Diatom silicon isotopes as a proxy for silicic acid utilisation: a southern ocean core top calibration
Diatom silicon isotopes as a proxy for silicic acid utilisation: a southern ocean core top calibration
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DOI：
10.1016/j.gca.2012.08.002
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发表时间：
2012-11
影响因子：
5
通讯作者：
K. Egan;R. Rickaby;M. Leng;K. Hendry;M. Hermoso;H. Sloane;H. Bostock;A. Halliday
中科院分区：
文献类型：
--
作者：
K. Egan;R. Rickaby;M. Leng;K. Hendry;M. Hermoso;H. Sloane;H. Bostock;A. Halliday
尽管越来越多的工作使用硅藻δ 30 Si来重建过去的草酸利用变化，但很少有研究专注于用现代海洋学条件校准岩心顶部数据。在这项研究中，微过滤技术被用来划分南大洋核心顶部二氧化硅到狭窄的尺寸范围，分离成分，如放射虫，海绵骨针和粘土矿物硅藻。这些组分的硅同位素分析表明，包含少量的非硅藻材料可以显著抵消测量的真正硅藻δ 30 Si。一旦选择了正确的粒度级（通常为2-20μm），硅藻δ 30 Si显示出与地表水柠檬酸浓度的强负相关性（R2=0.92），高度支持硅藻δ 30 Si作为柠檬酸利用率的代表的定性使用。岩心顶部硅藻δ 30 Si与已发表的原位研究中混合层过滤硅藻δ 30 Si匹配良好，表明溶解作用或早期成岩作用对南大洋沉积物中硅藻δ 30 Si的影响很小或没有影响。然而，当使用单一源项时，岩心顶部硅藻δ 30 Si显示出对南大洋简单瑞利或稳态模型的较差拟合。相反，只有当考虑到涌上的藻酸浓度和δ 30 Si的初始条件的变化时，这些模型才能描述数据，这可能会给硅藻δ 30 Si对过去藻酸利用的定量重建带来一些误差。
Despite a growing body of work that uses diatom δ30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ30Si. Once the correct size fraction is selected (generally 2–20μm), diatom δ30Si shows a strong negative correlation with surface water silicic acid concentration (R2=0.92), highly supportive of the qualitative use of diatom δ30Si as a proxy for silicic acid utilisation. The core top diatom δ30Si matches well with mixed layer filtered diatom δ30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ30Si in sediments from the Southern Ocean. However, the core top diatom δ30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ30Si.