For the first time, satellite imagery has allowed scientists to observe how icebergs in a remote corner of Antarctica can disrupt an entire marine ecosystem.

Using data from three orbiting satellites, researchers have been monitoring a Connecticut-size iceberg called B-15 that broke from Antarcticas massive Ross Ice Shelf in March 2000. Within a few months, B-15 had fractured into smaller bergs that formed dams along the coast preventing thousands of square miles of pack ice from drifting out of the Ross Sea.

As a result, large stretches of normally open ocean were covered with ice -from November 2000 to March 2001. During these crucial spring and summer months, the Ross Sea usually teems with life, as tons of microscopic marine algae called phytoplankton undergo reproductive blooms.

The Ross Sea ecosystem depends on phytoplankton a primary food source for shrimp-like krill, which in turn are consumed by fish, seals, whales and penguins.

Phytoplankton need open water to reproduce, but satellite data revealed that last seasons abnormally high levels of pack ice caused a 40 percent decline in plankton productivity.

B-15 was one of the largest icebergs ever recorded from the Ross Ice Shelf, said Kevin R. Arrigo, assistant professor of geophysics at Stanford and lead author of the Antarctica satellite study.

B-15 broke into smaller pieces that prevented the normal movement of sea ice out of the region, he explained. Sea ice is very effective at blocking light, so the phytoplankton couldnt grow there was just too much ice around.

The krill is gone

Arrigo and his colleagues described their results in the April 6 issue of Geophysical Research Letters, a publication of the American Geophysical Union.

This is the first time that satellite imagery has been used to document the potential for large icebergs to substantially alter the dynamics of a marine ecosystem, Arrigo noted.

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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
22-Apr-2002