The sediments of "Iceberg Alley," north of the Weddell Sea Embayment of Antarctica, are a key archive of Antarctic Ice Sheet and Southern Ocean history but are challenging to date at orbital timescales due to lack of foraminifera. We present a relative paleomagnetic intensity (RPI) chronology for sediments deposited across the Pliocene-Pleistocene Transition (3.14-1.75 Ma) at Dove Basin, International Ocean Discovery Program (IODP) Sites U1536 and U1537. Leveraging the well-defined magnetizations of these deep-sea contourite deposits, for the first time we correlate a Dove Basin RPI proxy to a North Atlantic RPI template that is intercalibrated with benthic delta 18O and lithologic signals that record the history of Northern Hemisphere glaciation intensification (iNHG) from similar to 2.7 Ma. Our new RPI chronology demonstrates a close relationship between sedimentation rates and physical lithology, with high accumulation occurring at times of high biogenic silica concentrations. This relationship is found at both long periods that reflect the amplitude modulation of orbital forcing and at glacial-interglacial timescales. Moreover, the chronology indicates a transition in the pacing of lithologic variability during iNHG from having greater precession-paced variations than benthic delta 18O prior to 2.8 Ma and obliquity-paced variations after 2.6 Ma that are nearly identical to benthic delta 18O. A clear and persistent influence of precession, especially during extreme early Pleistocene interglacial intervals (high biogenic silica and high accumulation rates) nevertheless persisted during times of high variance in both precession and obliquity forcing-most notable during Marine Isotope Stages 87, 89, and 91.

How fast future sea level rises will depend on the Antarctic Ice Sheet (AIS) response to warming. AIS projections are shaped by the assumption that sea-level peaks during past interglacials occurred after the North American ice sheet complex (NAIS) disappeared. We synthesize evidence from paleoceanography and allied disciplines to argue that NAIS persisted into some of the warmest interglacials of the last million years. We show that overlooking NAIS persistence may lead to underestimation of AIS sensitivity to warming, and propose that this paradigm shift opens research avenues that can increase confidence in the accuracy of climate and sea-level projections.

The timing, magnitude, and evolution of sea-level change during the Last Interglacial period (Marine Isotope Stage (MIS) 5e) are subjects of ongoing debate. Previous estimates of global mean sea level (GMSL) generally converged on values of 5 to 10 meters above present levels, with one or more oscillations of up to several meters. However, more recent studies suggest considerably lower GMSL that peaked below 5 meters. Ancient coral reefs play a pivotal role in providing reliable constraints on MIS 5e sea level because they are often well preserved in the fossil record and can yield precise ages through U-series dating. Here we present a new series of high-precision U-series ages combined with detailed stratigraphic analysis and accurateelevation measurements of emergent in-situ fossil corals from Turks and Caicos Islands. We sampled well-preserved MIS 5e corals outcropping along the coastlines of North Caicos, Middle Caicos, West Caicos, and Providenciales islands. We identified corals from several paleo-habitats, including platform edge reefs and both isolated corals and patch reefs from the paleo-lagoon. The dominant coral species include Orbicella annularis, Pseudodiploria, Acropora palmata, Acropora cervicornis, and Porites porites. Many fossil corals show evidence of post-depositional alteration of their primary geochemistry. Their utility is therefore limited by their preservation. To identify unaltered corals and maximize the likelihood of closed to near-closed system behavior of our samples, we apply rigorous threshold criteria that screen samples by their mineralogy, U concentration, δ234Uinitial, and amount of detrital component. We further correct the ages for diagenetic disturbance of the U-Th isotope ratios. These results allow us to provide new sea-level constraints during MIS-5e and to assess the amount of ice melt during this period of pronounced warming.

Abstract We document an apparent downward displacement of the Matuyama‐Brunhes magnetic reversal by ∼20 m at Scotia Sea International Ocean Discovery Program Site U1538 (Pirie Basin) by comparison with the well‐defined paleomagnetic record at nearby Site U1537 (Dove Basin). Detailed stratigraphic correlation between the two sites is possible due to similar lithologic variations. However, the two sites have distinctly different porewater geochemistry. Notably, Site U1538 indicates a greater demand for electron acceptors to oxidize organic carbon and Fe2+ enrichment below the depth of SO42− depletion. Magnetic parameters indicate enrichment of an authigenic magnetic mineral with strong remanence properties around the depth of SO42− depletion (∼46 m at Site U1538) relative to magnetic parameters at correlative depths at Site U1537. Fe2+ enrichment below the depth of SO42− depletion is not predicted based on the energetically favorable order of electron acceptors for microbial respiration but is documented here and in other depositional settings. This indicates Fe2+ production exceeds the production of H2S by SO42− reduction, providing a geochemical environment that favors the production and preservation of ferrimagnetic remanence‐bearing iron sulfides over paramagnetic pyrite and, thus, a mechanism for deep chemical remanent magnetization acquisition at depths of tens of meters. The influence of authigenic ferrimagnetic iron sulfides on paleomagnetic signals can be difficult to demonstrate with magnetic properties alone; therefore, this finding has implications for evaluating the fidelity of magnetostratigraphic records with complementary geochemical data. Such situations should be considered in other depositional environments with similar porewater Fe2+ accumulation below the SO42− reduction depth.

AbstractMarine fallout ash beds can provide continuous, time‐precise records of highly explosive arc volcanism that can be linked with the climate record. An evaluation of revised Plio‐Pleistocene (0–4 Myr) tephrostratigraphies from Ocean Drilling Program Sites 881, 882, and 884 confirms cyclicity of the Kamchatka‐Kurile arc volcanism and a marked increase just after the intensification of the Northern Hemisphere glaciation at 2.73 Ma. The compositional constancy of the Kamchatka‐Kurile volcano‐magma systems through time points to external modulation of volcanic cyclicity and frequency. The stacked tephra record reveals periodic peaks in arc volcanicity at ∼0.3, ∼1.0, ∼1.6, ∼2.5, and ∼3.8 Myr that coincide with maxima of the global ice volume variability that have been linked with the amplitude modulation of the precession (0.3, 1.0 Myr) and obliquity (1.6, 2.5 and 3.8 Myr) bands. A simple model of a decreasing obliquity variance across the mid‐Pleistocene Transition at constant precession variance produces an excellent correlation of ash bed cycles with the variability of global benthic δ18O (r2 = 0.75), which implies that climate, and not direct orbital forcing, modulates Kamchatka‐Kurile arc volcanism. The rising influence of precession variance in the Kamchatka‐Kurile ash bed record after the mid‐Pleistocene Transition contrasts with the dominant 100 kyr signal in the benthic δ18O global ice volume variability, which may either reflect limitations of the ash bed record or an regional rather than global influence of ice volume variability. Our results indicate that climate influences the Kamchatka‐Kurile arc volcanism, which may influence climate only by feedback.

Global mean sea level during the mid-Pliocene epoch (∼3 Ma), when CO2 and temperatures were above present levels, was notably higher than today due to reduced global ice sheet coverage. Nevertheless, the extent to which ice sheets responded to Pliocene warmth remains in question owing to high levels of uncertainty in proxy-based sea level reconstructions as well as solid Earth dynamic models that have been used to evaluate a limited number of data constraints. Here, we present a global dataset of 10 wave-cut scarps that formed by successive Pliocene sea level oscillations and which are observed today at elevations ranging from ∼6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface TerraceM, we extrapolate the cliff and platform surfaces to determine the elevation of the scarp toe, which in most settings is buried under meters of talus. We correct the scarp-toe elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in Pliocene paleo-shoreline elevations around the globe. We next determine the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (buoyancy and viscosity) constrained by seismic tomography models, geodynamic observations, and rock mechanics laboratory experiments. Finally, we identify preferred dynamic topography change predictions based on their agreement with scarp elevations and use our most confident result to estimate a Pliocene global mean sea level based on one scarp from De Hoop, South Africa. This inference (11.6 ± 5.2 m) is a downward revision and may imply that ice sheets were relatively resistant to warm Pliocene climate conditions. We also conclude, however, that more targeted model development is needed to more reliably infer mid-Pliocene global mean sea level based on all scarps mapped in this study.

Over the last 3.3 million years, the Antarctic Ice Sheet (AIS) has undergone phases of ice sheet growth and decay, impacting sea level and climate globally. Presently, the largely marine-terminating AIS loses mass primarily by iceberg calving and basal melt of ice shelves. Quantifying past rates and timing of AIS melt is vital to understanding future cryosphere and sea level changes. One proxy for past ice sheet instabilities is iceberg rafted debris (IRD) fluxes. However, traditional methods of IRD quantification are labor-intensive. Here, we present a new method of identifying IRD grains in sediment core X-ray images using a convolutional neural network machine learning algorithm. We present a 3.3-million-year record of AIS IRD melt events using sediment cores from International Ocean Discovery Program Sites U1536, U1537, and U1538 in the Southern Ocean's "Iceberg Alley." We identify two increases in the IRD fluxes throughout this period, at similar to 1.8 and 0.43 Ma. We propose that after 1.8 Ma, the AIS expanded and transitioned from a primarily terrestrial-terminating to a primarily marine-terminating ice sheet. Therefore, after 1.8 Ma, glacial terminations and AIS iceberg discharge are associated with variations in global ice volume, presumably through the mechanism of sea level and, therefore, grounding line change. The second AIS regime change occurs during the Mid-Brunhes Event (similar to 0.43 Ma). After this time, there are heightened and continuous IRD fluxes at each glacial termination, indicating increased AIS size and instability after this time. Understanding the timing and magnitude of the melt and retreat of the Antarctic Ice Sheet (AIS) in the past can help us understand its sensitivity to future global climate change. One way to understand ice sheets in the past is to identify and quantify sand to pebble-sized rock and mineral grains incorporated into ice sheets and exported to the ocean by icebergs. These so-called iceberg rafted debris (IRD) grains get deposited on the seafloor when icebergs melt, and they are easily identifiable in deep-sea sediment core X-ray images. Here, we present an artificial intelligence image detection method to identify IRD in sediment cores collected in the heart of "Iceberg Alley," a region that today receives the majority of Antarctic icebergs. We find that over the past 3.3 million years, there have been two increases in the amount of IRD deposited. We propose that the first major increase in IRD just after 1.8 Ma is evidence of an expansion of the AIS to an ice sheet with marine margins and ice shelves. We further propose that after 430,000 years ago, the AIS undergoes additional expansion and sees consistent, rapid retreat at the end of each global glaciation. We present a machine learning method to quantify iceberg rafted debris (IRD) in deep-sea sediment cores We quantify IRD at three International Ocean Discovery Program sites in the heart of Iceberg Alley over 3.3 million years We propose that Antarctica transitions from a primarily terrestrial-terminating to marine-terminating ice sheet 1.8 million years ago

Accurate characterization of Last Interglacial (MIS 5e; -129-116 ka) sea level is important for understanding ice sheet sensitivity to climate change, with implications for predicting future sea-level rise. Here we present a record of MIS 5e sea level based on high-precision U-series ages of 23 corals with precise elevation measurements from reefs around Crooked Island, Long Cay, Long Island, and Eleuthera, The Bahamas. Rigorous screening criteria identified the most pristine samples, and nearly all samples show a narrow delta 234Uinitial range between 143.8 and 151.3 parts per thousand. We infer global mean sea level (GMSL) from these local observations by correcting them for glacial isostatic adjustment (GIA) and long-term subsidence. For GIA, we consider a range of ice histories and Earth viscosity structures. We identify, via Bayesian inference, the range of isostatic and GMSL histories that are consistent with MIS 5e observations across The Bahamas. When applying an open-system correction to our ages, we find that MIS 5e GMSL likely peaked higher than 1 m, but very unlikely exceeded 2.7 m. Our posterior GMSL is lower than previous estimates, but consistent with recent results of modeling and observations. Additionally, sea level observations at other locations (Seychelles, Western Australia, Yucatan) are only slightly above/within the 95% range of predicted local sea level, i.e., GIA plus GMSL, for our open-system/closed-system results. Our relatively constant MIS 5e GMSL indicates that Greenland and Antarctica melted beyond their present extents and, given the insolation forcing, that their contributions to GMSL were likely out-of-phase. These results indicate that the ice sheets may be very sensitive to regional temperature, which has important implications for their combined impact on global sea levels at a time when greenhouse gases increases are causing simultaneous warming at both poles.

Quantifying variability in, and identifying the mechanisms behind, East Asian dust production and transport across the last several million years is essential for constraining future dust emissions and deposition. Our current understanding of East Asian dust dynamics through the Quaternary is primarily limited to low‐resolution records from the North Pacific Ocean, those from the Chinese Loess Plateau (CLP), and paleoenvironmental reconstructions from arid basins. All are susceptible to sediment winnowing and focusing as well as input of poorly constrained or unidentified non‐dust detrital material. To avoid these limitations, we examine high‐resolution, constant flux proxy‐derived dust fluxes from the North Pacific and find evidence for higher glacial dust fluxes in the late Pliocene‐early Pleistocene compared to the late Pleistocene‐Holocene. Our results suggest decreasing dust transported to the mid‐latitude North Pacific Ocean from eastern Asia across the Quaternary. This observation is ostensibly at odds with previous dust records from marine sediments and the CLP, and with the perception of higher East Asian dust production and transport during the late Pleistocene associated with the amplification of glaciations. We provide three possible scenarios to describe the ∼2,700‐ky evolution of eastern Asia glacial dust dynamics, and discuss them in the context of sediment production, availability, and atmospheric circulation. Our data and proposed driving mechanisms not only raise questions about the framework typically used to interpret dust archives from East Asia and the North Pacific Ocean, but also provide a roadmap for hypothesis testing and future work necessary to produce better‐constrained records of paleo‐dust fluxes.

Supporting data of Li et al., Global Biogeochemical cycles

Global mean sea level (GMSL) reconstructions from past interglacial periods help us understand the sensitivity of ice sheets to a warming climate. In this study, we focus on Marine Isotope Stage 5a (MIS 5a), a warm period that peaked 82,000 years ago and for which current GMSL estimates remain widely uncertain (ranging from-28 m to +1 m). Here we reconstruct relative sea level (RSL) based on an extensive and exquisitely preserved fossil coral reef at Cave Hill, Barbados, which has not been examined before. We dated one coral sample (Acropora palmata) from this outcrop using U-series dating and ob-tained a closed system age of 82.5 +/- 0.4 ka and an open system age of 83.3 +/- 0.7 ka (2s), which confirm that the reef formed during MIS 5a. We determine RSL based on the elevation of 222 fossil corals within the outcrop from three species (Acropora palmata, Siderastrea radians, Favia fragum). The coral elevations are combined using Bayesian inference to obtain a posterior common RSL, with present-day water depths of each species as priors. We use our inference scheme and synthetic datasets to explore the number and species of corals needed for a robust RSL estimate and find that if approximately 5 corals are sampled, roughly half of which have a narrow living depth range (0 to-10 m), the accuracy and precision of the inferred RSL is around 1.5 m. This value improves to less than 0.5 m if more corals (approximately 20) are sampled, especially if these have narrow living depth ranges. These tests can guide future coral sampling at other outcrops. After inferring RSL from the real coral elevations, we correct it for long-term uplift, using the elevation of the adjacent MIS 5e sea level outcrop to calculate an uplift rate of 0.522 +/- 0.036 m/kyr (1s), and for glacial isostatic adjustment. We find that GMSL most likely peaked at-22.3 m relative to present GMSL (-32.5 m to-10.7 m, 95% credible interval). This work provides a new estimate for MIS 5a GMSL that is lower than results from most previous studies, and confirms sequentially decreasing GMSL during the MIS 5e, 5c, and 5a precessional insolation peaks, indicating increased ice sheet growth and cooling into the ice age following the peak interglacial MIS 5e. (C) 2022 Elsevier Ltd. All rights reserved.

Microbial communities are found throughout the biosphere, from human guts to glaciers, from soil to activated sludge. Understanding the statistical properties of such diverse communities can pave the way to elucidate the common mechanisms ...Multiple ecological forces act together to shape the composition of microbial communities. Phyloecology approaches—which combine phylogenetic relationships between species with community ecology—have the potential to disentangle such forces but are often ...

Early Pleistocene Marine Isotope Stage (MIS)‐31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000‐year resolution, spanning 1.110–1.030 Ma, diatom‐based reconstruction of primary productivity, relative sea surface temperature changes, sea‐ice proximity/open ocean conditions and diatom species absolute abundances during MIS‐31, from the Scotia Sea (59°S) using deep‐sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time‐stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS‐31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere‐phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea‐ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub‐ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS‐31, a warmer than Holocene interglacial.

Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency. Sedimentary ancient DNA (sedaDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and sedaDNA damage analysis) metagenomic marine eukaryote sedaDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote sedaDNA record of ~1 Mio. years and diatom and chlorophyte sedaDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU, psbO). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that sedaDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.

The Red Sea is a maritime rift. Tsunamigenic submarine landslides are common in these deep, steep‐sided, and seismically active basins. Because the rift is narrow, tsunami formed on one margin dissipate little before impacting the opposite side. Red Sea slope failures are therefore especially hazardous. We examine the tsunamigenic potential of an incipient landslide in the Tiran Straits that started, but then stopped after a short distance. Radiometric and biotic analyses fix the age of this landslide to within the last 500 years. Tsunami modeling of the incipient slide predicts ∼10 m wave heights on the Egyptian coastline. Of present concern is that the slope will eventually slide to completion with even more hazardous results. Tsunami simulated for this future event are twice as large as that generated by the incipient slide, so the threat posed by a future slide is consequential. Sharm El Sheikh, an Egyptian resort town now lies in its path, as does “The Line,” a vast Saudi infrastructure project. This study warns of credible tsunami risk in the rapidly urbanizing Tiran Straits.

The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO 2 levels.

Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to "dirty" icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world.

Formation temperature was measured by the advanced piston corer temperature tool (APCT-3), Sediment Temperature Tool (SET), or sediment temperature pressure tool (SETP) and reduced to in situ temperature and (for SETP) pressure estimates. These data are compiled per instrument run and assigned to a core (the core cut with the APCT-3 cutting shoe or the core following the SET deployment).