Variations in Earth’s orbit pace global ice-volume and sea-level changes, but the variability in the response for different sectors of the Antarctic Ice Sheet to orbitally forced climate change remains unclear. Here we present geological records of iceberg-rafted debris and other proxies from locations adjacent to the West Antarctic Ice Sheet (WAIS) with comparisons to an existing East Antarctic Ice Sheet (EAIS) record over the time interval ~3.3–2.3 million years ago. Iceberg calving events from the WAIS recorded in Ross Sea sediment cores show a linear response to orbital forcing at timescales corresponding to obliquity (~40,000 years) and precession (~23,000–19,000 years) modulated by eccentricity (~100,000 years). This contrasts with an existing record adjacent to the EAIS, which does not contain obliquity pacing. Combined with ice-sheet model sensitivity tests, the geological data show that the WAIS is highly dynamic and responsive to oceanic melt driven by changes in Southern Ocean circulation, together with atmospheric forcing through variations in local insolation. Conversely, the EAIS appears less responsive to oceanic forcing, despite being the dominant source of meltwater to the global ocean during the mid-Pliocene. Our results imply a substantial role for atmospheric warming on mid-Pliocene sea-level from both WAIS and EAIS. The West Antarctic Ice Sheet responded to different natural forcing mechanisms than the East Antarctic Ice Sheet through the mid-Pliocene due to a greater sensitivity to oceanic feedbacks, according to iceberg-rafted debris records and ice-sheet modelling experiments.

Drill cores from the Antarctic continental shelf are essential for directly constraining changes in past Antarctic Ice Sheet extent. Here, we provide a sedimentary facies analysis of drill cores from International Ocean Discovery Program (IODP) Site U1521 in the Ross Sea, which reveals a unique, detailed snapshot of Antarctic Ice Sheet evolution between ca. 18 Ma and 13 Ma. We identify distinct depositional packages, each of which contains facies successions that are reflective of past baseline shifts in the presence or absence of marine-terminating ice sheets on the outermost Ross Sea continental shelf. The oldest depositional package (>18 Ma) contains massive diamictites stacked through aggradation and deposited in a deep, actively subsiding basin that restricted marine ice sheet expansion on the outer continental shelf. A slowdown in tectonic subsidence after 17.8 Ma led to the deposition of progradational massive diamictites with thin mudstone beds/laminae, as several large marine-based ice sheet advances expanded onto the mid- to outer continental shelf between 17.8 Ma and 17.4 Ma. Between 17.2 Ma and 15.95 Ma, packages of interbedded diamictite and diatom-rich mudstone were deposited during a phase of highly variable Antarctic Ice Sheet extent and volume. This included periods of Antarctic Ice Sheet advance near the outer shelf during the early Miocene Climate Optimum (MCO)-despite this being a wellknown period of peak global warmth between ca. 17.0 Ma and 14.6 Ma. Conversely, there were periods of peak warmth within the MCO during which diatom-rich mudstones with little to no ice-rafted debris were deposited, which indicates that the Antarctic Ice Sheet was greatly reduced in extent and had retreated to a smaller terrestrial-terminating ice sheet, most notably between 16.3 Ma and 15.95 Ma. Post-14.2 Ma, diamictites and diatomites contain unambiguous evidence of subglacial shearing in the core and provide the first direct, well-dated evidence of highly erosive marine ice sheets on the outermost continental shelf during the onset of the Middle Miocene Climate Transition (MMCT; 14.2-13.6 Ma). Although global climate forcings and feedbacks influenced Antarctic Ice Sheet advances and retreats during the MCO and MMCT, we propose that this response was nonlinear and heavily influenced by regional feedbacks related to the shoaling of the continental shelf due to reduced subsidence, sediment infilling, and local sea-level changes that directly influenced oceanic influences on melting at the Antarctic Ice Sheet margin. Although intervals of diatom-rich muds and diatomite indicating open-marine interglacial conditions still occurred during (and following) the MMCT, repeated advances of marine-based ice sheets since that time have resulted in widespread erosion and overdeepening in the inner Ross Sea, which has greatly enhanced sensitivity to marine ice sheet instability since 14.2 Ma.

Recent changes in US oceanographic assets are impacting scientists' ability to access seafloor and sub‐seafloor materials and thus constraining progress on science critical for societal needs. Here we identify national infrastructure needs to address critical science questions. This commentary reports on community‐driven discussions that took place during the 3‐day FUTURE of US Seafloor Sampling Capabilities 2024 Workshop , which used an “all‐hands‐on‐deck” approach to assess seafloor and sub‐seafloor sampling requirements of a broad range of scientific objectives, focusing on capabilities that could be supported through the US Academic Research Fleet (US‐ARF) now or in the near future. Cross‐cutting issues identified included weight and size limitations in the over‐boarding capabilities of the US‐ARF, a need to access material at depths greater than ∼20 m below the seafloor, sampling capabilities at the full range of ocean depths, technologies required for precise navigation‐guided sampling and drilling, resources to capitalize on the research potential of returned materials, and workforce development.

North Atlantic Deep Water (NADW), the return flow component of the Atlantic Meridional Overturning Circulation (AMOC), is a major inter-hemispheric ocean water mass with strong climate effects but the evolution of its source components on million-year timescales is poorly known. Today, two major NADW components that flow southward over volcanic ridges to the east and west of Iceland are associated with distinct contourite drift systems that are forming off the coast of Greenland and on the eastern flank of the Reykjanes (mid-Atlantic) Ridge. Here we provide direct records of the early history of this drift sedimentation based on cores collected during International Ocean Discovery Programme (IODP) Expeditions 395C and 395. We find rapid acceleration of drift deposition linked to the eastern component of NADW, known as Iceland-Scotland Overflow Water at 3.6 million years ago (Ma). In contrast, the Denmark Strait Overflow Water feeding the western Eirik Drift has been persistent since the Late Miocene. These observations constrain the long-term evolution of the two NADW components, revealing their contrasting independent histories and allowing their links with climatic events such as Northern Hemisphere cooling at 3.6 Ma, to be assessed.

Antarctica's continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides.

Studies of plants in modern catchment systems can serve to improve the level of understanding of sedimentary plant wax hydrogen isotope (delta 2H) data by directly investigating the link between local climate conditions, plant source water, leaf water, and plant lipids for individual plant species. Here we present such an application to compare two lake catchments with different basin morphologies in Estonia. We sampled leaf and xylem water, as well as leaf waxes from the seven common plant species in each catchment, and soil water. We then measured the delta 2H values of all waters, and of n-alkanes (delta 2Hn-alk) from the plant waxes, as well as surface lake sediments. We applied a Pe ' clet modified Craig-Gordon leaf water model using local precipitation isotope and climate data to characterize the delta 2H values of the biosynthetic source water pool throughout the entire growth season. The data and model results provide a detailed view of how the input hydro-climatic signals from the precipitation delta 2H values were modified by environmental and plant physiological conditions and ultimately by the biosynthetic isotope fractionation associated with n-alkane production by each plant species. We report both average apparent (epsilon app = -92 +/- 21 %o) and biosynthetic (epsilon bio = -132 +/- 19 %o) hydrogen isotope fractionation factors of all species from the studied catchments. This information serves as a foundation for sedimentary organic geochemistry and paleoclimate studies, which allows for more direct and quantitative links to be made between sedimentary plant wax delta 2H values and the climate signal contained in plant source water.

Radiocarbon-dated peat cores collected from an ombrotrophic bog in southern Estonia record shifting environmental conditions and carbon accumulation rates in northern Europe during the late Holocene. Modern observations indicate that the water balance of the peatland is highly influenced by changes in relative humidity, followed by temperature and precipitation. The modern δ18O and δ2H values of surface water suggest that the groundwater is an integration of several months of precipitation. There also appears to be little or no direct influence of surface evaporation on the water within the bog, suggesting that water loss is preferentially through transpiration and sub-surface flow. Bulk peat δ13C values exhibit a trend of higher values through the late Holocene, suggesting a pattern of overall increased surface wetness. The δ15N values were low from ~4130 to 3645 cal yr BP, suggesting drier conditions, followed by intermediate values until ~2995 cal yr BP. The δ15N values decrease again from ~2995 to 2470 cal yr BP, suggesting a return to drier conditions, followed by intermediate values until ~955 cal yr BP. The δ15N values were high, suggesting wetter conditions from ~955 to 250 cal yr BP, followed by intermediate values through the modern. Carbon accumulation rates were low to intermediate from ~4200 to 2470 cal yr BP, followed by intermediate-to-high values until ~1645 cal yr BP. Carbon accumulation rates were then low until ~585 cal yr BP, followed by intermediate values through the modern. The geochemical data, combined with observed changes in peat composition and regional proxies of temperature and water table fluctuations through the late Holocene, suggest that carbon accumulation rates were relatively low under dry and warm conditions, whereas accumulation was generally higher (up to ~80 g C m−2 yr−1) when the climate was wetter and/or colder. These findings further suggest that future environmental changes affecting the regional water balance and temperature will impact the potential for northern peatlands to capture and store carbon.

This study combines field structural analysis with thin‐section petrography, U‐Pb dating, and strontium, carbon and oxygen isotopic analysis of calcite fracture fills to constrain the evolution of the 2‐5 km scale paleofluid system around the faulted, plunging fold nose comprising the southern termination of the Gypsum Valley salt wall in the Paradox Basin, U.S.A. Brittle deformation in this region began with the formation of a down‐to‐the‐northeast, counter‐regional fault and then progressed into jointing and faulting in a radial pattern, followed by jointing in a concentric pattern. Coupled with increases in fracture abundance toward the faults, multiple stages of mineralization suggest that the faults served as efficient and long‐lived conduits for vertical fluid migration. Although fracture cement textures and calcite colour are variable throughout the area, the distribution of these characteristics does not correlate with fracture orientation, relative age, stratigraphic or structural position. Irrespective of the type of calcite comprising the fracture cements, δ 13 C values average near −7‰ (VPDB), whereas δ 18 O values cluster into groups whose averages are roughly 6‰ apart, with the more negative grouping stratigraphically restricted to fracture cements in Jurassic rocks. The stratigraphic segregation of δ 18 O values suggests the paleofluid system contained two distinct paleofluids, a more recent one comprised of meteoric waters and an older one comprising brine that originated in Pennsylvanian strata. 87 Sr/ 86 Sr ratios in fracture‐filling calcite cements indicate that the older fluid underwent fluid‐rock interaction with Permian strata and that this evolved fluid migrated upwards along the faults until the Triassic or Jurassic. Thereafter, fluid migrating along the faults was more meteoric and appears to have migrated downward along the faults, where it interacted with Permian strata. Consistent U‐Pb dates from carbonates precipitated from the older fluid suggest this stage of the paleofluid system was active around 240 Ma. Local burial history models and published temperatures for fracture cements elsewhere in the basin suggest the younger stage of the paleofluid system occurred during the Latest Cretaceous to Oligocene. This study highlights the spatial and temporal complexity of fluid systems in the vicinity of salt structures and emphasises the need to interpret them through careful integration of high resolution stratigraphic and structural data in the context of evolving salt tectonics.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

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 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.

Abstract We present the first zircon‐based U‐Pb geochronology, trace element concentrations, and O and Hf isotope compositions for Snæfell, an off‐rift volcano in eastern Iceland. These data provide constraints on the longevity and petrogenetic conditions of the Snæfell magmatic system. U‐Pb zircon ages range from 545 ± 59 to 266 ± 16 ka (2SE), but differences between grain core and mantle ages within each sample reveal zircon residence times of 100–200 kyr—far longer than observed at other Neovolcanic systems in Iceland. Zircon δ18O is restricted to ∼3.5–4‰, and zircon εHf ranges ∼+13 to ∼+17, which is substantially more radiogenic than Snæfell basalts. This combined O and Hf isotopic perspective suggests rhyolite petrogenesis at Snæfell can be attributed to fractional crystallization of mantle‐derived basaltic magmas with limited influence of pre‐existing crustal material. Trace element evidence further characterizes the magmatic source material: Sc/Yb <∼0.01 suggests an amphibole‐free petrogenetic environment, and Ti concentrations in zircon <5 ppm suggest a cool, near‐solidus, crystallization environment for the majority of the zircon's pre‐eruptive history, with elevated Ti in zircon surfaces suggesting a late thermal perturbation, perhaps a mafic input that remobilized (to the point of eruption triggering) near‐solidus magmas. These zircon‐based conclusions are broadly consistent with previous interpretations of rhyolite petrogenesis conditions at Snæfell but provide a multi‐faceted perspective with more detailed resolution of source materials, magma generating processes, system longevity, and pre‐eruptive conditions.

Additional information regarding methods (Reflection seismic processing, Drill-site measurements, Core-log-seismic correlations, Spatial Velocity calculations, and Reflection Tomography model) and regional stratigraphy descriptions, as well as detailed considerations regarding the opal distribution and depth.

Holocene environmental change in the northern and central Nile Valley was controlled primarily by shifts in the Intertropical Convergence Zone over time, leading to changes in aridity and water availability for early occupants of the region. Although local environmental changes may help to motivate societal changes such as those in settlement patterns or technological productions, evidence from pedogenic carbonates at Sai Island, in northern Sudan, indicate that the most significant environmental changes predated a key shift in local food production from foraging to pastoralism. Changes in local environmental conditions from a wetter and more diverse vegetative context to a more arid and C 4 ‐dominant landscape occurred during the occupation of Khartoum Variant foragers, whereas later Abkan pastoralists arrived without any notable differences in the region compared to the environments inhabited by the most recent foragers. The lack of an external environmental driver for food production changes at Sai suggests that other, potentially cultural factors were more important in these economic decisions in the mid‐Holocene.

R.M. McKay, L. De Santis, D.K. Kulhanek, J.L. Ash, F. Beny, I.M. Browne, G. Cortese, I.M. Cordeiro de Sousa, J.P. Dodd, O.M. Esper, J.A. Gales, D.M. Harwood, S. Ishino, B.A. Keisling, S. Kim, S. Kim, J.S. Laberg, R.M. Leckie, J. Müller, M.O. Patterson, B.W. Romans, O.E. Romero, F. Sangiorgi, O. Seki, A.E. Shevenell, S.M. Singh, S.T. Sugisaki, T. van de Flierdt, T.E. van Peer, W. Xiao, and Z. Xiong2

P-wave velocity data were measured on undisturbed section halves using pairs of piezoelectric transducers mounted in bayonets that are inserted into soft sediment along the JRSO-defined y-axis and/or z-axis. Report includes P-wave velocity in y and/or z direction, bayonet separation, traveltime between transducers, and first arrival picks.

Magnetic susceptibility was measured on whole-round sections (and rarely section halves) on the Whole-Round Multisensor Logger (WRMSL) and/or Special Task Multisensor Logger (STMSL) using a Bartington MS2 meter and a 90 mm or 80 mm MS2C loop. As volume of the sample is not controlled for this experiment, susceptibility units are recorded in instrument units and are not volume-corrected.

The marine-based West Antarctic Ice Sheet (WAIS) is currently locally retreating because of shifting wind-driven oceanic currents that transport warm waters toward the ice margin, resulting in ice shelf thinning and accelerated mass loss. Previous results from geologic drilling on Antarctica’s continental margins show significant variability in ice sheet extent during the late Neogene and Quaternary. Climate and ice sheet models indicate a fundamental role for oceanic heat in controlling ice sheet variability over at least the past 20 My. Although evidence for past ice sheet variability is available from ice-proximal marine settings, sedimentary sequences from the continental shelf and rise are required to evaluate the extent of past ice sheet variability and the associated forcings and feedbacks. International Ocean Discovery Program Expedition 374 drilled a latitudinal and depth transect of five sites from the outer continental shelf to rise in the central Ross Sea to resolve Neogene and Quaternary relationships between climatic and oceanic change and WAIS evolution. The Ross Sea was targeted because numerical ice sheet models indicate that this sector of Antarctica responds sensitively to changes in ocean heat flux. Expedition 374 was designed for optimal data-model integration to enable an improved understanding of Antarctic Ice Sheet (AIS) mass balance during warmer-than-present climates (e.g., the Pleistocene “super interglacials,” the mid-Pliocene, and the Miocene Climatic Optimum). The principal goals of Expedition 374 were to • Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates; • Reconstruct ice-proximal oceanic and atmospheric temperatures to quantify past polar amplification; • Assess the role of oceanic forcing (e.g., temperature and sea level) on AIS variability; • Identify the sensitivity of the AIS to Earth’s orbital configuration under a variety of climate boundary conditions; and • Reconstruct Ross Sea paleobathymetry to examine relationships between seafloor geometry, ice sheet variability, and global climate. To achieve these objectives, postcruise studies will • Use data and models to reconcile intervals of maximum Neogene and Quaternary ice advance and retreat with far-field records of eustatic sea level; • Reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach; • Reconstruct Neogene and Quaternary sea ice margin fluctuations and correlate these records to existing inner continental shelf records; • Examine relationships among WAIS variability, Earth’s orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and • Constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics. Expedition 374 departed from Lyttelton, New Zealand, in January 2018 and returned in March 2018. We recovered 1292.70 m of R.M. McKay et al. Expedition 374 summary IODP Proceedings 2 Volume 374 high-quality core from five sites spanning the early Miocene to late Quaternary. Three sites were cored on the continental shelf (Sites U1521, U1522, and U1523). At Site U1521, we cored a 650 m thick sequence of interbedded diamictite and diatom-rich mudstone penetrating seismic Ross Sea Unconformity 4 (RSU4). The depositional reconstructions of past glacial and open-marine conditions at this site will provide unprecedented insight into environmental change on the Antarctic continental shelf during the late early and middle Miocene. At Site U1522, we cored a discontinuous late Miocene to Pleistocene sequence of glacial and glaciomarine strata from the outer shelf with the primary objective of penetrating and dating RSU3, which is interpreted to reflect the first continental shelf– wide expansion of East and West Antarctic ice streams. Site U1523, located on the outer continental shelf, targeted a sediment drift beneath the westward-flowing Antarctic Slope Current (ASC) to test the hypothesis that changes in ASC vigor regulate ocean heat flux onto the continental shelf and thus ice sheet mass balance. We also cored two sites on the continental rise and slope. At Site U1524, we recovered a Plio–Pleistocene sedimentary sequence from the levee of the Hillary Canyon, one of the largest conduits of Antarctic Bottom Water from the continental shelf to the abyssal ocean. Site U1524 was designed to penetrate into middle Miocene and older strata, but coring was initially interrupted by drifting sea ice that forced us to abandon coring in Hole U1524A at 399.5 m drilling depth below seafloor (DSF). We moved to a nearby alternate site on the continental slope (Site U1525) to core a single hole designed to complement the record at Site U1524. We returned to Site U1524 after the sea ice cleared and cored Hole U1524C with the rotary core barrel system with the intention of reaching the target depth of 1000 m DSF. However, we were forced to terminate Hole U1524C at 441.9 m DSF because of a mechanical failure with the vessel that resulted in termination of all drilling operations and forced us to return to Lyttelton 16 days earlier than scheduled. The loss of 39% of our operational days significantly impacted our ability to achieve all Expedition 374 objectives. In particular, we were not able to recover continuous middle Miocene sequences from the continental rise designed to complement the discontinuous record from continental shelf Site U1521. The mechanical failure also meant we could not recover cores from proposed Site RSCR-19A, which was targeted to obtain a high-fidelity, continuous record of upper Neogene and Quaternary pelagic/hemipelagic sedimentation. Despite our failure to recover a continental shelf-to-rise Miocene transect, records from Sites U1522, U1524, and U1525 and legacy cores from the Antarctic Geological Drilling Project (ANDRILL) can be integrated to develop a shelf-to-rise Plio–Pleistocene transect.