Life beyond the ice: Marine ecosystems in the southern ocean

Abstract

The Antarctic Circumpolar Current isolates Antarctic waters and their living organisms from warmer waters to the north. Over the last 25-35 million years, this isolation has led to specific environmental conditions, including a sharp drop in water temperatures south of the Polar Frontal Zone and the formation of sea ice during winter. Three key factors control productivity in the Southern Ocean today. Firstly, the Southern Ocean contains about 1.8 times as much oxygen as tropical seawater because more oxygen can dissolve in water at lower temperatures. Secondly, upwelling currents bring nutrients from the seabed to feed microscopic algae at the surface, and, lastly, the seasonal formation of sea ice has a profound impact on marine life. In addition, there is a long period of low or no light in winter, extreme physical disturbance from icebergs and a very high level of coastal productivity. All these factors have been important in the evolution of the characteristic Southern Ocean species and have resulted in a high degree of endemism, particularly in certain groupings of Antarctic organisms such as crustaceans and fish. The Southern Ocean represents 9.6 % of the world’s oceans and is a key part of Earth’s system. As the climate changes and sea level rises, the behavior of deepocean currents associated with the global thermohaline conveyor belt is altered and marine organisms respond. Our knowledge of the Southern Ocean has increased considerably in the last 20 years, but our understanding of adaptations, biological cycles and responses to change is still poor and more research is needed.