Observations of Wind-Induced Motion in the Arctic Marginal Ice Zone

Abstract:

The increasingly recognized importance of the Marginal Ice Zone (MIZ) in the global and Arctic climate systems necessitates study of the complex processes at work in the interactions between ice floes, the ocean, and the atmosphere. This study uses observations of surface currents and floe drift speeds to explore the hydrodynamic processes driven by interactions with surface winds surrounding isolated small floes in the Arctic summertime MIZ. The 2013 MIZOPEX campaign flew several unmanned aircraft over the MIZ north of Oliktok Point, AK. These flights had two primary missions: dropping microbuoys into areas of open water between ice floes, and imaging in both thermal and visible using airborne systems. The Air-Deployed Micro Buoys (ADMB) drifted with surface currents, providing a measure of current speeds from the GPS track. ADMB were equipped with a string of thermistors extending two meters below the surface, which measured near-surface temperature gradients. Analysis of visible aerial imagery of ice floes is used to retrieve floe drift speeds from sequential photos by using aircraft telemetry to geolocate the images. Wind speeds from NCEP reanalysis and nearby met data are compared to surface currents and floe drift speeds; surface currents are approximately 4% of wind speeds, which agree well with lab measurements. Thermal imagery from the campaign show cold wakes at the surface near ice floes in certain wind conditions. The spatial view provided by airborne measurements, when combined with subsurface temperature gradients and the relation between drift and current speeds to local wind forcing, paints a picture of the physical interaction between an isolated ice floe in the MIZ and the open water surrounding it.