Huge Antarctic Iceberg Maes a Big Splash on Sea Life

NASA satellites observed the calving, or breaking off,
of one of the largest icebergs ever recorded, named “C-19”.

C-19 separated from the western face of the Ross Ice Shelf
in Antarctica in May 2002, splashed into the Ross Sea, and
virtually eliminated a valuable food source for marine life.
The event was unusual, because it was the second-largest
iceberg to calve in the region in 26 months.

Over the last year, the path of C-19 inhibited the growth of
minute, free-floating aquatic plants called phytoplankton
during the iceberg’s temporary stopover near Pennell Bank,
Antarctica. C-19 is located along the Antarctic coast and
has diminished little in size. Since phytoplankton is at the
base of the food chain, C-19 affects the food source of
higher-level marine plants and animals.

Kevin R. Arrigo and Gert L. van Dijken of Stanford
University, Stanford, Calif., used chlorophyll data from
NASA’s Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The
instrument, on the OrbView-2 satellite, also known as
SeaStar, was used to locate and quantify the effects of C-19
on phytoplankton. The researchers were able to pinpoint
iceberg positions by using images from the Moderate
Resolution Imaging Spectroradiometer (MODIS), an instrument
aboard NASA’s Terra and Aqua satellites. The findings from
this NASA-funded study appeared in a recent issue of the
American Geophysical Union’s Geophysical Research Letters.

C-19 is about twice the size of Rhode Island. When it broke
off the Ross Ice Shelf, the iceberg was 32 km (almost 20
miles) wide and 200 km (124 miles) long. It was not as large
as the B-15 iceberg that broke off of the same ice shelf in
2001 but among the largest icebergs ever recorded.

Since it was so large, C-19 blocked sea ice from moving out
of the southwestern Ross Sea region. The blockage resulted
in unusually high sea-ice cover during the spring and
summer. Consequently, light was blocked. Phytoplankton
blooms that occur on the ocean surface were dramatically
diminished, and primary production was reduced by over 90
percent, relative to normal years.

Primary production is the formation of new plant matter by
microscopic plants through photosynthesis. Phytoplankton is
at the base of the food chain. If they are not able to
accomplish photosynthesis, all organisms above them in the
food chain will be affected. “Calving events over the last
two decades indicate reduced primary productivity may be a
typical consequence of large icebergs that drift through the
southwestern Ross Sea during spring and summer,” Arrigo
said.

Arrigo and van Dijken also used imagery from the Defense
Meteorological Satellite Program (DMSP) satellite Special
Sensor Microwave Imager and Scanning Multichannel Microwave
Radiometer, managed by the U.S. Department of Defense. The
data was used to monitor the impact of C-19 on the movement
of sea ice. The data is archived at the National Snow and
Ice Data Center, University of Colorado, Boulder.

Arrigo said most of the face of the Ross Ice Shelf has
already calved. There is another large crack, but it is very
difficult to predict if and when another large iceberg will
result.

NASA’s Earth Science Enterprise is dedicated to
understanding the Earth as an integrated system and applying
Earth System Science to improve prediction of climate,
weather, and natural hazards using the unique vantage point
of space.

For more information and images, on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2003/1010iceberg.html

For information about SeaWiFS on the Internet, visit:
http://seawifs.gsfc.nasa.gov/

For information about MODIS on the Internet, visit:
http://modis.gsfc.nasa.gov/

For information about DMSP, visit:
http://www.dmsp.ngdc.noaa.gov/