PP029-0016
Utilizing shipboard sediment green-blue color ratio to constrain glacial-interglacial changes in South Pacific diatom productivity
Friday, 11 December 2020
Poster
Chen Li1, Vincent J Clementi2, Samantha Claudia Bova2, Yair Rosenthal2, Christopher D Charles3, James Wright4, Zhimin Jian5 and Scientific Team of Expedition 379T , (1)Tongji University, Shanghai, China, (2)Rutgers University, Department of Marine and Coastal Sciences, New Brunswick, NJ, United States, (3)Scripps Institution of Oceanography, La Jolla, CA, United States, (4)Rutgers University New Brunswick, Department of Earth and Planetary Sciences, New Brunswick, NJ, United States, (5)Tongji University, State Key Laboratory of Marine Geology, Shanghai, China
Abstract:
Shipboard-generated records of the spectral Green/Blue (G/B) ratio measured on sediment cores recently collected from the Chile Margin during
JOIDES Resolution Expedition 379T (JR100) show a strong coherence with Antarctic ice core records in extraordinary resolution, suggesting climate-related controls. Shipboard smear slides also indicate a link between lithology and sediment color (e.g., higher diatom abundances in greener sediment intervals), suggesting that in addition to a stratigraphic tool G/B could also be used as a climate archive. Historically, primary productivity records of opal mass accumulation rates (MAR) are typically low-resolution and derived by time-consuming wet-alkaline methods. Here, we test the utility of G/B as a proxy for opal productivity in two sediment cores collected by Expedition 379T: Sites J1002 (46° 4.2964′S, 75° 41.2300′W, 1534 m) and J1007 (36° 32.5400′S, 73° 39.9900′W, 808 m). Calibration of the G/B proxy was based on correlations between the sediment G/B ratio and opal content (opal%) measured by wet-alkaline digestion. Strong exponential correlations were found between G/B and opal% at both sites (J1002: n=13, r
2=0.82, p<0.01; J1007: n=25, r
2=0.57, p<0.01).
We generate continuous records of opal% and opal MAR with these calibrations. Opal MAR at both sites show distinct glacial-interglacial variability, with the highest opal flux found during Marine Isotope Stage 3. The coincidence with opal MAR changes in the eastern equatorial Pacific supports a connection between the high and low latitudes through nutrient-rich Southern Ocean Intermediate Waters (SOIW). Along the Chile Margin, higher diatom production inferred from greater opal MAR was found in intervals with and contracted Southern Ocean sea ice, suggesting that contracted sea ice and reduced stratification in the Antarctic Zone yield Si-enriched SOIW. With , Si is delivered to lower latitudes and supports diatom production. Overall, these high-resolution records confirm the hypothesis that the Southern Ocean exerts a significant control on low-latitude productivity by modulating macronutrient content in exported SOIW.
