Increased glacial-age ventilation of the Chilean margin by Antarctic Intermediate Water

• Published in: Nature Geoscience
• Main Authors: Muratli, JM, Chase, Z, Mix, AC, McManus, J
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2010
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Antarctic; Pacific; Antarc*
• Online Access: http://www.nature.com/ngeo/journal/v3/n1/abs/ngeo715.html; https://doi.org/10.1038/ngeo715; http://ecite.utas.edu.au/67719

Antarctic Intermediate Water is, at present, a water massthat brings oxygen to intermediate depths throughout theSouthern Hemisphere oceans. Models have suggested thatintermediate waters had higher concentrations of oxygenduring the last glacial period1,2, consistent with globallyreduced denitrification3 and increased production of AntarcticIntermediate Water4. However, some palaeoceanographicreconstructions5,6 have indicated that production decreased inthe southeast Pacific Ocean at this time. Here we analyse theconcentrations of Re and Mn, the sedimentary concentrationsof which are controlled by the amount of dissolved oxygenat the sea floor, from three sediment cores located along theChilean margin for the past 30,000 years. Our results fromthe cores, which bracket the present-day water-column extentof Antarctic Intermediate Water, show that the depth rangeof well-oxygenated Antarctic Intermediate Water increasedoff Chile during the Last Glacial Maximum. Dissolved oxygencontent began to decrease approximately 17,000 years ago,coincident with rapid Antarctic warming and a poleward shiftof the southern westerly winds7. Our estimates of productivityfrom accumulation rates of organic carbon and opal do notco-vary with the seafloor oxygen variations, ruling out localcontrol of seafloor oxygenation. We conclude that the dataare best explained by a combination of increased oxygenationand increased flux of Antarctic Intermediate Water during theLast Glacial Maximum.