Changes in terrestrial weathering following glacial retreat reveal processes altering North Atlantic neodymium isotopes

Abstract Anomalously unradiogenic neodymium in authigenic phases of the North Atlantic during glacial terminations has been attributed to weathering of glacial sediments derived from shield rocks. However, mechanisms producing unradiogenic neodymium and their link to terrestrial processes remain poorly constrained. Here we analyze neodymium isotopes from co-located stream water and sediment across a deglaciating landscape in southwest Greenland. Dissolved neodymium is ~8 ɛNd units less radiogenic than bedload in recently exposed watersheds. In watersheds with longer exposure time, dissolved neodymium is ~10 ɛNd units and particulate neodymium ~3 ɛNd units higher, decreasing the offset to ~1 unit. This shift results from preferential weathering of minerals with low samarium/neodymium ratios and winnowing of the fine fraction of recently exposed sediments. Variations in the influx and weathering extent of shield-derived sediment alter neodymium isotopic compositions of North Atlantic seafloor sediment and seawater, constraining interpretations of past ice sheet loss and deep ocean circulation.