Toward Calibrating for Bottom Water Oxygenation Using Magnetofossils: New Insights From Southeast Atlantic and Northeast Pacific Surface Sediments

Abstract Accurate estimation of past ocean oxygen concentrations is vital for understanding the ocean's response to global climate change, but proxies for reconstructing bottom water oxygen (BWO) are limited. Magnetofossils, produced by magnetotactic bacteria, are sensitive to redox conditions in various environments. However, the relationship between magnetofossils and BWO has not been well‐established. Here, we present the first calibration of the magnetofossil‐hosted BWO proxy using surface sediments along oxygen gradients in the Southeast Atlantic and Northeast Pacific. Our results show that magnetofossil dimensional features and magnetic properties are linearly correlated with known BWO profiles (60–230 μmol/kg). Specifically, higher proportions of cuboctahedral magnetofossils coupled with more biogenic soft components are associated with higher BWO levels, and vice versa. These findings confirm that magnetofossils can serve as a valuable proxy for quantifying past oxygen concentrations globally, expanding the application of BWO proxies for paleoclimate reconstructions.