Dynamic collapse and regrowth of the Antarctic Ice Sheet in the Weddell Sea sector during the middle Miocene: A novel multi-proxy sedimentary provenance approach using in-situ87Rb/87Sr dating of detrital K-feldspar

Abstract

The latest generation of Antarctic paleo-ice sheet models, incorporating bedrock paleo-topography, reconstruct the development of substantial ice-sheet embayments during the Mid-Miocene Climate Optimum, a warm period between ∼17–15 Ma ago. Here, we test these models using ice-rafted debris (IRD) recovered from the central Weddell Sea (Ocean Drilling Program Site 113–694). These IRD are entrained by the ice-sheet expanding into the embayment during the cooling associated with the subsequent Mid-Miocene Climate Transition and ultimately delivered to the deep marine sink by iceberg armadas during higher-frequency instability events. Due to the near-absence of heavy minerals in these volumetrically small samples, we utilise the novel in-situ K-feldspar 87Rb/87Sr provenance technique by laser-ablation inductively coupled mass spectrometer equipped with a mass-filtered reaction cell. We combine these single-grain ages with in-situ Pb-isotope analysis, as well as 40Ar/39Ar dating of a subset of grains. Results identify the Antarctic Peninsula and southern Dronning Maud Land as key sediment sources, including grains sourced from within the Recovery subglacial basin. These findings support ice sheet instability consistent with reconstructions of major ice sheet embayments formed by climatic conditions analogous to those predicted by modern anthropogenic warming trajectories. Additionally, in-situ87Rb/87Sr and Pb-isotope analysis of detrital K-feldspar provide a high-throughput alternative to conventional single grain U-Pb or 40Ar/39Ar analysis, especially in small samples where the heavy mineral fraction is limited or absent.