Unravelling contamination signals in biogenic silica oxygen isotope composition: the role of major and trace element geochemistry
Unravelling contamination signals in biogenic silica oxygen isotope composition: the role of major and trace element geochemistry
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DOI：
10.1002/jqs.1171
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发表时间：
2008-05-01
影响因子：
2.3
通讯作者：
Marsh, Nicholas G.
中科院分区：
文献类型：
--
作者：
Brewer, Tim S.;Leng, Melanie J.;Marsh, Nicholas G.
硅藻二氧化硅的氧同位素组成(O-18三角洲(硅藻))为古气候研究提供了有价值的信息，在许多湖泊和海洋沉积物中碳酸盐替代物稀有或不存在。不幸的是，在大多数沉积物中与硅藻一起发现的矿物和岩石碎片可能会有问题，因为所使用的方法将从沉积物中的所有成分中释放氧气，产生高频噪音和低频漂移，这可能与气候信号相似。迄今为止，矿物污染的清除在很大程度上依赖于化学浸出和物理分离技术(例如筛分、密度)的结合。这种组合的效率可能很低，而且经常会有相当大比例的污染物存在于提纯的硅藻样本中。利用电子光学成像和全岩地球化学法对先前“提纯”的硅藻样品进行了质量平衡，从而确定了残留污染物的类型和比例。通过将这些信息与测量的污染物氧同位素比率结合起来，就有可能从O-18三角洲(硅藻)记录中消除污染影响。对来自提洛湖(埃塞俄比亚)和贝加尔湖(西伯利亚)的岩芯模拟了与碳酸盐、特弗拉和淤泥有关的污染影响。在这两个湖泊中，新建模的三角洲O-18(硅藻)曲线显示的高频噪声较少，因此能够更好地分辨率低频气候信号。(C)自然环境研究理事会(NERC)版权2008年。经NERC许可复制。由John Wiley&Sons Ltd.出版。
The oxygen isotope composition of diatom silica (delta O-18(diatom)) provides valuable information for palaeoclimate studies where carbonate proxies are either rare or absent in many lakes and ocean sediments. Unfortunately, mineral and rock fragments found alongside diatoms in most sediments can be problematic as the method used will liberate oxygen from all components within the sediment, producing both high-frequency noise and low-frequency excursions that can resemble climate signals. Removal of mineral contamination to date has largely relied upon the combination of chemical leaching and physical separation techniques (e.g. sieving, density). This combination can be inefficient and often significant proportions of contaminants are present in the 'purified' diatom sample. Using electron optical imaging and whole-rock geochemistry on previously 'purified' diatom samples, a mass balance approach has been developed whereby the types and proportions of residual contaminants are identified. By integrating this information with measured oxygen isotope ratios of the contaminants, it is then possible to remove contamination effects from the delta O-18(diatom) record. Contamination effects relating to carbonates, tephra and silt are modelled for cores from Lake Tilo (Ethiopia) and Lake Baikal (Siberia). In both lakes the new modelled delta O-18(diatom) curves show less high-frequency noise, thus enabling better resolution of low-frequency climate signals. (c) Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons Ltd.