RECONSTRUCTION OF OCEAN CONDITIONS DURING THE LATE PLEISTOCENE-HOLOCENE WITH MARINE CORE SAMPLES FROM THE COAST OF CHILE

ODP Site 1234 was drilled in 1015 m water on a flat bench of the Chilean continental slope at 36°S. Its location within the Peru-Chile upwelling system and at a water depth sensitive to changes in subsurface water masses makes Site 1234 well suited to examine ocean conditions through time. Here, we focus on characterizing changes in ocean conditions during marine isotope stages (MIS) 1-3. This research was done in an undergraduate paleoclimatology and paleoceanography class during Spring 2022. X-ray fluorescence (XRF) was completed on 53 samples, and coarse-fraction compositional point counts were completed on 32 samples to 24 mcd. The Heusser et al (2006) age model was applied, dating our samples back to 41 ka. Br was used as an indicator of marine paleoproductivity and/or organic carbon preservation, Fe/Al as an indicator of reducing conditions, the siliceous to calcareous (sil/cal) microfossil abundance as an indicator of upwelling, and the benthic forams Uvigerina and Bolivina, as suboxic and dysoxic indicators. Our results show more similar ocean conditions during MIS 3 and 2, compared to the MIS 1 interglacial. MIS 3 and 2 were characterized by low Br, variable Fe/Al ratios, variable sil/cal ratios, and variable amounts of Uvigerina. Millennial oscillations in ocean and climate conditions likely influenced these variations. Peaks in sil/cal ratios in MIS 3 correspond to times of low Uvigerina, which may mark times of upwelling of more oxygenated waters, perhaps due to increased influence of Antarctic Intermediate Waters (AAIW). In contrast, MIS 1 was characterized by high Br, high Fe/Al ratios, the presence of Bolivina, and very few siliceous microfossils. High Br is consistent with high total organic carbon (TOC; de Bar et al, 2018). There are differing views on whether the increased TOC after the last glacial maximum (LGM) indicates higher productivity or less oxygen being ventilated from the AAIW leading to preservation of organic carbon. Our data supports the latter hypothesis. These findings are consistent with interpreting the transition into MIS 1 as a drier, warmer climate accompanied by warmer ocean waters, decreased upwelling, and decreased oxygen during this interglacial period. Further research will be done in Fall 2022, improving on point counts analyses.