Massive climate change rocked ecosystems, animals 55 million years ago
Rhett A. Butler, mongabay.com
November 14, 2005


Continued increases in greenhouse gas concentrations in the atmosphere from the combustion of fossil fuels could trigger large-scale changes in global biodiversity and require thousands of years of recovery according to recent research on an extreme global warming episode 55 million years ago.

James Zachos, professor of Earth sciences at the University of California, Santa Cruz, led an international team of scientists that analyzed marine sediments deposited during a period of extreme global warming known as the Paleocene-Eocene Thermal Maximum (PETM), in which temperatures rose by as much as 10 degrees in a relatively short period of time. Sediment cores drilled from the ocean floor revealed an abrupt change in ocean chemistry at the start of the PETM 55 million years ago, followed by a recovery that took at least 80,000 years.

"Most people have not thought about the long-term fate of all that carbon and what's involved in removing it from the system. There is a long timescale for the recovery, tens of thousands of years before atmospheric carbon dioxide will start to come back down to pre-industrial levels," Zachos said in a June press release.

Impact in the seas

This absorption of carbon dioxide by the world's oceans will have a significant impact on marine organisms if past events are any indication of the future. When carbon dioxide dissolves in water it makes the water more acidic by stripping out carbonate ions, which are essential for marine organisms to build calcium carbonate shells and exoskeletons. During the PETM, ocean acidification likely caused a mass extinction of phytoplankton -- microorganisms key to the prehistoric food chain. In September 2005, a team of scientists writing in Nature warned that the same fate could befall modern day marine life. Their projections show that by 2100, the amount of carbonate available for marine organisms could drop by 60%. In surface ocean waters, where acidification starts before spreading to the deep sea, there may be too little carbonate for organisms to form shells as soon as 2050. The regions most affected would be the Southern Ocean around Antarctic and the subarctic Pacific Ocean.

The loss of these small organisms would have a disastrous impact on predators -- including salmon, mackerel, herring, cod -- that rely on them as a food source and could spell trouble for other species.


The pteropod or sea butterfly is one marine organism that could suffer in more acidic seas. A recent experiment by Victoria Fabry at California State University San Marcos found that the shells of pteropods, when subjected to conditions as projected by the model for the year 2100, rapidly dissolved. Photo courtesy of USGS.
The concerns over increasing acidity of the world's oceans extends to other parts of the world as well. In July, a report by the Royal Society, said that rising carbon levels will make if harder for sea creatures like coral, shell fish and star fish to form shells and skeletons. Further, higher levels of carbon dioxide and warmer seas will reduce the amount of oxygen available to ocean life. Another study, released in the September issue of Geology, suggests that dramatically warmer ocean temperatures may have contributed to the worst mass extinction on record. During the Permian extinction, which occurred some 250 million years ago, about 95% of ocean's life forms became extinct.

On land: changing forests

Based on new findings on the PETM, increasing amounts of greenhouse gasses in the atmosphere will also have dramatic impacts on land ecosystems. Research released last week in Science reports that a rapidly warming climate 55 million years ago caused significant changes in forest composition and distribution.

"It indicates that should we have a period of rapid global warming on that scale today, we might expect very dramatic changes to the biota of the planet, not just the mammals and other vertebrates, but forests also completely changing," said Jonathan Bloch, a University of Florida vertebrate paleontologist and member of the research team for the Science paper.

After an initial period of increasing aridity in northern latitudes like the study site of Bighorn Basin in northwestern Wyoming, it appears that plants species migrated towards higher latitudes and forests transitioned towards warm tropical ecosystems with closely spaced trees, ideal for the evolution of primates. Further, global warming allowed mammals -- including rhinos and the earliest known horse -- to emigrate across northern land bridges to expand into new habitats.

Lead author of the study, Scott Wing, a paleobiologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., says that similar rapid changes in plant life might be expected in the future as a result of human-induced global warming.

"No two events are ever exactly the same," Wing said, "but the history of life on this planet has a lot to tell us about our possible future."

While modern day warming is thought to be tied to anthropogenic sources such as the combustion of fossil fuels and the conversion of forests for agriculture, the massive spike in atmospheric greenhouse gases 55 million years ago is believed to have resulted from the rapid decomposition of frozen methane hydrate deposits found in the deep ocean near continental margins and in the Arctic. According to Zachos, the methane would have reacted with oxygen to produce huge amounts of carbon dioxide, also a potent greenhouse gas.

Scientists are concerned that a parallel release of frozen methane deposits today could trigger a similarly catastrophic climate event. At the 2005 Annual Conference of the Royal Geographical Society, Mark Maslin, a senior researcher for the London Environmental Change Research Centre, warned that continued warming could destabilize gas hydrates deposits at the bottom of the ocean and in Arctic permafrost and result in a massive release of methane gas into the atmosphere.

"The destabilization of gas hydrates is likely to be a serious hazard in the near future due to the effects of global warming," said Dr Maslin. "Research already exists to suggest that the release of hydrates increased global temperature 18,000 years ago, and we now face a similar threat as our global temperature continues to rise."

While scientists are just beginning to unlock the mysteries of the colossal warming event of 55 million years ago, it is clear that rapid climate change can have significant ramifications for Earth's ecosystems and species.

"Even after humans stop burning fossil fuels, the impacts will be long-lasting," Zachos said.




Scott L. Wing, Guy J. Harrington, Francesca A. Smith, Jonathan I. Bloch, Douglas M. Boyer, and Katherine H. Freeman
"Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary."
Science 11 November 2005; 310: 993-996 [DOI: 10.1126/science.1116913]

James C. Zachos, Ursula Röhl, Stephen A. Schellenberg, Appy Sluijs, David A. Hodell, Daniel C. Kelly, Ellen Thomas, Micah Nicolo, Isabella Raffi, Lucas J. Lourens, Heather McCarren, and Dick Kroon
"Rapid Acidification of the Ocean During the Paleocene-Eocene Thermal Maximum"
Science 10 June 2005

James C. Orr, Victoria J. Fabry, Olivier Aumont, Laurent Bopp, Scott C. Doney, Richard A. Feely, Anand Gnanadesikan, Nicolas Gruber, Akio Ishida, Fortunat Joos, Robert M. Key, Keith Lindsay, Ernst Maier-Reimer, Richard Matear, Patrick Monfray, Anne Mouchet, Raymond G. Najjar, Gian-Kasper Plattner, Keith B. Rodgers,, Christopher L. Sabine, Jorge L. Sarmiento, Reiner Schlitzer, Richard D. Slater, Ian J. Totterdell, Marie-France Weirig, Yasuhiro Yamanaka and Andrew Yool
"Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms"
Nature 437, 681-686 (29 September 2005) | doi: 10.1038/nature04095

Jeffrey T. Kiehl and Christine A. Shields. 2005:
"Climate simulation of the latest Permian: Implications for mass extinction."
Geology: Vol. 33, No. 9, pp. 757–760.

This article also used information from press releases related to these papers.









CITATION:
Rhett A. Butler, mongabay.com (November 14, 2005).

Massive climate change rocked ecosystems, animals 55 million years ago.

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