The Southern Ocean winter may be harsh, cold, and dark, but the spring and summer bring a sudden burst of activity.
The seasonal phenomenon of the reduction in sea ice extent and the subsequent growth of massive blooms of plant plankton, drives the life cycles of many Antarctic marine species. In spring, these blooms form in the open ocean as warming temperatures cause sea ice to break up and melt. The disappearance of the ice provides the sunlight required for photosynthesis. The subsequent increase in productivity directly or indirectly supports the entire foodweb, from seafloor creatures to birds and mammals.
Plankton is part of a complex Antarctic system in which nutrient-rich currents interact with seafloor features, sea ice, and ice shelves to generate the conditions necessary for plant growth. The formation of large Southern Ocean polynyas, open-ocean regions surrounded by ice, is an integral part of the ecosystem. As the ice disappears from these areas, nutrients in sea water combined with sunlight results in plankton blooms.
The polynya in the Ross Sea, the largest on earth, contributes to the Ross Sea being the most productive stretch of ocean around the Antarctic continent. This productivity ultimately makes it possible for 38% of the world’s emperor penguins to breed in the Ross Sea region.
Indeed, plankton blooms are especially critical in Antarctica because plankton is required to support the huge swarms of krill that in turn feed squid, fish, seals, whales, penguins and even a species of starfish. Plankton is a food source for many other small species such as copepods that are in turn consumed by larger organisms. Furthermore, many species breed in Antarctica during spring, increasing their need for food to feed growing offspring. Disruptions due to climate change can affect these seasonal patterns of sea ice extent and plankton growth, and therefore can have a major impact on Antarctic species.