Multi-isotope investigation of paleozoic climate an environment: a new approach using redox sensitive stable isotope tracers

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In the past 540 million years, sea level has been much higher than today, causing large areas of the paleocontinents to be submerged. If submergence occurred when a continent was near the equator, limestones were deposited. The seas have long since retreated from the continents, but the limestones remain. Inside the limestones there are geochemical clues in the form of isotopic fingerprints that we can use to understand the nature of the Earth's past environment and climate. By making our measurements in stratigraphic successions of ancient marine limestones we can track the evolution of the Earth's environment and climate over time. The isotopic fingerprints tell us about the ancient carbon cycle and greenhouse effect, sea level, and seawater circulation patterns in epicontinental seas, temperature, and salinity of marine waters. This type of information informs our thinking and models on the relationship between climate and sea level circulation patterns, or climate and continental weathering rates in the past. And it bears on the debate regarding the impact of anthropogenic carbon dioxide on contemporary global warming. My work is focused on refining interpretations of carbon isotope records through time, developing models of ancient carbon cycling, and advancing the application of isotope tracers like neodymium, which I have found to be related to sea level changes in the past. New research will add significantly to this repertoire of isotopic tools; including, for the first time, a proxy indicator of dissolved oxygen levels in ancient seawater-stable isotope variations of uranium and chromium. The behavior of uranium and chromium isotopes will be first studied in modern environments. This will involve sampling ocean waters, stratified waters in coastal seas, and even a modern stratified lake with no dissolved oxygen in the bottom waters. These modern studies will characterize the range of chromium and uranium isotope fractionation in modern systems, and the processes that control the isotope fractionations. These findings will inform on the utility of uranium and chromium isotope fingerprints in ancient marine sediments as tools for tracking changing oxygen levels in the earth's shallow seas and oceans over time.