Deep sea paleoceanographic changes in the Southeastern Pacific over the last 400 kyr and its linkage to the Antarctic Circumpolar Current and Patagonian Ice Sheet

Antarctic Intermediate Water (AAIW) plays a significant role in transporting large volumes of relatively cool water masses to low latitudes and modulating climate. This study investigates the deep sea paleoceanographic evolution of the Southeastern Pacific (SEP) Ocean and the influence of the Patagonian Ice Sheet (PIS) and Antarctic Circumpolar Current (ACC) dynamics in modulating AAIW formation. Sediment core samples from International Ocean Discovery Program (IODP) Site U1542, located at 1101 m depth on the Chilean margin, and under the influence of AAIW, were analysed for benthic foraminiferal assemblages, surface productivity, and major minerals to achieve the objectives. Six benthic foraminifera biofacies are delineated using multivariate analyses, suggesting changes in bottom water conditions related to oxygenation and organic flux. Changes in biofacies suggest a change from well-ventilated bottom water with an intermediate flux of organic matter in the SEP from 400 to 240 ka, followed by a reduction in bottom water oxygenation coupled with higher nutrient and organic flux from 240 ka through the Holocene boundary, except for a short interval of low productivity and increased ventilation from 130 to 100 ka. PIS expansion and contraction control the nutrient flux and extent of ACC in the SEP, which modulates the formation of AAIW during various glacial-interglacial periods. ACC variability proxy show a 100 kyr cycle as observed in the Asian monsoon records, whereas SEP bottom water characteristic variability shows 44 kyr obliquity cycle, supporting the role of the Southern Ocean in modifying marine carbon reservoirs by influencing AAIW production.