The intensification of northern component deep water formation during the mid-Pleistocene climate transition

Poirier, Robert
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University of Delaware
This work examines the deep-water hydrography at Ocean Drilling Program (ODP) Site 1063 (subtropical North Atlantic, ~4600m) throughout the mid Pleistocene climate transition (MPT) by using high resolution benthic stable isotope (δ18O, δ13C) analyses from ~500 to 750 ka (Marine Isotope Stages [MIS] 13-18). The record fills a gap in published records creating a continuous composite stable isotope time series from ~250 to 1000 Ka (MIS 8-29). The benthic foraminiferal δ18O composite provides age control through tuning to the global stack of Lisiecki and Raymo [2005]. The benthic foraminiferal δ13C record provides a proxy for changes in the relative flux of the lower-most component of northern-sourced deep waters from MIS 8 to MIS 29. Comparison of the δ13C record with others from the Atlantic basin indicates that a unique increase occurred in the interglacial δ13C values recorded at Site 1063 at ~700 ka (MIS 17). While interglacial δ13C values consistently overlap with those recorded in the deep South Atlantic prior to this time, they consistently approach those recorded in the deep North Atlantic thereafter. By comparing the Site 1063 data to 16 other published records from sites throughout the Atlantic Ocean, I deduce that an initial enhancement of NADW production likely occurred within MIS 19, not affecting the deepest region of the North Atlantic until MIS 17. The change in deep-ocean circulation occurred without any change in orbital forcing, and pre-dates the onset of more extreme Pleistocene interglacial warmth (MIS 11) by 300-400 kyr. These results provide new evidence for the northwest migration of the interglacial Arctic Front position during this time, likely relating to Eurasian ice sheet dynamics and intensifying glacial terminations within the Norwegian-Greenland Sea during the MPT.