Mapping Potential Timing of Ice Algal Blooms From Satellite

As Arctic sea ice and its overlying snow cover thin, more light penetrates into the ice and upper ocean, shifting the phenology of algal growth within the bottom of sea ice, with cascading impacts on higher trophic levels of the Arctic marine ecosystem. While field data or autonomous observatories provide direct measurements of the coupled sea ice-algal system, they are limited in space and time. Satellite observations of key sea ice variables that control the amount of light penetrating through sea ice offer the possibility to map the under-ice light field across the entire Arctic basin. This study provides the first satellite-based estimates of potential sea ice-associated algal bloom onset dates since the launch of CryoSat-2 and explores how a changing snowpack may have shifted bloom onset timings over the last four decades. Light plays a key role in sustaining life in the ocean. In the polar regions, sea ice and its overlying snow cover limit the amount of light reaching the upper Light plays a key role in sustaining life in the ocean. In the polar regions, sea ice and its overlying snow cover limit the amount of light reaching the upper ocean. Ice algae mainly live at the bottom centimeters of the ice and are important primary producers, using CO2 and inorganic nutrients to release O2 and create organic matter that is available to other trophic levels of the marine ecosystem. Every year rapid growth of bottom-ice algae, known as the bloom onset, is triggered by the return of the sun and the increase in light intensities above that needed for photosynthesis to occur. Studies have shown that ice algae are shade adapted and can bloom under very low light conditions, yet the impact of recent changes in the snow-ice cover that allow more light to penetrate earlier in the spring season remain uncertain. This study takes satellite data to map how ice algal bloom onset may be changing over time. New processing methods to satellite data allow for daily under-ice light mapping Satellite approaches allow for scaling up to the pan-Arctic scale Phenology of ice-algal bloom onset is strongly tied to snow cover variability