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Global redox state of the ocean during Cretaceous oceanic anoxic events: new insights from molybdenum isotopes

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Modern tool to study ancient oceans

Researchers devised a new method that uses molybdenum in ocean floor sediments to estimate global oxygen levels in the ocean during periods of global climate change.

Climate Change and Environment

Oceanic anoxic events (OAEs) are historic periods of low oxygen in the ocean, which scientists can detect in specific types of sedimentary rock. While this method can identify local hotspots of euxinia (complete lack of dissolved oxygen), there has been no reliable way to test for ocean-wide euxinia. The EU-funded MOLY-OAES project developed a method to test ocean-wide euxinia using isotopes of the element molybdenum (Mo). The first site sampled was not suitable for testing this process because conditions were not fully euxinic. The other three sites, however, were suitable for testing the molybdenum proxy method. By comparing molybdenum isotopic composition with that of the modern ocean, researchers showed that the method was suitable to evaluate climate conditions. The new method allowed researchers to better understand climate conditions associated with these Cretaceous OAEs. A major finding was that ocean oxygenation fluctuated rapidly during the OAEs, suggesting that the global ocean was resilient to certain amounts of environmental change. The other important finding was that for one of the OAEs there is evidence for a euxinic environment that expanded and moved over time. The work of MOLY-OAES has expanded knowledge of OAEs in Cretaceous oceans. It has also provided a tool to better understand how oceans are influenced by climate change.

Keywords

Oceans, molybdenum, oxygen levels, climate change, oceanic anoxic events, sedimentary rock, euxinia, Cretaceous, ocean oxygenation, euxinic environment

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