The dynamic sulfur cycle and ocean deoxygenation during the PETM


In light of the increasing concern over global warming, it is of great importance to understand how biogeochemical cycles have in the past and may in the future interact with climate changes and to predict the potential consequences for our planet. The net loss of dissolved oxygen (so-called ocean deoxygenation) is one of the lesser-known aspects of anthropogenic climate warming. Recent studies suggest that the total oxygen mass in the oceans has shrunk by approximately 2% since 1950, and the volume of suboxic ocean water will expand by 50% by the end of this century. Paleoceanographic records provide potential analogues for how global and regional water column deoxygenation relates to varying pCO2 levels, particularly during striking hyperthermal events like the Paleocene-Eocene Thermal Maximum (PETM, ~ 55.6 Ma). While the estimated carbon release rate for the PETM is only one-tenth of the current anthropogenic release rate, the total amount is similar to the IPCC RCP8.5 emission scenario (2000 Gt C by 2100). Marine sulfate S- and O-isotope records suggest that during this hyperthermal episode the oxygen minimum zone has expanded by one order of magnitude to 10-20% of the global ocean volume and may reach sulfidic at the immediate water depth. While this transient sulfide reservoir leaves almost no sedimentary record, it paints a much more dynamic picture of the biogeochemical sulfur cycle elucidating the feedback mechanism for the rapid transition and recovery of anoxic waters. The toxicity of hydrogen sulfide will render two of the largest and least explored ecosystems on Earth, the mesopelagic and bathypelagic zones, uninhabitable by multicellular organisms.


Weiqi Yao received her Ph.D. degree at the University of Toronto before she worked as a postdoctoral fellow at Harvard University. She joined the Southern University of Science and Technology faculty in the summer of 2021 and is now an associate professor in the Department of Ocean Science and Engineering. Weiqi is interested in the global C-S-O cycles, paleoceanography, and paleoclimatology on various geological timescales. Stable isotope geochemistry and numerical modeling are the primary approaches for her research. Through investigating the Cenozoic seawater chemistry (elemental and isotopic compositions) archived in marine barite and foraminifera, Weiqi's work provides new insights into the rapid response and feedback of biogeochemical processes to extreme climate, redox conditions, and Earth’s surface processes. The overarching goal is to better understand and address important questions in climatic and environmental sciences with an emphasis on anthropogenic impacts. 


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