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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.

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.

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.

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.

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.

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