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首页> 外文期刊>Geochemical Journal >Mn/Ca ratio in planktonic foraminifer from ODP Site 1144, the northern South China Sea: A possible paleoclimate indicator
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Mn/Ca ratio in planktonic foraminifer from ODP Site 1144, the northern South China Sea: A possible paleoclimate indicator

机译：南海北部ODP 1144号站浮游有孔虫中的Mn / Ca比：可能的古气候指示

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摘要

We report here high-resolution Mn/Ca ratios of planktonic foraminifer, Globigerinoides sacculifer from ODP Site 1144 in the northern South China Sea (SCS). The variation pattern of the Mn/Ca ratios of G. sacculifier from the top 170 mcd is very similar to those of the generally used paleoclimate records. such as delta O-18 of Globigerinoides ruber and SSTs derived from Mg/Ca ratios of G. sacculifer. Robust Milankovitch periodicities are presented in the power spectrum of the Mn/Ca record, as well its in those of the other paleoclimate records, Suggesting orbital forcing for the variation of the Mn/Ca ratios. Further spectral analysis indicates that the variations of the Mn/Ca ratios lead those of the delta O-18 of G. ruber at all the orbital periodicities, and are roughly in pace with or slightly lead those of the SSTs at eccentricity and obliquity periodicities, but lag behind that of the SSTs at precession periodicity. This suggests that the driven forcing for the variation of the Mn/Ca ratios mainly associate with those for the SSTs. Comparisons between the Mn/Ca ratios and other geochemical proxies for redox condition in sediments show that higher Mn/Ca ratios of G. sacculifer generally correspond to higher authigenic Mn concentrations and lower contents of total Sulfur (TS) and total organic carbon (TOC). Thus, the Mn coatings in the G. sacculifer at ODP Site 1144 are mainly associated with Mn oxides. and the variation of the Mn/Ca ratios of G. sacculifer appears to indicate changes of redox condition in sediments. Exception is observed at the top 10 mcd, in which the Mn/Ca ratios show an upward decreasing trend and low core-top values, while other proxies Suggest oxic environment in this section. The low Mn/Ca ratios agree with the general low Mn/Ca ratios in foraminifer tests from core-top sediments in the SCS. and seem to attribute to the fact that authigenic Mn precipitation are mainly generated within sediment column rather than at sediment Surface and the oxidation states for them may change from Mn(III) oxyhydroxides to Mn(IV) oxides after burial. However, details are not well known yet. Despite Of Such Uncertainties, the response of the variation of the Mn/Ca ratios of G. sacculifer to paleoclimate changes is significant, indicating that it is an informative paleoclimate indicator.
机译：我们在这里报告了南海北部（SCS）ODP站点1144的浮游有孔虫，球藻有球藻的高分辨率Mn / Ca比值。糖化芽孢杆菌的Mn / Ca比值从前170兆cd开始的变化模式与通常使用的古气候记录非常相似。例如球形双歧球菌（Globigerinoides ruber）的delta O-18和由葡萄球菌Mg / Ca之比得出的SST。在Mn / Ca记录的功率谱中以及在其他古气候记录的功率谱中都显示出鲁棒的Milankovitch周期性，这提示了Mn / Ca比值变化的轨道强迫。进一步的光谱分析表明，Mn / Ca比值的变化在所有轨道周期中都领先于红宝石三角洲O-18，并且在偏心率和倾角周期中与SST的变化大致相当或略微领先，但是在进动周期上落后于SST。这表明Mn / Ca比值变化的驱动强迫主要与SST的强迫有关。沉积物中Mn / Ca比值与其他地球化学替代物对氧化还原条件的比较表明，沙门氏菌的Mn / Ca比值较高通常对应于较高的自生Mn浓度和较低的总硫（TS）和总有机碳（TOC）含量。因此，在ODP位点1144处的葡萄球菌中的Mn涂层主要与Mn氧化物有关。葡萄球菌的Mn / Ca比值的变化似乎表明沉积物中氧化还原条件的变化。在顶部的10个mcd处观察到例外，其中Mn / Ca比显示出上升的趋势并且中心顶值低，而其他代理建议在此部分中的含氧环境。低锰/钙比与SCS岩心顶沉积物中有孔虫试验中一般低锰/钙比相符。似乎归因于这样一个事实，即自生的Mn沉淀主要在沉积物柱内而不是在沉积物表面产生，并且它们的氧化态可能在掩埋后从Mn（III）的羟基氧化物变为Mn（IV）的氧化物。但是，细节还不为人所知。尽管存在此类不确定性，但葡萄球菌的Mn / Ca比值的变化对古气候变化的响应仍然很显着，这表明它是一个有用的古气候指标。

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