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EPS Seminar: Dr. Preston Cosslett Kemeny - Mountain high, valley low, river wide: biogeochemical insights into the relationship between weathering and climate

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The long-term stability of Earth’s climate requires a delicate balance between carbon inputs to and outputs from the ocean-atmosphere system. These fluxes are brought into balance through chemical weathering, which has traditionally been viewed as a temperature-dependent process that lowers atmospheric CO2 by converting silicate minerals into carbonate minerals. However, recent research has shown that sulfide oxidation during chemical weathering counteracts the effects of silicate weathering and increases atmospheric CO2. The relative importance of these weathering processes is currently not well constrained but can be diagnosed from the dissolved ionic and isotopic composition of river water. In this seminar, I will discuss new geochemical data from two river systems and an inversion of global river data to quantify controls of sulfide oxidation and its role in the relationship between weathering and climate. First, using sulfur isotopic and spectroscopic observations of water and sediment samples from an Icelandic catchment, I will demonstrate that rivers can faithfully record the sulfur isotopic composition of weathering lithologies even in the presence of biological sulfur cycling. Second, I will address long-standing hypotheses linking Cenozoic cooling with Himalayan weathering by presenting evidence for extensive sulfide oxidation within central Nepal. Finally, I will present new computational tools for river inversion calculations and apply them to a global dataset to quantify the overall importance of sulfide oxidation and show that the sulfur isotopic composition of crustal sulfide is substantially heavier than predicted from common models of the global sulfur cycle. I will conclude the seminar with a discussion of future carbon-cycle research directions utilizing emerging forms of isotope ratio mass spectrometry. 

 

Dr. Preston Cosslett Kemeny is currently a T.C. Chamberlin and NSF postdoctoral fellow at the University of Chicago. He received a PhD in Geochemistry from Caltech in 2022, where he was supported by the Hertz and NDSEG fellowships. Prior to Pasadena, Preston graduated summa cum laude from Princeton University in 2015 with a degree in Geosciences. He is originally from NY, has a retired racing greyhound named Tethys, and wrote the Wikipedia article on the reference materials used in stable isotope analysis.​​​​​​

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