A foraminifera fossil (Photo courtesy of Ellen Thomas, Yale University, and Paul Pearson)
Researchers in the are pairing chemical analyses with micropaleontology鈥攖he study of tiny fossilized organisms鈥攖o better understand how global marine life was affected by a rapid warming event more than 55 million years ago.
Their findings are the subject of an article in the journal (John Wiley & Sons, 2014).
“Global warming impacts marine life in complex ways, of which the loss of dissolved oxygen [a condition known as hypoxia] is a growing concern” says , assistant professor of Earth sciences and a member of 黑料不打烊’s . 鈥淢oreover, it鈥檚 difficult to predict future deoxygenation that is induced by carbon emissions, without a good understanding of our geologic past.”
Lu says this type of deoxygenation leads to larger and thicker oxygen minimum zones (OMZs) in the world鈥檚 oceans. An OMZ is the layer of water in an ocean where oxygen saturation is at its lowest.
Zunli Lu
Much of Lu’s work revolves around the Paleocene-Eocene Thermal Maximum (PETM), a well-studied analogue for modern climate warming. Documenting the expansion of OMZs during the PETM is difficult because of the lack of a sensitive, widely applicable indicator of dissolved oxygen.
To address the problem, Lu and his colleagues have begun working with iodate, a type of iodine that exists only in oxygenated waters. By analyzing the iodine-to-calcium ratios in microfossils, they are able to estimate the oxygen levels of ambient seawater, where microorganisms once lived.
Fossil skeletons of a group of protists known as foraminiferas have long been used for paleo-environmental reconstructions. Developing an oxygenation proxy for foraminifera is important to Lu because it could enable him study the extent of OMZs 鈥渋n 3-D,鈥 since these popcorn-like organisms have been abundant in ancient and modern oceans.
鈥淏y comparing our fossil data with oxygen levels simulated in climate models, we think OMZs were much more prevalent 55 million years ago than they are today,鈥 he says, adding that OMZs likely expanded during the PETM. 鈥淒eoxygenation, along with warming and acidification, had a dramatic effect on marine life during the PETM, prompting mass extinction on the seafloor.鈥
Xiaoli Zhou in the lab
Lu thinks analytical facilities that combine climate modeling with micropaleontology will help scientists anticipate trends in ocean deoxygenation.聽Already, it’s been reported that modern-day OMZs, such as ones in the Eastern Pacific Ocean, are beginning to expand. “They’re natural laboratories for research,” he says, regarding the interactions between oceanic oxygen levels and climate changes.”
The article鈥檚 lead author is , a Ph.D. student of Lu鈥檚 in 黑料不打烊鈥檚 Earth sciences department. Other coauthors are , a senior research scientist in geology and geophysics at Yale University; , professor of biogeochemistry at the University of Oxford (U.K.); and , assistant professor of oceanography at the University of Texas at Arlington.
