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Abstract. The penultimate deglaciation (PDG, ∼138–128 thousand years before present, hereafter ka) is the transition fromthe penultimate glacial maximum (PGM)to the Last Interglacial (LIG, ∼129–116 ka).The LIG stands out as one of the warmest interglacials of the last 800 000 years (hereafter kyr),with high-latitude temperature warmer than today and global sea level likely higher by at least 6 m.Considering the transient nature of the Earth system,the LIG climate and ice-sheet evolution were certainly influenced by the changesoccurring during the penultimate deglaciation.It is thus importantto investigate, with coupled atmosphere–ocean general circulation models (AOGCMs),the climate and environmental response to the large changesin boundary conditions(i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice-sheet geometry and associated meltwater fluxes) occurring during the penultimate deglaciation. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocolto perform transient simulations of the last deglaciation (19–11 ka; although the protocol covers 26–0 ka).Similar to the last deglaciation, the disintegration of continental ice sheets during the penultimate deglaciation led to significant changesin the oceanic circulation during Heinrich Stadial 11 (∼136–129 ka).However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the Past Global Changes (PAGES)-PMIP working group on Quaternary interglacials (QUIGS), we propose a protocol to perform transient simulations of the penultimate deglaciationunder the auspices of PMIP4.This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice sheets as well as freshwater input from the disintegration ofcontinental ice sheets.This experiment is designed for AOGCMs to assessthe coupled response of the climate system to all forcings.Additional sensitivity experiments are proposed to evaluate the response to each forcing.Finally, a selection of paleo-records representing different parts of the climate system is presented, providing an appropriatebenchmark for upcoming model–data comparisons across the penultimate deglaciation.
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Rapid northern hemisphere ice sheet melting during the penultimate deglaciation
Abstract The rate and consequences of future high latitude ice sheet retreat remain a major concern given ongoing anthropogenic warming. Here, new precisely dated stalagmite data from NW Iberia provide the first direct, high-resolution records of periods of rapid melting of Northern Hemisphere ice sheets during the penultimate deglaciation. These records reveal the penultimate deglaciation initiated with rapid century-scale meltwater pulses which subsequently trigger abrupt coolings of air temperature in NW Iberia consistent with freshwater-induced AMOC slowdowns. The first of these AMOC slowdowns, 600-year duration, was shorter than Heinrich 1 of the last deglaciation. Although similar insolation forcing initiated the last two deglaciations, the more rapid and sustained rate of freshening in the eastern North Atlantic penultimate deglaciation likely reflects a larger volume of ice stored in the marine-based Eurasian Ice sheet during the penultimate glacial in contrast to the land-based ice sheet on North America as during the last glacial.
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- Award ID(s):
- 1702816
- PAR ID:
- 10353203
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The formation of North Atlantic Deep Water (NADW) is an important component of the Atlantic Meridional Overturning Circulation’s redistribution of solar heat to the northern latitudes, and is sensitive to salinity perturbations in its source locations. Fresh glacial meltwater lowers the density of seawater, potentially influencing affect the strength and position of the density-driven overturning circulation. During Heinrich Stadial 1, the Laurentide Ice Sheet retreated rapidly from its maximum southeastern extent during the Last Glacial Maximum, sending icebergs and meltwater into the western North Atlantic. The Bermuda Rise is located in the deep western subtropical North Atlantic, where Antarctic Bottom Water mixes with newly formed NADW. Sediment proxy records from the Bermuda Rise have demonstrated that the strength of the NADW varied with abrupt deglacial climate changes (e.g., McManus et al., 2004, Nature). This study seeks to explore the influence of meltwater pulses from the Laurentide and Greenland ice sheets on NADW during the last deglaciation through the lens of the transport and deposition of silt and clay by deep ocean currents. We present a detailed record of fine-grained sediment provenance across the deglaciation using K’/Ar ages from Bermuda Rise Core KNR191-CDH13 (33 41.2 N, 57 36.9 W, 4583 m). The K’/Ar ages are based on measured 40Ar* (radiogenic product of 40K) and an assumed K concentration of 2% (The 40Ar* measurements are rapid and simple, allowing the development of high resolution records. Initial results from deglacial sediments on Bermuda Rise display values within the range of K’/Ar ages documented by previous studies of iceberg deposition from the North Atlantic, from ~400 to 1,200 Ma (e.g., Jantschik and Huon,1992, Eclogae geol. Helv.; Hemming et al., 2002, Chem. Geol.).more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-022-31619-3
