The reduction of anthropogenic methane emissions is a priority due to its potent global warming potential. Radiocarbon (C-14) can distinguish between methane from natural biogenic and fossil fuel sources, however, the analysis of methane C-14 by conventional accelerator mass spectrometry (AMS) techniques is demanding. At SUERC, a prototype positive ion mass spectrometer (PIMS) is set up to directly analyze C-14 in methane with minimal sample preparation. Methane gas was mixed with a stoichiometric amount of oxygen in an open split and admitted directly into the source. A series of modern, blank and unknown methane samples were clearly distinguishable by their C-14/C-13 raw ratios. The collision cell gas flowrate was then increased to lower the limit of detection. We obtained a corrected C-14/C-13 raw ratio of less than 2 & times; 10(-13) for blank fossil methane which corresponds to a radiocarbon age greater than 50 kyr. Modern biogenic methane had a measured C-14/C-13 raw ratio approaching 1 & times; 10(-10) which is consistent with the nominal value of contemporary atmospheric methane. These first results indicate that PIMS has the potential to be a valuable new analytical technique for screening the C-14 content of biogas and in climate research studies.

A glacial trimline at high elevations in West Antarctica informs on previous warm-based glaciation that occurred during an earlier stage of Antarctic Ice Sheet evolution. A multi-million-year history of theses landscapes has previously been evidenced in a few disparate locations. Here we present new cosmogenic nuclide analyses (Be-10 and Al-26) from a total of 60 samples (clasts and bedrock) at high elevations in several hard-to-access locations across the interior of West Antarctica. In the Sentinel Range of the Ellsworth Mountains this trimline occurs at the highest elevations of any sites in West Antarctica (similar to 3000 m asl). These new data reveal that clasts and bedrock, both above and below the trimline, have long exposure histories with minimum exposure-burial histories of 0.9-2.6 Ma. Accounting for low rates of erosion extends these exposure-burial histories to 2.7-4.8 Ma. Under the assumption of cyclical exposure-burial for proportions of glacial-interglacial cycles we show that some of our samples have exposure-burial histories extending back to the Miocene. We also present new data from the nearby Heritage Range where our new data supports previous work potentially extends the inferred persistence of the location of the West Antarctic ice sheet divide to >2.1 Ma. Finally, we present new data from two isolated nunataks (Mount Woollard and Mount Johns) located deep in the interior of the West Antarctic Ice Sheet near the main ice divide. Paired nuclide analyses of samples from these nunataks also shows long exposure histories and unambiguous evidence of past burial within the last similar to 100 ka. Such a thickening is not currently represented in ice-sheet models.

ABSTRACT Radiocarbon ( 14 C) measurements undertaken by the NERC Radiocarbon Laboratory using accelerator mass spectrometry (AMS) are now freely available on a new online database. The data presented covers measurement of the wide range of sample types that are processed for research projects in the fields of Earth and environmental science, supported by the United Kingdom’s Natural Environment Research Council. Sample types within the database include organic remains, soils, sediments, carbonates, dissolved organic and inorganic carbon, and carbon dioxide. Currently, the database contains 14 C data for over 2400 individual samples that were measured and reported between 2005 and 2013, but it is envisaged that this will expand considerably as more data are made available. Contextual information such as sampling location and associated publications are provided where available, and searches can be performed on sample location, sample type, project number, and publication code. This new database compliments an existing, publicly available database of measurements performed using radiometric methods by the laboratory which has recently been expanded to present over 2000 measurements. It is hoped that this archive will prove useful to workers in the community who would benefit from greater availability of measurements for particular locations or sample types, and for the purposes of performing meta-analyses, and/or synthesis of larger datasets.

The Scottish Universities Environmental Research Centre (SUERC) has analysed >100,000 individual graphite preparations with two accelerator mass spectrometers. Analysis quality is maintained by a programme of secondary-standards measurement, and annual assessment of the resulting large dataset can provide insight into subtle effects. The same analyses that are used to derive external errors within individual batches of samples, or to monitor inter-batch variance, are also employed in aggregate to determine overall instrument and process performance. The recent 2021 findings are consistent with prior years', including the apparent contradiction that secondary standard analysis can be both consistent and slightly discordant between the two instruments. However, individual sample radiocarbon measurement on both machines remains accurate and typically 3 parts per thousand precise.

Reference materials are key for assessing inter-laboratory variability and measurement quality, and for placing analytical uncertainty bounds on sample analyses. Here, we investigate four years of data resulting from repeated processing of the CRONUS-N reference material for cosmogenic 10Be and 26Al analyses. At University of Vermont, we prepared a CRONUS-N aliquot with most of our sample batches from 2013 to 2017; these reference material samples were then distributed to four different accelerator mass spectrometry facilities, yielding 7310Be analyses and 58 26Al analyses. We determine CRONUS-N 10Be concentrations of (2.26 +/- 0.14) x 105 atoms g-1 (n = 73, mean, 1 SD) and 26Al concentrations of (1.00 +/- 0.08) x 106 atoms g-1 (n = 58, mean, 1 SD). We find a reproducibility of 6.3% for 10Be and 7.7% for 26Al (relative standard deviations). We also document highly variable 27Al and Mg concentrations and a 10Be dispersion twice as large as the mean AMS analytic uncertainty. Analyses of the CRONUS-N material with and without density separation demonstrate that non-quartz minerals are present in the material and have a large impact on measured concentrations of 27Al, 10Be, and impurities; these non-quartz minerals represent only a very small portion of the total mass (0.6-0.8%) but have a dis-proportionally large effect on the resulting data. Our results highlight the importance of completely removing all non-quartz mineral phases from samples prior to Be/Al extraction for the determination of in situ cosmogenic 10Be and 26Al concentrations.

AbstractWe describe the glacial geomorphology and initial geochronology of two ice-free valley systems within the Neptune Range of the Pensacola Mountains, Antarctica. These valleys are characterized by landforms associated with formerly more expanded ice sheet(s) that were at least 200 m thicker than at present. The most conspicuous features are areas of supraglacial debris, discrete debris accumulations separated from modern-day ice and curvilinear ridges and mounds. The landsystem bears similarities to debris-rich cold-based glacial landsystems described elsewhere in Antarctica and the Arctic where buried ice is prevalent. Geochronological data demonstrate multiple phases of ice expansion. The oldest, occurring > 3 Ma, overtopped much of the landscape. Subsequent, less expansive advances into the valleys occurred > 2 Ma and > ~1 Ma. An expansion of some local glaciers occurred < 250 ka. This sequence of glacial stages is similar to that described from the northernmost massif of the Pensacola Mountains (Dufek Massif), suggesting that it represents a regional signal of ice-sheet evolution over the Plio-Pleistocene. The geomorphological record and its evolution over millions of years makes the Neptune Range valleys an area worthy of future research and we highlight potential avenues for this.

Preserved remnants of fluvial activity in deserts constitute evidence for changing boundary conditions. The Atacama Desert of northern Chile is the global end-member for aridity, so the history of relict stream networks in this region is a record of how landscapes develop under extreme conditions. On Pampa de Tana in northern Chile (19.4 degrees S), a series of channel forms that are presently inactive but in the past flowed westward are incised into the surface of a fault bounded, topographically elevated portion of the El Diablo Formation, a regionally extensive, relict pediment. We measure cosmic-ray produced Be-10, Al-26 and Ne-21 in fluvial deposits to date the timing of abandonment of three channels and couple this with topographic profile information from a SPOT-6 derived, 2 m resolution digital elevation model. We find two of the channels were abandoned approximately > 5.6 Myr and 2.0 Myr ago. One channel is still capable of flow and has ages suggesting it was fluvially active within the last few hundred thousand years. Using the paleochannel ages measured here and published ages for the end of aggradation of the El Diablo Formation we estimate the rates of fluvial channel incision before channel abandonment, and uplift rates on the faults after channel abandonment. Maximum uplift rates of similar to 12 m/Myr over the last 2 Myr are found. In general, while rates of uplift are relatively low they are several-fold more rapid than the rates of fluvial incision prior to channel abandonment. This implies that westward channel flow was interrupted by uplift of topography above a blind NW-SE striking reverse fault that affects the Central Depression, an alluvial forearc basin. We consider also that shrinkage of the upstream catchment area by stream capture, promoted via headward erosion and lateral expansion of adjacent canyons (quebradas) could be a factor in the abandonment of the channels on Pampa de Tana. Our results highlight the polygenetic nature of this landscape and show that relatively minor amounts of fault displacement in hyperarid regions can have implications for stream network evolution. Even subtle topographic uplift upstream should be taken into account when fluvial deposits are used as proxies for long-term environmental conditions.

In situ cosmogenic nuclides are widely employed to quantify topographic and geomorphic landscape evolution. However, few studies are devoted to investigating possibly unsteady denudation. In this work the denudation rates of five surface bedrock and one depth profile are measured using in situ cosmogenic Cl-36 in different climate zones in China; cosmogenic Cl-36 is a powerful proxy for the surface denudation processes of carbonate landscapes in different climatic gradients since carbonates are more sensitive to climate change than silicates. Compiling previous worldwide surface denudation studies in different gradients, we find that: (I) denudation rate increases systematically with mean annual precipitation (MAP) in arid climatic zones (MAP lower than similar to 700 mm yr(-1)) and is dominated by long-term climatic gradients; (II) humid climatic zone (MAP greater than similar to 700 mm yr(-1)) denudation rates are about constrained to 34.1. 11.7 mm kyr(-1) by carbonate dissolution kinetics; and (III) denudation rate is also influenced by short-term physical erosion or abrupt erosive events. Accordingly, the reconstructed evolutionary history of the Guizhou depth profile results from either a relatively high denudation rate (55.5(-4.4)(+5.6) mm kyr(-1)) and long duration exposure (274(-147)(+120) ka), or an alternative a low denudation rate (0.8(-0.8)(+13.3) mm kyr(-1)) and a recent abrupt erosive event (13.0(-1.6)(+1.9) ka). These two possible solutions suggest that assumed long-term averaged denudation rate can conceal episodic erosion events. Given tectonic quiescence we propose that climate change might mainly control an erosive event during the last glacial termination (similar to 14 ka), which also implies that caution should be taken when determining the denudation rate of a landscape where climate change and/or tectonic activity plays an important role.

Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparisonmaterial (ICM) for in situ-produced cosmogenic 36Cl and natural chlorine (Clnat) analysis. The sample CoCal-N isderived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystalof alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologneand a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N(between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) havebeen undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internallaboratory scatter of the 36Cl concentrations indicates no overdispersion for half of the laboratories and 3.9 to7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regardingtheir 36Cl and Clnat concentrations. The grand average (average calculated from the average of eachlaboratory) yields initial consensus 36Cl concentrations of (3.74 ± 0.10)×106 at 36Cl/g (CoCal-N) and(2.93 ± 0.07)×106 at 36Cl/g (CoFsp-N) at 95% confidence intervals. The coefficient of variation is 5.1% and4.2% for CoCal-N and CoFsp-N, respectively. The Clnat concentration corresponds to the lower and intermediaterange of typical rock samples with (0.73 ± 0.18) μg/g in CoCal-N and (73.9 ± 6.8) μg/g in CoFsp-N. Wediscuss the most relevant points of the sample preparation and measurement and the chlorine concentrationcalculation to further approach inter-laboratory comparability. We propose to use continuous measurements ofthe ICMs to provide a valuable quality control for future determination of 36Cl and Clnat concentrations.

The Chernobyl Exclusion Zone (CEZ) represents a unique natural laboratory that received significant 129I contamination across a range of soils and land-use types in a short time period in 1986. Data are presented on 129I and 127I in soil samples collected from highly contaminated areas in the CEZ in 2015. The geometric mean (GM) total concentration of stable iodine (127I) was 6.7 × 10-7 g g-1 and the (GM) total concentration of 129I was 2.39 × 10-13 g g-1, equivalent to 1.56 mBq kg-1. GM total 127I concentration is below the European average soil concentration of 3.94 × 10-6 g g-1, while 129I is significantly higher than the pre-Chernobyl activity concentration for 129I of 0.094 mBq kg-1. Significant differences were found in the extractability of native, stable 127I and 129I almost 30 years after the introduction of 129I to the soils. Both 127I and 129I were predominantly associated with alkaline-extractable soil organic matter, established using a three-step sequential extraction procedure. Whereas 127I was significantly correlated with gross soil organic matter (measured by loss on ignition), however, 129I was not. The ratio of 129I/127I was significantly lower in extracts of soil organic matter than in more labile (soluble and adsorbed) fractions, indicating incomplete equilibration of 129I with native 127I in soil humic substances after 29 years residence time in the CEZ soils. The initial physico-chemical form of 129I in the CEZ soils is unknown, but the widespread presence of uranium oxide fuel particles is unlikely to have influenced the environmental behaviour of 129I. Our findings have implications for long-term radiation dose from 129I in contaminated soils and the use of native, stable 127I as a proxy for the long-term fate of 129I.

There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being Be-10 and Al-26 in quartz. To extract and then separate these radio-nuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N Be-10 targets were then measured at seven different AMS facilities and five of the preparation laboratories had their Al-26 targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) Be-10 and that it has low concentrations of the major elements that can interfere with Be and Al extraction chemistry and AMS measurements. We derive preliminary concentrations for Be-10 and Al-26 in CoQtz-N as 2.53 +/- 0.09 x 10(6) at/g and 15.6 +/- 1.6 x 10(6) at/g, respectively, at the 95% confidence limit.

The identification of interferences to In-129(+) (n = 3-6) was conducted with a 5 MV tandem accelerator mass spectrometer at SUERC. In addition to Te-128, the detectable interferences to 12 MeV I-129(3+) ions include Ca-43(1+) and Sr-86(2+) which are likely injected as (CaSr-)-Ca-43-Sr-86, (CaSO3-)-Ca-43-S-32-O-18, etc. whereas those to 15 MeV I-129(4+) ions include S-32(1+) injected as (CaSO3-)-Ca-43-S-32-O-18, Cu-65(2+) as (CuCuH-)-Cu-63-Cu-65-H-1, Mo-97(3+) as (MoO2-)-Mo-97-O-16. The 18 MeV I-129(5+) ions might be interfered by Se-77(3+) and (104)pd(4+) (or Ru-104(4+)) and the 21 MeV I-129(6+) ions by C-43(2+), Cu-55(3+), Sr-86(4+) and Pd-108(5+) (or Ag-107(5+), Cd-108(5+)). Apart from Te-128, these ions can be fully separated from I-129 in the gas ionization detector equipped with a thin SiN membrane window and propane gas, which contributes negligibly to the I-129-AMS detection for samples after careful chemical preparation. Although the I-129 background is mainly controlled by Te content and the source memory, the rareness of Te in natural environmental samples results in our routine background I-129/I-127 level in range of similar to 10(-14). The precision and accuracy of 3% can be routinely achieved at I-129/I-127 > 10(-12) level at SUERC.

This corrigendum fixes an error in the reporting of 21 Ne concentrations, which affected one batch of samples that included the bedrock depth profile from which cosmogenic 10 Be, 26 Al and 21 Ne were modelled to constrain the age and exposure history of the Patriot Hills (Fig. 8 in the manuscript).Re-modelling the cosmogenic nuclide data using the corrected 21 Ne data yields an apparent exposure age of 3.5-5.1 Ma.This corrects an age published as 2.1-2.6 Ma in Sugden et al. ( 2017), and reinforces the conclusion of the original paper that the glacial trimline is pre-Quaternary and that the climatic conditions necessary for its erosion last occurred in the Mid-Miocene.The revised Supplementary Table 1 has been updated with corrected 21 Ne concentrations and consistent reporting of 10 Be concentrations.The revised Supplementary Table 2 has been updated with 21 Ne exposure ages for the affected batch of samples.Below, we describe the revised model results and present a revised Fig. 8. Tables 1 and2, Fig. 8 and its caption replace those in the original paper.

The retreat history of the Antarctic Ice Sheet is important for understanding rapid deglaciation, as well as to constrain numerical ice sheet models and ice loading models required for glacial isostatic adjustment modelling. There is particular debate about the extent of grounded ice in the Weddell Sea embayment at the Last Glacial Maximum, and its subsequent deglacial history. Here we provide a new dataset of geomorphological observations and cosmogenic nuclide surface exposure ages of erratic samples that constrain the deglacial history of the Pensacola Mountains, adjacent to the present day Foundation Ice Stream and Academy Glacier in the southern Weddell Sea embayment. We show there is evidence of at least two glaciations, the first of which was relatively old and warm-based, and a more recent cold-based glaciation. During the most recent glaciation ice thickened by at least 450 m in the Williams Hills and at least 380 m on Mt Bragg. Progressive thinning from these sites was well underway by 10 ka BP and ice reached present levels by 2.5 ka BP, and is broadly similar to the relatively modest thinning histories in the southern Ellsworth Mountains. The thinning history is consistent with, but does not mandate, a Late Holocene retreat of the grounding line to a smaller-than-present configuration, as has been recently hypothesized based on ice sheet and glacial isostatic modelling. The data also show that clasts with complex exposure histories are pervasive and that clast recycling is highly site-dependent. These new data provide constraints on a reconstruction of the retreat history of the formerly-expanded Foundation Ice Stream, derived using a numerical flowband model. (C) 2016 The Author(s). Published by Elsevier Ltd.

The Burhan Budai Shan in NE Tibet represents a key location for examining the variable influence of the mid‐latitude westerly and monsoonal circulations on late Quaternary glaciations in this sector of the Tibetan Plateau. Our study investigates the glacial history of mountains near Lake Donggi Cona (35°17′N, 98°33′E) using field mapping in combination with 10 Be surface exposure dating and numerical reconstructions of former glacial equilibrium line altitudes (palaeo‐ ELA ). A set of 23 new exposure ages, collected from moraines in four glacial valleys, ranges from 45 to 190 ka, indicating ice expansion during the early and middle part of the last glacial cycle, and during the penultimate and possibly an earlier Mid‐Pleistocene glaciation. Ice advances reaching 12–15 km in length occurred at around 190–180 ka (≥ MIS 6), between 140–100 ka (late MIS 6/ MIS 5), and 90–65 ka (late MIS 5/early MIS 4), with a maximum ELA depression of 400–500 m below the estimated modern snowline. Exposure ages from the valley headwaters further indicate a small glaciation between c . 60–50 ka (late MIS 4/early MIS 3), which was essentially restricted to the cirque areas. Significantly, we find no evidence for any subsequent glaciation in the area during MIS 2 or the Holocene period. These results indicate a diminishing trend of glaciation in the region since at least MIS 4, and corroborate the case of a ‘missing LGM ’ in the more interior parts of the northeastern Tibetan Plateau. The emerging pattern suggests that the most favourable conditions for glaciation during the Late Pleistocene correspond to periods of relatively moderate cooling combined with an intermediate or rising East Asian monsoon strength.

Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36 Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36 Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (10 4 yr; 10 2 km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting.

The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the lower-elevation Piedmont and higher-elevation Blue Ridge physiographic provinces. To understand better the rate at which this landform and the adjacent landscape are changing, we measured cosmogenic beryllium-10 (Be-10) in quartz separated from sediment samples (n=50) collected in 32 streams and from three exposed bedrock outcrops along four transects normal to the escarpment, allowing us to calculate erosion rates integrated over 10(4)-10(5)years. These basin-averaged erosion rates (5.4-49m Myr(-1)) are consistent with those measured elsewhere in the southern Appalachain Mountains and show a positive relationship between erosion rate and average basin slope. Erosion rates show no relationship with basin size or relative position of the Brevard fault zone, a fundamental structural element of the region. The cosmogenic isotopic data, when considered along with the distribution of average basin slopes in each physiographic province, suggest that the escarpment is eroding on average more rapidly than the Blue Ridge uplands, which are eroding more rapidly than the Piedmont lowlands. This difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates. Copyright (c) 2016 John Wiley & Sons, Ltd.

Radiocarbon (14C) has been measured in single tree ring samples collected from the southwest of the Fukushima Dai-ichi Nuclear Power Plant. Our data indicate south-westwards dispersion of radiocarbon and the highest 14C activity observed so far in the local environment during the 2011 accident. The abnormally high 14C activity in the late wood of 2011 ring may imply an unknown source of radiocarbon nearby after the accident. The influence of 14C shrank from 30 km during normal reactor operation to 14 km for the accident in the northwest of FDNPP, but remains unclear in the southwest.