Abstract
Foraminifera abundance and stable isotope records from ODP Site 984 (61.25°N, 24.04°W, 1648 m) in the North Atlantic are used to reconstruct surface circulation variations and the relative strength of the North Atlantic Deep Water (NADW) formation over the period spanning the peak warmth of Marine Interglacial Stage (MIS) 9e (~324–336 ka). This interval includes the preceding deglaciation, Termination 4 (T4), and the subsequent glacial inception of MIS 9d. The records indicate a greatly reduced contribution of NADW during T4, as observed in more recent deglaciations. In contrast with the most recent deglaciation, the lack of a significant NADW signal extended from T4 well into the peak interglacial MIS 9e and persisted nearly until the transition to the subsequent glacial stage MIS 9d. Although NADW formation resumed during MIS 9e, only depths greater than 2000 m appear to have been ventilated. The poorly ventilated intermediate depth of Site 984 (<2000 m) may have resulted on one hand from a general reduction of deep water ventilation by NADW during the study interval or, on the other hand, from different pathways of the spread of newly formed NADW that bypassed the study location. The intermediate depths may have also been invaded by southern-sourced waters as the formation of intermediate depth NADW weakened. The absence of any significant NADW signal at the water depth of Site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks (MIS 5e and the Holocene). Despite the perturbed intermediate depth circulation, oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of MIS 9e.
Highlights
The Middle and Late Pleistocene have been characterized by repeated glaciations lasting tens of thousands of years, interspersed with much shorter relatively warm interglacial intervals, including the Holocene, which began approximately 11,000 years ago following the last ice age (Hays et al 1976; Imbrie et al 1984)
We examine the variations in surface and deep hydrographic properties throughout the interval containing Marine Interglacial Stage (MIS) 9e at a key location in the subpolar North Atlantic and assess the changes in deep ocean circulation. We consider their implications for heat transport to the north and deep water formation during MIS 9e compared with the climatic conditions that occurred within the subsequent intervals of peak interglacial warmth, MIS 5e, and the Holocene
It is bathed at depth by the Iceland Sea Overflow Waters (ISOW) that contribute to the modern North Atlantic Deep Water (NADW) (Oppo et al 2006, 2015; Thornalley et al 2013), and sits within the core of the Glacial North Atlantic Intermediate Water (Oppo and Lehman 1993; Raymo et al 2004; Curry and Oppo 2005; Praetorius et al 2008)
Summary
The Middle and Late Pleistocene have been characterized by repeated glaciations lasting tens of thousands of years, interspersed with much shorter relatively warm interglacial intervals, including the Holocene, which began approximately 11,000 years ago following the last ice age (Hays et al 1976; Imbrie et al 1984). These studies disagreed about the exact level of warm sea surface temperatures within MIS 9e, they generally agreed that it may have been somewhat reduced compared with the Holocene, as the establishment of interglacial warming was abbreviated at an early stage (Venz et al 1999; Flower et al 2000; Voelker and de Abreu 2011) This evidence of relatively mild interglacial conditions in the high latitude North Atlantic contrasts in turn with global sea level records indicating diminished continental ice (Shackleton 1987; Stirling et al 2001; Lisiecki and Raymo 2005) and with southern hemisphere records, which suggests that MIS 9 was nearly the most prominent interglacial interval (Petit et al 1999; Hodell et al 2000; King and Howard 2000). We consider their implications for heat transport to the north and deep water formation during MIS 9e compared with the climatic conditions that occurred within the subsequent intervals of peak interglacial warmth, MIS 5e, and the Holocene
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