NERC Radiocarbon Facility Environment

East Kilbride, United Kingdom

NERC Radiocarbon Facility Environment

East Kilbride, United Kingdom
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Smith J.A.,British Antarctic Survey | Hillenbrand C.-D.,British Antarctic Survey | Kuhn G.,Alfred Wegener Institute for Polar and Marine Research | Larter R.D.,British Antarctic Survey | And 4 more authors.
Quaternary Science Reviews | Year: 2011

The Amundsen Sea Embayment (ASE) drains approximately 35% of the West Antarctic Ice Sheet (WAIS) and is one of the most rapidly changing parts of the cryosphere. In order to predict future ice sheet behaviour, modellers require long-term records of ice-sheet melting to constrain and build confidence in their simulations. Here, we present detailed marine geological and radiocarbon data along three palaeo-ice stream tributary troughs in the western ASE to establish vital information on the timing of deglaciation of the WAIS since the Last Glacial Maximum (LGM). We have undertaken multi-proxy analyses of the cores (core description, shear strength, x-radiographs, magnetic susceptibility, wet bulk density, total organic carbon/nitrogen, carbonate content and clay mineral analyses) in order to: (1) characterise the sedimentological facies and depositional environments; and (2) identify the horizon(s) in each core that would yield the most reliable age for deglaciation. In accordance with previous studies we identify three key facies, which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments. These facies are: i) subglacial, ii) proximal grounding line, and iii) seasonal open marine. In addition, we incorporate ages from other facies (e.g., glaciomarine diamictons deposited at some distance from the grounding line, such as glaciogenic debris flows and iceberg-rafted diamictons and turbates) into our deglacial model. In total, we have dated 78 samples (mainly the acid insoluble organic (AIO) fraction, but also calcareous foraminifers), which include 63 downcore and 15 surface samples. Through careful sample selection prior to dating, we have established a robust deglacial chronology for this sector of the WAIS. Our data show that deglaciation of the western ASE was probably underway as early as 22,351 calibrated years before present (cal yr BP), reaching the mid-shelf by 13,837 cal yr BP and the inner shelf to within c.10-12 km of the present ice shelf front between 12,618 and 10,072 cal yr BP. The deglacial steps in the western ASE broadly coincide with the rapid rises in sea-level associated with global meltwater pulses 1a and 1b, although given the potential dating uncertainty, additional, more precise ages are required before these findings can be fully substantiated. Finally, we show that the rate of ice-sheet retreat increased across the deep (up to1600 m) basins of the inner shelf, highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation. © 2010 Elsevier Ltd.

Hillenbrand C.-H.,British Antarctic Survey | Smith J.A.,British Antarctic Survey | Kuhn G.,Alfred Wegener Institute for Polar and Marine Research | Esper O.,Alfred Wegener Institute for Polar and Marine Research | And 6 more authors.
Journal of Quaternary Science | Year: 2010

Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is challenging because of the rarity of calcareous (micro-) fossils and the recycling of fossil organic matter. Consequently, radiocarbon (14C) ages of the acid-insoluble organic fraction (AIO) of the sediments bear uncertainties that are difficult to quantify. Here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional14C dating of the AIO in bulk samples yielded age reversals down-core, but at all sites the AIO14C ages obtained from diatomaceous ooze within the diatom-rich unit yielded similar uncorrected14C ages between 13517 56 and 11543 47 years before present (a BP). Correction of these ages by subtracting the core-top ages, which probably reflect present-day deposition (as indicated by210Pb dating of the sediment surface at one core site), yielded ages between ca. 10500 and 8400 cal. a BP. Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1300 a indicated deposition of the diatom-rich sediments between 14100 and 11900 cal. a BP. Most of these ages are consistent with age constraints between 13.0 and 8.0ka for the diatom-rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves. As a third dating technique we applied conventional radiocarbon dating of the AIO included in acid-cleaned diatom hard parts extracted from the diatomaceous ooze. This method yielded uncorrected14C ages of only 5111 38 and 5106 38 a BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for14C dating. The deposition of the diatom-rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13ka BP. The deposition of diatomaceous oozes elsewhere on the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related. © 2009 John Wiley & Sons, Ltd.

Smith V.C.,University of Oxford | Mark D.F.,Scottish Universities Environmental Research Center | Staff R.A.,University of Oxford | Blockley S.P.E.,Royal Holloway, University of London | And 7 more authors.
Quaternary Science Reviews | Year: 2011

The varved Suigetsu (SG06) sediment core is potentially one of the most important and well-constrained mid-latitude palaeoclimate archives, recording continuous deposition during the last ∼150 kyrs. Numerous visible and non-visible volcanic ash layers form unique age markers within SG06. These ash layers are too fine and crystal-poor to be directly dated using the 40Ar/39Ar technique so the tephra were correlated to proximal volcanic deposits using their glass shard compositions. A high-precision 40Ar/39Ar sanidine age of 10.0 ± 0.3 ka (1σ, n = 34, MSWD = 0.71, p = 0.89) was obtained for the SG06-1288 (U-Oki) proximal tephra (Ulleungdo U4). 40Ar/39Ar yields a precision of ±3% near the younger limit of the method, with improved precision possible for older SG06 samples. Such 40Ar/39Ar ages for tephra layers can provide invaluable tie-points within the Lake Suigetsu SG06 sequence, giving independent verification of the core's varve chronology, allowing for the calibration of cosmogenic nuclide production, and providing a precise chronology beyond the varve limit. © 2011 Elsevier Ltd.

Austin W.E.N.,University of St. Andrews | Hibbert F.D.,University of St. Andrews | Rasmussen S.O.,Copenhagen University | Peters C.,University of St. Andrews | And 2 more authors.
Quaternary Science Reviews | Year: 2012

Two high resolution marine sediment cores located 83 km apart in the NE Atlantic have been studied: MD95-2006 (Barra Fan; 57°01.82 N, 10°03.48 W; 2120 m water depth) and MD04-2822 (Rockall Trough; 56°50.54 N, 11°22.96 W; 2344 m water depth). The records are anchored to the NGRIP ice core stratigraphy and GICC05 chronology by the presence of geochemically characterized Fugloyarbanki tephra and further tested by radiocarbon age control. Replicated sea surface temperature (SST) records show evidence for an abrupt and short-lived warming within Greenland Stadial (GS)-3, to which we tentatively assign an age of ca 25.6-24.8 kyr GICC05 b2k. Based on these and another marine palaeoclimate record (LINK17) from the Faroe-Shetland Channel, we propose a new three-fold event stratigraphy for GS-3 within the North East Atlantic region. The recognition of this warming event within GS-3 in NE Atlantic SST records demonstrates that such events may not readily be identified within the coldest stadials of the Greenland ice cores, highlights the need for carefully constructed event stratigraphies (independently tested by the use of tephra isochrones and radiocarbon) and illustrates pervasive millennial-scale climate variability of the North Atlantic region (Dansgaard-Oeschger (D/O) events) is deeply embedded in the dynamics of Atlantic Meridional Overturning Circulation (AMOC). © 2010 Elsevier Ltd.

Briones M.J.I.,University of Vigo | Briones M.J.I.,UK Center for Ecology and Hydrology | Garnett M.H.,NERC Radiocarbon Facility Environment | Ineson P.,University of York
Soil Biology and Biochemistry | Year: 2010

A radiocarbon approach was used to investigate the roles of temperature and soil fauna activity in the turnover of 'old' non-labile carbon in a peatland ecosystem. We investigated the impacts of enchytraeids on carbon turnover in two different soil layers, with different incorporation of the 'bomb' peak, when incubated at two different temperatures. Results showed that, in agreement with previous studies, warmer temperatures promoted reproduction rates of enchytraeids, with the top layer supporting higher animal densities and biomass. With independence of the animal treatment, soil respiration in the top 5 cm was four times higher than in the deeper layer suggesting that decomposition was greater in the upper layer, with the response being greater at the highest temperature treatment. Furthermore, independent of temperature, the presence of enchytraeids in the top layer significantly enhanced the release of non-labile C as DOC. Similarly, at the bottom layer, 'older' C sources were mobilised in response to warming and a greater amount of pre-bomb carbon was released into the soil solution at 20 °C when the worms were present. A strong positive link between the ages of the C assimilated by the animals and released through mineralization suggests an important role of soil biology in the mobilisation of the older C pools in soils and should be taken into account in developing global C models to predict the response of soil C dynamics to climate change. © 2010 Elsevier Ltd. All rights reserved.

Garnett M.H.,NERC Radiocarbon Facility Environment | Dinsmore K.J.,UK Center for Ecology and Hydrology | Billett M.F.,UK Center for Ecology and Hydrology
Science of the Total Environment | Year: 2012

Radiocarbon dating has the capacity to significantly improve our understanding of the aquatic carbon cycle. In this study we used a new passive sampler to measure the radiocarbon ( 14C) and stable carbon (δ 13C) isotopic composition of dissolved CO 2 for the first time in a peatland stream throughout a complete year (May 2010-June 2011). The in-stream sampling system collected time-integrated samples of CO 2 continuously over approximately 1month periods. The rate of CO 2 trapping was proportional to independently measured streamwater CO 2 concentrations, demonstrating that passive samplers can be used to estimate the time-averaged dissolved CO 2 concentration of streamwater. While there was little variation and no clear trend in δ 13CO 2 values (suggesting a consistent CO 2 source), we found a clear temporal pattern in the 14C concentration of dissolved CO 2. The 14C age of CO 2 varied from 707±35 to 1210±39years BP, with the youngest CO 2 in the autumn and oldest in spring/early summer. Mean stream discharge and 14C content of dissolved CO 2 were positively correlated. We suggest that the observed pattern in the 14C content of dissolved CO 2 reflects changes in its origin, with older carbon derived from deeper parts of the peat profile contributing proportionally more gaseous carbon during periods of low stream flow. © 2012 Elsevier B.V.

Garnett M.H.,NERC Radiocarbon Facility Environment | Hardie S.M.L.,University of Glasgow | Hardie S.M.L.,Scottish Crop Research Institute | Murray C.,NERC Radiocarbon Facility Environment
Radiocarbon | Year: 2011

We developed and tested a new method to separate CO2 and CH4 from bulk gas samples for radiocarbon and stable-carbon analysis that utilizes a zeolite molecular sieve. To validate the technique, tests were performed using a suite of standard gases, composed of CO2 and CH4 of distinctly different isotopic composition. We employed the method to investigate the carbon isotopic composition of samples of dissolved CO2 and CH4 collected in situ from the near surface to deep layers of an ombrotrophic raised peat bog. Results showed that the age of both the CO2 and CH4 components of the dissolved gases increased with depth from ~0-300 BP at 0.25 m to ~4000 BP at 4 m. CH4 was mainly similar or slightly older in age compared to CO2, with the greatest difference in ages occurring at 1 m depth where CH4 was older by 430-615 yr. The δ13C values of CO2 increased with depth from -12.4‰ and -8.0‰ at 0.25 m to +6.9‰ and +8.3‰ at 4 m, whereas the δ13C of CH4 stayed in the range -58.4‰ to -70.6‰. The 14C results from the deepest layers are consistent with a similar source for both gases. 14C ages for the CO2 component were younger compared to CH4, within the shallower depths of the peat bog (≤1 m) and demonstrate the incorporation of acrotelm-derived respired CO2 into the catotelm. © 2011 by the Arizona Board of Regents on behalf of the University of Arizona.

Ahad J.M.E.,Geological Survey of Canada | Ganeshram R.S.,University of Edinburgh | Bryant C.L.,NERC Radiocarbon Facility Environment | Cisneros-Dozal L.M.,NERC Radiocarbon Facility Environment | And 3 more authors.
Marine Chemistry | Year: 2011

Diagnostic molecular ratios and compound-specific 13C and 14C analyses were used to identify n-alkane sources in surface sediments collected along a transect from an urbanized estuary draining a peat-rich catchment (Tyne, UK). The most abundant homologues were generally C29 or C31, and the carbon preference index (CPI; 1.8 to 6.4) and average chain length (ACL; 28.5 to 29.5) of C25-C33 n-alkanes became progressively lower in samples closer to the mouth of estuary. δ13C signatures of C19-C31 n-alkanes ranged from -37.1 to -29.3‰ and in general became more depleted with increasing carbon number. Δ14C values for C21 (-945 to -738‰) were significantly more depleted compared to C29 (-591 to -65‰) and C31 (-382 to -96‰), pointing to a much higher component of fossil (i.e., 14C-free) carbon in the shorter homologue. The radiocarbon contents for these three n-alkanes decreased toward the North Sea, which in conjunction with an up to 4‰ seaward 13C-enrichment in C29 and C31 and seaward decreases in CPI and ACL pointed to petrogenic hydrocarbon contamination in lower estuarine sediments. Independent 13C and 14C mass balances used to calculate the relative proportions of modern (i.e., plant wax) and fossil (i.e., petrogenic) n-alkanes yielded similar results and demonstrated that mixing with marine-derived organic matter (OM) or microbial degradation during estuarine transport led to a seaward decline in modern, longer-chain homologues, resulting in an increasingly larger fossil carbon contribution toward the mouth of estuary. The ability to clearly distinguish anthropogenic from natural inputs suggests that compound-specific radiocarbon analysis can successfully delineate the age of terrigenous OM delivered to the coastal zone even near historically polluted systems such as the Tyne. © 2011.

Walker R.T.,University of Oxford | Claisse S.,University of Oxford | Telfer M.,University of Oxford | Nissen E.,University of Cambridge | And 3 more authors.
Geosphere | Year: 2010

We investigate the late Quaternary history of slip on the Kamena Vourla and Arkitsa normal faults, which are segments of a fault system bounding the south coast of the Gulf of Evia in central Greece, and which we refer to as the Coastal Fault System. We examine two river terraces, near the village of Molos, which are found within the uplifted footwall of the Kamena Vourla fault. The upper terrace is ~20 m above the present river level and appears to represent fan deposition into the main river channel from surrounding tributaries. The lower terrace, ~8 m above the present-day river bed, represents an interval of river-bed aggradation and correlates with the surface of a delta on the hanging-wall side of the fault. GPS profiles show a 6 ± 0.1 m vertical offset of the lower terrace surface as it crosses the fault. Preliminary dating of the two terrace levels, using both optical luminescence and radiocarbon methods, provides inconclusive results. The lower terrace, however, grades toward the present-day sea level and correlates with the surface of a delta on the hanging-wall side of the fault; it is, therefore, likely to date from ~6 ka, when sea level stabilized at its present-day highstand. With an age of ~6 ka, the 6 m vertical displacement of the lower terrace yields an estimate of ~1.2-2.0 mm/yr for the Holocene rate of slip across the Kamena Vourla fault. This rate of slip is comparable with an estimated rate of ~0.7-2.0 mm/yr for the central (Arkitsa) segment of the Coastal Fault System, and with a 0.4-1.6 mm/yr slip rate measured on the easternmost (Atalanti) segment. These estimates of Holocene slip rates are consistent with the 1-3 mm/yr of present-day extension across the Gulf of Evia measured by GPS, arguing against large changes in rate of extension through the Holocene. Both the Arkitsa and Kamena Vourla faults are clearly active and despite an absence of historical earthquakes on either fault, they should be considered to be a major hazard to local populations. However, further dating studies and palaeoseismic investigations are required before the slip rate and history can be fully quantified. © 2010 Geological Society of America.

Garnett M.H.,NERC Radiocarbon Facility Environment | Hartley I.P.,University of Exeter
Atmospheric Environment | Year: 2010

Radiocarbon (14C) analysis of atmospheric CO2 can provide information on CO2 sources and is potentially valuable for validating inventories of fossil fuel-derived CO2 emissions to the atmosphere. We tested zeolite molecular sieve cartridges, in both field and laboratory experiments, for passively collecting atmospheric CO2. Cartridges were exposed to the free atmosphere in two configurations which controlled CO2 trapping rate, allowing collection of sufficient CO2 in between 1.5 and 10 months at current levels. 14C results for passive samples were within measurement uncertainty of samples collected using a pump-based system, showing that the method collected samples with 14C contents representative of the atmosphere. δ13C analysis confirmed that the cartridges collected representative CO2 samples, however, fractionation during passive trapping means that δ13C values need to be adjusted by an amount which we have quantified. Trapping rate was proportional to atmospheric CO2 concentration, and was not affected by exposure time unless this exceeded a threshold. Passive sampling using molecular sieve cartridges provides an easy and reliable method to collect atmospheric CO2 for 14C analysis. © 2009 Elsevier Ltd. All rights reserved.

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