Knowledge regarding former behavior of the East Antarctic Ice Sheet (EAIS) is crucial for assessing global sealevel change and understanding the global climate system. Yet, it remains challenging to examine pre-Last Glacial Maximum (LGM) glacial histories of the EAIS due to the limitations of the traditional geologic records. Recent studies suggest that blue ice areas (BIAs) and associated deposits (e.g. supraglacial moraines) have a potential to overcome this problem. However, the relationship between blue-ice evolution and climate changes is not yet well examined. In this study, we investigate two types of BIAs in the Grove Mountains, EAIS, on the basis of surface exposure dating of erratic boulders and cobbles on blue-ice moraines at Mount Harding and Escarpment. Here, we present 27 new ages, including single (10Be; n = 10) and paired (10Be and 26Al, n = 17) exposure-ages. The newly-obtained ages, along with previously-published 10Be data (n = 40), indicate that the studied BIAs have been relatively stagnant since the LGM, and that blue-ice moraines formed in a closed system are much older than those built in the absence of a barrier. Also, the compilation implies multiple phases of preLGM ice flow that corresponded to global cold periods. We suggest that there was likely a response of blue-ice evolution to Antarctic glaciations on orbital timescales.

Since the 1990s, geomorphologists have utilized measurements of cosmogenic 10Be concentrations from stream sand to quantify erosion rates across landscapes. Few studies employ 10Be sample collection strategies that specifically test the spatial and temporal reproducibility of10Be data. Here, we examine the reproducibility of 10Be measurements after the 2018 Woolsey Fire, the largest historical wildfire to burn through the Santa Monica Mountains, California, USA. The fire was followed by 13 atmospheric rivers and other high rainfall storms in the subsequent wet season. We present 60 new 10Be concentration measurements, comprising 3-6 temporal replicate samples of stream sand (and for some samples including different grain-sizes) from seven basins across the Santa Monica Mountains, collected between 2016 and 2021, five of which burned in the fire. We use these data to test whether 10Be concentrations measured from samples collected after the fire differ from those collected before the fire. Such data test inferences about soil mixing and changing erosion dynamics, specifically depth, in sampled basins. We find that most 10Be concentrations reproduced within 2 sigma measurement uncertainties. Only three post-fire 10Be concentrations from burned basins deviate more than 2 sigma from pre-fire values. We suggest that 10Be concentrations of temporal replicates in this study reproduce well because most post-fire erosion in this landscape was shallow. Where deep erosion or erosion at higher elevations occurred, the effects of these processes on 10Be measurements appear to be transient and would be missed unless sampling occurs closely following a rainstorm or wildfire. Our findings show that 10Be concentrations generally reproduce well in this steep, tectonically active and rapidly eroding landscape with a Mediterranean climate, despite the presence of wildfires and heavy rainfall events caused by atmospheric rivers.

A key challenge when evaluating mountain glacier change, particularly in the context of climate change, is that glacial geological research often operates within discrete timescales. Studies typically examine long-term glacier change over centuries to millennia or short-term change spanning days to decades. Bridging these temporal gaps is essential for refining projections of glacier mass loss and enhancing our understanding of the future of mountain glaciers, particularly in regions like the Himalayas. The closely monitored Gangotri Glacier in the Bhagirathi catchment of the Garhwal Himalaya provides an excellent opportunity to define the timing and drivers of late Quaternary glacier change from similar to 80 ka to present. By integrating new and recalculated glacial geochronological datasets with instrumental and remote sensing data, we present a comprehensive glacial chronostratigraphy for the Bhagirathi catchment. Tracking of the glacier terminus position and equilibrium-line altitudes over the past similar to 80 ka shows that Gangotri Glacier has been progressively retreating during this time. We provide strong evidence that Gangotri Glacier is sensitive to short-and long-term climate changes. The accelerated retreat in recent decades is likely driven by climate change-induced shifts in global temperature and precipitation patterns. This study highlights the importance of evaluating glacier change across multiple timescales, as this has enabled us to more confidently conclude that the retreat of mountain glaciers such as Gangotri Glacier will continue and possibly accelerate in response to ongoing climate change.

During the last decade there has been an increase in the study of transient topography because it gives information about surface uplift history. The onset of transient topography forms after a gain in potential energy which leads to the creation of slopes at the outlet of catchment. It is followed by a wave of transient erosion that propagates upstream along the main river, then across tributaries, and from the tributaries to the hillslopes. Records of incision history such as topographic data and landform dating can be gathered into inversion schemes to reconstruct base-level fall and uplift history. In this study, we employ a reversible jump Markov chain Monte Carlo Bayesian algorithm to perform an inversion of topographic data, landform dates, and erosion rates in order to unravel surface uplift history. By adopting a probabilistic approach, we generate an ensemble of solutions that comprise various combinations of model parameters. This methodology enables us to estimate uncertainties in the timing and amount of changes in uplift rates. In the forward model we use the non-linear analytical solutions of the stream power incision model that states that incision I = KAmSn is simply a function of S, the local channel gradient, and A, drainage area above that point and K incapsulates climatic conditions, geometrical and hydraulic characteristics of the stream, bedrock resistance to erosion. Our inversion is constrained by new river-sands 10Be cosmogenic nuclide data, and by incision rates derived from river terraces from the literature. Millennial scale erosion rates and topographic metrics helps us to calibrate the empirical scaling parameters of the stream power incision law. We apply our model to the Atlantic rivers draining NW Iberia where canyons are incised in low-relief erosional surfaces that developed in the last 100 Ma. We show that the transient topography is compatible with a regional late Cenozoic uplift of several hundreds of meters, most likely in response to a mantle-related continental-scale uplift.

Cosmic ray exposure (CRE) ages provide information about the parent bodies and source regions of meteorite classes. Cosmogenic noble gases are often used to quantify exposure time scales ranging from tens of ka to hundreds of Ma. The production rate of cosmogenic noble gases is primarily controlled by a meteorite's chemical composition. Historically, an average chemical composition for an entire meteorite class or subgroup was used to calculate production rates. At the scale needed for noble gas measurements, however, some meteorites exhibit mineral abundance variabilities that translate into chemical heterogeneities, necessitating subsample-specific production rates. We find that the metal and sulfide content can vary significantly between similar to 100 and 300 mg subsamples of the same enstatite (E) chondrite, leading to >10% differences in cosmogenic Ne-21 production rates between subsamples. We demonstrate an approach to determining subsample-specific production rates using E chondrites. We use electron microprobe analysis and X-ray computed microtomography to quantify the chemical composition and abundances, respectively, of metal, sulfide, and silicate minerals in six E chondrites and calculate subsample-specific production rates of He-3 and Ne-21. By applying this method to more E chondrite subsamples alongside noble gas measurements, we may begin to address broader questions, such as whether peaks in the E chondrite CRE age distribution can be attributed to distinct impact events.

Deep exposures of soil profiles on Miocene or Mio-Pliocene alluvial deposits were studied along a 500 km N-S transect in the Atacama Desert. These ancient deposits, with excellent surface preservation, now stand many meters above a broad incised PlioPleistocene alluvial terrain. Total geochemical analyses and mass balance calculations allowed the establishment of elemental gains, losses, and redistribution in the soils. From north to south (presently hyperarid to arid), the ancient soils reveal an increase in losses of rock-forming elements (Si, Al, Fe, K, Mg). Additionally, rare earth elements (REE) show losses with increasing southerly latitude and systematic patterns with soil depth. Some REEs appear to be unique chemical tracers of exogenous dust and aerosol additions to the soils. The removal of major elements and REEs is impossible in the present climate (one of salt and dust accumulation), revealing that for a significant period following the deposition of the alluvium, soils were exposed to rainfall, chemical weathering, and mass loss-with a geographical pattern that mirrors the present rainfall gradient in the region. Following the cessation of weathering, the pre-weathered soils have undergone enormous dust and salt accumulations, with the rates and types of salt accumulation consistent with latitude: (1) carbonate in the south and (2) sulfate, chlorides, and nitrates to the north. The quantity, and apparent rates, of salt accumulation have a strong latitudinal trend. Isotopes of sulfate have predictable depth patterns based on isotope fractionation via vertical reaction and transport. The relict hyperarid soils are geochemically similar to buried Miocene soils (ca. 10-9 Ma) in the region, but they differ from older Miocene soils, which formed in more humid conditions. The overall soil record for the Atacama Desert appears to be the product of changes in Pacific Ocean sea surface temperatures over time, and resulting changes in rainfall. The mid-Miocene was relatively humid based on buried soil chemistry and evidence of fluvial activity. The mid to late Miocene cooling (ca. 10-5.5 Ma) appears to have aridified the region based on paleosol soil chemistry. Pliocene to earliest Pleistocene conditions caused weathering of the relict soils examined here, and regional fluvial activity. Since the earliest Pleistocene, the region has largely experienced the accumulation of salts and, except for smaller scale oscillations (glacial-interglacial), has experienced protracted hyperaridity.

The Aguas Zarcas (Costa Rica) CM2 carbonaceous chondrite fell during nighttime in April 2019. Security and dashboard camera videos of the meteor were analyzed to provide a trajectory, light curve, and orbit of the meteoroid. The trajectory was near vertical, 81° steep, arriving from an ~109° (WNW) direction with an apparent entry speed of 14.6 ± 0.6 km s −1 . The meteoroid penetrated to ~25 km altitude (5 MPa dynamic pressure), where the surviving mass shattered, producing a flare that was detected by the Geostationary Lightning Mappers on GOES‐16 and GOES‐17. The cosmogenic radionuclides were analyzed in three recovered meteorites by either gamma‐ray spectroscopy or accelerator mass spectrometry (AMS), while noble gas concentrations and isotopic compositions were measured in the same fragment that was analyzed by AMS. From this, the pre‐atmospheric size of the meteoroid and its cosmic ray exposure age were determined. The studied samples came from a few cm up to 30 cm deep in an object with an original diameter of ~60 cm that was ejected from its parent body 2.0 ± 0.2 Ma ago. The ejected material had an argon retention age of 2.9 Ga. The object was delivered most likely by the 3:1 or 5:2 mean motion resonances and, without subsequent fragmentation, approached the Earth from a low i < 2.8° inclined orbit with a perihelion distance q = 0.98 AU close to the Earth's orbit. The steep entry trajectory and high strength resulted in deep penetration in the atmosphere and a relatively large fraction of surviving mass.

We reevaluated pairing relationships among 56 Antarctic howardites, eucrites, and diogenites (HED) from the Miller Range ice fields (MIL) based on new measurements of cosmogenic radionuclides and bulk composition of 28 HED samples and one HED‐related dunite. These measurements were combined with petrographic examinations and find locations of the majority of the HED samples at MIL. During these studies, we reclassified 1 howardite, MIL 07665, as a brecciated diogenite and eight howardites as brecciated eucrites. We conclude that 18 of the 23 diogenites belong to a single large pairing group of brecciated diogenites. This pairing group includes at least seven samples with bulk compositions that indicate they contain 10%–25% of eucritic material, so technically the meteorites of this pairing group cross the boundary between diogenites and howardites. We also identified several smaller pairing groups (of 2–5 members each) among the eucrites and two paired samples among the howardites. The pairing relationships among the Miller Range eucrites are not fully resolved yet, as the collection contains many small specimens (<10 g) that were not included in this study. Altogether, we conclude that the 56 HED meteorites at Miller Range represent between 19 and 26 individual falls.

We describe and analyze the glacial geomorphology and new 10Be cosmogenic surface exposure ages from moraines deposited before Marine Isotope Stage (MIS) 2 around Nevado de Cha & ntilde;i (24 degrees 4 ' S, 65 degrees 45 ' W), a north-south-trending massif located in the arid subtropical mountains of northwestern Argentina. We combine these data with previously published ages in order to establish a glacier chronology around the massif and the central Andes. The results show at least three phases of glacier expansions occurred before the global Last Glacial Maximum, (i) during MIS 6, (ii) close to the transition from MIS 4 to MIS 3, and (iii) during mid-late MIS 3. Based on a comparison of the timing of glacier advances with other glacial and paleoclimatic proxies elsewhere, we infer that glaciers grew in this arid region of the subtropical Andes during periods of reduced temperatures and wetter conditions, ultimately due to intensification of the South American Summer Monsoon. In contrast, during MIS 5 no glacial activity was recorded around the massif, and we infer that even if wetter conditions prevailed in the region the temperature was not sufficiently low to support glaciations.

The “light mantle” deposit at the base of South Massif in the Moon's Taurus‐Littrow Valley was a primary science target for the Apollo 17 exploration. The possibility that it was a landslide triggered by ejecta from Tycho Crater is critical for establishing the age of Tycho and constraining recent lunar impact chronology; however, the mechanism of emplacement of the deposit has recently been questioned. The newly opened 73001/73002 double drive tube from Station 3 sampled 70.6 cm deep into the regolith and represents the first stratigraphic section of an extraterrestrial landslide deposit returned to Earth. Here we provide an overview of the stratigraphy of the 73001/73002 core based on top to bottom variations revealed by coordinated laboratory analyses and explore constraints on the emplacement of the light mantle deposit. Briefly, the upper ∼10 cm of 73002 contains a disturbed zone from space weathering and emplacement of ejecta from a nearby crater that excavated and ejected basaltic material. Below 10 cm is a nearly uniform unit of immature regolith. These data support a single event for the emplacement of the deposit at this location, followed by weathering and mixing of materials from nearby crater ejecta in the upper 10 cm. Slight variations in chemistry and clast components may reflect the relative stratigraphy of the South Massif slope, with material toward the bottom of 73001 originating from lower slopes and material from higher up in the core representing regolith from higher up the South Massif slopes.

Abstract. Since the 1990s, analysis of cosmogenic nuclides, primarily 10Be, in quartz-bearing river sand, has allowed for quantitative determination of erosion rates at a basin scale. Paired measurements of in situ cosmogenic 26Al and 10Be in sediment are less common but offers insight into the history of riverine sediment moving down slopes and through drainage basins. Prolonged sediment burial (>105 years), a violation of assumptions underlying erosion rate calculations, is indicated by higher 26Al-based than 10Be-based erosion rates due to preferential loss of shorter-lived 26Al by decay when quartz is shielded from cosmic rays. Here, we use a global compilation of 26Al and 10Be data generated from quartz-bearing fluvial sediment samples (n = 624, including 121 new measurements) and calculate the discordance between erosion rates derived from each nuclide. We test for correlations between such discordance and topographic metrics for drainage basins, allowing us to infer the likelihood of sediment burial during transport in different geomorphic settings. We find that nearly half of samples (n = 276) exhibit discordance (> 1σ uncertainty) between erosion rates derived from 10Be and 26Al, indicating sediment histories that must include extended burial during residence on hillslopes and/or in the fluvial system after or during initial near-surface exposure. Physical basin parameters such as basin area, slope, and tectonic activity exhibit significant correlation with erosion rate discordance whereas climatic parameters have little correlation. Our analysis suggests that 26Al/10Be erosion rate discordance occurs more regularly in basins larger than 1,000 km2, particularly when such basins have low average slopes and are in tectonically quiescent terrains. Sediment sourced from smaller, steeper basins in tectonically active regions is more likely to have similar 10Be and 26Al erosion rates indicative of limited storage and limited burial during residence in the hillslope and fluvial sediment system. The data and analysis we present demonstrate that paired 26Al and 10Be analyses in detrital fluvial samples can provide a window into watershed processes, elucidating landscape behavior at different spatial scales and allowing a deeper understanding of both sediment routing systems and whether erosion rate assumptions are violated. Large lowland basins are more likely to transport detrital sediment that has experienced prolonged sediment storage and burial either on hillslopes and/or in fluvial networks; thus, erosion rates from such basins are lower limits due to nuclide decay during storage. Conversely, samples from smaller upland basins are more likely to provide reliable erosion rates.

Reconstructions of palaeoseismicity are useful for understanding and mitigating seismic hazard risks. We apply cosmogenic 36Cl exposure-age dating and measurements of rare-earth elements and yttrium (REE-Y) concentrations to the palaeoseismic history of the Sparta Fault, Greece. Bayesian-inference Markov chain Monte Carlo (MCMC) modelling of 36Cl concentrations along a 7.2 m long vertical profile on the Sparta Fault scarp at Anogia indicate an increase in the average slip rate of the scarp from 0.8-0.9 mm yr-1 6.5-7.7 kyr ago to 1.1-1.2 mm yr-1 up to the devastating 464 BCE earthquake. The average exhumation of the entire scarp up to the present day is 0.7-0.8 mm yr-1. Modelling does not indicate additional exhumation of the Sparta Fault after 464 BCE. The Sparta Fault scarp is composed of fault breccia, containing quartz and clay-lined pores, in addition to host-rock-derived clasts of calcite and microcrystalline calcite cement. The impurities control the distribution of REE-Y in the fault scarp surface and contribute spatial variation to 36Cl concentrations, which precludes the identification of individual earthquakes that have exhumed the Sparta Fault scarp from either of these data sets. REE-Y may illustrate processes that localize slip to a discrete fault plane in the Earth's near-surface, but their potential use in palaeoseismicity would benefit from further evaluation.

This study investigates the expected cosmic-ray exposure (CRE) of meteorites if they were to be ejected by a near-Earth object, that is, from an object already transferred to an Earth-crossing orbit by an orbital resonance. Specifically, we examine the CRE ages of CI and CM carbonaceous chondrites (CCs), which have some of the shortest measured CRE ages of any meteorite type. A steady-state near-Earth carbonaceous meteoroid probability density function is estimated based on the low-albedo near-Earth asteroid population, including parameters such as the near-Earth dynamic lifetime, the impact probability with the Earth, and the orbital parameters. This model was then compared to the orbits and CRE ages of the five CC falls with precisely measured orbits: Tagish Lake, Maribo, Sutter's Mill, Flensburg, and Winchcombe. The study examined two meteoroid ejection scenarios for CI/CM meteoroids: Main Belt collisions and ejections in near-Earth space. The results indicated that applying a maximum physical lifetime in near-Earth space of 2-10 Myr to meteoroids and eliminating events evolving onto orbits entirely detached from the Main Belt (Q < 1.78 au) significantly improved the agreement with the observed orbits of carbonaceous falls. Additionally, the CRE ages of three of the five carbonaceous falls have measured CRE ages one to three orders of magnitude shorter than expected for an object originating from the Main Belt with the corresponding semi-major axis value. This discrepancy between the expected CRE ages from the model and the measured ages of three of the carbonaceous falls indicates that some CI/CM meteoroids are being ejected in near-Earth space. This study proposes a nuanced hypothesis involving meteoroid impacts and tidal disruptions as significant contributors to the ejection and subsequent CRE age accumulation of CI/CM chondrites in near-Earth space.

The persistence and size of the Greenland Ice Sheet (GrIS) through the Pleistocene is uncertain. This is important because reconstructing changes in the GrIS determines its contribution to sea level rise during prior warm climate periods and informs future projections. To understand better the history of Greenland’s ice, we analyzed glacial till collected in 1993 from below 3 km of ice at Summit, Greenland. The till contains plant fragments, wood, insect parts, fungi, and cosmogenic nuclides showing that the bed of the GrIS at Summit is a long-lived, stable land surface preserving a record of deposition, exposure, and interglacial ecosystems. Knowing that central Greenland was tundra-covered during the Pleistocene informs the understanding of Arctic biosphere response to deglaciation.

Northwest Africa (NWA) 12384 is a lunar polymict breccia composed almost entirely of basaltic components. The clast content includes low- to very-low-Ti volcanic picritic glass, basaltic vitrophyre, and crystalline pigeonite basalt-an assemblage of volcanic materials that can be tested for petrogenetic relationships. We present the inferred history of select mare components of NWA 12384 as suggested by texture, mineralogy, and petrography, and compare them to Apollo samples and other lunar meteorites. In addition, we used the volcanic glasses in the breccia as a primary composition for crystallization modeling and comparison to the lithic clast compositions. We find that the mafic clasts in NWA 12384 cannot be derived from the picritic glass through a common liquid line of descent because of higher Ti content, though they may have crystallized from a separate, common liquid line of descent. These clasts could represent local source-region heterogeneity or differential assimilation of more Ti-rich material. Pb-Pb SIMS analyses of a large basalt clast in NWA 12384 reveal an age of 3044 +/- 41 Ma (2 sigma), which is used together with the chemical data and 4 pi cosmic ray exposure age of less than 20 kyr and terrestrial age of between 3.1 and 17.3 kyr to constrain the possible locations of provenance for this meteorite.

The US Antarctic Search for Meteorites (ANSMET) discovered a dense cluster of 88 ordinary chondrites with a total mass of more than 100 kg on a blue ice area (BIA) of 1.6 x 0.3 km(2) near the Otway Massif, Grosvenor Mountains, Antarctica. The larger masses (weighing up to 29 kg) were found at one end of an oval-shaped pattern and the smaller masses (50-200 g) at the other end. We measured concentrations of the cosmogenic radionuclides Be-10 (half-life-1.36 x 10(6) year) and Cl-36 (3.01 x 10(5) year) in the metal fraction of 17 H chondrites, including 14 fragments of this cluster, to verify the hypothesis that this meteorite cluster on the Otway Massif BIA represents a meteorite strewn field produced by the atmospheric breakup of a single meteoroid. The Be-10 and Cl-36 concentrations confirm that 10 out of 14 H chondrites from different locations within this small area are paired fragments of the same meteorite fall, while the four other H chondrites represent two additional-smaller-falls. The radionuclides suggest a pre-atmospheric mass of 200-400 kg for the large pairing group, suggesting that 25%-50% of the meteoroid survived atmospheric entry. Based on the distribution of the paired H chondrites and evidence of their common cosmic-ray exposure history in space, we conclude that most of the 88 meteorites within this small area represent a meteorite strewn field. The small size of the strewn field suggests that the meteoroid entered at a steep angle (>60 degrees), while the low amount of fusion crust on most meteorite surfaces most likely indicates atmospheric break up at low altitude, while additional fragmentation of a large surviving fragment may have occurred during impact on the ice. This well-documented strewn field provides a good opportunity to apply model simulations of the atmospheric fragmentation of this object as a function of entry angle, velocity, and meteoroid strength. Cosmogenic C-14 analyses in two members of the Otway Massif pairing group yield a terrestrial age of 15.5 +/- 1.5 kyr, which represents the time elapsed since this meteorite fell on Earth. The excellent preservation of an Antarctic meteorite strewn field suggests that the Otway Massif BIA represents a relatively stagnant blue ice field.

Since the impact ∼50,000 yr ago, surface runoff has entrained and transported sediment from the walls to the floor of Meteor Crater (Arizona, USA). Previous work interpreted this erosion and deposition to be due to predominantly fluvial (i.e., dilute water transport) processes. However, light detection and ranging (LiDAR)−derived topographic data and field observations indicate that debris flows dominated, which were likely generated by runoff that entrained the talus that borders bedrock cliffs high on the crater walls. The low gradient of the crater floor caused debris flows to stop, leaving lobate deposits, while fluvial processes delivered sediment toward the center of the crater. Cosmogenic radionuclide dating of levee deposits suggests that debris-flow activity ceased in the late Pleistocene, synchronous with regional drying. Assuming a rock-to-water ratio of 0.3 at the time of transport by mass flows, it would have taken ∼2 × 106 m3 of water to transport the estimated ∼6.8 × 106 m3 of debris-flow deposits found at the surface of the crater floor. This extensive erosion would require ∼6 m of total runoff over the 0.35 km2 upslope source area of the crater, or ∼18 mm of runoff per debris-flow event. Much more runoff did occur, as evidenced by crater lake deposits, Holocene fluvial activity (which produced little erosion), and contemporary rainfall rates. Rarely on Earth is the total amount of water that creates and runs through a landscape estimated, yet such calculations are commonly done on Mars. Our analysis suggests that erosional and depositional landforms may record only a small fraction of the total runoff.