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.