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New satellite image guides ship operations

Global climate change recorded in antarctic marine fossils

Science notebook--News from Antarctica and beyond

New satellite image guides ship operations

While working in the Ross Sea, the R/V Nathaniel B. Palmer received a surprising image from a new National Aeronautics and Space Administration (NASA) satellite called SeaWiFs. The image, which revealed dramatic and unexpected mesoscale variations in pigment concentrations of the southern Ross Sea, presented researchers aboard the Palmer with a serendipitous opportunity to study the processes and conditions associated with the formation of high-chlorophyll features in the Ross Sea and to gather in situ information that could be used to improve algorithms used to construct models of pigment concentrations. On the basis of the image, biologist Walker O. Smith, Jr., (University of Tennessee-Knoxville) and his team from the Antarctic Environment and Southern Ocean Process Study (AESOPS) decided to change the cruise schedule to allow 2 days of sampling of the feature.

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.


Global climate change recorded in antarctic marine fossils

An ancient type of marine community typical of those found 450 million years ago has been discovered in antarctic fossils of near-modern age. A National Science Foundation-sponsored expedition to Seymour Island off the Antarctic Peninsula unearthed an ecological anomaly: fossil communities only 40 million years old dominated by brittle stars and sea lilies (marine invertebrates like starfish).

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.