Understanding first-year ice thickness variability using IceBridge measurements and drift track analysis

In a first-year ice dominated environment, positive climate feedbacks in the Arctic persist from year to year when increased summertime melt results in decreased ice growth the following winter. In this presentation, we describe a novel approach to evaluating the impacts of delayed freeze-up, oceanic heat flux, and variable atmospheric forcing on end-of-season first year ice thickness. Parcels of first-year sea ice selected from IceBridge sea ice thickness retrievals are tracked backwards through their winter drift paths using the Pathfinder Ice Motion product. The freeze-up date for each parcel is determined by tracing the drift path through the SSMI Ice Concentration product, and summertime mixed layer heat is estimated from the NOAA Optimal Interpolation SST product at the locations of freeze-up and the end-of-season measurement. Over-winter atmospheric forcing is estimated from integrating the drift path through the MERRA2 reanalysis product using a simple 1-D ice growth model. The end of season ice thickness distributions can then be analyzed in the context of the processes that drive ice growth. The summer mixed layer temperature at the end-of-season measurement location, the integrated atmospheric forcing, and the length of the growth season are the three parameters, after end-of-season snow depth, most correlated with the ice thickness. Controlling for these other factors, delaying freeze-up by one week leads to 5.3 cm thinner ice cover at the end of the season. Warming summer ocean temperatures contribute to delayed freeze-up, but even after controlling for changing freeze-up dates and atmospheric forcing, each degree (C) of warmer summertime temperatures results in 1.9 centimeters of thinner ice cover at the end of the winter season. This indicates that oceanic heat flux due to trapped seasonal heat compounds the loss of ice growth due to delayed freeze-up resulting in thinner first-year ice cover in the Arctic seasonal ice zones.