Global warming: Are oceans headed for a dead zone?

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.


One thought on “Global warming: Are oceans headed for a dead zone?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s