Quantification of Foraminifer and Coccolith Carbonate in South Atlantic Surface Sediments by Means of Carbonate Grain-Size Distributions
Quantification of Foraminifer and Coccolith Carbonate in South Atlantic Surface Sediments by Means of Carbonate Grain-Size Distributions
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DOI：
10.2110/jsr.2005.036
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发表时间：
2005-05
影响因子：
2
通讯作者：
M. Frenz;K. Baumann;B. Boeckel;René Höppner;R. Henrich
中科院分区：
文献类型：
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作者：
M. Frenz;K. Baumann;B. Boeckel;René Höppner;R. Henrich
这项研究提出了南大西洋中大西洋海脊海洋表面沉积物的差异碳酸盐预算，其结果基于碳酸盐颗粒尺寸组成。在分离成沙子、淤泥和粘土子部分后，使用 SediGraph 5100 测量淤泥粒度分布。我们发现了区域特征粒度分布，总体最小值为 8 毫米等效球体直径 (ESD)。 SEM 观察表明，粗颗粒（0.8 毫米 ESD）归因于浮游有孔虫及其碎片，细颗粒（0.8 毫米 ESD）归因于石珊瑚。在此划分的基础上，计算了有孔虫和颗石虫对沉积物碳酸盐收支的贡献的区域变化。在中温区沉积物中，有孔虫碳酸盐占主导地位，而在贫营养区，颗石岩则贡献了大部分碳酸盐。颗石石的颗粒尺寸在水深范围内保持恒定，这表明与有孔虫相比，碳酸盐溶解的敏感性较低。最后，将细粉粒 (0.8 mm ESD) 中的特征粒度分布与使用 SEM 进行计数和生物测量的石石组合结合起来。淤泥部分中的颗石岩主要是大型物种（长度 4 毫米）。较小的物种（长度，4 毫米）属于粘土部分（2 毫米 ESD）。最常见的颗石石种类的平均长度与具有形状因子的粒度分布（ESD）中的突出峰相关。建议使用与这些峰拟合的高斯分布下方的面积作为比传统体积估计更精确地定量估计单个颗石岩物种的碳酸盐贡献的方法。将碳酸盐定量划分为颗石藻产生的部分和有孔虫分泌的部分，使得能够更精确地估计碳循环中消耗和释放的CO 2 的源/汇关系。球石长度和颗粒尺寸 (ESD) 的分配表明了在依赖于非混合信号或轻微混合信号（例如同位素研究）的研究中不同球石种类的分离或积累的尺寸窗口。
This study presents a differentiated carbonate budget for marine surface sediments from the Mid-Atlantic Ridge of the South Atlantic, with results based on carbonate grain-size composition. Upon separation into sand, silt, and clay sub-fractions, the silt grain-size dis- tribution was measured using a SediGraph 5100. We found regionally characteristic grain-size distributions with an overall minimum at 8 mm equivalent spherical diameter (ESD). SEM observations reveal that the coarse particles (.8 mm ESD) are attributed to planktic for- aminifers and their fragments, and the fine particles (,8 mm ESD) to coccoliths. On the basis of this division, the regional variation of the contribution of foraminifers and coccoliths to the carbonate budget of the sediments are calculated. Foraminifer carbonate dominates the sed- iments in mesotropic regions whereas coccoliths contribute most car- bonate in oligotrophic regions. The grain size of the coccolith share is constant over water depth, indicating a lower susceptibility for car- bonate dissolution compared to foraminifers. Finally, the characteristic grain-size distribution in fine silt ( ,8 mm ESD) is set into context with the coccolith assemblage counted and biometrically measured using a SEM. The coccoliths present in the silt fraction are predominantly large species (length . 4 mm). Smaller species (length , 4 mm) belong to the clay fraction (,2 mm ESD). The average length of most frequent coccolith species is connected to prominent peaks in grain-size distri- butions (ESD) with a shape factor. The area below Gaussian distri- butions fitted to these peaks is suggested as a way to quantitatively estimate the carbonate contribution of single coccolith species more precisely compared to conventional volume estimates. The quantitative division of carbonate into the fraction produced by coccoliths and that secreted by foraminifers enables a more precise estimate for source/sink relations of consumed and released CO 2 in the carbon cycle. The allocation of coccolith length and grain size (ESD) suggests size windows for the separation or accumulation of distinct coccolith species in investigations that depend on non to slightly-mixed signals (e.g., isotopic studies).