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Although hundreds of cores have been collected on the Antarctic continental shelf over the past five decades, definitive interpretations of depositional environments associated with marine-based ice advance and retreat are hindered by similarities in sediment facies and a lack of geomorphic context. The recent use of an advanced multibeam bathymetry system allows for more detailed ice sheet reconstructions from glacial landforms that were previously not resolved with older generation systems. Here we present results from a recent cruise to the Ross Sea, Antarctica that focuses on integrating sediment facies analyses into a geomorphic framework to confidently determine depositional environments and sedimentological processes since the Last Glacial Maximum. Grain-size analysis, geotechnical properties, and micropaleontology from targeted sediment cores are used to develop improved criteria for making the distinction between subglacial diamictons and ice-proximal diamictons, which can be applied to geomorphically blind sediment cores. Our consideration of geomorphic context while interpreting sediment facies has also allowed us to determine that most debris melted out of the base of paleo-ice shelves in the Ross Sea only 1.2 km seaward of the grounded ice margin. Additionally, we find that agglutinated foraminifera specimens are characteristic of sluggish marine currents and a resulting accumulation of siliceous detritus rich in organic matter; however, calcareous specimens dominate in higher-energy current settings and in ice-proximal environments with lesser amounts of siliceous detritus and associated organic material. Overall, sedimentary successions record contrasting behaviors of the West Antarctic and East Antarctic ice sheets that extended onto the continental shelf during the Last Glacial Maximum. Not only is this coupled geomorphic and sedimentologic approach useful for understanding glacimarine processes and ice-sheet retreat patterns, but it is essential for selecting appropriate facies transitions for chronological constraints of past ice sheet behavior.

Optically stimulated luminescence (OSL) dating has recently been applied to crystalline (i.e. igneous and metamorphic) rock surfaces. With the advent of this technique, early studies can guide improvements to the methodology that will lead to more robust age constraints. Low OSL sensitivity, poor measurement reliability, and equivalent dose scatter are common problems with dating quartz from crystalline rock surfaces. We investigate OSL characteristics of quartz extracted from crystalline Antarctic beach cobbles. Comparison of OSL behavior with cathodoluminescene characteristics and mineral composition and texture does not show a distinct relationship, suggesting luminescence behavior results from the natural radiation environment and post-crystallization transport history, rather than provenance source and the nature of crystal defects. Elemental composition of processed samples used for OSL measurements indicates standard methods of chemical preparation are not always suitable to extract pure quartz samples. Additionally, heterogeneous radiation production and attenuation poses a problem for estimating dose rates, in particular regarding beta contributions that dominate effective dose rates. We determine the sensitivity of effective dose rates to water content parameters and crystal size needed to calculate dose rates for crystalline rock surfaces. An increase in the value of all modelled parameters serves to reduce effective dose rates and, thus increase OSL ages. Dose rates are most sensitive to crystal size, which can introduce large uncertainty in burial ages from crystalline rocks due to heterogeneous crystal morphology (i.e. size and shape). This study provides a step forward in understanding the challenges and improving the methodology of luminescence dating of quartz from crystalline rock surfaces.

A lack of reliable chronology often leaves Antarctic ice sheet reconstructions incomplete. Despite being the most heavily investigated region of the Antarctic continental shelf, the post-Last Glacial Maximum (LGM) record of marine-based ice sheet dynamics in the Ross Sea has remained largely elusive and at odds with fringing terrestrial records of ice sheet decay. Issues with radiocarbon dating stem primarily from poorly preserved carbonate, contamination by glacially-recycled carbon, and insufficient consideration for glacial geomorphic context and sedimentary facies. We assess nearly 70 newly acquired and more than 200 published radiocarbon ages in the context of a consistent sedimentary facies and geomorphic framework to interpret the timing of the local glacial maximum and subsequent retreat of the East Antarctic Ice Sheet (EAIS) in the Ross Sea and potential causes of retreat. Compound-specific radiocarbon ages help to provide good constraints on open marine onset, and we demonstrate that, with proper corrections and considerations, acid insoluble organic (AIO) radiocarbon ages can be reliable in open marine sediments and carbonate ages can be reliable in grounding-zone proximal sediments. We find that the ice flowing through Pennell and JOIDES troughs remained at maximum extent for approximately 10,000 years before retreating at 15.1 and 13 cal ka BP, respectively. An ice shelf covered the outer continental shelf until ∼9.5 cal ka BP, after which it collapsed in JOIDES Trough, creating deep iceberg furrows. Retreat through Pennell Trough was more episodic, marked by grounding-zone wedges that backstep upstream and onto lateral banks creating deglacial emergent ice rises. As ice retreated from ∼9 to ∼4 cal ka BP, there was considerable reorganization of drainage and at least one episode of readvance through southern JOIDES Trough that began drawdown of terrestrial ice near Ross Island at ∼7.8 cal ka BP. The ice shelf appears to have retreated to a near-present configuration by 2 cal ka BP. However, due to inconsistencies in calendar ages, grounding line position must be inferred from relative chronology based on glacial landforms, which suggests grounded ice retreated nearly to Drygalski Ice Tongue and lingered atop Crary Bank where it was maintained by ice from David Glacier. Our reconstruction further suggests that the EAIS in the western Ross Sea was not a discernible contributor to Meltwater Pulse 1A, but likely contributed to eustatic sea level rise well through the middle—perhaps even late—Holocene.

Calmette Bay within Marguerite Bay along the western side of the Antarctic Peninsula contains one of the most continuous flights of raised beaches described to date in Antarctica. Raised beaches extend to 40.8 m above sea level (masl) and are thought to reflect glacial isostatic adjustment due to the retreat of the Antarctic Peninsula Ice Sheet. Using optically stimulated luminescence (OSL), we dated quartz extracts from cobble surfaces buried in raised beaches at Calmette Bay. The beaches are separated into upper and lower beaches based on OSL ages, geomorphology, and sedimentary fabric. The two sets of beaches are separated by a prominent scarp. One of our OSL ages from the upper beaches dates to 9.3 thousand years ago (ka; as of 1950) consistent with previous extrapolation of sea-level data and the time of ice retreat from inner Marguerite Bay. However, four of the seven ages from the upper beaches date to the timing of glaciation. We interpret these ages to represent reworking of beaches deposited prior to the Last Glacial Maximum (LGM) by advancing and retreating LGM ice. Ages from the lower beaches record relative sea-level fall due to Holocene glacial-isostatic adjustment. We suggest a Holocene marine limit of 21.7 masl with an age of 5.5–7.3 ka based on OSL ages from Calmette Bay and other sea-level constraints in the area. A marine limit at 21.7 masl implies half as much relative sea-level change in Marguerite Bay during the Holocene as suggested by previous sea-level reconstructions. No evidence for a relative sea-level signature of neoglacial events, such as a decrease followed by an increase in RSL fall due to ice advance and retreat associated with the Little Ice Age, is found within Marguerite Bay indicating either: (1) no significant neoglacial advances occurred within Marguerite Bay; (2) rheological heterogeneity allows part of the Antarctic Peninsula (i.e. the South Shetland Islands) to respond to rapid ice mass changes while other regions are incapable of responding to short-lived ice advances; or (3) the magnitude of neoglacial events within Marguerite Bay is too small to resolve through relative sea-level reconstructions. Although the application of reconstructing sea-level histories using OSL-dated raised beach deposits provides a better understanding of the timing and nature of relative sea-level change in Marguerite Bay, we highlight possible problems associated with using raised beaches as sea-level indices due to post-depositional reworking by storm waves.

Magnetic susceptibility (MS) of sediment and rock has been suggested as a tool to indicate changes in weathering patterns, source area, trace metals, and particle size, each of which may also provide a paleoclimate record. We test the utility of MS in recording previously documented climate changes within Holocene estuarine deposits from four bays along the Texas coast of the northwest Gulf of Mexico: Baffin, Copano, Corpus Christi, and Galveston Bays. MS analysis indicates three populations of anomalously high values: at or near the 8.2 ka climatic event, during the mid-Holocene at 5.5–5.0 ka, and at 3.6 ka. MS measurements from Copano and Corpus Christi Bay cores suggest that the 8.2 ka event may have been multiple events. Although the initial focus of this study was on the use of MS to record the 8.2 ka event, the younger MS anomalies that correlate within the mid-Holocene are equally important and more pronounced for the use of MS as a paleoclimate proxy. The strong correlation of anomalies between 5.5–5.0 ka within multiple cores suggests a regional response to environmental changes that affect the abundance of magnetic minerals in the bays. We use multiple analyses to attempt to determine the cause of the observed MS anomalies in the bays. Frequency-dependent MS indicates that the majority of measured samples, including the anomalies, have no biogenically produced ultrafine magnetite with the exception of anomalies at 8.5 ka, 8.3 ka, and 7.8 ka in Copano Bay. Particle size of the sediment is compared with MS measurements from Baffin and Copano Bays suggesting a weak correlation between particle size and MS. Inductively coupled plasma spectrometry and x-ray fluorescence fail to indicate anomalous values correlating with the observed MS anomalies. Both methods probably lack the resolution to detect the minor differences needed to cause the observed changes in MS. X-ray diffraction analysis indicates the possibility of a minor increase in magnetite at an MS anomaly in the Corpus Christi Bay record which may be sufficient in causing the elevated MS. We present three explanations of climate-controlled MS for the anomalous intervals. (1) Accelerated sea-level rise decreased the orbital depth of waves on the bottom of the bays. As a result, the sedimentation rate increased due to a higher accommodation for deposition. Due to rapid deposition, the flooding surface preserved authigenic ferromagnetic minerals within a redox layer which deterred the cycle of Fe from one phase to another. (2) An influx of detrital magnetite/maghemite to the bays occurred due to flash flooding during arid periods. (3) The MS anomalies observed in the cores represent an increase in background magnetic material. Models (1), (2), and (3) apply to the anomalies near 8.2 ka and only models (2) and (3) provide plausible explanations for the younger anomalies as there is no documentation of sea-level rise during those periods. Despite the uncertainties in the mechanisms behind the MS anomalies, the correlation of the climatic events within multiple bays along the Texas coast suggests that MS may provide a correlation tool within estuarine fills of the Gulf of Mexico Basin and perhaps across the globe.

The timing of the most recent Neoglacial advance in the Antarctic Peninsula is important for establishing global climate teleconnections and providing important post-glacial rebound corrections to gravity-based satellite measurements of ice loss. However, obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent Neoglacial advance in Antarctica has been hampered by the lack of historical records and the difficulty of dating materials in Antarctica. Here we use a new approach to dating flights of raised beaches in the South Shetland Islands of the northern Antarctic Peninsula to bracket the age of a Neoglacial advance that occurred between 1500 and 1700 AD, broadly synchronous with compilations for the timing of the Little Ice Age in the northern hemisphere. Our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent Neoglacial advance. In addition, these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the South Shetland Islands. We use a Maxwell viscoelastic model of glacial-isostatic adjustment (GIA) to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent Neoglacial advance. Our rebound model suggests that the subsequent melting of an additional 16–22% increase in the volume of ice within the South Shetland Islands would result in a subsequent uplift rate of 12.5 mm/yr that lasted until 1840 AD resulting in a cumulative uplift of 2.5 m. This uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent Neoglacial advance along the South Shetland Islands and falls within the range of uplift rates from similar settings such as Alaska.