Search

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 Antarcti

Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from far-field records(1-3) 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 weprovide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (similar to 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 akey step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution.

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

The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607–2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice–lithosphere interactions of the Greenland Ice Sheet.