THE INTENSIFICATION OF NORTHERN COMPONENT DEEP WATER FORMATION DURING THE MID-PLEISTOCENE CLIMATE TRANSITION

We examine 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 record from ~250 to 1000 Ka (MIS 8-25). 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 throughout this time period. Comparing the δ¹³C record to other records from the Atlantic basin indicates that a unique increase occurred in interglacial δ¹³C values recorded at Site 1063 at ~710 ka (MIS 17). While interglacial 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. This observation suggests that an increase occurred in the proportion of nutrient depleted deep waters bathing Site 1063 during interglacial intervals beginning at ~710 ka. No change occurred in minimum δ¹³C values during glacial intervals; they always overlap with those recorded in the South Atlantic. The timing of this distinct shift in interglacial deep water circulation does not correspond with a particularly strong Northern Hemisphere summer insolation maximum. Furthermore, we point out that the event predates the onset of more extreme Pleistocene interglacial warmth beginning with MIS 11 by about 300 kyr. This suggests that there is not a simple relationship between deep water circulation and the magnitude of interglacial warmth.