Marine Biology

iii. Polar seas

POLAR SEAS

In Polar areas, productivity is restricted to a single short period in the polar summer, usually July or August in the Arctic. At this time, the snow cover on the ice has disappeared, allowing sufficient light to enter the water through the ice to permit phytoplankton growth. In areas outside of the permanent ice pack, breakup of the ice at this time opens the leads, allowing sufficient light to enter the water and permitting phytoplankton growth. Following this single burst of growth, the production quickly declines. Nutrients are not limiting and the water column is never strongly stratified. The reason for the lack of production at other times is due primarily to lack of light. Light intensity is insufficient for a fall bloom, and during the long winter, light is either absent or prevented from reaching the water column by a layer of snow over the ice pack. (See a more detailed analysis of polar seas in Chapter 5.)