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  • 1
    In: Geochronology, Copernicus GmbH, Vol. 2, No. 1 ( 2020-04-17), p. 63-79
    Abstract: Abstract. The recent development of the MIni CArbon DAting System (MICADAS) allows researchers to obtain radiocarbon (14C) ages from a variety of samples with miniature amounts of carbon (〈150 µg C) by using a gas ion source input that bypasses the graphitization step used for conventional 14C dating with accelerator mass spectrometry (AMS). The ability to measure smaller samples, at reduced cost compared with graphitized samples, allows for greater dating density of sediments with low macrofossil concentrations. In this study, we use a section of varved sediments from Lake Żabińskie, NE Poland, as a case study to assess the usefulness of miniature samples from terrestrial plant macrofossils for dating lake sediments. Radiocarbon samples analyzed using gas-source techniques were measured from the same depths as larger graphitized samples to compare the reliability and precision of the two techniques directly. We find that the analytical precision of gas-source measurements decreases as sample mass decreases but is comparable with graphitized samples of a similar size (approximately 150 µg C). For samples larger than 40 µg C and younger than 6000 BP, the uncalibrated 1σ age uncertainty is consistently less than 150 years (±0.010 F14C). The reliability of 14C ages from both techniques is assessed via comparison with a best-age estimate for the sediment sequence, which is the result of an OxCal V sequence that integrates varve counts with 14C ages. No bias is evident in the ages produced by either gas-source input or graphitization. None of the 14C ages in our dataset are clear outliers; the 95 % confidence intervals of all 48 calibrated 14C ages overlap with the median best-age estimate. The effects of sample mass (which defines the expected analytical age uncertainty) and dating density on age–depth models are evaluated via simulated sets of 14C ages that are used as inputs for OxCal P-sequence age–depth models. Nine different sampling scenarios were simulated in which the mass of 14C samples and the number of samples were manipulated. The simulated age–depth models suggest that the lower analytical precision associated with miniature samples can be compensated for by increased dating density. The data presented in this paper can improve sampling strategies and can inform expectations of age uncertainty from miniature radiocarbon samples as well as age–depth model outcomes for lacustrine sediments.
    Type of Medium: Online Resource
    ISSN: 2628-3719
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2966593-0
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  • 2
    In: Journal of Biogeography, Wiley, Vol. 45, No. 11 ( 2018-11), p. 2564-2575
    Abstract: Refugia play a key role in conserving biodiversity during periods of unfavourable and highly variable regional climate. However, refugial populations are often small and fragmented, which makes their identification difficult. In this study, we investigate whether an area of complex topography in the southern foreland of the Alps could have provided a suitable microclimate to serve as a glacial refugium for temperate trees during the last glacial. Location The Euganean Hills in Northern Italy (Veneto). Methods We assessed the current microclimatic variability in the ecologically diverse region on a fine scale by recording half‐hourly near‐surface temperatures over a period of 11 months. After comparing our measurements with today's vegetation distribution, broad‐scale synoptic patterns, and topoclimatic factors, we estimated refugial suitability based on extreme temperatures, climatic stability, and difference from the regional average. Results Present‐day temperature gradients within the Euganean Hills are large enough to explain the presence of the temperate tree species Fagus sylvatica as well as Mediterranean Quercus ilex , two species that are absent elsewhere in the adjacent Po Plain. During winter, anticyclonic weather patterns resulted in strong atmospheric inversions, with temperatures increasing by +1°C/100 m in the hills relative to the surrounding Po Plain. Main conclusions Our high‐resolution climate data support multi‐proxy palaeoecological records identifying the Euganean Hills as a refugium for temperate trees. Temperature anomalies of 2–4°C relative to the surrounding Po Plain are sufficient to allow several temperate tree species to survive the Last Glacial Maximum ( LGM ) in the Euganean Hills under a harsh continental climate. Specifically, elevations 〉 200 m a.s.l. in the central parts of the hills may have provided suitable conditions for local LGM refugia. Regions of complex topography such as the Euganean Hills conserved past and present biodiversity and provide high‐priority areas for conservation under future climate warming.
    Type of Medium: Online Resource
    ISSN: 0305-0270 , 1365-2699
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 2020428-0
    detail.hit.zdb_id: 188963-1
    SSG: 12
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