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April 22, 2002
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 Ad‚lie 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:
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Contacts:
David E. Steitz
NASA Headquarters, Washington
202-358-1730
Cynthia O'Carroll
Goddard Space Flight Center, Greenbelt, Md.
301-614-5563
Harvey Leifert
American Geophysical Union, Washington
202-777-7507
Mark Shwartz
Stanford University News Service, Stanford, Calif.
650-723-9296
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The B-15 Iceberg That Blocked Phytoplankton Growth
This image of Antarctic icebergs was taken on
November 9, 2000 by the NOAA-12 satellite.
The image shows the B-15 iceberg breaking
into smaller icebergs (labeled B-15a,B-15b,
etc.). Research on the effect that icebergs
have on the local ecology began in early
November 2000.
The following are the rough estimates of the
sizes of the icebergs from satellite: C-16 was
~30 by ~10.5 miles, B-15A was ~96 by ~22
miles, B-15B was ~83 miles by ~23 miles, B-19
was ~27 miles) by ~3 miles, B-15C was ~13.5
by ~5 miles and B-15D was ~31.5 by ~7 miles.
All of these were measured at their widest
points.
CREDIT FOR IMAGE: Image from the
NOAA-12 satellite, as provided by the
Antarctic Meteorological Research Center,
SSEC, University of Wisconsin-Madison.
Changes Over Time and Phytoplankton Blooms
This 3-year time series of satellite imagery
show how iceberg calving in the Ross Sea has
reduced the amount of phytoplankton (tiny
ocean plants) through observations in
chlorophyll. The chlorophyll in the
phytoplankton allows them to photosynthesize
and also colors the water green, making the
blooms easier to spot by satellite.
Distributions of sea ice are depicted by the
dark gray color (from the Special Sensor
Microwave Imager (SSM/I)) and chlorophyll a is
depicted with the highest values in red and
the lowest in purple and blue (from SeaWiFS).
These images from 1998, 1999, and 2000 are
all from December, the peak month for the
annual phytoplankton bloom. Black areas are
open water regions obscured by clouds. Six of
the largest fragments of the B-15 iceberg that
calved in March 2000 are shown in white.
Light gray areas represent land and the Ross
Ice Shelf. Note that in 2000, the icebergs
were acting as a barrier preventing the sea ice
from drifting northwestward out of the region.
As a consequence of the additional ice cover,
phytoplankton abundance, as indicated from
chlorophyll a, was substantially lower in 2000
than in the preceding years.
CREDIT FOR IMAGE: Kevin Arrigo, Stanford
University, and NASA SeaWiFs Project/NASA
Goddard DAAC
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