This will draw upon evidence from studies of Heinrich Events from beyond the Last Glacial Cycle to address the question as to whether all Heinrich events were the same.
Beyond the tip of the iceberg: Heinrich(-like) Events during the Pleistocene
B.D.A. Naafs1,2*, J. Hefter1, R. Stein1, P. Ferretti3,4, S. Zhang5, and G.H. Haug2,6
1Alfred Wegener Institute for Polar and Marine Research, Department of Marine Geology and Paleontology, D-27568 Bremerhaven, Germany
2Leibniz Center for Earth Surface and Climate Studies, Institute for Geosciences, Potsdam University, D-14476 Potsdam, Germany
3CNR-IDPA Institute for the Dynamics of Environmental Processes and Department of Environmental Sciences, Informatics and Statistics, University Ca' Foscari of Venice, I-30123 Venice, Italy
4The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom
5Canada-Nunavut Geosciences Office, Iqaluit NU X0A 0H0, Canada
6Geological Institute, ETH Zürich, 8092 Zürich, Switzerland
*Correspondence: David Naafs
Heinrich Events are one of the most dramatic examples of abrupt/millennial-scale climate variability that characterized the last glacial (e.g., ; ; ) and as such have been a major research focus for the paleoceanographic community (). During Hudson Strait (HS) Heinrich Events (H1, 2, 4, and 5) part of the Laurentide ice sheet collapsed, sending massive amounts of iceberg through the Hudson Strait into the Labrador Sea and North Atlantic. Although most attention is paid to the Heinrich Events of the last glacial, with the drilling of new long and continuous high-resolution records from the North Atlantic (e.g., ODP Leg 162 and IODP Leg 303/306) it has become apparent that millennial-scale ice-rafting events are an integral part of Pleistocene climate (e.g., ; ; ; ; ; ; ; ). However, whether these ice-rafting events represent Heinrich(-like) Events remains controversial as the source of these ice-rafting events is often poorly constrained. The identification of Heinrich(-like) Events during older glacials is important as it can provide information about the processes, mechanisms, and necessary boundary conditions needed for Heinrich Events, which are still poorly understood.
In this context, here we review and discuss the occurrence of ice-rafting events in the mid-latitude North Atlantic during the entire Pleistocene (last 2.6 Ma). Using a combination of organic and inorganic source-indicators and several IODP Sites here we demonstrate that HS Heinrich(-like) Events are limited to the last 640 ka (MIS 16) (; ; ). We were able to pinpoint a specific rock formation () contributing to the organic fraction of ice-rafted debris (IRD) in HS Heinrich Layers and show that this source was identical for each HS Heinrich(-like) Events of the last 640 ka. This suggests that the Laurentide ice sheet had a similar configuration during the last 7 glacials, but was unable to generate massive ice-rafting events prior to MIS 16. Thus, although millennial-scale ice-rafting events were an integral part of Quaternary climate, HS Heinrich(-like) Events that involved instability of the Laurentide ice sheet were restricted to the last 640 ka. Their first occurrence is most likely related to a change in Laurentide ice sheet dynamics with a larger (volume) Laurentide ice sheet that was able to generate massive calving events for the first developing during MIS 16 (), in-line with modeled Laurentide ice sheet volume (). These results highlight the importance of IRD source indicators in long-term records as well as the role of the Laurentide ice sheet in the Mid-Pleistocene Transition that ended with MIS 16 and the appearance of the 100-ka world ().
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