The biological productivity in the Southern Ocean is mainly driven by the abundance of phytoplankton, which changes with seasons, fluctuations in sea ice and iron as well as light availability. The distribution of biological productivity is further modulated by ocean currents. Diatoms are a key element in the Southern Ocean's food web; thus, the effects of environmental changes on diatom population sizes have important implica...

The Southern Ocean is characterized by longitudinal water circulations crossed by strong latitudinal gradients. How this oceanographic background shapes planktonic populations is largely unknown, despite the significance of this region for global biogeochemical cycles. Here, we show, based on genomic, morphometric, ecophysiological and mating compatibility data, an example of ecotypic differentiation and speciation within an e...