Mark Clementz
Seawater is seawater, right?
Maybe not.
While researching the evolutionary ecology of sirenians, such as manatees and dugongs, University of Wyoming Geology And Geophysics Assistant Professor Mark T. Clementz unexpectedly stumbled across data that could change scientists' perception regarding climate during the Eocene, a major division of the geologic timescale some 50 million years ago.
In a paper published today (Friday) in the international journal Science, Clementz and co-author Jacob O. Sewall, a professor in the Department of Physical Sciences at Kutztown University in Pennsylvania, use their findings to dispute a popular scientific assumption regarding the temperature and composition of seawater during the time marked by the emergence of the first modern mammals.
"Most people have assumed that the oxygen isotopic composition of seawater in the past was very similar to that of today, where you have high values at low latitudes and low values at high latitudes," Clementz says. "But when we looked at the oxygen isotopic values of the fossils from low-latitude sites for the Eocene, they were much lower than we would predict.
"This suggests that low-latitude sites during the Eocene were much wetter than today," he says. "This created a very different distribution in the oxygen isotopic composition of seawater for this time interval, which would, in turn, significantly impact our estimates of paleoclimate and paleotemperature for the past."
He adds, "People have used this assumption of the oxygen isotopic values of seawater to constrain temperature estimates for the past . but we're showing that their assumption may be flawed, which could mean their estimates of water temperature are wrong."
A better understanding of climate during the Eocene, when there was a dramatic change in the Earth's atmosphere's carbon isotopic composition, could help scientists to prepare for changes that could accompany the current increase in atmospheric carbon concentrations from the burning of fossil fuels such as coal and petroleum.
"This study demonstrates the value of the fossil record and of examining the deep time record of paleoclimatogical events so that we can better understand climate change today," says Lisa Boush, program director in the National Science Foundation's Division of Earth Sciences, which funded the research. "This integrative and novel approach will potentially transform our way of thinking about the hydrologic response to global climate change."
In their paper, titled "Latitudinal Gradients in Greenhouse Seawater δ18O: Evidence from Eocene Sirenian Tooth Enamel," Clementz says he and Sewall use the isotopic composition of fossils from a broad time period and broad geographical area and climate simulation data to "add another wrinkle" to the long-running debate over Eocene climate.
"I wasn't looking at it from this direction when we started this project. I was looking at it to get a better understanding of the habitat and dietary preferences for these fossil species," says Clementz, whose research is part of his five-year NSF CAREER Award, which he won in 2009. "But once we started accumulating enough samples, we could step back and look at the big picture and see how it could be reflecting climate and environmental change."
To read the Science article, go to http://www.sciencemag.org/content/332/6028/455.full.
