Award: OCE-1946153

Intellectual Merit: The stable isotopes in marine sulfate minerals preserve a paleorecord of Earth’s climate and biological activity over billions of years. One stable isotope, 17O, has been used to infer atmospheric pCO2 and pO2 on the ancient Earth, using measurements of sulfate minerals between 2.3 and 0.5 billion years old. Here, we extend the measured 17O record of marine sulfate minerals to cover the last 130 million years of Earth history. For the first time, we collected measurements of marine barite minerals which form in the open ocean water column, and we compared these measurements to marine evaporite minerals which form in closed marine basins. We find that these marine sulfate minerals younger than 130 million years old do not carry atmospheric information, but instead primarily preserve information about microbial sulfur metabolisms and sulfur weathering from the continents. Our findings influence our understanding of how the earth system has evolved over the last 130 million years, between hothouse and icehouse states. For example, marine sulfate 17O tells us that there was relatively more microbial sulfur cycling in during the Cretaceous hothouse, which is consistent with other proxy records. The sulfate 17O record also preserves the increasing influence of sulfur weathering in rivers over the last 55 million years, which can record the influence of the Himalayan uplift as observed in other isotope records. Broader Impacts: This work has supported several junior female scientists in the form of mentoring from senior scientists and collaborators, funding for graduate and postdoctoral work, and travel to scientific meetings. This research has implications for the study of climate, especially related to the sulfur cycle and biological responses to a changing world. The record of 17O in marine sulfate minerals over the last 130 million years provides an additional constraint on the feedbacks between Earth’s changing climate, tectonics, and biosphere, which can be used to test hypotheses related to future climate change. Last Modified: 02/04/2023 Submitted by: Adina Paytan