, which captures the large scale features of motion reasonably well. Next, an iterative solver is applied to include the effects of Coriolis and sea surface tilt. Finally, comparison with the full rheology case shows that internal ice stress is necessary to reproduce the small scale features of ice motion. In regions of high ice concentration and during winter, rheological stresses become essential, and the free drift approximation no longer captures the observed motion.

Motivated by the limitations of the free drift approximation, the second part of this project examines how the presence of sea ice modifies the atmospheric stress transmitted to the ocean. In open water, wind stress acts directly on the ocean surface, whereas in ice covered regions the stress is applied to the ice and redistributed internally through rheological processes before reaching the ocean. Consequently, the stress experienced by the ocean differs from that applied at the surface. We analyze how internal ice stresses transform and redistribute atmospheric work across the ice pack, altering the effective surface stress and modulating Ekman pumping and ocean circulation within the Beaufort Gyre.