Past sea levels provide important constraints on global ice volumes, rates of tectonic motion, ice-sheet sea-level feedbacks, and the migration of species through time. Beneath formerly glaciated regions, the marine limit, the maximum extent of sea-levels after glacial retreat, provides some of the oldest post-Last Glacial Maximum (LGM) sea-level constraints. However, although the elevations of marine limits are plentiful, they often remain undated. In this study, we provide new age and elevation constraints on the late Pleistocene relative sea-level (RSL) history at 12 sites along the eastern flanks of the former Minch Ice Stream (MnIS) of northwest Scotland. Optically stimulated luminescence (OSL) was used to date the highest and presumably oldest preserved RSL indicators immediately after ice-sheet retreat. Although slightly older than earlier estimates, our ages confirm the early deglacial age of similar to 16.2-19.5 ka for the raised shorelines of northwest Scotland with declining marine limits north of the Isle of Skye from 26.2 +/- 4.8 m at Ardaneaskan to 12.8 +/- 4.8 m elevation at Achiltibuie, the latter of which lies inside the moraines of the Wester Ross Readvance. Our new OSL ages suggest deglaciation of the MnIS may have been slightly earlier than previously thought, although our large error bars highlight the need for additional age constraints. Our new RSL data provide important constraints for Glacial Isostatic Adjustment (GIA) models for Scotland and shed light on the behavior of the former MnIS, thought to be susceptible to marine ice-sheet instability.

Sea-level changes in polar environments are important for understanding the timing and magnitude of past ice-sheet changes. Most of the few records of such past sea-level changes in Antarctica are those derived from raised beach ridges. Many studies using raised beach ridges to reconstruct past sea levels across Antarctica commonly assume that they only record falling sea levels. However, their internal architecture may contain a record of other oscillations in relative sea-level (RSL) change. In this study, we examine the internal architecture of a well-developed set of raised beach ridges on Livingston Island of the Antarctic Peninsula using 10+ km of ground penetrating radar (GPR). Recalibrated published radiocarbon ages are used in combination with new optically stimulated luminescence (OSL) ages to compare beach morphology and stratigraphy to the glacial history of the region. Within this flight of raised beach ridges, evidence was found for both regressive and transgressive depositional patterns marked by progradational seaward dipping facies deposited during periods of RSL fall followed by erosion and deposition of landward dipping overwash and aggrading beds during interpreted periods of RSL rise. This succession is routinely located over a notch in the bedrock interpreted to represent a wave-cut feature. The ages of raised beach ridges underlain by wave-cut notches and composed of landward-dipping strata correlate with known Holocene ice advances at <500, similar to 2000, and similar to 5000 cal yrs BP. We propose that these transgressive phases are the result of glacial-isostatic adjustment (GIA). This GIA hypothesis further supports recent assertions of a much more dynamic RSL history for Antarctic coastlines, which may contaminate the Last Glacial Maximum RSL signal across Antarctica.

Raised shorelines provide important constraints on past sea levels, glacial isostatic adjustment (GIA), and rates and directions of vertical crustal motion. Although most raised shorelines across NW Scotland relate to post-Last Glacial Maximum (LGM) glacial-isostatic rebound, many undated shorelines lie above the marine limit established from isolation basins. Here, we present new optically stimulated luminescence (OSL) ages for a raised marine terrace at an elevation of 28 m in Slaggan Bay of NW Scotland. Four OSL ages suggest the feature is pre-LGM, likely Marine Isotope Stage (MIS) 3. Global mean sea levels (GMSL) during MIS 3 are thought to have been similar to 40-60 m below present across most of the globe. We use a pair of GIA models to determine what ice sheet and sea-level scenarios might provide an explanation for these anomalously high sea levels during MIS 3. Our results suggest that in the absence of tectonic activity, such high MIS 3 shorelines across NW Scotland require a MIS 4 ice sheet in Scotland, with postglacial rebound of the crustal depression following its demise during MIS 3 responsible for the elevated shoreline features at that time. (c) 2025 John Wiley & Sons, Ltd

Understanding drivers of marine-terminating ice sheet behavior is important for constraining ice contributions to global sea level rise. In part, the stability of marine-terminating ice is influenced by solid Earth conditions at the grounded-ice margin. While the Cordilleran Ice Sheet (CIS) contributed significantly to global mean sea level during its final post-Last-Glacial-Maximum (LGM) collapse, the drivers and patterns of retreat are not well constrained. Coastal outcrops in the deglaciated Puget Lowland of Washington State – largely below sea level during glacial maxima, then uplifted above sea level via glacial isostatic adjustment (GIA) – record the late Pleistocene history of the CIS. The preservation of LGM glacial and post-LGM deglacial sediments provides a unique opportunity to assess the variability in marine ice sheet behavior of the southernmost CIS. Based on paired stratigraphic and geochronological work, with a newly developed marine reservoir correction for this region, we identify that the late-stage CIS experienced stepwise retreat into a marine environment between 15 000 and 14 000 years before present, consistent with timing of marine incursion into the region reported in earlier works. Standstill of marine-terminating ice for at least 500 years, paired with rapid vertical landscape evolution, was followed by continued retreat of ice in a subaerial environment. These results suggest rapid rates of solid Earth uplift and topographic support (e.g., grounding zone wedges) stabilized the ice margin, supporting final subaerial ice retreat. This work leads to a better understanding of shallow-marine and coastal-ice-sheet retreat and is relevant to sectors of the contemporary Antarctic and Greenland ice sheets and marine-terminating outlet glaciers.

Global sea levels during the last interglacial (LIG), 129,000-116,000 years ago, may have reached as much as 5-10 m higher than present. However, the elevation of the LIG highstand varies locally due to tectonics, subsidence, steric effects, and glacial isostatic adjustment (GIA). The variability brought upon by GIA can be used to constrain the past distribution of ice sheets including the source of higher sea levels during the LIG. In spite of its importance for fingerprinting the source of additional meltwater at the LIG, little is known about the elevation of LIG sea levels across Antarctica. In this study we review the geologic constraints on the elevation of the LIG highstand across Antarctica. We find that although several Late Pleistocene sea-level constraints are available across the continent very few of them provide definitive LIG ages. Arguably the most probable LIG sea-level indicators come from East Antarctica but most of them have age constraints approaching the limits of radiocarbon dating (>similar to 45 ka) with many likely dating to Marine Isotope Stage 3, not the LIG. For West Antarctica, Late Pleistocene sea level constraints are confined to a few poorly or completely undated possible examples from the Antarctic Peninsula. Our review suggests that much more work is needed on constraining the elevation of the LIG highstand across Antarctica.

In order to reconstruct past environmental conditions along the north-eastern Antarctic Peninsula, we documented changes in grain size, grain roundness, onlap as seen in ground-penetrating radar reflection profiles and ice-rafted debris on a set of 36 raised beaches developed over the last ~7.7 ± 0.9 ka on Joinville Island. The most pronounced changes in beach character occur at ~2.7–3.0 ka. At this time, there appears to have been a reintroduction of less rounded material, the development of stratification within individual beach ridges, an introduction of seaweed and limpets to the beach deposits, a change in clast provenance (although slightly earlier than the change in cobble roundness) and a shallowing of the overall beach plain slope. Prolonged cooling associated with the Neoglacial period may have contributed to these changes, as the readvance of glaciers could have changed the provenance of the beach deposits and introduced more material, leading to the change in roundness of the beach cobbles and the overall slope of the beach plain. This study suggests that late Holocene environmental change left a measurable impact on the coastal zone of Antarctica.

Understanding drivers of marine-terminating ice sheet behavior is important for constraining ice contributions to global sea-level rise. In part, the stability of marine-terminating ice is influenced by solid-Earth conditions at the grounded-ice margin. While the Cordilleran Ice Sheet (CIS) contributed significantly to global mean sea level during its final post-Last Glacial Maximum (LGM) collapse, the drivers and patterns of retreat are not well constrained. Coastal outcrops in the deglaciated Puget Lowland of Washington state - largely below sea level during glacial maxima, then uplifted above sea level via glacial isostatic adjustment (GIA) - record late Pleistocene history of the CIS. The preservation of LGM glacial and post-LGM deglacial sediments provides a unique opportunity to assess variability in marine ice-sheet behavior of the southernmost CIS. Based on paired stratigraphic and geochronological work with a newly developed marine-reservoir correction for this region, we identify that the late-stage CIS experienced stepwise retreat into a marine environment about 12,000 years before present, placing glacial ice in the region for about 3,000 years longer than previously thought. Stand-still of marine-terminating ice for a millenia, paired with rapid vertical landscape evolution, was followed by continued retreat of ice in a subaerial environment. These results suggest rapid rates of solid Earth uplift and topographic support (e.g., grounding-zone wedges) stabilized the ice-margin, supporting final subaerial ice retreat. This work leads to a better understanding of shallow marine and coastal ice sheet retreat; relevant to sectors of the contemporary Antarctic and Greenland ice sheets and marine-terminating outlet glaciers.

The development and application of lumi-nescence dating and dosimetry techniques have grown exponentially in the last several decades. Luminescence methods provide age control for a broad range of geological and archaeological contexts and can char-acterize mineral and glass properties linked to geologic origin, Earth-surface processes, and past exposure to light, heat, and ioniz-ing radiation. The applicable age range for luminescence methods spans the last 500,000 years or more, which covers the period of modern human evolution, and provides context for rates and magnitudes of geologi -cal processes, hazards, and climate change. Given the growth in applications and publi-cations of luminescence data, there is a need for unified, community-driven guidance re-garding the publication and interpretation of luminescence results. This paper presents a guide to the essen-tial information necessary for publishing and archiving luminescence ages as well as supporting data that is transportable and expandable for different research objectives and publication outlets. We outline the in-formation needed for the interpretation of luminescence data sets, including data as-sociated with equivalent dose, dose rate, age models, and stratigraphic context. A brief review of the fundamentals of luminescence techniques and applications, including guid-ance on sample collection and insight into laboratory processing and analysis steps, is presented to provide context for publishing and data archiving.

Recognition of how dynamic the Antarctic ice sheets and glaciers were during the late Holocene has grown in recent years. Proxy data suggests the presence of Neoglacial advances but few moraines or glacial features from this time have been dated compared to glaciated landscapes of the Northern Hemisphere. Debate continues on whether parts of Antarctica experienced glacial advance at the same time as the "Little Ice Age" (LIA), which is well-documented in the Northern Hemisphere. We provide new evidence for late Holocene glacial fluctuations at three locations along the Antarctic Peninsula. A moraine or till sheet from a tidewater glacier cross cuts a series of dated raised beaches at Tay Head, Joinville Island along the northwestern Weddell Sea. At Spark Point, on Greenwich Island, a glacier has overrun Holocene raised beaches and a shell-bearing marine deposit is reworked into a glacial diamicton. A third site in Calmette Bay within the larger Marguerite Bay also contains a recent moraine that cuts across a series of dated raised beach ridges. The new ages constraining these glacial advances are in broad agreement with the handful of other existing ages on moraines and proxy records suggestive of cooler conditions within the Antarctic Peninsula. Combining available timing constraints into a Bayesian model yields an age of 400 to 90 cal BP (1550-1860 CE; 95%) for the LIA across the Antarctica Peninsula. Consideration of a two-phase glacial advance within our Bayesian framework does fit more of the data from across the Antarctic Peninsula and suggests advances from 575 to 330 cal BP (1375-1620 CE) and 400 to 50 cal BP (1550-1900 CE). However, more work is needed to determine if such a two-phase advance occurred. Regardless, its similar timing within the Antarctic Peninsula to that of the Northern Hemisphere supports recent assertions of a volcanic or solar forcing for the LIA. These recent readvances also provide a possible mechanism for changes in the rates of Holocene relative sea-level change recorded across the Antarctic Peninsula suggesting that the Antarctic ice sheets may have been more responsive to past climate changes than previously thought and glacial isostatic adjustment from the LIA and possibly other Holocene glacial oscillations is superimposed upon the longer relaxation from the Last Glacial Maximum. (C) 2021 The Authors. Published by Elsevier Ltd.

Major advances in planetary science will be driven by determining absolute ages of geologic units on multiple bodies in the inner Solar System in the next decade.Absolute ages calibrate bodyspecific chronologies and create a framework for understanding Solar System formation, the effects of impact bombardment on life, and the evolution of planets and their interiors.We recommend that the Decadal Survey:• Support Mars Sample Return to ensure the return to Earth of a set of carefully-chosen, well-documented samples for geochronology and other critical studies of Mars' evolution and past habitability.• Prioritize sample-return missions from planetary bodies in the inner Solar System that would answer fundamental questions about the timing of major events in planetary history.• Advocate for sustained funding for in situ dating instruments to continue to raise their technology readiness levels for future exploration of planetary surfaces.• Include a Solar System chronology mission on the New Frontiers mission list, setting the science goals of such a mission but allowing flexibility in how those goals are accomplished.• Reemphasize the importance of an investment strategy for laboratory instrumentation and curation sufficient to provide for both replacement of existing capacity and development of new capabilities.• Recommend that NASA partner with NSF on their Decadal geochronology initiative to leverage NASA's investments in infrastructure supporting planetary geochronology.

Abstract. Feldspar, used for infrared stimulated luminescence (IRSL) dating, is known as a dosimeter which might not completely retain the environmental dose over time, therefore leading to age underestimation. The dose leakage is believed to be caused by non-thermal (anomalous) charge redistribution in the crystal and reflected in an IRSL signal which diminishes with time accordingly. After laboratory irradiation, this signal decline may be monitored by successive IRSL readouts following increasing delay times. Hence, tests of anomalous signal fading are integral steps of IRSL dating procedures applied to feldspar and feldspar-bearing polyminerals. In these measurements IR-stimulation is in most cases preceded by thermal pretreatment (preheating) of the sample. Per common practise, preheating is performed immediately after laboratory irradiation to avoid unwanted electron redistribution assumed to occur if preheating is performed immediately before the delayed IRSL-readout. Here we compile a series of single aliquot regeneration (SAR) measurements questioning this practice. As a result, the fading measurements may possibly reveal post-irradiation afterglow. The results also suggest that data curves resembling anomalous fading may be caused by insufficient control of the readout temperature waning with increasing delay time. The unwanted effects are observed best for IRSL at room-temperature and on luminescence readers with an out-of-date steering software, but they are relevant also for IRSL at elevated temperature and on modern readers, likely including novel post-IR IRSL (pIRIR) protocols. For temperatures as homogeneous as possible during IRSL readout of the (fading) dose, we recommend preheating immediately prior to (delayed) IRSL-readout in order to avoid measurement artefacts either resembling entirely anomalous fading of the IRSL-signal or increasing the true values. It should be noticed that multifold SAR protocol and measurement parameters, like e.g. the type of luminescence reader or the use of N2 flow, may further modify the course of the data values and therefore the amount of the measured signal loss in a particular time interval after laboratory irradiation. Furthermore, calculations of signal fading (g-value) should consider only IRSL-readout after a minimum delay time after laboratory irradiation to avoid including possible post-irradiation afterglow in g-value determination. The measurements compiled in the present study were performed on polymineral fine grains extracted from loess-borne samples from southern Germany and a limnic sample from Mexico. Therefore, the observations are assumed to be not only of local or regional interest but they appear to be of general relevance to SAR fading tests. However, with respect to the likely varying temperatures during IRSL readout of the fading dose administered in the laboratory, the observations are at least partly owed to the promptly measured test dose for normalizing the preceding (fading) dose. This is in contrast to classical multiple aliquot additive (MAA) measurements in which preheating may be replaced by long storage of a sample after laboratory irradiation and in which fading tests may be designed to also correct for possibly (slightly) changing IRSL readout temperatures at different delay times. Thus, the observations are at least partly SAR-immanent.

Author(s): Theilen, Brittany | Advisor(s): Simms, Alexander R | Abstract: The sedimentary characteristics of raised beach deposits are a potential archive of past wave climate as well as processes acting on beaches. In this study I examine changes in the grain-size, grain roundness, and spatial density of ice-rafted debris from two sets of raised beaches on opposite sides of the Antarctic Peninsula (AP): Joinville Island along the Eastern AP (EAP), and Livingston Island along the Western AP (WAP). All beaches were labeled starting at the closest proximity to the modern shoreline. Overall, the 9 beaches on Livingston Island are stratified with poorly sorted clasts compared to the better sorted 21 stratified lower beaches and 15 unstratified upper beaches on Joinville Island. The dissimilarity likely reflects the difference in foreshore gradient between the two islands. The Joinville profile is steeper, allowing waves to break on the coastline with high energy while the Livingston profile is shallower, enabling wave attenuation before reaching the shoreline. Grains on the raised beaches of Joinville Island show an overall increase in roundness through time while grain size shows low variability. However, the roundness trend is interrupted at beaches 5, 13-15.5, and 28. Beach 5 exhibits less and beach 28 exhibits more rounding than the general trend. Less rounding of sediments within beach 5 could be explained by short open water seasons with an increase in sea ice while the opposite could hold true for beach 28. The transition between beaches 13 and 15.5 indicates a decrease in roundness over time, opposite the overall roundness trend. The ages of beaches 15.5-13 (~2.8-2.3 cal. kyr BP) coincides with the onset of the Neoglacial time period ~3 cal. kyr BP. The presence of sea-ice or increased glacial activity could hinder clast rounding or introduce less rounded materials during cooler periods associated with this Neoglacial time period. Grains within Livingston Island beach ridges also show an overall increase in roundness through time but no coherent trends in grain size. However, Livingston Island contains two types of beach deposits: strand plains and beach ridges, the latter of which are interpreted as storm ridges. Strand plains were deposited by normal swash processes and exhibit sub-angular to sub-rounded sediments. Typically, storm ridge sediments would be less rounded, characteristic of high energy storm deposits, than the strand plain deposits, roundness and grain size are uncorrelated. However, the beach ridges contain sub-rounded to rounded deposits while the strand-plain deposits are sub-angular to sub-rounded. Ground penetrated radar profiles through the beach ridge crests suggest they bury older strand-plain deposits. Therefore, I suggest the more rounded nature of the beach ridge deposits on Livingston Island is due to the recycling of older strand-plain deposits by storms.