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.

Images and video are available at:

Information on SeaWiFS can be found at:

Information on icebergs is available on the National Snow and
Ice Data Center Web site at: