Inconsistencies between 14C and short-lived radionuclides-based sediment accumulation rates: Effects of long-term remineralization
Inconsistencies between 14C and short-lived radionuclides-based sediment accumulation rates: Effects of long-term remineralization
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DOI：
10.1016/j.jenvrad.2016.07.028
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发表时间：
2017-08-01
影响因子：
2.3
通讯作者：
Filley, T. R.
中科院分区：
文献类型：
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作者：
Baskaran, M.;Bianchi, T. S.;Filley, T. R.
C-14是过去50年来用于研究地质、地球化学和地球物理问题的最广泛使用的地质计时仪。当沉积速率外推用于超出测年范围的时间尺度时，建立精确的沉积速率对于重建古气候、生态和环境研究是至关重要的。然而，在人类活动未受干扰的沉积物岩心中，短期和长期沉积速率之间的一致性尚未显示出来。在这里，我们表明，来自佛罗里达州泥石湖的一个富有机(>；70%)沉积物岩心的基于AMS C-14的长期质量积累速率(MAR)类似于使用(239,240)PB，Cs-137和过量(210)PB(Pb-210(Xs))获得的短期MAR的5倍。测得的Pb-210(Xs)、Cs-137和(Pu)-P-239,240的沉积物清单与采样点的大气降尘相当，表明在过去几十年中几乎没有加速的沉积物侵蚀。Pu-239、Pu-240存在尖锐的落尘峰，表明沉积物混合很少。Cs-137和铂-239、铂-240的穿透深度比预期的要深得多，这是由于它们在沉积后的迁移性所致。用连续层的C-14年龄计算的MAR也表明火星随着深度的增加而减少，反映了渐进的再矿化作用。用一级动力学方法求出沉积物再矿化速率为4.4×10~(-4)y(~(-1))，表明从长期来看，富有机沉积物的再矿化作用影响长期MAR，但不影响C-14/C-12的比值。因此，使用C-14(和其他基于同位素的方法)获得的MAR和线性沉积速率可能是错误的，尽管C-14年龄可能不会受到这种再矿化的影响。有机质的长期再矿化速率与水体系中元素的生物地球化学循环有直接关系，需要考虑元素的质量平衡。(C)2016爱思唯尔有限公司。保留所有权利。
C-14 is the most widely utilized geochronometer to investigate geological, geochemical and geophysical problems over the past 5 decades. Establishment of precise sedimentation rates is crucial for the reconstruction of paleo-climate, -ecological and - environmental studies when extrapolation of sedimentation rates is utilized for time scales beyond the dating range. However, agreement between short-term and long-term sedimentation rates in anthropogenically unperturbed sediment cores has not been shown. Here we show that the AMS C-14-based long-term mass accumulation rate (MAR) of an organic rich (>70%) sediment core from Mud Lake, Florida to be similar to 5 times lower than the short-term MAR obtained using (239,240)pb, Cs-137 and excess (210)pb (Pb-210(xs)). The measured sediment inventories of Pb-210(xs), Cs-137 and (PU)-P-239,240 are comparable to the atmospheric fallout for the sampling site, indicating very little accelerated sediment erosion over the past several decades. Presence of sharp fallout peaks of Pu-239,Pu-240 indicates very little sediment mixing. The penetration depths of Cs-137 and Pt-239,Pt-240 were found to be much deeper than expected and this is attributed to their post-depositional mobility. MAR calculated using C-14-ages in successive layers also indicated decreasing MARs with depth, and was reflective of progressive remineralization. Using first-order kinetics, the sediment remineralization rate was found to be 4.4 x 10(-4) y(-1) and propose that over the long-term, remineralization of organic-rich sediment affected the long-term MAR, but not the ratio of C-14/C-12. Thus, the MAR and linear sedimentation rate obtained using C-14 (and other isotope-based methods) could be erroneous, although C-14 ages may not be affected by such remineralization. Long-term remineralization rates of organic matter has a direct bearing on the biogeochemical cycling of elements in aqueous systems and mass balance of elements needs to be taken into consideration. (C) 2016 Elsevier Ltd. All rights reserved.