IODP Exp 361 SAFARI Moratorium: Glacial terminations of the Plio-Pleistocene

The last 5Myr or so witnessed significant global cooling and the development of ~100kyr glacial/interglacial cyclicity. The Mid-Pleistocene transition (MPT; ~1250-700ka) marks a shift from glacial cycles dominated by obliquity forcing (the '40kyr world') to the much larger amplitude cycles that characterise the Late Pleistocene. The so-called '100kyr problem' stems from the fact that orbital forcing at ~100kyr (eccentricity) is too weak to explain the observed glacial cyclicity. Furthermore there was no apparent change in insolation forcing across the MPT that could explain the change from 40kyr to ~100kyr periodicity. Recent studies have implicated the influence of sub-orbital climate oscillations in the timing and amplitude of glacial terminations during the Late Pleistocene. Here we propose to test for the presence and amplitude of sub-orbital scale events associated with glacial terminations over the past 5 Myr.

Specifically, we will focus on the role of the Agulhas Leakage (warm and salty waters entering the Atlantic Ocean from the Indian Ocean) in propagating the recovery of interglacial mode circulation within the Atlantic basin during deglacial transitions.

We will employ an integrated approach, using multiple measurement techniques and core sites. Our approach will be to identify glacial terminations based on ship-board measurements and the results of XRF core scanning prior to the sampling party. We will then perform high resolution measurements (e.g. XRF scans, foraminiferal stable isotopes and planktonic foraminiferal faunal counts) across a selection of terminations to assess the magnitude of millennial-scale perturbations and their timing, relative to the specific termination in question (as determined by benthic foraminiferal d18O). We will also investigate conditions bracketing each deglacial sequence (i.e. the preceding glacial and subsequent interglacial intervals) in order to assess potential linkages between the magnitudes of millennial-scale perturbations and the termination itself. Surface temperature reconstructions (from foraminiferal fauna) would be compared with XRF scans of Fe/Ti/Al/Ca to proxy riverine runoff, in order to assess the compound effects of frontal movements associated with abrupt changes in ocean circulation. Benthic foraminiferal d13C will be employed to assess corresponding changes in ocean circulation associated with the surface changes we reconstruct.

Glacial terminations to be investigated will include T2, 5 and 7 and a selection of earlier transitions. Specific terminations will be identified during the cruise as material is collected and initial screening / age model development proceeds.

Beneficiaries and benefits

The academic beneficiaries of our project will be:

Paleoclimate scientists. We will produce proxy records of climate variability that will inform debate over the mechanisms of glacial termination during the Plio-Pleistocene. In particular we will focus on the Agulhas Leakage, as system that lies at the southern end of the so-called instantaneous bipolar seesaw. As such we will shed light on a significant problem from a different perspective as commonly taken (i.e. the North Atlantic).

Climate and Paleoclimate modellers. Our results will provide important constraints on the possible driving mechanism of deglaciation through time (across the Mid Pleistocene Transition). The potential impact of differing climate state for the effects of abrupt changes on ocean circulation will also be addressed. These results will inform climate modellers in terms of experimental design and interpretation.

Non-academic beneficiaries of the project will include bodies such as the Intergovernmental Panel on Climate Change (IPCC). The latest report of the IPCC (AR5) contained a chapter dedicated to paleoclimate, which made use of findings such as those to be attained during this project. Moreover, the IPCC, as well as many national governmental bodies make use of climate model predictions that rely on our understanding of the physical processes that underlie the climate system. The knowledge gained from this project will provide constraints that can be used to assess the ability of climate models to simulate natural climate variability, which will provide confidence in their ability to predict changes possible in the future.

Other non-academic beneficiaries will include the general public and student bodies, through the enhancement of our understanding of Earth's climate as a natural system.