Bihari Árpád, Karlik Máté, Mîndrescu Marcel, Szalai Zoltán, Grădinaru Ionela, Kern Zoltán
Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research, Hungarian Academy of Sciences, Bem tér 18/C, H-4026, Debrecen, Hungary.
Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Budaörsi út 45, H-1112, Budapest, Hungary.
J Environ Radioact. 2018 Jan;181:32-41. doi: 10.1016/j.jenvrad.2017.10.009. Epub 2017 Oct 31.
Fallout isotope (PbCs and Am) based dating has been carried out on the near-surface sediment core collected from Lake Bolătău-Feredeu (Bukovina, Romania). The motivation was to improve the chronology of this recent section in connection with significant fluctuations observed in sediment accumulation rates, particle size distribution and primordial radioisotope (i.e. K and Th) composition. Previously only an extrapolation of a broad-range OxCal age-depth model, which was based on 8 AMS radiocarbon dates from the deeper part of a parallel sediment sequence and tentatively validated for the upper part using the double peaks of the Cs activity concentration distribution, was available for the studied section (1-24 cm). Parallel to the previous Cs measurement, Pb and Ra (for a more detailed, Pb-based chronology), Am (for an additional time-marker), as well as K and Th concentrations have also been determined by gamma-spectrometry. In case of the Pb-based chronology, due to a large deviation from a pure exponential distribution, the Constant Flux (CF) model has been used for the calculation of sediment ages and accumulation rates. Although the broad-range OxCal and the CF model were broadly similar down to 22 cm, the Pb-based ages are clearly superior in terms of uncertainty in the uppermost 12 cm, while the broad-range model has smaller uncertainty below 20 cm (>150 years). The CF model gave an average mass accumulation rate of (0.08 ± 0.03) g cm yr for sections 0-11 cm, and (0.03 ± 0.01) g cm yr for sections 12-22 cm, respectively. Significant changes have been observed in the depth distribution of both the particle size distribution and the elemental/isotopic composition of the sediment record, most likely related to the variation observable in the intensity and volume of precipitation in the catchment. The obtained high-resolution records of Lake Bolătău, including multiple radioisotopes, can serve as a regional benchmark for similar studies.
已对从博拉陶 - 费雷代乌湖（罗马尼亚布科维纳）采集的近地表沉积物岩芯进行了基于沉降同位素（铅 - 铯和镅）的年代测定。这样做的动机是，鉴于在沉积物堆积速率、粒度分布和原生放射性同位素（即钾和钍）组成方面观察到显著波动，要完善该近期时段的年代学。此前，对于所研究的剖面（1 - 24厘米），仅有基于来自平行沉积物序列较深部分的8个加速器质谱放射性碳测年数据的宽范围OxCal年龄 - 深度模型的外推结果，该模型曾通过铯活度浓度分布的双峰对上部进行了初步验证。与之前的铯测量并行，还通过伽马能谱法测定了铅和镭（用于更详细的基于铅的年代学）、镅（用于额外的时间标记）以及钾和钍的浓度。对于基于铅的年代学，由于与纯指数分布存在较大偏差，采用了恒定通量（CF）模型来计算沉积物年龄和堆积速率。尽管宽范围的OxCal模型和CF模型在深度达22厘米时大致相似，但基于铅的年龄在最上部12厘米的不确定性方面明显更优，而宽范围模型在20厘米以下（>150年）的不确定性较小。CF模型给出0 - 11厘米剖面的平均质量堆积速率为(0.08 ± 0.03)克/平方厘米·年，12 - 22厘米剖面的平均质量堆积速率为(0.03 ± 0.01)克/平方厘米·年。在沉积物记录的粒度分布以及元素/同位素组成的深度分布中均观察到显著变化，这很可能与集水区降水量强度和总量的可观测变化有关。所获得的包含多种放射性同位素的博拉陶湖高分辨率记录可作为类似研究的区域基准。
