Cosmogenic 10Be Research Articles

Disentangling magnetic and environmental signatures of sedimentary 10Be/9Be records

Reconstructions of the global production rate of the cosmogenic isotope 10Be from sedimentary records of authigenic 10Be/9Be ratios have been successfully used to obtain independent estimates of geomagnetic dipole moment variations caused by field excursions or reversals. In this study, we assess the reliability of 10Be/9Be as a proxy for the cosmogenic 10Be production rate by evaluating two potential biasing sources represented by sediment composition and climatic modulation. For this purpose, we compare five high-resolution 10Be/9Be records of the Matuyama-Brunhes (M-B) field reversal from sediment cores of the Indian, West Pacific, and North Atlantic oceans. Significant increase of 10Be/9Be ratios at ∼774 ka is explained in terms of the dominant control of geomagnetic modulation during the M-B reversal. Results do not support the existence of a direct proportionality between measured sedimentary 10Be/9Be ratio and cosmogenic 10Be production rate, as shown by 10Be/9Be records that offset relative to each other during and outside the M-B reversal.Residual differences between offset-corrected rescaled records do not appear to be related to an incomplete correction of variable sediment scavenging efficiencies by 9Be normalization. Instead, these differences can be explained by a common climatic modulation model, assuming a linear relation between 10Be/9Be and the global 10Be production rate with site- and time-dependent additive and multiplicative coefficients. These coefficients are linear functions of a single global climate proxy identified with the benthic δ18O record. Additive coefficients are almost constant in time and can represent up to ∼60% of the average 10Be/9Be value during periods of stable field polarity. Multiplicative coefficients are also site-specific, with mean values representing the bulk scavenging efficiency of the site, and variations about this mean expressing a multiplicative climatic modulation of the 10Be production rate. The amplitude of this modulation amounts to 10–15% of the maximum variations recorded during the M-B reversal and is sufficiently large to mask minor variations of the dipole moment during stable polarity periods. Reconstructions of the geomagnetic dipole intensity can benefit from the information about climatic modulation effects gained with our modelling approach. Best suited sites for magnetic field reconstructions should be characterized by minimal Be-recycling contributions from ancient 10Be reservoirs and minimal climatic modulation, as far as it can be determined from relative comparisons with other records. These conditions are most likely encountered in open basins at sites (1) with < 2.8 km water depth, (2) > 200 km offshore, and (3) located underneath a large current system extending over regions with minimum terrigenous inputs. Scaling all records with respect to a chosen reference enables to produce 10Be/9Be stacks with reduced noise and short-term local environmental effects. Differences between stacks obtained in this manner highlight global climatic effects that need to be considered when generating calibrated reconstructions of the geomagnetic dipole moment.

Quaternary landscape evolution in a tectonically active rift basin (paleo-lake Mweru, south-central Africa)

Located between the Northern Province of Zambia and the southeastern Katanga Province of the Democratic Republic of Congo, Lakes Mweru and Mweru Wantipa are part of the southwest extension of the East African Rift System (EARS). Fault analysis reveals that, since the Miocene, movements along the active Mweru-Mweru Wantipa Fault System (MMFS) have been largely responsible for the reorganization of the landscape and the drainage patterns across the western branch of the EARS. To investigate the spatial and temporal patterns of fluvial-lacustrine landscape development, we determined in-situ cosmogenic 10Be and 26Al using Accelerator Mass Spectrometry. A total of twenty-six quartzitic bedrock samples were collected from knickpoints across the Mporokoso Plateau (south of Lake Mweru) and the eastern part of the Kundelungu Plateau (north of Lake Mweru). Samples from the Mporokoso Plateau and close to the MMFS provide evidence of temporary burial. By contrast, surfaces located far from the MMFS appear to have remained uncovered since their initial exposure as they show consistent 10Be and 26Al exposure ages ranging up to ~830 ka. Reconciliation of the observed burial patterns with morphotectonic and stratigraphic analysis reveals the existence of an extensive paleo-lake during the Pleistocene. Through hypsometric analyses of the dated knickpoints, the potential maximum water level of the paleo-lake is constrained to ~1200 m asl. High denudation rates (up to ~40 mm ka−1) along the eastern Kundelungu Plateau suggest that footwall uplift, resulting from normal faulting, caused rapid river incision, thereby controlling paleo-lake drainage. The complex exposure histories recorded by 10Be and 26Al may be explained because of lake water-level fluctuations caused by active normal faulting along the MMFS coupled with intense climate variations across southeastern Africa.

Initial measurement of beryllium-9 using high-resolution inductively coupled plasma mass spectrometry allows for more precise applications of the beryllium isotope system within the Earth Sciences.

Precise and accurate determination of the ratio of the cosmogenic nuclide 10 Be to the stable isotope 9 Be (10 Be/9 Be) is needed across multiple fields of research within the Earth Sciences. Current techniques used to measure the 9 Be content of geological materials generally require a large amount of sample or solution aliquot and present a large range of analytical precisions. A range of geological reference materials underwent whole-rock dissolution and "strong" (0.04 M NH2 OH.HCl in 25% acetic acid) and "weak" (0.02 M NH2 OH.HCl in 10% acetic acid) leaching to represent a range of potential applications within the geosciences. After treatment, the 9 Be and major element (Na, Ca, Mg, Fe, Mn, Al and Ti) content of sample solutions were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) using a Thermo® ELEMENT XR instrument. The 9 Be concentration of whole-rock and leaching solutions displayed a wide range of values within each geological reference material, generally following a uniform relationship implying a potential kinetic control on NH2 OH leaching, as suggested by major element profiles. A precision of 0.1 to 1.4% is achieved independent of sample size or leaching strength. Initial results suggest that the use of HR-ICP-MS improves the precision of 9 Be analysis for a range of geological reference materials. A high precision is maintained despite reducing the sample size or strength of leaching solution. This has implications for the use of the Be isotope system within the Earth Sciences by reducing the propagated uncertainty of 10 Be/9 Be ratios or the mass of sample or 9 Be aliquot used.

Rockwall Slope Erosion in the Northwestern Himalaya

AbstractRockwall slope erosion is an important component of alpine landscape evolution, yet the role of climate and tectonics in driving this erosion remains unclear. We define the distribution and magnitude of periglacial rockwall slope erosion across 12 catchments in Himachal Pradesh and Jammu and Kashmir in the Himalaya of northern India using cosmogenic 10Be concentrations in sediment from medial moraines. Beryllium‐10 concentrations range from 0.5 ± 0.04 × 104 to 260.0 ± 12.5 × 104 at/g SiO2, which yield erosion rates between 7.6 ± 1.0 and 0.02 ± 0.004 mm/a. Between ∼0.02 and ∼8 m of rockwall slope erosion would be possible in this setting across a single millennium, and &gt;2 km when extrapolated for the Quaternary period. This erosion affects catchment sediment flux and glacier dynamics, and helps to establish the pace of topographic change at the headwaters of catchments. We combine rockwall erosion records from the Himalaya of Himachal Pradesh, Jammu and Kashmir, and Uttarakhand in India and Baltistan in Pakistan to create a regional erosion data set. Rockwall slope erosion rates progressively decrease with distance north from the Main Central Thrust and into the interior of the orogen. The distribution and magnitude of this erosion is most closely associated with records of Himalayan denudation and rock uplift, where the highest rates of change are recorded in the Greater Himalaya sequences. This suggests that tectonically driven uplift, rather than climate, is a first order control on patterns of rockwall slope erosion in the northwestern Himalaya. Precipitation and temperature would therefore come as secondary controls.

Transformation of high-relief canyon topography by an ancient rock avalanche, Hop Valley, Zion National Park, Utah, USA

Zion National Park preserves a rich geological record of Holocene landslide-dammed canyons in its deeply incised topography, with 11 hypothesized valley-blocking deposits within the park boundaries. Despite consistent stratigraphic, tectonic, and climatic settings, the occurrence of and subsequent landscape response to these natural dams varies. As such, the region provides a unique natural laboratory for quantifying the effect and evolution of landslide dams in high-relief canyon topography. Here we present a detailed study of a rock avalanche deposited at the mouth of Hop Valley in Zion National Park, describing its age, size, emplacement conditions, impact on local geomorphology and sedimentology, as well as the subsequent usage of the valley by native Ancestral Puebloans. Topographic reconstructions indicate the original deposit was ~75 million m3 and 1.5 km long with a maximum thickness of 180 m. New ages from cosmogenic 10Be surface exposure dating indicate a single-event failure at 6.7 ± 0.7 ka. The rock avalanche impounded ~55 million m3 of sediment, transforming Hop Valley from a relatively narrow gorge to a broad flat-floored canyon. Stratigraphic sections of accumulated upvalley sediments, calculated sedimentation rates (averaging 8.2 ± 0.8 m/ky), and paleoclimate records suggest the deposit primarily dammed sediment, rather than water, to produce an extensive alluvial plain. This detailed case-history analysis, together with our review of other Holocene landslide dams in Zion National Park, helps clarify the legacy of valley-blocking mass movements in steep canyon topography.

Geomorphic constraints on the development of a blind-thrust induced landform, south-central Mongolia: Insights into foreberg growth

Forebergs are landforms characterized by low, elongated ridges or hills rising above the surrounding alluvial fans or floodplains, and are typically formed by folding associated with thrust faulting. Forebergs in the Gobi-Altay range, south-central Mongolia, have developed in the forelands of mountains transpressionally uplifted in restraining bends along the E–W-trending sinistral strike-slip Bogd fault. Along the easternmost part of the Bogd fault, six forebergs have formed in the foreland of the Artz Bogd restraining-bend. We surveyed one of these forebergs to ascertain the fault geometry associated with its formation and understand how it has developed over time. This foreberg is ~6 km long and ~1 km wide and rises about 40 m above the low-lying floodplain. We also constrained its evolution using cosmogenic 10Be denudation rates measured from individual catchments along the foreberg, and morphometric analyses using a high-resolution DEM generated from images captured by an unmanned aerial vehicle. We suggest that the foreberg evolved via fault-propagation folding, developing an asymmetric across-foreberg topographic profile. This asymmetry results in differences in 10Be catchment-wide denudation rates and geomorphic metrics between its northern and southern slopes, causing migration of the drainage divide of the growing foreberg to adjust to the tectonic regime. By analyzing the along-foreberg variation in denudation rates and geomorphic metrics, we infer that the foreberg formed via lateral growth and linking of four discrete segments. Our study illuminates the formation of a unique landform and sheds light on how a structure enlarges both vertically and laterally during the early stage of thrust-related fold developments.

Which is the best 9Be carrier for 10Be/9Be accelerator mass spectrometry?

Commercial 9Be solutions used for chemical preparation of samples for accelerator mass spectrometry contain the cosmogenic long-lived radionuclide 10Be at elevated but different 10Be/9Be levels. Within a systematic study of recently produced solutions, comparison to published data and new data on customised solutions from minerals, we recommend - if no customised solution is available - the 9Be solutions from Australian Chemical Reagents (ACR) or from LGC. They contain 10Be/9Be at the 3.4 × 10−15 level, which is still suitable for the majority of Earth science applications, compared to customised solutions at the 10−16 level for lowest-level studies. Commercial solutions from Scharlab having different lot numbers, i.e. an identification number assigned to a particular lot of material from a single manufacturer, vary in 10Be/9Be by up to a factor of nine. Hence, it seems an advisable strategy to buy a bigger quantity of a single production batch (such as 10 × 100 ml bottles of 9Be at 1 g l−1) and have them tested once at any AMS facility before first use.•The best 9Be carrier for low-level 10Be/9Be applications is a customised one from minerals like phenakite.•The best 9Be carriers for medium- and high-level 10Be/9Be applications are currently from Australian Chemical Reagents (ACR) or from LGC.•As 9Be carriers from Scharlab of different batches (LOT) contain 10Be/9Be at different levels, it is advisable to buy a bigger number of bottles of the same LOT of commercial carriers after being identified to have reasonably low isotope ratios.

Nonlinear forcing of climate on mountain denudation during glaciations

Denudation is one of the main processes that shapes landscapes. Because temperature, precipitation and glacial extents are key factors involved in denudation, climatic fluctuations are thought to exert a strong control on this parameter over geological timescales. However, the direct impacts of climatic variations on denudation remain controversial, particularly those involving the Quaternary glacial cycles in mountain environments. Here we measure in situ cosmogenic 10Be concentration in quartz in marine turbidites of two high-resolution cores collected in the Mediterranean Sea, providing a near-continuous (temporal resolution of ~1–2 kyr) reconstruction of denudation in the Southern Alps since 75 kyr ago (ka). This high-resolution palaeo-denudation record can be compared with well-constrained climatic variations over the last glacial cycle. Our results indicate that total denudation rates were approximately two times higher than present during the Last Glacial Maximum (26.5–19 ka), the glacial component of the denudation rates being \(1.5_{ - 1.0}^{ + 0.9}\) mm yr−1. However, during moderately glaciated times (74–29 ka), denudation rates were similar to those today (0.24 ± 0.04 mm yr−1). This suggests a nonlinear forcing of climate on denudation, mainly controlled by the interplay between glacier velocity and basin topography. Hence, the onset of Quaternary glaciations, 2.6 million years ago, did not necessarily induce a synchronous global denudation pulse.

Coastal chalk cliff retreat rates during the Holocene, inferred from submarine platform morphology and cosmogenic exposure along the Normandy coast (NW France)

Submerged marine terraces potentially provide crucial information on past sea-level variations and paleo-coastline locations that may be used to estimate long-term coastal erosion rates. The Normandy coastline has recently been surveyed using a shallow water high-resolution mapping system. We identified a new continuous submarine platform, called the inner platform, limited by a shore parallel edge located between -9 m and -10 m (NGF) along the Normandy chalk coastline. A lower rock platform, called the outer platform, ranging from about -14 m to -17 m (NGF) appears locally. This corresponds to inherited preserved submarine terraces created during a past sea level highstand. The high cosmogenic 10Be concentration measured at the end of Mesnil-Val inner shore platform (including intertidal and subtidal shore platforms) is attributed to the last glacial cliff location at 6.5 ky ± 1 ky. From the spatial edge location of the inner platform in Normandy, we estimated cliff retreat rates since 6.5 ky ± 1 ky ranging from 0.051 ± 0.008 m/y to 0.090 ± 0.014 m/y from place to place. Comparisons with the current coastal chalk cliffs indicate a mean retreat rate estimated over the contemporary period suggesting such long-term retreat rates are 33% to 57% lower than the contemporary ones (0.10 m/y to 0.18 m/y). This confirms a contemporary acceleration of chalk cliff system retreat rates.

Quantifying rates of Quaternary landscape evolution in Grand Teton National Park using in situ cosmogenic 10Be, 14C, and 36Cl dating

In Grand Teton National Park (GTNP), both glacial and tectonic activity have played major roles in shaping the landscape. Here, we evaluate the impacts of late Quaternary Teton Fault slip and subglacial erosion in GTNP. We are in the process of using 10Be surface exposure dating to generate records of time-integrated Teton Fault slip at multiple locations throughout GTNP, which will allow us to assess spatial and temporal patterns tectonic activity over the past ~15 ka. We are also working to determine rates of subglacial erosion through 10Be-14C-36Cl triple isotope dating. The results obtained through this novel combination of cosmogenic nuclide techniques will contribute toward a unified view of landscape evolution in alpine environments. Featured photo by Bonnie Robinson, taken from the AMK Ranch photo collection.

Reconstruction of Heliospheric Modulation Potential Based on Data on the Content of the Cosmogenic Isotope 10Be in Greenland Ice and the Extremes of Solar Activity from the End of the 14th Century

The heliospheric modulation potential was reconstructed based on data from the North Greenland Ice Core Project (NGRIP) on the content of the cosmogenic isotope 10Be in the Greenland ice from the end of the 14th century CE. This time interval includes global solar-activity minima, such as the Sporer (≈1460–1550 CE), Maunder (≈1645–1715 CE), and Dalton (≈1790–1830 CE) minima. The reconstruction results show that, although the duration of the Dalton minimum is small, the depth of the Maunder minimum could be comparable to the depth of the Dalton minimum. The Sporer minimum may be less deep than the Maunder minimum.

Solar activity reconstructed on the basis of radiocarbon data and climate change from 17000 to 5000 BC

The data on the content of cosmogenic isotopes 14C and 10Be in the Earth’s atmosphere at a time interval of 15000-5000 BC were analyzed. On Earth at this time there was a transition from the ice age to the Holocene. The reconstruction of Wolf numbers based on radiocarbon data is presented, which describes solar activity and takes into account changes in the Earth’s climate during the period under consideration. The increase in global temperature during the transition to the Holocene was accompanied by a sequence of warming (for example, Meiendorf warming) and cooling. The obtained reconstruction of Wolf numbers indicates that at separate time intervals: 13600-13000, 9300-9000, 8300-8000 BC the Sun was in a state of deep minima of activity. We also note the activity minima at ≈ 10700 and 7500 BC. The periods of extremely high activity of the Sun were also distinguished, so at maxima ≈ 12350 and 6715 BC. Values of Wolf numbers could exceed 200. The duration of the first of these periods was several hundred years, and at that time Meiendorf warming took place on Earth (≈12500-11850 BC). The question arises: are these events related?

Lagged atmospheric circulation response in the Black Sea region to Greenland Interstadial 10

Northern Hemispheric high-latitude climate variations during the last glacial are expected to propagate globally in a complex way. Investigating the evolution of these variations requires a precise synchronization of the considered environmental archives. Aligning the globally common production rate variations of the cosmogenic radionuclide 10Be in different archives provides a tool for such synchronizations. Here, we present a 10Be record at <40-y resolution along with subdecadal proxy records from one Black Sea sediment core around Greenland Interstadial 10 (GI-10) ∼41 ka BP and the Laschamp geomagnetic excursion. We synchronized our 10Be record to that from Greenland ice cores based on its globally common production rate variations. The synchronized environmental proxy records reveal a bipartite climate response in the Black Sea region at the onset of GI-10. First, in phase with Greenland warming, reduced sedimentary coastal ice rafted detritus contents indicate less severe winters. Second, and with a lag of 190 (± 44) y, an increase in the detrital K/Ti ratio and authigenic Ca precipitation point to enhanced regional precipitation and warmer lake surface temperatures. We explain the lagged climatic response by a shift in the dominant mode of atmospheric circulation, likely connected with a time-transgressive adjustment of the regional thermal ocean interior to interstadial conditions.

The fall, recovery, classification, and initial characterization of the Hamburg, Michigan H4 chondrite.

The Hamburg meteorite fell on January 16, 2018, near Hamburg, Michigan, after a fireball event widely observed in the U.S. Midwest and in Ontario, Canada. Several fragments fell onto frozen surfaces of lakes and, thanks to weather radar data, were recovered days after the fall. The studied rock fragments show no or little signs of terrestrial weathering. Here, we present the initial results from an international consortium study to describe the fall, characterize the meteorite, and probe the collision history of Hamburg. About 1 kg of recovered meteorites was initially reported. Petrology, mineral chemistry, trace element and organic chemistry, and O and Cr isotopic compositions are characteristic of H4 chondrites. Cosmic ray exposure ages based on cosmogenic 3He, 21Ne, and 38Ar are ~12 Ma, and roughly agree with each other. Noble gas data as well as the cosmogenic 10Be concentration point to a small 40–60 cm diameter meteoroid. An 40Ar‐39Ar age of 4532 ± 24 Ma indicates no major impact event occurring later in its evolutionary history, consistent with data of other H4 chondrites. Microanalyses of phosphates with LA‐ICPMS give an average Pb‐Pb age of 4549 ± 36 Ma. This is in good agreement with the average SIMS Pb‐Pb phosphate age of 4535.3 ± 9.5 Ma and U‐Pb Concordia age of 4535 ± 10 Ma. The weighted average age of 4541.6 ± 9.5 Ma reflects the metamorphic phosphate crystallization age after parent body formation in the early solar system.

Earthquake Hazard Uncertainties Improved Using Precariously Balanced Rocks

AbstractProbabilistic seismic hazard analysis (PSHA) is the state‐of‐the‐art method to estimate ground motions exceeded by large, infrequent, and potentially damaging earthquakes; however, a fundamental problem is the lack of an accepted method for both quantitatively validating and refining the hazard estimates using empirical geological data. In this study, to reduce uncertainties in such hazard estimates, we present a new method that uses empirical data from precariously balanced rocks (PBRs) in coastal Central California. We calculate the probability of toppling of each PBR at defined ground‐motion levels and determine the age at which the PBRs obtained their current fragile geometries using a novel implementation of cosmogenic 10Be exposure dating. By eliminating the PSHA estimates inconsistent with at least a 5% probability of PBR survival, the mean ground‐motion estimate corresponding to the hazard level of 10−4 yr−1 (10,000 yr mean return period) is significantly reduced by 27%, and the range of estimated 5th–95th fractile ground motions is reduced by 49%. Such significant reductions in uncertainties make it possible to more reliably assess the safety and security of critical infrastructure in earthquake‐prone regions worldwide.

The depositional flux of meteoric cosmogenic 10Be from modeling and observation

Meteoric cosmogenic 10Be is a powerful tracer to quantify dates and rates of Earth surface processes over timescales of 103-105 yrs. A prerequisite for its applications is knowledge of the flux at which 10Be, produced in the atmosphere, is delivered to the Earth surface. Four entirely independent approaches are available to quantify this flux: 1) General Circulation Models (GCM) combined with 10Be production functions and aerosol dynamics; 2) 10Be in precipitation collections; 3) 10Be inventories in dated soil profiles; 4) riverine 10Be exported in solid and dissolved forms. We compiled and reprocessed published globally distributed 10Be flux data from each of these methods and compared them with each other after normalization to a common atmospheric production rate. Based on precipitation records, we propose a simple framework to discriminate between two delivery effects on 10Be fluxes. In the additive effect water vapor and 10Be are continuously accumulating during long-distance transport, leading to an increase in 10Be flux with precipitation rate. In the dilution effect, the 10Be flux is delivered from proximal vapor sources, limited by the rate of 10Be introduction from the stratosphere and independent of precipitation rate. Both effects are mostly present in combination, and the relative weight of either effect depends on vapor condensation rate and on the ratio of vapor condensation area to precipitation area. A comparison between precipitation-derived fluxes and GCM-derived fluxes shows that half of the precipitation estimates are >2 times greater than GCM-derived fluxes. By comparison, soil- and GCM-derived fluxes agree within a factor of 2 for more than half (∼57%) of the dataset, and the remaining soil estimates (∼43%) are much lower than GCM-derived fluxes. 71% of 10Be flux estimates from riverine export using 10Be (meteoric)/9Be ratios also agree with GCM-derived fluxes within a factor of 2. We explain the precipitation-derived fluxes that commonly exceed all other estimates by short-term stochasticity in precipitation events that might introduce a measurement time-interval bias towards higher fluxes. This bias is not present over longer-term (103-105 yrs) flux estimates like those from soil profiles. Soil-derived fluxes might still present an underestimation when retention of 10Be in soil is incomplete. We recommend producing more 10Be depositional flux data from soil inventories with full Be retention, as these generate in our view the most relevant estimates for applications of meteoric 10Be on millennial-scale Earth surface processes.

Deglaciation of Pope Glacier implies widespread early Holocene ice sheet thinning in the Amundsen Sea sector of Antarctica

The Amundsen Sea sector of the Antarctic ice sheet presently dominates the contribution from Antarctica to sea level rise. Several large ice streams that currently drain the sector have experienced rapid flow acceleration, grounding line retreat and thinning during the past few decades. However, little is known of their longer-term – millennial-scale – retreat history, despite the reliance of several ice sheet and glacial-isostatic adjustment models on such data for improving sea level prediction from this critical region. This study investigates the timing and extent of surface lowering of one of those ice streams, Pope Glacier, since the Last Glacial Maximum (LGM), using glacial-geological evidence for former ice cover. We present a new deglacial chronology for the glacier, derived from surface exposure dating of glacially-deposited cobbles and ice-scoured bedrock from Mount Murphy and its surrounding peaks. Cosmogenic 10Be exposure ages from 44 erratic cobbles and 5 bedrock samples, and in situ 14C exposure ages from one erratic and 8 bedrock samples are predominantly in the range 5.5-16 ka. Although 10Be inheritance from prior exposure is prevalent in some erratics and probably all bedrock samples, none of the ages pre-date the LGM. From these results we infer that the surface of Pope Glacier lowered by 560 m during the early- to mid-Holocene (9-6 ka), at an average rate of 0.13 ± 0.09/0.04 m yr−1. The lowering coincided with a period of enhanced upwelling of warm Circumpolar Deep Water onto the continental shelf in the region. A reduction in buttressing − facilitated by such upwelling − by an ice shelf that is thought to have spanned the embayment until 10.6 cal kyr BP could have triggered simultaneous early Holocene thinning of Pope Glacier and glaciers elsewhere in the Amundsen Sea Embayment.

Cosmogenic exposure dating reveals limited long-term variability in erosion of a rocky coastline

Predicted sea-level rise and increased storminess are anticipated to lead to increases in coastal erosion. However, assessing if and how rocky coasts will respond to changes in marine conditions is difficult due to current limitations of monitoring and modelling. Here, we measured cosmogenic 10Be concentrations across a sandstone shore platform in North Yorkshire, UK, to model the changes in coastal erosion within the last 7 kyr and for the first time quantify the relative long-term erosive contribution of landward cliff retreat, and down-wearing and stripping of rock from the shore platform. The results suggest that the cliff has been retreating at a steady rate of 4.5 ± 0.63 cm yr−1, whilst maintaining a similar profile form. Our results imply a lack of a direct relationship between relative sea level over centennial to millennial timescales and the erosion response of the coast, highlighting a need to more fully characterise the spatial variability in, and controls on, rocky coast erosion under changing conditions.

Interpretation, age and significance of a relict paraglacial and periglacial boulder-dominated landform assemblage in Alnesdalen, Romsdalsalpane, southern Norway

A boulder-dominated landform assemblage in an alpine setting in Norway is described, interpreted and dated using a combination of Schmidt-hammer exposure-age dating (SHD) and cosmogenic 10Be surface-exposure dating. The origin and formation of these features is determined from their morphology, topographic setting and age. Three main components of the assemblage are recognized. First a ~300 m long and ~160 m wide, tongue-shaped rock-slope failure with a SHD age of 11.49 ± 0.82–12.96 ± 0.86 ka is identified on the basis of its planform, thickness, ‘runout distance’ and association with a fractured backing scarp. This is interpreted as a relict paraglacial landform triggered by deglaciation. Second, a 400-m long unequivocal pronival (protalus) rampart with an SHD age of 6.95 ± 0.97–8.35 ± 1.21 ka is identified on the basis of its narrow ridge form aligned close to the foot of an extensive talus slope. Although formation of the rampart probably commenced with deglaciation, the younger SHD ages indicate formation at a diminishing rate through the Holocene. Third, a ~550 m by ~150 m lobate component with transverse ridges, longitudinal and transverse depressions and enclosed pits, previously identified as a rock glacier, is dated to 11.33 ± 0.83–13.33 ± 0.90 ka with the Schmidt hammer and between 13.3 ± 2.0–14.7 ± 2.0 ka with 10Be. This third component may also be a product of rock-slope failure but attribution to rock-glacier creep associated with either interstitial ice (permafrost) or buried glacier ice during the Allerød Interstadial – Younger Dryas Stadial, and to which one or more rock-slope failures contributed debris, cannot be rejected. The advantages and limitations of compiling such evidence for identifying, differentiating and classifying apparently similar boulder-dominated colluvial landforms are exemplified.

Atmospheric residence times and excess of unsupported 210Po in aerosol samples from the Kuwait bay-northern gulf

The concentration of cosmogenic radionuclide 7Be and the naturally occurring radionuclide 222Rn and its progenies 210Pb, 210Po, and 214Pb were measured in the ground surface air in the urban area of the northern Arabian Gulf close to Kuwait Bay. A high-volume air sampler connected with a five-stage cascade impactor was used to collect approximately 1800 cubic meter weekly for a period of one year. The concentrations of 210Pb and 210Po varied from 0.35 to 1.65 mBq m−3 and from 0.23 to 3.2 mBq m−3, respectively; the 210Po/210Pb activity ratio was close to one. The average concentration of 7Be was 6.24 mBq m−3, ranging from 3 to 10 mBq m−3. The temporal variations of 210Pb, 210Po and 7Be showed maximum concentrations of 210Po and 7Be in occurred summer months. The observed excess of 210Po concentrations can be attributed to the local and long-range transport of suspended dust with 210Pb and 210Po in radioactive equilibrium state, oil industry emissions, local resuspended dust and the sea-salt-aerosols from the Arabian Gulf. The range of the residence time estimation using the 222Rn/210Pb and 214Pb/210Pb activity ratio methods ranged from three to five days. Moreover, the estimated residence time by the application of 7Be from the activity median aerodynamic diameter method was 4.2 days. The method of using the 210Po/210Pb activity ratio was invalid because of the excess 210Po sources of anthropogenic origin. Therefore, extensive accurate diurnal measurements of 214Pb and 222Rn can be applied in hot arid regions for better aerosols residence time estimation.