Oceans cover 70% of the Earth’s surface, play a vital role in global climate and are home to varied and productive ecosystems. Marine photosynthesis sequesters carbon, impacts biogeochemical cycles and forms the basis for the majority of marine biological production. Despite its importance, marine photosynthesis is difficult to study due to the diversity of photosynthetic organisms and environments. This is particularly the case in polar oceans where inaccessibility hinders our ability to study unique ecosystems that are under threat by our changing climate. In this seminar I will discuss adaptations for photosynthesis at subzero temperatures, fluctuating salinity and low light. I will demonstrate how these adaptations enable algae to maintain high rates of primary production that support polar marine ecosystems and exert a large influence on the dissolved biogeochemistry of this region.