The Sediment Green‐Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin
The Sediment Green‐Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin
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DOI：
10.1029/2022gc010350
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发表时间：
2022-01
期刊：
影响因子：
3.7
通讯作者：
Chen Li;V. Clementi;S. Bova;Y. Rosenthal;L. Childress;J. Wright;Z. Jian
中科院分区：
文献类型：
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作者：
Chen Li;V. Clementi;S. Bova;Y. Rosenthal;L. Childress;J. Wright;Z. Jian
最近在D/V JOIDES Resolution Expedition 379 T（JR 100）期间从智利边缘收集的沉积物岩心记录了船上生成的绿色/蓝色（G/B）比率记录的变化。这些变化与底栖有孔虫δ 18 O、南极冰芯记录和沉积物岩性（例如，硅藻丰度较高的绿色沉积物间隔），这表明气候相关的控制G/B。在这里，我们测试的效用G/B作为一个代理硅藻生产力在站点J1002和J1007通过校准G/B测量生物蛋白石。在这两个地点测得的蛋白石%和G/B之间的强指数相关性。我们使用经验回归来生成智利边缘蛋白石含量（蛋白石%）的高分辨率记录。更高的生产力往往导致更多的减少沉积条件。氧化还原敏感的沉积物U/Th通常与两个站点的重建蛋白石%共变，支持沉积物颜色，沉积物U/Th和生产力之间的关联。最后，我们计算了在过去的150，000年中，地点J1007的蛋白石质量积累率（MAR）。来自站点J1007的G/B衍生的蛋白石MAR记录在很大程度上跟踪了来自赤道南太平洋和赤道东太平洋（EEP）传统湿碱消化的现有记录，在250 ka时具有共同的蛋白石通量峰值，这表明EEP中硅藻生产力的增加可能是由南大洋的营养供应增强而不是之前提出的尘埃输入驱动的。总的来说，我们的研究结果确定G/B比作为一个有用的工具，有可能产生可靠的，高分辨率的古海洋记录，规避传统的费力的方法。
Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard‐generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate‐related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high‐resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox‐sensitive sedimentary U/Th generally co‐varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B‐derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet‐alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high‐resolution paleoceanographic records that circumvent the traditionally laborious methodology.