The sediment green-blue color ratio as a proxy for biogenic silica
productivity along the Chilean Margin.
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.