Science notebook--News from Antarctica and beyond
The SeaWiFs satellite, launched last summer, is still undergoing testing,
but it is already returning impressive and valuable images from the world's
oceans. For the past 2-3 months, personnel from NASA's Goddard Space Flight
Center, the Scripps Institution of Oceanography, and the National Science
Foundation's support contractor, Antarctic Support Associates, have worked
to set up a system to collect, process, and transmit SeaWiFs images to
AESOPS cruises--a system that promises to become widely used in the future.
Employing satellite images to guide studies represents an exciting new
tool that can help scientists zero in on important ocean phenomena and
can enable researchers, especially those in remote areas, to use limited
field time effectively.
In a paper detailing the findings, published in the October 1997 issue of the journal Geology, Richard Aronson and his coauthors contend that as Antarctica entered its current cold phase, cooling ocean temperatures suppressed predation and spurred a dramatic increase in nutrients upwelling in the southern oceans surrounding the continent. "This discovery is a good example of how global climate change can have severe impacts on marine life," commented Aronson, senior marine scientist at Dauphin Island Sea Lab.
The comparative numbers of different organisms occupying particular ecological niches--that is, the community structure--reflected in the Seymour Island fossils unearthed by Aronson and his team was much more typical of the shallow seas of 150 to 450 million years ago. After that, predation by newly evolved fish and other creatures confined brittle stars and sea lilies to deep-sea habitats. Aronson and his coauthors believe that when antarctic temperatures began to plummet, however, predation was disrupted--some predator populations shrank and others became extinct--and the archaic community structure reappeared. In fact, the brittle stars and sea lilies that are clustered in dense beds of fossils show few arm injuries, an indication that predation was light.
Bottom dwellers such as brittle stars and sea lilies require abundant nutrients. According to the authors, global cooling accelerated about 40 million years ago in the late Eocene, and this long-term trend was accompanied by increased upwelling in the southern oceans, including around the Antarctic Peninsula, and more nutrients became available. The authors also point out that today, living bottom-dwelling communities in antarctic waters also show archaic characteristics. They suggest that perhaps conditions in the Antarctic or in the southern oceans generally work in some way to maintain these old-fashioned community structures.