Climate variability and ice-sheet dynamics during the last three glaciations

Stephen P Obrochta,Thomas J Crowley,James E.T Channell,David A Hodell,Paul A Baker,Arisa Seki,Yusuke Yokoyama

doi:10.1016/j.epsl.2014.09.004

Abstract

A composite North Atlantic record from DSDP Site 609 and IODP Site U1308 spans the past 300,000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations. Hematite-stained grains exhibit similar repetitive down-core variations within the Marine Isotope Stage (MIS) 8 and 4–2 intervals, but little cyclic variability within the MIS 6 section. There is also no petrologic evidence, in terms of detrital carbonate-rich (Heinrich) layers, for surging of the Laurentide Ice Sheet through the Hudson Strait during MIS 6. Rather, very high background concentration of iceberg-rafted debris (IRD) indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events, such as expanded sea ice over deepwater formation sites. Altered (sub)tropical precipitation patterns and Antarctic warming during high orbital precession and low 65°N summer insolation appear related to high abundance of Icelandic glass shards and southward sea ice expansion. Differing European and North American ice sheet configurations, perhaps aided by larger variations in eccentricity leading to cooler summers, may have contributed to the relative stability of the Laurentide Ice Sheet in the Hudson Strait region during MIS 6.

Highlights

Climate was relatively unstable during the last glaciation, Marine Isotope Stages (MIS) 4–2 (e.g., Dansgaard et al, 1993)
iceberg-rafted debris (IRD) deposited during Heinrich Events H1 to H6 (Bond et al, 1992), and results from Site 609 were the first to demonstrate a link between North Atlantic sea surface temperature (SST) and Greenland air temperature (Bond et al, 1993), leading to the observation that progressively cooler Greenland insterstadials were bundled between Heinrich Events (“Bond Cycle”)
A composite North Atlantic record from DSDP Site 609 and its reoccupation, IODP Site U1308, encompasses the past three glaciations and shows that variability within MIS 6 differs substantially from that exhibited by the two surrounding glaciations

Summary

Introduction

Climate was relatively unstable during the last glaciation, Marine Isotope Stages (MIS) 4–2 (e.g., Dansgaard et al, 1993). Instability and freshwater forcing on millennial scales appear to play a role in Dansgaard– Oeschger (D–O) variability (e.g., Menviel et al, 2014). Pioneering sedimentological studies, such as those conducted at classic DSDP Site 609 from the central sub-polar North Atlantic Ocean (Bond et al, 1992, 1993; Bond and Lotti, 1995), provided the first evidence that the high-amplitude, rapid climate shifts first observed for the last glaciation in Greenland ice cores probably affected a much wider area. Sites 609/U1308 are strategically positioned to record changing climate conditions in the North Atlantic Basin and surrounding continental regions. The rationale for drilling Site U1308 was to recover a demonstrably complete stratigraphic section using modern coring methods to replace the remaining material from the Site 609 cores that is in poor condition (Expedition 303 Scientists, 2006)

Methods

Results

Discussion

Conclusion