Massive Icebergs May Affect Antarctic Sea Life And Food Chain

TERRADAILY

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. Image by Kevin Arrigo, Stanford University, and NASA/Orbital SeaWiFs Project

Greenbelt - Apr 29, 2002
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. Click here for animation of chlorophyll amounts over the years. 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.

TERRADAILY

Color Of Ocean Yields Global Warming Clues

Santa Barbara - Apr 28, 2002
A green ocean is a productive ocean; the light from the sun helps the phytoplankton -- tiny ocean plants -- to be productive. This production in turn drives ocean food webs.

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