Huge Antarctic Iceberg Makes A Big Splash On Sea Life

Elvia Thompson
Headquarters, Washington              October 1, 2003
(Phone: 202/358-1696)

Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-4044)

Mark Shwartz
Stanford University News Service, Calif.
(Phone: 650/723-9296)

RELEASE: 03-309

HUGE ANTARCTIC ICEBERG MAKES 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/


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