POSTER Session 3

MODELING CHANGES IN LIGHT AVAILABILITY IN THE BARENTS SEA AND ARCTIC OCEAN DRIVEN BY SEA ICE DECLINE OVER THE LAST FOUR DECADES

Light is a key environmental driver for high-latitude marine ecosystems, determining onset and length of the phytoplankton growth season and imposing constraints and opportunities for visually feeding predators and their prey. Temperature increase and sea ice decline is causing fundamental shifts in polar marine environments, including light availability. Bordering the Arctic Ocean is the Barents Sea, which is one of the fastest warming regions in the world in terms of air temperature. An oceanographically complex and ecologically rich shelf sea with substantial fisheries, the Barents Sea is important for observing Arctic climate change. Here, we use the HEIMDALL hyperspectral irradiance model to estimate changes in the Barents Sea light climate, over the latitudinal gradient 72˚-83˚N from 1979 to 2022. The magnitude and spectral composition of light entering the ocean depends largely on the sun elevation, cloud cover, and sea ice and snow cover, but also water column properties. We have used existing observational and reanalysis products for sea ice and cloud cover (ERA5, OSI SAF, PIOMAS) and regional estimates of chl-a seasonality to calculate pelagic light availability. Our modeling results suggest a strong increase in PAR in the central part of this region (75˚-81˚N), approximately 140% on average between the decades 1979-1988 and 2013-2022. Decline in sea ice concentration and snow thickness are the predominant drivers, leading to an expansion of the phytoplankton growth season. We further assess the influence of CDOM on light availability in the central Arctic Ocean and in coastal areas, where CDOM is often optically dominant.

*Håkon Sandven, University of Bergen, Norway, [email protected], https://orcid.org/0000-0002-8042-510X

Stacey Connan-McGinty, University of Strathclyde, United Kingdom, [email protected], https://orcid.org/0000-0001-8661-8984

Børge Hamre, University of Bergen, Norway, [email protected], https://orcid.org/0000-0002-0135-0542

Mats A. Granskog, Norwegian Polar Institute, Norway, [email protected], https://orcid.org/0000-0002-5035-4347

Anders Frugård Opdal, University of Bergen, Norway, [email protected], https://orcid.org/0000-0002-7246-6622

David McKee, University of Strathclyde, United Kingdom, and University of Tromsø, Norway, [email protected], https://orcid.org/0000-0001-8023-5923

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