| Autor: |
Li, Chen, Clementi, Vincent J., Bova, Samantha C., Rosenthal, Yair, Childress, Laurel B., Wright, James D., Jian, Zhimin |
| Předmět: |
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| Zdroj: |
Geochemistry, Geophysics, Geosystems: G3; Sep2022, Vol. 23 Issue 9, p1-16, 16p |
| Abstrakt: |
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. Plain Language Summary: The color of marine sediments often corresponds to oceanic and sedimentary processes that can influence the global climate system. Visual inspection of new sediment cores collected from the Chilean Margin revealed substantial downcore changes in green and blue sediment colors. Greener sediment intervals were usually enriched with diatoms, whereas bluer sediments were rich in clay minerals. A specialized camera was used to scan the cores and enable us to quantitatively describe the core colors using the green/blue (G/B) ratio. The similarity of the downcore G/B ratio with Antarctic ice core records suggests that it may serve as a quick tool to estimate the age of the cores during the cruise. In this paper, we show that changes in the G/B ratio are a function of diatom (biogenic opal) productivity and use a calibrated relationship to calculate a continuous record of opal flux at the Chilean Margin over the last 150,000 years. A distinct opal flux maxima at 50,000 years ago is observed, similar to previous studies in the eastern equatorial Pacific. This common event implies a tight link between the high‐ and low‐latitude eastern Pacific Ocean, potentially attributable to enhanced nutrient supply from the Southern Ocean. Key Points: Sediment green‐to‐blue ratio serves as a novel proxy for changes in diatom productivity on the Chilean MarginHigh‐resolution opal mass accumulation rates derived from green‐to‐blue ratio agree with existing records for the last 150 kyrThe green‐to‐blue ratio proxy is potentially applicable in other regions of high diatom productivity with a site‐specific calibration [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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