Massive phytoplankton blooms under Arctic sea ice

The seasonal sea ice and snow cover inthe Arctic Ocean strongly reflect andattenuate incoming solar radiation. Con-sequently, current estimates of pan-Arctic pri-mary productivity assume that the growth and biomass of phytoplankton, free-floating single-celled photosynthetic organisms at the base of the marine food web, are negligible in waters beneath ice because of insufficient light (1). However, during the 2011 ICESCAPE (Im-pacts of Climate on EcoSystems and Chemis-try of the Arctic Pacific Environment) cruise, we observed a massive phytoplankton bloom that had developed beneath the 0.8- to 1.3-m-thick first-year sea ice on the Chukchi Sea continental shelf. From 4 to 8 July, we sampled (2) along tw