Trends in Winter Light Environment Over the Arctic Ocean: A Perspective From Two Decades of Ocean Color Data

The last few decades have seen a decrease in Arctic ice cover, leading to changes in the structure and function of marine ecosystems. Yet sustained long-term observations of the marine environment are difficult to acquire. Harsh environments limit in situ measurements, while low light and high solar angles hinder ocean color observations from satellite. Here we use masks of validinvalid oceancolor pixels to diagnose ocean conditions and nd strong positive trends in the Arctic openwater season close to the ice sheet, generally consistent with sea ice products from satellites. The North East Atlantic with no seasonal ice cover shows weaker, but signicant trends indicative of decreasing winter cloud cover.Decreases in both sea ice and cloud cover will increase light availability at the sea surface and potentially enhance phytoplankton growth. Our method allows the winter light conditions to be studied at temporal and spatial scales relevant for phytoplankton dynamics