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首页> 外文期刊>Paleoceanography >Toward better paleocarbonate ion reconstructions: New insights regarding the CaCO3 size index
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Toward better paleocarbonate ion reconstructions: New insights regarding the CaCO3 size index

机译：寻求更好的古碳酸根离子重建：有关CaCO3尺寸指数的新见解

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The reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the CaCO3 cycle to the decrease in atmospheric CO2 content during glacial time. Such reconstructions have been challenging because each of the existing paleo-[CO3 (2-)] indices has serious limitations. In this study, we reexamine the Broecker-Clark CaCO3 size index by analyzing the < 20 mu m, 20 to 38 mu m, and 38 to 63 mu m fractions in sediments from the Ontong-Java Plateau and the Ceara Rise. Scanning electron microscope analyses demonstrate that the less than 20 mm CaCO3 is dominated by coccoliths and the greater than 20 mm CaCO3 is dominated by foraminifera. Our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera. Referenced to a core top sample from 2.31 km depth in a core top sample from 4.04 km depth on the Ontong-Java Plateau, similar to 70% of the foraminifera CaCO3 was dissolved as opposed to only similar to 7% of the coccolith CaCO3. We found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 mm in size, and thus the Broecker-Clark size index is not a measure of the extent of fragmentation. Rather, it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths. On the basis of these results, we propose a new dissolution index which involves the ratio of dissolution-susceptible foraminifera CaCO3 to total CaCO3.
机译：重建古碳酸盐离子浓度为冰川时期CaCO3循环对大气CO2含量降低的贡献提供了重要的限制。由于每个现有的古[CO3（2-）]指数都有严重的局限性，因此这种重构一直具有挑战性。在这项研究中，我们通过分析Ontong-Java高原和Ceara Rise沉积物中的<20μm，20至38μm和38至63μm的馏分，重新检查了Broecker-Clark CaCO3粒径指数。扫描电子显微镜分析表明，小于20毫米的CaCO3由椰壳石为主，大于20毫米的CaCO3由有孔虫为主。我们的结果清楚地表明，椰菜比有孔虫对溶解的抵抗力要强得多。在Ontong-Java高原上以深度为2.31 km的岩心顶部样品为参考，深度为4.04 km的岩心顶部样品，溶解了大约70％的有孔虫CaCO3，而仅溶解了7％的球藻CaCO3。我们发现，有孔虫壳的溶解不会产生大量小于63 mm的碎片，因此Broecker-Clark尺寸指数不能衡量碎片的程度。相反，它是有孔虫相对于椰菜差异溶解程度的一种度量。基于这些结果，我们提出了一个新的溶出指数，其中涉及溶出敏感性有孔虫CaCO3与总CaCO3的比率。

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