West Antarctica’s transition to its first extensive glaciation likely post-dated the establishment of the East Antarctic Ice Sheet (EAIS) by more than 10 million years, yet the timing and nature of West Antarctic Ice Sheet (WAIS) development have remained poorly constrained due to the absence of reliable sediment records. Newly recovered sediment sequences drilled with the seafloor drill rig MARUM-MeBo70 during RV Polarstern Expedition PS104 from the eastern Amundsen Sea Embayment were explored using multi-proxy sediment analyses alongside biostratigraphic and isotopic dating methods. These revealed ice-proximal terrigenous and diatomaceous diamictites as well as diatomaceous mudstones indicating the advance of a substantial WAIS to these drill sites already prior to the Oligocene–Miocene transition (~23 million years ago). Coupled climate-ice sheet modelling simulates the growth of a distinct WAIS separated from the EAIS, which expanded far into basins below sea level. Therefore, our new sedimentary data validate these model results and demonstrate that extensive WAIS expansion to the coast occurred several million years earlier than previously thought.

Mass loss from polar ice sheets is poorly constrained in estimates of future global sea-level rise. Today, the marine-based West Antarctic Ice Sheet is losing mass at an accelerating rate, most notably in the Thwaites and Pine Island glacier drainage basins. Early Pliocene surface temperatures were about 4 °C warmer than preindustrial and maximum sea level stood ~20 m above present. Using data from a sediment archive on the Amundsen Sea continental rise, we investigate the impact of prolonged Pliocene ocean warmth on the ice-sheet-ocean system. We show that, in contrast to today, during peak ocean warming ~4.6 - 4.5 Ma, terrigenous muds accumulated rapidly under a weak bottom current regime after spill-over of dense shelf water with high suspended load down to the rise. From sediment provenance data we infer major retreat of the Thwaites Glacier system at ~4.4 Ma several hundreds of km inland from its present grounding line position, highlighting the potential for major Earth System changes under prolonged future warming.

Present-day sediment influx to the northern Red Sea is dominated by aeolian dust because of its position between the large deserts of northern Africa, the Arabian Peninsula, and the Levant, as well as the absence of discharge from perennial rivers. However, sediment cores retrieved from the northern Red Sea reveal strong temporal variability in dust influx to the basin on glacial–interglacial timescales and several shorter-term strong episodes of fluvial input. We report new palaeoclimate and sediment provenance records for the last ca. 220 kyr from marine sediment core KL23, retrieved from the northern part of this basin. Our data suggest that the Nile delta became a major dust source during glacial conditions, in response to the glacioeustatic sea-level fall and associated subaerial exposure of volcanic-rich debris originally transported down the River Nile from the Ethiopian Highlands. Windblown dust from this delta source is characterized by high smectite concentrations and Ti contents. It is transported to the northern Red Sea on prevailing NNW winds. Our data also suggest a contribution of kaolinite-rich windblown dust from Egypt, Sinai, and the Levant to KL23 on the same winds. The activity of this source is hydrologically controlled, with minima in kaolinite concentrations documenting phases of increased humidity, probably due to enhanced Mediterranean cyclogenesis and a southward expansion of the Mediterranean winter rains. Short-term reactivations of wadi systems during fluvial episodes are identified by maxima in the abundance of clay-sized terrigenous sediment components, high chlorite concentrations, and high εNd. These episodes correlate with phases of reduced aeolian influx to the northern Red Sea and coincide with African humid periods, both in timing and relative intensity. This result implies that the Mediterranean climate system and the African monsoon are closely coupled.

One of Earth’s most fundamental climate shifts, the greenhouse-icehouse transition 34 million years ago, initiated Antarctic ice sheet buildup, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7 to 33.2 million years ago) that immediately followed this transition—a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization—is uncertain. In this work, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin—a key region for understanding Antarctic ice sheet evolution. These data indicate a cool-temperate environment with mild ocean and air temperatures that prevented West Antarctic Ice Sheet formation. Climate–ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.

Provenance records from sediments deposited offshore of the West Antarctic Ice Sheet (WAIS) can help identify past major ice retreat, thus constraining ice-sheet models projecting future sea-level rise. Interpretations from such records are, however, hampered by the ice obscuring Antarctica's geology. Here, we explore central West Antarctica's subglacial geology using basal debris from within the Byrd ice core, drilled to the bed in 1968. Sand grain microtextures and a high kaolinite content (similar to 38-42%) reveal the debris consists predominantly of eroded sedimentary detritus, likely deposited initially in a warm, pre-Oligocene, subaerial environment. Detrital hornblende 40Ar/39Ar ages suggest proximal late Cenozoic subglacial volcanism. The debris has a distinct provenance signature, with: common Permian-Early Jurassic mineral grains; absent early Ross Orogeny grains; a high kaolinite content; and high 143Nd/144Nd and low 87Sr/86Sr ratios. Detecting this "fingerprint" in Antarctic sedimentary records could imply major WAIS retreat, revealing the WAIS's sensitivity to future warming. Ice loss from the West Antarctic Ice Sheet (WAIS) could potentially raise global sea level by up to 4 m over the coming decades to centuries. However, projections of sea-level contributions from the WAIS are highly uncertain. Understanding when the WAIS was smaller in warm times in the Earth's more recent history would reduce these uncertainties, but direct evidence for the most recent large-scale WAIS retreat is lacking. Tracing the source of sediments deposited offshore will help detect WAIS retreat because, under a smaller WAIS, there would be more erosion of presently ice-covered areas in central West Antarctica. However, the subglacial geology of central West Antarctica is poorly known, making it difficult to identify a WAIS retreat signal in sedimentary records. Here, we present new results from debris in the Byrd ice core, drilled in the center of the WAIS to its base in 1968. The mineralogical, geochemical and age compositions of the debris provide a distinct geological "fingerprint" that should be identifiable in sedimentary records. This fingerprint can be searched for in existing and upcoming Antarctic drill core records, which will ultimately help constrain the environmental conditions that would lead to future WAIS retreat and the resulting sea-level rise. Debris from the base of the Byrd ice core comprises predominantly of sedimentary strata weathered before the onset of Antarctic glaciation 40Ar/39Ar dated hornblende grains support evidence for recent subglacial volcanism Byrd geochemical data reveal the provenance signature expected in marine sediments following major West Antarctic Ice Sheet retreat

The oceanography of the Red Sea is controlled by the restricted exchange of water masses with the Indian Ocean and by high evaporation rates due to the arid climate of the surrounding land areas. In the northern Red Sea, the formation of oxygen-rich subsurface water ventilates the deeper parts of the basin, but little is known about the variability in this process in the past. The stable oxygen and carbon isotope records of epibenthic foraminifera from a sediment core of the central Red Sea and comparison with existing isotope records allow for the reconstruction of changes in the Red Sea overturning circulation (ROC) during Marine Isotope Stage 3. The isotope records imply millennial-scale variations in the ROC, in phase with the climate variability in the high northern latitudes. This suggests an immediate response of dense-water formation to the regional climate and hydrology of the northern Red Sea. Deep-water formation was intensified under the influence of cold and hyper-arid conditions during Heinrich stadials and was diminished during Dansgaard–Oeschger interstadials. While these changes are reflected in both stable oxygen and carbon isotope records, the latter data also exhibit changes in phase with the African–Indian monsoon system. The decoupling of the stable carbon and oxygen isotope records at the summer monsoon maximum centered around 55–60 ka may be associated with an increased inflow of nutrient-rich intermediate waters from the Arabian Sea to the central Red Sea. This process fueled local surface water productivity, resulting in enhanced remineralization of sinking organic matter and release of 12C at intermediate water depths.

Today, relatively warm Circumpolar Deep Water is melting Thwaites Glacier at the base of its ice shelf and at the grounding zone, contributing to significant ice retreat. Accelerating ice loss has been observed since the 1970s; however, it is unclear when this phase of significant melting initiated. We analyzed the marine sedimentary record to reconstruct Thwaites Glacier's history from the early Holocene to present. Marine geophysical surveys were carried out along the floating ice-shelf margin to identify core locations from various geomorphic settings. We use sedimentological data and physical properties to define sedimentary facies at seven core sites. Glaciomarine sediment deposits reveal that the grounded ice in the Amundsen Sea Embayment had already retreated to within ~45 km of the modern grounding zone prior to ca. 9,400 y ago. Sediments deposited within the past 100+ y record abrupt changes in environmental conditions. On seafloor highs, these shifts document ice-shelf thinning initiating at least as early as the 1940s. Sediments recovered from deep basins reflect a transition from ice proximal to slightly more distal conditions, suggesting ongoing grounding-zone retreat since the 1950s. The timing of ice-shelf unpinning from the seafloor for Thwaites Glacier coincides with similar records from neighboring Pine Island Glacier. Our work provides robust new evidence that glacier retreat in the Amundsen Sea was initiated in the mid-twentieth century, likely associated with climate variability.

Extensive ice coverage largely prevents investigations of Antarctica’s unglaciated past. Knowledge about environmental and tectonic development before large-scale glaciation, however, is important for understanding the transition into the modern icehouse world. We report geochronological and sedimentological data from a drill core from the Amundsen Sea shelf, providing insights into tectonic and topographic conditions during the Eocene (~44 to 34 million years ago), shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from >40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a >1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.

Detrital smectite is a ubiquitous clay mineral in marine sediments and has a variable total Fe, Al, and Mg composition depending on the source, i.e., bedrock or unconsolidated sedimentary strata, the smectite is derived from. Analyses of elemental composition of smectite minerals in marine sediments can help to differentiate the smectite sources and, thus, sediment provenance, with potentially far-reaching paleo-environmental implications. In this study, we investigated the smectite compositions of modern-latest Holocene seafloor surface sediments deposited offshore from the Amundsen Sea drainage sector, where the West Antarctic Ice Sheet is currently unstable and losing mass due to ocean-forced melting, to detect and understand the variabilities of their elemental composition and geographical distribution. The smectite composition in continental rise sediments was compared to that of potential source areas on the Amundsen Sea continental shelf and in the sub-Antarctic South Pacific basin. Furthermore, we analyzed the smectite composition of sediments in continental rise cores deposited during the last glacial and last interglacial periods to reconstruct source variations over glacial-interglacial cycles. In particular, high contents of Al–Fe-rich smectite indicate that the glacial sediments had been supplied from the coastal region around Pine Island Bay by the cross-shelf advance of the West Antarctic Ice Sheet during the last glacial period. This clearly contrasts with the smectite minerals in rise sediments deposited during the present and the last interglacial periods that are composed of two distinct smectite types (Mg-rich and Al-rich, respectively), indicating their supply from multiple sources. During interglacials, Mg-rich smectite is probably transported by Circumpolar Deep Water from the sub-Antarctic South Pacific basin to the continental rise, while Al-rich smectite is supplied as part of ice rafted debris and by marine currents from the coasts around the Amundsen Sea embayment. Our research demonstrates that analysis of the elemental composition of smectite minerals on the Amundsen Sea continental margin provides a valuable tool to trace variations in sources for detrital sediment components and their pathways throughout glacial-interglacial cycles.

Climatic and associated hydrological changes controlled the transport processes and composition of the sediments in the central Red Sea during the last ca. 200 kyr. Three different source areas for mineral dust are identified. The dominant source is located in the eastern Sahara (Sudan and southernmost Egypt). We identify its imprint on Red Sea sediments by high smectite and Ti contents, low 87Sr / 86Sr, and high εNd. The availability of deflatable sediments was controlled by the intensity of tropical rainfall and vegetation cover over North Africa linked to the African monsoon. Intense dust input to the Red Sea occurred during arid phases, and low input occurred during humid phases. A second, less significant source indicated by palygorskite input is probably located on the eastern Arabian Peninsula and/or Mesopotamia, while the presence of kaolinite suggests an additional minor dust source in northern Egypt. Our grain size data reflect episodes of fluvial sediment discharge to the central Red Sea and document the variable strength in response to all of the precession-paced insolation maxima during our study interval including both those that were strong enough to trigger sapropel formation in the eastern Mediterranean Sea and those that were not. The African humid period most strongly expressed in our Red Sea record was the one during the Eemian last interglacial at ca. 125 ka (when the Baraka River was far more active than today), followed by those at 198, 108, 84, and 6 ka.

. Nioghalvfjerdsbrae, or 79 ◦ N Glacier, is the largest marine-terminating glacier draining the Northeast Greenland Ice Stream (NEGIS). In recent years, its ∼ 70 km long fringing

Neodymium (Nd) isotopes have been utilized as a tracer of water mass source in the modern ocean and in palaeoceanographic studies, though the oceanic cycling of Nd is not yet fully constrained. Recent studies have highlighted the importance of processes that occur near the seawater – sediment interface in altering the Nd isotopic composition of bottom waters. The two major observed processes “boundary exchange” and “benthic flux” have been suggested as playing an important role in setting water mass compositions, however, more studies are needed to constrain their chemical mechanism and the extent to which these processes set the composition of deep waters. The Antarctic continental margin is an important place to study these processes because Antarctic-sourced waters dominate the Southern Ocean and ventilate the global deep ocean. This study is the first to measure and compare seawater, porewater and sediment data from along the margin of Antarctica to examine the nature of potential boundary processes. We show that a process similar to boundary exchange seems to be occurring within porewaters, modifying porewater chemistry by shifting its Nd isotopic ratios to more radiogenic values without significantly increasing the concentration of dissolved Nd. We hypothesize that this shift results from partial dissolution of radiogenic detrital particles, such as smectite, amphibole and/or volcanic glass, while re-scavenging maintains low Nd concentrations. We infer the existence of benthic flux of porewaters to deep waters by examining chemical gradients in porewaters and show that it is much lower on the Antarctic margin compared to other studies. Benthic flux appears to be slightly higher along the Antarctic Peninsula than in the Bellingshausen Sea due to partial degradation of organic matter and associated dissolution of Fe-Mn oxyhydroxides. Taken together, boundary processes do not significantly change the Nd isotopic composition of Antarctic margin seawater because while the porewaters have an altered Nd isotopic composition the Nd concentration of these porewaters is low compared to other settings.

Reconstructing the advance and retreat of past ice sheets provides important long-term context for recent change(s) and enables us to better understand ice sheet responses to forcing mechanisms and external boundary conditions that regulate grounding line retreat. This study applies various radiocarbon dating techniques, guided by a detailed sedimentological analyses, to reconstruct the glacial history of Anvers-Hugo Trough (AHT), one of the largest bathymetric troughs on the western Antarctic Peninsula (WAP) shelf. Existing records from AHT indicate that the expanded Antarctic Peninsula Ice Sheet (APIS) advanced to, or close to, the continental shelf edge during the Last Glacial Maximum (LGM; 23-19 cal kyr BP [ 1/4 calibrated kiloyears before present]), with deglaciation of the outer shelf after-16.3 cal kyr BP. Our new chronological data show that the APIS had retreated to the middle shelf by-15.7 cal kyr BP. Over this 600-year interval, two large grounding-zone wedges (GZW) were deposited across the middle (GZW2) and inner shelf (GZW3), suggesting that their formation occurred on centennial rather than millennial timescales. Expanded sequences of sub-ice shelf sediments occur seaward of the inner GZW3, which suggests that the grounding line remained stationary for a prolonged period over the middle shelf. Grounding-line retreat rates indicate faster retreat across the outer to middle shelf compared to retreat across the middle to inner shelf. We suggest that variable retreat rates relate to the broad-scale morphology of the trough, which is characterised by a relatively smooth, retrograde seabed on the outer to middle shelf and rugged morphology with a locally landward shallowing bed and deep basin on the inner shelf. A slowdown in retreat rate could also have been promoted by convergent ice flow over the inner shelf and the availability of pinning points associated with bathymetric highs around Anvers Island and Hugo Island.(C) 2022 The Authors. Published by Elsevier Ltd.

Because ice shelves respond to climatic forcing over a range of time scales, from years to millennia, an understanding of their long-term history is critically needed for predicting their future evolution. We present the first detailed reconstruction of the Larsen C Ice Shelf (LCIS), eastern Antarctic Peninsula (AP), based on data from sediment cores recovered from below and in front of the ice shelf. Sedimentologic and chronologic information reveals that the grounding line (GL) of an expanded AP ice sheet had started its retreat from the midshelf prior to 17.7 +/- 0.53 calibrated (cal.) kyr B.P., with the calving line following similar to 6 k.y. later. The GL had reached the inner shelf as early as 9.83 +/- 0.85 cal. kyr B.P. Since ca. 7.3 ka, the ice shelf has undergone two phases of retreat but without collapse, indicating that the climatic limit of LCIS stability was not breached during the Holocene. Future collapse of the LCIS would therefore confirm that the magnitudes of both ice loss along the eastern AP and underlying climatic forcing are unprecedented during the past 11.5 k.y.

North African greening phases, during which large rivers ran through the Sahara Desert, occurred repeatedly during the Quaternary and are regarded as key periods for the development of past human populations. However, the timing and mechanisms responsible for the reactivation of the presently dormant fluvial systems remain highly uncertain. Here we present hydroclimate changes over the past 160,000 years, reconstructed from analyses of the provenance of terrestrial sediments in a marine sediment record from the Gulf of Sirte (offshore Libya). By combining high-resolution proxy data with transient Earth system model simulations, we are able to identify the various drivers that led to the observed shifts in hydroclimate and landscapes. We show that river runoff occurred during warm interglacial phases of Marine Isotope Stages 1 and 5 due to precession-forced enhancements in the summer and autumn rainfall over the entire watershed, which fed presently dry river systems and intermittent coastal streams. In contrast, shorter-lasting and less-intense humid events during glacial Marine Isotope Stages 3 and 4 were related to autumn and winter precipitation over the Libyan coastal regions driven by Mediterranean storms. Our results reveal large shifts in hydroclimate environments during the last glacial cycle, which probably exerted a strong evolutionary and structural control on past human populations, potentially pacing their dispersal across northern Africa. The presence of large rivers in North Africa critical for Quaternary human migrations were controlled by a combination of orbital forcing and Mediterranean storminess, according to terrestrial proxy records from a marine core off Libya integrated with paleoclimate modelling.

The Eocene-Oligocene Transition (~34.4–33.7 Ma) marks a major step in the long-term evolution from the greenhouse climate of the Early Palaeogene to the icehouse regime of the Late Neogene and Quaternary. However, it remains uncertain which landmasses were covered by ice sheets during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma), an interval of peak glaciation inferred from deep-sea benthic foraminifera oxygen isotope records that immediately follows the Eocene-Oligocene Transition. The scarcity of Late Eocene and Early Oligocene continental and shallow-marine records in both Arctic and Antarctic regions has prevented the reconstruction of environmental conditions and ice-sheet extent during the Early Oligocene, which is critical for assessing ice–ocean–atmosphere interactions during early stages of the Cenozoic icehouse. Here, we present the first Early Oligocene shallow-marine record from the Pacific margin of West Antarctica, recovered from the central Amundsen Sea Embayment shelf on RV Polarstern expedition PS104 at Site 21. Marine mudstones recovered at this site document the presence of a vegetated archipelago at a palaeo-latitude of 73.5°S. Pollen assemblages and organic biomarker proxies indicate a cool-temperate Nothofagus-dominated forest situated within a productive marine archipelago. No evidence for marine terminating ice was detected in the cores from Site 21, thus indicating that the West Antarctic Ice Sheet was small or entirely absent during the Early Oligocene.

The African monsoon system controlled the mobilisation and delivery of clay-sized sediment particles to the Eastern Mediterranean Sea in the late Quaternary. During African Humid Periods of the last 200 kyr, smectite-rich suspension load was provided by the Nile river and by palaeo-rivers discharging into the Gulf of Sirte. After the termination of the African Humid Periods, kaolinite- and palygorskite-rich clay was mobilised from desiccated soils, lake and river beds, and delivered in form of dust pulses to the Eastern Mediterranean Sea. Magnitude and abruptness of the dust pulses depend on the distance of the accumulation sites from the dust sources. Proximal sites experienced large amounts of dust from local sources, while more distal sites received dust from the wider Saharan region, documenting the time-transgressive termination of the humid periods. The strengths of individual dust pulses reflect the intensity of the preceding humid periods. Distinct droughts during the last glacial period can be associated with Heinrich events and are best documented at a semi-distal site, illustrating links between the African monsoon and the climate of the high-latitudes.