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The sediment green-blue color ratio as a proxy for biogenic silica productivity along the Chilean Margin.
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  • Chen Li,
  • Vincent J Clementi,
  • Samantha Claudia Bova,
  • Yair Rosenthal,
  • Laurel B Childress,
  • James Wright,
  • Zhimin Jian
Chen Li
Tongji University

Corresponding Author:1532983@tongji.edu.cn

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Vincent J Clementi
Rutgers University
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Samantha Claudia Bova
Rutgers University
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Yair Rosenthal
Rutgers, The State University of New Jersey
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Laurel B Childress
International Ocean Discovery Program, Texas A&M University
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James Wright
Rutgers University
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Zhimin Jian
State Key Laboratory of Marine Geology, Tongji University
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Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document high- and low-frequency variability in shipboard-generated records of the spectral Green/Blue (G/B) ratio. These changes show a strong coherence with foraminiferal isotope composition, 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 ratio. 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 content and the G/B ratio were found at both sites. We use the empirical regressions to generate continuous records of opal contents (opal%) on the Chilean Margin. 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 Ocean, with a common opal flux peak at ~ 50 ka suggesting that this increased diatom productivity in the eastern equatorial Pacific was likely driven by enhance 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.