Increased Light Availability in the Northern Barents Sea Driven by Sea Ice Loss

The Barents Sea region is a hotspot for global climate change, with larger-than-average temperature increase and sea ice loss. This has led to massive changes in the underwater light environment, which is a key environmental driver for polar marine ecosystems given the extreme seasonal variability. The ecosystem consequences of a changing underwater lightscape remains poorly characterized. Here, we model the changes in availability of photosynthetically available radiation EPAR ${E}_{PAR}$ in the Barents Sea from 1979 to 2022, using the underwater irradiance model HEIMDALL, which is developed and validated for use in the Barents Sea and has recently been expanded for use in ice-covered or ice-influenced waters. Our results show that the potential growth season for phytoplankton has become more than 1 month longer in large parts of the northern Barents Sea. The largest changes have been in the northeastern part of the region with up to 60 days. The primary environmental driver for light availability is the sea ice concentration (SIC), particularly in spring, with a Kendall rank correlation coefficient tau $\tau $ = -0.69. Cloud cover and phytoplankton are important second-order factors (tau $\tau $ = -0.4 after controlling for SIC), whereas snow and ice thickness have a negligible effect after controlling for SIC due to strong interdependencies. We observe a partially stepwise change in the 2000s, but sea ice driven interannual variability has been large throughout the period. Sea ice and snow have a limited impact on the spectral quality of light, omitting any impurities or sea ice algae.