Description: The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions.

Description: In this paper we analyze how oceanic circulation affects sediment deposition along a sector of the Ross Sea continental margin, between the Iselin Bank and the Hillary Canyon, and how these processes evolved since the Late Miocene. The Hillary Canyon is one of the few places around the Antarctic continental margin where the dense waters produced onto the continental shelf, mainly through brine rejection related to sea ice production, flow down the continental slope and reach the deep oceanic bottom layer. At the same time the Hillary Canyon represents a pathway for relatively warm waters, normally flowing along the continental slope within the Antarctic Slope Current, to reach the continental shelf. The intrusion of warm waters onto the continental shelf produces basal melting of the ice shelves, reduces their buttressing effect and triggers instabilities of the ice sheet that represent one of the main uncertainties in future sea level projections. For this study we use seismic, morpho-bathymetric and oceanographic data acquired in 2017 by the R/V OGS Explora. Seismic profiles and multibeam bathymetry are interpreted together with age models from two drilling sites (U1523 and U1524) of the International Ocean Discovery Program (IODP) Expedition 374. Oceanographic data, together with a regional oceanographic model, are used to support our reconstruction by showing the present-day oceanographic influence on sediment deposition. Regional correlation of the main seismic unconformities allows us to identify eight seismic sequences. Seismic profiles and multibeam bathymetry show a strong influence of bottom current activity on sediment deposition since the Early Miocene and a reduction in their intensity during the mid-Pliocene Warm Period. Oceanographic data and modelling provide evidence that the bottom currents are related to the dense waters produced on the Ross Sea continental shelf and flowing out through the Hillary Canyon. The presence of extensive mass transport deposits and detachment scarps indicate that also mass wasting participates in sediment transport. Through this integrated approach we regard the area between the Iselin Bank and the Hillary Canyon as a Contourite Depositional System (ODYSSEA CDS) that offers a record of oceanographic and sedimentary conditions in a unique setting. The hypotheses presented in this work are intended to serve as a framework for future reconstructions based on detailed integration of lithological, paleontological, geochemical and petrophysical data.

Description: Early to Middle Miocene sea-level oscillations of approximately 40–60 m estimated from far-field records1–3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene4,5. 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.

Description: This dataset consists of terrigenous grain-size data from Integrated Ocean Drilling Program (IODP) Sites 342-U1406 and 342-U1411 and lithogenic isotope (Hf, Nd, Pb/Pb) data from IODP Site 342-U1411. These two sites are in the Newfoundland ridges contourite drift complex and were cored during IODP Expedition 342 (Paleogene Newfoundland Drifts) in summer 2012. The grain-size data consists of 137 samples from Site 342-U1406 and 192 samples from Site 342-U1411 and was measured with a Micromeritics SediGraph 5120 particle size analyzer. The Hf and Nd data consists of 30 samples from Site 342-U1411 and were measured using a ThermoFisher Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS). The Pb/Pb data consists of 23 samples from Site 342-U1411 were also measured using a ThermoFisher Neptune MC-ICPMS. All data were generated between the years 2014 and 2019. The timespan of the data set is from ~35 Ma to 26 Ma (9 Myr total duration). Sample resolution ranges and is up to one sample per 10-15 kyr during the Eocene-Oligocene Transition (EOT; 33.65-34.44 Ma) and intervals immediately prior (35-34.44 Ma) and immediately after (33.65-32.5 Ma). Sortable silt metrics (abundance and mean) were calculated from the grain-size data and used to reconstruct bottom-current and paleocirculation history. The lower-resolution lithogenic isotope data is used to infer sediment source (provenance) changes across the EOT.

Description: The seafloor provides high-resolution, but relatively static, perspectives of submarine sediment-routing systems, which can be employed in the development of predictive models of deep-water stratigraphic sequences. We compare 31 seafloor canyon-and-channel systems from predominantly siliciclastic continental margins and discuss their morphologic variability. The longest canyon-and-channel systems of this study generally correspond with relatively mature, passive continental margins associated with some of the largest deep-sea fans in the world with long-term, voluminous, mud-rich sediment supply. Shorter, lower-relief canyon-and-channel systems generally correspond with immature margins associated with relatively meager, sand-rich or mixed-caliber sediment supply. Seafloor continental-margin relief nonlinearly corresponds with canyon-and-channel-system length, with very high-relief margins exhibiting longer canyon-and-channel systems than predicted by a linear relationship. Nonlinearity in our observations can be accounted for by the increased occurrence and magnitude of submarine mass wasting in higher-relief and correspondingly longer canyon-and-channel systems, limitations of relief imposed by the maximum depths of ocean basins, and sediment-gravity-flow dynamics. These interpretations of controls on canyon-and-channel geomorphology represent extrinsic characteristics of land-to-deep-sea sediment supply and basin or continental-margin framework and intrinsic sediment-gravity-flow dynamics.We demonstrate that insights into seafloor channel processes, morphologic products, and scaling relationships can be broadly applied to predicting ancient subsurface and outcropping deep-water stratigraphic sequences. Our comparative analysis suggests that knowledge of the thickness of an ancient basin-margin stratigraphic sequence can be employed in order to generally predict the basinward extent of a paleo-canyon-and-channel system and underlying depositional fan. The application also potentially works in reverse: intimate knowledge of the deep-water component of a continental margin or basin margin can facilitate understanding of up-depositional-dip stratigraphic architectures where data might be lacking.