The penultimate deglaciation: protocol for Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 transient numerical simulations between 140 and 127 ka, version 1.0

Abstract

Abstract. The penultimate deglaciation (PDG, ∼138–128 thousand years before present, hereafter ka) is the transition from the 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 changes occurring during the penultimate deglaciation. It is thus important to investigate, with coupled atmosphere–ocean general circulation models (AOGCMs), the climate and environmental response to the large changes in 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 protocol to 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 changes in 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 deglaciation under 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 of continental ice sheets. This experiment is designed for AOGCMs to assess the 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 appropriate benchmark for upcoming model–data comparisons across the penultimate deglaciation.

Drivers of the evolution and amplitude of African Humid Periods

“…Climatic changes across the penultimate deglaciation and the LIG. The transient simulation of the penultimate deglaciation (Full, Methods) is performed with the Earth system model LOVECLIM 35 , and is forced by changes in orbital parameters 36 , greenhouse gases 37 , ice-sheet topography and associated albedo, as well as meltwater input in the North Atlantic following the PMIP4 protocol 38 (Methods). As boreal summer insolation and greenhouse gases increase across the deglaciation (Fig.…”

“…1h, green) obtained from marine sediment core GeoB7925-1 from the western African margin, and which provides an estimate of runoff from the western part of the Sahara 20 . The initially published age model of this core 20 was revised here using the radiometrically-dated time scale of speleothems from Corchia Cave 40,45 , in order to match the latest chronological improvements proposed for Termination II and the LIG 38 . This record suggests very dry conditions during HS11, followed by an increase in precipitation and peak wet conditions at ~127 ka lasting until ~124 ka.…”

Millennial scale feedbacks determine the shape and rapidity of glacial termination

“…For example, sea-level reconstructions beyond the last glacial maximum are uncertain and inconsistent (e.g. throughout MIS 3 60,61 and across MIS 5a/4 89,90 and Termination 2 [91][92][93][94] ; Fig. 4), making it difficult to test our ideas about changing AMOC stability as a driver for deglacial oscillations in ocean circulation or even to assess the boundary controls on the occurrence of millennial-timescale variability on G-IG timescales.…”

“…Many of the exciting theoretical discoveries made over the past few years have been obtained using a single model, leaving their results vulnerable to possible inadequacies in a particular model. Projects such as PMIP 94,95 will allow more confidence to be gained (or not) in proposed mechanisms as will efforts to compare unforced (e.g. without freshwater forcing) AMOC oscillations in a variety of different model setups.…”

Genesis, Evolution, and Genetic Diversity of the Hexaploid, Narrow Endemic Centaurea tentudaica

“…The niche model under current conditions was projected to the LGM, LIG, and PGM using paleoclimatic layers from Oscillayers (https://doi.org/10.5061/dryad.27f8s90). The altitude layer of the three past environmental conditions was constructed from the present layer by adding 120 m to each pixel to simulate the LGM altitude conditions [65,66], by subtracting 2.15 m to each pixel to the LIG conditions [67], and by adding 90 m to the PGM conditions [68]. Soil and pH layers were assumed to be the same as in present conditions.…”