RAPID: Impacts of Increased Light Transmittance on Ocean Heating, Primary Productivity, and Carbon Cycling Across a Pacific Arctic Continental Shelf Gradient

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Arctic sea ice is undergoing tremendous changes. There has been a pronounced decrease in summer sea ice cover, an overall thinning of the ice, and a lengthening of the summer melt season. Some of the greatest changes in sea ice cover across the pan-Arctic have been observed in the Chukchi and Beaufort Seas surrounding Alaska, where there has been substantial loss of perennial sea ice that persists year-round (including during summer). This Pacific Arctic sector is also among the most biologically productive marine ecosystems in the world and is an important region to monitor for the flow of carbon. Although sea ice is a dominant feature in these shallow marine environments at high-latitudes, we are only beginning to understand how changes in sea ice cover (through its influence on light, seawater temperature, salinity, and nutrient availability) will affect ecosystems in these regions. In particular, earlier ice-free conditions in the spring (as well as later ice-free conditions in the fall) have disrupted the timing of algae blooms and the livelihoods of marine mammals farther up the food chain. This research is focusing upon measurements of light transmittance through the ocean water column collected at science stations during the Synoptic Arctic Survey (SAS) cruise on the US Coast Guard Ship Healy. Measurements of light transmittance through the water column will further our understanding of how light impacts heat distribution, algae growth, and carbon flows throughout the region. In addition, this project is supporting an early-career researcher and the team is contributing material for numerous undergraduate courses and partnering with the Girls Inc. organization to involve middle and high school students in opportunities to learn about Arctic Ocean science.This research is establishing new measurements of light transmittance (320–780 nm) through the uppermost ~30–50 m of the ocean water column at observation points across a continental shelf gradient (over the Chukchi Shelf into the deep Arctic Ocean basin, with the return southward over the Chukchi Borderlands). These measurements are providing the baseline knowledge necessary to understand how light availability in the water column changes spatially (across a ~2000 km long continental shelf/latitudinal gradient) as well as temporally (across a seasonal gradient from early September through late October). Using these measurements, the team is testing the hypothesis that light transmittance increases with declines in sea ice cover and varies with light absorbing impurities in the water column. The seasonal timing and geographic location of the SAS cruise provide a rare opportunity to further assess the connections of late-open-water-season light transmittance to all three research focal areas of the SAS science and implementation plan: (1) physical drivers, (2) ecosystem responses, and (3) carbon cycling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.