Tracing West Antarctic Subglacial Weathering Fluxes Across the MPT Using Osmium Isotopes

Abstract Quaternary climate is characterized by glacial‐interglacial cyclicity, as evidenced by global benthic foraminifera (δ 18 O benthic ) records. These records, although temporally comprehensive and global in scale, do not easily highlight regional variations in ice sheet dynamics, making it challenging to decouple ice sheet behavior in the Northern Hemisphere from the Southern Hemisphere. Differences between SH and global δ 18 O benthic records across the Mid‐Pleistocene suggest an underrepresentation of Antarctic Ice Sheet (AIS) dynamics at this time. To isolate AIS Mid‐Pleistocene behavior from the global δ 18 O benthic record, we compare a new seawater osmium (Os) isotope record from International Ocean Discovery Program Site U1536 in the Scotia Sea with recently published records of ice‐rafted debris and SH stable isotope records across the interval from 1.24 million years ago (Ma) to 470 thousand years ago (ka). Additionally, we provide Os isotope composition and concentration data from Antarctic bedrock samples to fingerprint possible Os sources influencing the marine sedimentary record. At U1536, we observe a consistently less radiogenic signal ( 187 Os/ 188 Os < 1.06) likely sourced from erosion of the younger West Antarctic bedrock, with little to no influence from the older, more radiogenic East Antarctic bedrock. Unradiogenic excursions (downturns in 187 Os/ 188 Os) occur at MIS 31 and MIS 15‐13, suggesting a greater flux of weathered material from West Antarctic bedrock. Lastly, the average Os isotope composition of the Scotia Sea is significantly and consistently less radiogenic than the North Atlantic at this time, suggesting heterogeneity of Os in the global ocean during the Middle Pleistocene.