image: This is the view across the chalk section at Eastbourne, Southern England, which was sampled for this study. The limestones preserve the chemistry of the oceans, allowing scientist to reconstruct past anoxic events. view more
Credit: PNAS
Uranium isotopes in sediments from Oceanic Anoxic Event 2 (OAE2) suggest that the event, which occurred 94 million years ago, may have been two episodes of anoxia expansion, driven by atmospheric carbon dioxide injection and separated by a cold reoxygenation event. Periods of rapid climate warming throughout Earth's history have been associated with episodes of ocean anoxia, although the extent and rate of development of such anoxic events are poorly constrained. Matthew Oliver Clarkson and colleagues analyzed a high-resolution record of uranium isotopes in marine sediments and coupled the results with biogeochemical cycle models to investigate OAE2, which occurred during the Mesozoic Era. The authors noted two distinct decreases in ?238U isotope values during OAE2, suggesting two periods of widespread anoxia development. Modeling dynamics of carbon, phosphorus, and uranium during OAE2 replicated the trends seen in the uranium isotope record and provided insight into the magnitudes of carbon and phosphorus released during such an event. The authors report that OAE2 was likely a result of two large carbon dioxide releases from large igneous provinces. According to the authors, coupling geochemistry with modeling enabled resolution of the exceptionally long OAE2 into two distinct deoxygenation events.
Article #17-15278: "Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2," by Matthew Oliver Clarkson et al.
MEDIA CONTACT: Matthew Oliver Clarkson, Swiss Federal Institute of Technology in Zurich, SWITZERLAND; tel: +41 446324578; e-mail: <matthew.clarkson@erdw.ethz.ch>
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