events partly force the extent and duration of sea ice in the Bering Sea.
During the 1970s, when the PDO was in a negative phase, sea ice was extensive.
In the next decade, sea ice did not progress as far south nor last as long.
Recently the character of sea ice extent and duration has changed again,
but not as a return to the behavior of the 1970s.
Sea ice is a controlling factor
in the timing of the spring phytoplankton bloom, the annual spurt of energy
at the base of the food chain. FOCI uses moorings to measure light penetration,
chlorophyll content, and other parameters of the waters over the shelf.