Intra- and inter-annual uranium concentration variability in a Belizean stalagmite controlled by prior aragonite precipitation : a new tool for reconstructing hydro-climate using aragonitic speleothems.
Intra- and inter-annual uranium concentration variability in a Belizean stalagmite controlled by prior aragonite precipitation : a new tool for reconstructing hydro-climate using aragonitic speleothems.
复制标题
伯利兹石笋的年内和年际铀浓度变化受先前文石沉淀的控制：利用文石洞穴重建水文气候的新工具。
DOI：
10.1016/j.gca.2016.06.037
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发表时间：
2016-10
影响因子：
5
通讯作者：
R. A. Jamieson;J. Baldini;M. Brett;J. Taylor;Harriet E. Ridley;C. Ottley;Keith M. Prufer;J. Wassenburg;D. Scholz;S. Breitenbach
中科院分区：
文献类型：
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作者：
R. A. Jamieson;J. Baldini;M. Brett;J. Taylor;Harriet E. Ridley;C. Ottley;Keith M. Prufer;J. Wassenburg;D. Scholz;S. Breitenbach
由于文石类洞穴沉积物可进行高精度U-Th定年，因此越来越多地被用作古气候档案。从快速增长的文石石笋的代理记录，精确地定年的时间尺度，可以允许调查气候事件发生在年度甚至亚年度的时间尺度与最小的时间不确定性。然而，许多微量元素的行为，如铀，在文石的洞穴沉积物，迄今为止还没有以及在方解石的洞穴沉积物的约束。在此，我们利用在洞穴沉积物中从方解石到文石的矿物学转变过程中测量的铀浓度变化来计算铀在文石洞穴沉积物中的分配系数（导出DU = 3.74 ± 1.13）。由于我们计算的DU大大高于1，由于岩溶水停留时间的增加而增加的先前文石沉淀应强烈控制石笋文石U/Ca值。因此，铀浓度文石洞穴应充当有效raining.We测试使用高分辨率ICP-MS衍生的微量元素数据集从伯利兹石笋的优秀代理。YOK-G是一个来自伯利兹Yok Balum洞穴的文石石笋，具有非常强大的月分辨年代学，使用年度δ 13 C循环构建。我们解释的季节性U/Ca的变化，在YOK-G的变化，反映了变化的降雨量驱动的量和季节性的变化之前的文石沉淀。U/Ca记录强烈表明，现代干燥发生在伯利兹，这种干燥主要是由于雨季降雨量减少。这与已发表的YOK-G稳定同位素数据一致，也非常强烈地表明现代降雨量减少，以前被解释为ITCZ向南移位的结果。我们的研究结果强烈表明，U/Ca值在文石洞穴沉积物是很好的代理降雨量的变化。这种新的工具，结合特殊的年代控制特征的文石石笋和现代微分析技术提供的高空间分辨率，应有助于建设新的精美解决降雨记录，提供罕见的见解季节性变化以及长期变化的当地补给条件。
Aragonitic speleothems are increasingly utilised as palaeoclimate archives due to their amenability to high precision U–Th dating. Proxy records from fast-growing aragonitic stalagmites, precisely dated to annual timescales, can allow investigation of climatic events occurring on annual or even sub-annual timescales with minimal chronological uncertainty. However, the behaviour of many trace elements, such as uranium, in aragonitic speleothems has not thus far been as well constrained as in calcitic speleothems. Here, we use uranium concentration shifts measured across primary calcite-to-aragonite mineralogical transitions in speleothems to calculate the distribution coefficient of uranium in aragonitic speleothems (derivedDU= 3.74 ± 1.13). Because our calculatedDUis considerably above 1 increased prior aragonite precipitation due to increased karst water residence time should strongly control stalagmite aragonite U/Ca values. Consequently, uranium concentrations in aragonitic speleothems should act as excellent proxies for effective rainfall.We test this using a high-resolution ICP-MS derived trace element dataset from a Belizean stalagmite. YOK-G is an aragonitic stalagmite from Yok Balum cave in Belize with an extremely robust monthly-resolved chronology built using annual δ13C cycles. We interpret seasonal U/Ca variations in YOK-G as reflecting changes in the amount and seasonality of prior aragonite precipitation driven by variable rainfall amounts. The U/Ca record strongly suggests that modern drying has occurred in Belize, and that this drying was primarily caused by a reduction in wet season rainfall. This is consistent with published stable isotope data from YOK-G also very strongly suggesting modern rainfall reductions, previously interpreted as the result of southward ITCZ displacement. Our results strongly suggest that U/Ca values in aragonitic speleothems are excellent proxies for rainfall variability. This new tool, combined with the exceptional chronological control characteristic of aragonitic stalagmites and the high spatial resolution afforded by modern microanalytical techniques, should facilitate the construction of new exquisitely resolved rainfall records, providing rare insights into seasonality changes as well as long-term changes in local recharge conditions.