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In summer 2016, more than 50 Arctic Barren Ground caribous were found dead on Prince Charles Island (Nunavut, Canada), a species recently classified as threatened. Neither predator nor sign of diseases was observed and reported. The main hypothesis is that caribous were not able to access food due to a very dense snow surface, created by a strong storm system in spring. Using satellite microwave data, a significant increase in brightness temperature polarization ratio at 19 and 37GHz was observed in spring 2016 (60% higher than previous two winter seasons). Based on microwave radiative transfer simulations, such anomaly can be explained with a very dense snow surface. This is consistent with the succession of storms and strong winds highlighted in ERA-Interim over Prince Charles Island in spring 2016. Using several sources of data, this study shows that changes in snow conditions explain the caribou die-off due to restricted foraging.

Plain Language Summary In this paper, it is discussed that the snow conditions could be caused by the massive die-off events of the caribou herd on Price Charles Island, Nunavut. Using ERA-Interim reanalysis data, it is possible to find the reason of surface snow condition changes. This change creates an anomaly in signal, in particularly using different parameters derived from passive microwave data (brightness temperature) from SSM/I and SSMI/S sensors. Moreover, modeling of brightness temperature using radiative transfer model in passive microwaves domain, allowed to determine new thresholds for high density layer detection, may have an ecological consequence (food do not accessible for several ungulates).