MASSIVE
ICEBERGS MAY AFFECT ANTARCTIC SEA LIFE AND FOOD CHAIN
NASA-funded
research using satellite data has shown large icebergs that have broken off from
Antarctica's Ross Ice Shelf are dramatically affecting the growth of minute plant
life in the ocean around the region -- plant life vital to the local food chain. Scientists
say the icebergs appear to have caused a 40 percent reduction in the size of the
2000-2001 plankton bloom in one of Antarctica's most biologically productive areas.
The icebergs decrease the amount of open water that the plants need for reproduction.
After
the calving, or "breaking off," of the B-15 iceberg in March of 2000,
researchers used imagery from NASA's SeaWiFS (Sea-viewing Wide Field-of-view Sensor)
satellite and data from the Defense Meteorological Satellite Program to see the
effect that large icebergs have on phytoplankton (minute floating plants) blooms.
The B-15 iceberg that broke off the Ross Ice Shelf and drifted into the southwestern
Ross Sea was as large as the state of Connecticut (approximately 10,000 square
kilometers or 3,900 square miles) "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,"
said Kevin Arrigo, a researcher at Stanford University, Stanford, Calif. Arrigo
and his colleagues are publishing their results in a paper titled "Ecological
Impact of a Large Antarctic Iceberg," in an upcoming issue of Geophysical
Research Letters. NASA's
Thorsten Markus of the Goddard Space Flight Center, Greenbelt, Md., a co-author
on the paper, noted that SeaWiFS satellite imagery enabled researchers to see
that large icebergs such as the B-15 restricted the normal drift of pack ice.
Normally, when the winds shift, ice is carried out into the Ross Sea, creating
open ocean space and a breeding ground for phytoplankton. The icebergs, however,
created a blockage that resulted in heavier spring/summer pack-ice cover than
previously recorded. Since
the area of sea ice was more extensive, the area suitable for phytoplankton growth
was reduced, and as a result, so was the length of the algal growing season. Since
the B-15 iceberg was so large, plankton productivity throughout the region was
more than 40 percent below normal. The
southwestern Ross Sea is one of the most biologically productive regions in the
Southern Ocean surrounding Antarctica. This is partly due to the large and persistent
areas of open water that form during the Antarctic spring when pack ice drifts
out of the Ross Sea. In
the springtime, winds shift in the area of the Ross Sea and clear away sea ice,
forming the Ross Sea polynya (an area of open water surrounded by sea ice) where
phytoplankton flourish. However, when large icebergs calve, such as B-15, sea
ice is not as easily moved by winds, severely reducing the area of open water.
Phytoplankton
are a critical part of the entire ecosystem in the Ross Sea, since they sustain
marine mammals and birds in the region. During periods where there are no large
icebergs, phytoplankton thrive, and so do those organisms that feed on them. The
region also is home to 22 percent of the world population of circumpolar Emperor
penguins and 30 percent of Adélie penguins. This
research is a part of NASA's Earth Science Enterprise, a long-term research effort
dedicated to help us better understand and protect our home planet. Back
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