NSF PR 97-69 - November 24, 1997
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Global Climate Change Recorded in Antarctic Marine
Fossils
An ancient type of marine community typical of 450
million years ago has resurfaced 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).
The authors of the paper detailing the findings, published
in the October, 1997 issue of the journal Geology,
believe that as Antarctica entered its current deep
freeze, cooling ocean temperatures suppressed predation
and spurred a dramatic increase in nutrients upwelling
in the Southern Ocean surrounding the continent. "This
discovery is a good example of how global climate
change can have severe impacts on marine life," said
Richard Aronson, senior marine scientist at Dauphin
Island Sea Lab and lead author of the paper.
The community structure reflected in the Seymour Island
fossils -- that is, the comparative numbers of different
organisms occupying particular ecological niches --
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 habitats in the depths of
the sea.
The paper's authors believe that when Antarctic temperatures
began to plummet, however, predation was disrupted
-- some predator populations shrank and others went
extinct -- and the archaic community structure reappeared.
In fact, the brittle stars and sea lilies 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
also require abundant nutrients. "Global cooling accelerated
about 40 million years ago in the late Eocene, and
this longterm trend was accompanied by increased upwelling
in the Southern Ocean, including around the Antarctic
Peninsula," the authors said, which made more nutrients
available.
The authors also point out that today, living bottom-dwelling
communities in Antarctic waters also show archaic
characteristics. Perhaps conditions in the Antarctic
or in the Southern Ocean generally work in some way
to maintain these old-fashioned community structures,
they suggest.
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