Northern Hemispheric Trigger for The Mid-Pleistocene Transition

The earth's climate changed fundamentally during the Mid-Pleistocene Transition (MPT, 1250 ka to 750 ka), when glacial-interglacial periodicity shifted from 41- to 100 kyr, and glacial periods became more intense, with no substantial change in the orbital-Milankovitch forcing. A recent study (Pena and Goldstein, Science, 2014) from the South Atlantic Ocean found evidence for a major disruption in the Atlantic Meridional Overturning Circulation (AMOC) between MIS 25-21 ( 950-850 ka), which may have triggered intensified glacial periods and the onset of the 100 kyr cycles. We present new evidence that the onset of the MPT initiated in the Northern Hemisphere (as opposed to the southern hemisphere). Using Nd isotopes as water mass tracers, from deep sea cores along a meridional section of the Atlantic Ocean, we have reconstructed the changes to the AMOC prior to and through the MPT. Our results show a distinctive pattern of changes toward more negative ɛNd values during glacials in the North Atlantic, compared to the rest of the basin, starting at MIS 38 ( 1250 ka) and culminating during MIS 26 ( 960 ka), signaling progressively higher inputs from the surrounding Precambrian shield regions into the North Atlantic. Our MIS 26 data document a prominent spike of shield-derived Nd, unprecedented for a glacial period, indicating a major shield erosional event. This was followed by the AMOC disruption and the recurring 100 kyr glacial-interglacial periodicity. This new, Atlantic-wide view of the AMOC throughout the MPT interval points to a Northern Hemisphere sourced initiation, possibly through regolith loss (Clark et al. QSR, 2006), which would have facilitated increased growth and thickening of Northern Hemisphere ice-sheets, leading to changes in the ice-sheet and forcing feedbacks.