*[Enwl-eng] Global Warming May Make for Dying Oceans

[ENWLine]

*Global warming: Are oceans headed for a dead zone?*

Posted on February 25, 2013 by Bob Berwyn

Illustration Omitted:
Jurassic-era fossils are offering new climate clues. Early
Jurassic warming nearly wiped out all marine life

By Summit Voice

FRISCO --- Careful analysis of the marine fossil record from the Early
Jurassic era (about 180 million years ago), suggests that warmer global
temperatures and lower oxygen levels led to dramatic ecosystem changes,
with a near extinction of ocean life.

Those ecosystems later rebouned, but with a completely different species
composition, according to Plymouth University (UK) scientists who
studied ocean sediments along the North Yorkshire coast.

"Our study of fossil marine ecosystems shows that if global warming is
severe enough and lasts long enough it may cause the extinction of
marine life, which irreversibly changes the composition of marine
ecosystems," said researchers Richard Twitchett.

The findings are based on a study of edimentary rocks and the marine
fossils they contained, providing information about the environmental
conditions on the sea floor at the time the rocks were laid down. With
colleagues from the University of Leeds, the team then compared that
record with published data on changes in temperature, sea level and
oxygen concentrations.

"Back in the laboratory, we broke down the samples and identified all of
the fossils, recording their relative abundance much like a marine
biologist would do when sampling a modern environment. Then we ran the
ecological analyses to determine how the marine seafloor community
changed through time," said Dr. Silvia Danise.

The team found a 'dead zone' recorded in the rock, which showed
virtually no signs of life and contained no fossils. This was followed
by evidence of a return to life, but with new species recorded.

"The results show in unprecedented detail how the fossil Jurassic
communities changed dramatically in response to a rise in sea level and
temperature and a decline in oxygen levels," Twitchett said.

"Patterns of change suffered by these Jurassic ecosystems closely mirror
the changes that happen when modern marine communities are exposed to
declining levels of oxygen. Similar ecological stages can be recognised
in the fossil and modern communities despite differences in the species
present and the scale of the studies."

The results of the Natural Environment Research Council-funded project
were published this month in the PLOS ONE scientific journal.




http://summitcountyvoice.com/2013/02/25/global-warming-are-oceans-headed-for-a-dead-zone/


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