The Impacts of Thermal Fronts and Sea Ice Motion on the Variability of Arctic Near-Surface Currents

The dynamics of sea ice and the upper ocean play a vital role in understanding present and future trends in the dynamics of the Arctic region and serve as the mediator for fluxes between the atmosphere and ocean surface. The complex interplay between surface level winds, sea ice motion, and near-surface currents generates a series of potential feedbacks which can nonlinearly impact Arctic upper ocean dynamics. It is well observed that surface level winds induce motion in sea ice as a result of the stress imparted on the ice. Additionally, the same surface winds can impart a stress on the ocean surface, which induces a background Ekman current that advects sea ice with it as a conservative tracer. However, it has also been shown that large patches of sea ice may serve as a quasi-solid boundary for surface currents, generating a nonlinear feedback between sea ice, ocean currents, and surface winds. The nonlinear ice-ocean-wind feedback process can also be further complicated by the intrusion of warm water masses and the development of oceanic thermal fronts, which can generate secondary circulations in the larger-scale dynamics. Although varying models for the feedback process have been proposed, it is clear that the changing ice cover has a nonlinear effect on high latitude ocean dynamics. For this reason, observations of sea ice cover, drift, and ocean near-surface currents at high latitudes are key observational variables for better understanding the rapidly changing Arctic sea ice landscape. At present, observations of the ice-ocean-wind feedback process remain limited, with many observational surface current products lacking coverage in high latitude regions entirely, and others providing only geostrophic and wind-driven surface currents that do not account for the impacts of sea ice. While such estimates are useful in understanding the global ocean circulation, accurate observations of the ice-ocean-wind feedback are needed to understand the amplifying effect of anthropogenic climate variability on the arctic region. In this talk, data from a Regional Arctic Reanalysis (RARE) forced by ERA-5 surface winds, alongside observations of Sea Ice motion and concentration from the National Sea Ice Data Center (NSIDC) are used to investigate the impacts of sea ice motion and Sea Surface Temperature (SST) fronts on near-surface current variability in the Arctic. From this investigation, a methodology is constructed to semi-empirically assimilate sea ice motion and SST observations into a diagnostic observational near-surface current product. The assimilation of sea ice motion and SST imagery allows for the extension of observational surface current products to regions with high sea ice concentration. Additionally, when compared to other observational surface current products, the incorporation of sea ice motion and SST imagery results in an increased ability to reconstruct variability seen in in situ observations. This methodology represents a potential improvement to observations of the near-surface ocean in the Arctic region which could contribute to better understanding of the dynamics driving rapid changes in high latitude oceans.