Strengthened Icelandic Ice Sheet control on Northeast Atlantic neodymium isotope variability across the Mid-Pleistocene Transition

The Mid-Pleistocene Transition (MPT) marks one of the most profound reorganizations of the Earth’s climate system over the Quaternary. During this interval, the dominant glacial-interglacial cyclicity shifted from 40 kyr to 100 kyr without a corresponding change in orbital forcing, implying fundamental internal feedbacks within the climate system. Post-MPT glaciations became longer (up to ~60 kyr), more severe, and characterized by larger and more stable Northern Hemisphere ice sheets. Despite intensive research into the mechanisms driving the MPT, the response of ocean trace metal cycling to Northern Hemisphere ice-sheet dynamics remains poorly constrained, limiting our ability to fully integrate ice-sheet evolution with changes in ocean circulation, elemental cycling, and the carbon cycle.

Here we present a new authigenic neodymium isotope (ε_Nd) record from ODP Site 982 (1134 m water depth), spanning 1.4–0.6 Ma and capturing the MPT. Our record reveals clear and systematic glacial-interglacial ε_Nd variability linked to the evolving Icelandic Ice Sheet (IIS) and its modulation of volcanic erosion and weathering fluxes into the NE Atlantic, coupled with southward shifts in deep-water formation during glacials. Before the MPT, interglacial ε_Nd values of -13.5 to -12.5 indicate persistent influence of Labrador Sea-derived waters, whereas glacial intervals are marked by more radiogenic ε_Nd from -11 around 1.4 Ma to -9 by 1.1 Ma, reflecting increasing Icelandic volcanic input influence associated with IIS expansion. From ~1.1 Ma onward, the ε_Nd contrast between climate states intensifies and reaches its strongest amplitude, with interglacials becoming slightly more unradiogenic (to -14) and glacials reaching radiogenic values up to -8. This persistent pattern of radiogenic in glacials and unradiogenic in interglacials continues into later cycles, indicating that Icelandic volcanic weathering and IIS extent reached their maximum expression since the MPT. Our results demonstrate that the IIS exerted first-order control on NE Atlantic seawater Nd isotope cycling during glacial periods, and that this modulation strengthened across and after the MPT. Importantly, the gradual amplification of Icelandic erosion signals suggests that Northern Hemisphere ice-sheet expansion (at least in Iceland) was a response to, rather than the initial trigger of, the MPT, consistent with coupled ice-sheet–carbon cycle feedback frameworks.