Oscillations in ice sheet extent during early and middle Miocene are intermittently preserved in the sedimentary record from the Antarctic continental shelf, with widespread erosion occurring during major ice sheet advances, and open marine deposition during times of ice sheet retreat. Data from seismic reflection surveys and drill sites from Deep Sea Drilling Project Leg 28 and International Ocean Discovery Program Expedition 374, located across the present-day middle continental shelf of the central Ross Sea (Antarctica), indicate the presence of expanded early to middle Miocene sedimentary sections. These include the Miocene climate optimum (MCO ca. 17−14.6 Ma) and the middle Miocene climate transition (MMCT ca. 14.6−13.9 Ma). Here, we correlate drill core records, wireline logs and reflection seismic data to elucidate the depositional architecture of the continental shelf and reconstruct the evolution and variability of dynamic ice sheets in the Ross Sea during the Miocene. Drill-site data are used to constrain seismic isopach maps that document the evolution of different ice sheets and ice caps which influenced sedimentary processes in the Ross Sea through the early to middle Miocene. In the early Miocene, periods of localized advance of the ice margin are revealed by the formation of thick sediment wedges prograding into the basins. At this time, morainal bank complexes are distinguished along the basin margins suggesting sediment supply derived from marine-terminating glaciers. During the MCO, biosiliceous-bearing sediments are regionally mapped within the depocenters of the major sedimentary basin across the Ross Sea, indicative of widespread open marine deposition with reduced glacimarine influence. At the MMCT, a distinct erosive surface is interpreted as representing large-scale marine-based ice sheet advance over most of the Ross Sea paleo-continental shelf. The regional mapping of the seismic stratigraphic architecture and its correlation to drilling data indicate a regional transition through the Miocene from growth of ice caps and inland ice sheets with marine-terminating margins, to widespread marine-based ice sheets extending across the outer continental shelf in the Ross Sea.

Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from farfield records 1,2,3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth 2 . This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene 4,5 . Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here, we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72-17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution.

No abstract

Abstract. Ice sheet models must be able to accurately simulate palaeo ice sheets to have confidence in their predictions of future Antarctic ice mass loss and resulting global sea-level rise, particularly over longer timescales. This requires accurate reconstructions of the extent and flow patterns of palaeo ice sheets using real-world data. Such reconstructions can be achieved by tracing the detrital components of offshore sedimentary records back to their source areas on land. However, sediment provenance data and ice sheet model results have not been directly linked, despite the complimentary information each can provide the other. Here, we present a computational framework (Tracing Antarctic Sediment Provenance, TASP) that predicts marine geochemical sediment provenance data using the output of numerical ice sheet modelling. The ice sheet model is used to estimate the spatial pattern of erosion rates and to trace ice flow pathways. Beyond the ice sheet margin, simple approximations of modern detrital particle transport mechanisms using ocean reanalysis data produce a good agreement between our predictions for the modern ice sheet/ocean system and marine surface sediments. Comparing results for the modern system to seafloor surface sediment measurements will allow application of the method to past ice sheet configurations. TASP currently predicts neodymium isotope compositions using the PSUICE3D ice sheet model, but it has been designed so that it could be adapted to predict other provenance indicators or use outputs of other ice sheet models.

<p>Tracing the provenance of Antarctic sediments yields unique insights into the form and flow of past ice sheets. However, sediment provenance studies are typically limited to qualitative interpretations by uncertainties regarding subglacial geology, glacial erosion, and transport of sediment both subglacially and beyond the ice sheet margin. Here, we forward model marine geochemical sediment provenance data, in particular neodymium isotope ratios. Numerical ice-sheet modelling predicts the spatial pattern of subglacial erosion rates for a given ice sheet configuration, then ice flow paths are traced to the ice sheet margin. For the modern ice sheet, simple approximations of glacimarine sediment transport processes produce a good agreement with Holocene surface sediments in many areas of glaciological interest. Calibrating our model to the modern setting permits application of the approach to past ice sheet configurations, which show that large changes to sediment provenance over time can be reconstructed around the West Antarctic margin. This first step towards greater integration of Antarctic sediment provenance data with numerical modelling offers the potential for advances in both fields.</p>