3.2.2 Life in the polar seas
Life in the polar sea ice forms part of a web of interactions, which Dr Mark Brandon discusses with Brett Westwood as he considers the tiny life trapped in the sea ice that is the foundation for the entire food chain at the poles.
Life in the polar seas
Seawater freezes at −1.9° C, but because of the anomalous relationship between the density and temperature of water, ice floats, insulating the water underneath from the cold air above. Except in very shallow areas, the sea-ice does not extend to the sea-bed, even at the North Pole. Storms and currents sometimes break up the ice, creating many temporary, and some permanent, areas of open water even at high latitudes in mid-winter. Such turbulence also oxygenates the water and admits more light, making the environment much more hospitable to larger organisms.
The movements of ocean currents are complex and may change erratically from year to year. This often results in an upwelling of deep water rich in nutrients and promotes high primary productivity in the sea. In most arctic regions, the sea is both warmer and more productive than the land. So at high latitudes there are many more organisms in the sea than on land, at least during the brief summer, and, as in the case of the baleen and sperm whales, some are very large.
You heard previously how Dr Mark Brandon and colleagues studied krill under the sea ice. In this video scientists from the British Antarctic Survey (BAS) are trawling for krill and sorting them for later analysis – some task!
As you watch listen out for answers to the following questions:
- What is the role of krill in the Antarctic food chains?
- How do the food chains in the polar seas compare with those introduced earlier by Professor David Streeter in the oak wood?
DR. DAVID ROBINSON: This huge net is being used to trawl the polar seas for krill, as part of a research programme. In the folds at the bottom of the net are thousands of these prawn-like crustaceans. Krill are a key component of the main food web in the southern oceans.
MALE SPEAKER 1: Do you want me to--
MALE SPEAKER 2: In the net too.
MALE SPEAKER 1: Yeah.
MALE SPEAKER 2: I think there'll be more water on deck tomorrow morning.
DR. DAVID ROBINSON: They're an essential source of food for numerous animals, from fish and birds to the largest of the whales, the blue whale. In recent years, krill have even been harvested commercially.
FEMALE SPEAKER: Yeah.
MALE SPEAKER 3: Is there anything on that or is it just a surface layer of krill?
DR. DAVID ROBINSON: Sorting the sample is a painstaking task, as the scientists pick out individual krill to place them in trays for later analysis.