Optical properties of ocean waters beneath melt-season first-year sea ice in the Chukchi Sea

The Chukchi Sea has experienced significant declines in sea ice over recent decades, including reductions in thickness as well as duration of sea ice cover (driven by both earlier breakup and later formation of seasonal first-year sea ice). These changes in sea ice in turn have important cascading impacts on the physical, biological, and biogeochemical state of the overall marine environment throughout the region. Measurements of the transmission of solar radiation through sea ice is critical for understanding the potential implications of these recent shifts in sea ice, including impacts on the heat balance of the ice itself and underlying ocean waters. Furthermore, the overall transmission of light through ice that is thinner and exhibits more surface melt ponds may enhance biological production and significantly impact the biogeochemistry within the sea ice as well as the water column below. Here, we present observations of downwelling irradiance and upwelling radiance profiles in the top 30-50 meters of ocean waters below sea ice, collected at ten sites ~50-200 km northwest of Barrow, Alaska in the Chukchi Sea. Profiles were collected during the summer melt season in June and July of 2010 as part of NASA’s Impacts of Climate Change on the Ecosystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) mission. The profiling radiometers collected measurements with 19 channels (320, 340, 380, 395, 412, 443, 465, 490, 510, 532, 555, 560, 625, 665, 670, 683, 710, and 780 nm, as well as PAR/Natural Fluorescence) under both bare ice and melt ponded ice surfaces. Based on the last 30 years of SMMR and SSM/I passive microwave satellite data, these sites show drastic reductions in sea ice cover (losing ~24-30 days/decade of sea ice cover, ~11-13 days/decade as earlier sea ice breakup and ~13-17 days/decade as later sea ice formation). As such, this is a region particularly susceptible to climate warming and important for continued monitoring and assessment of the potential ramifications of a declining sea ice cover.