The penultimate deglaciation: protocol for PMIP4 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 to the Last Interglacial (LIG, ~ 129–116 ka). The LIG stands out as one of the warmest interglacials of the last 800 ka, with high-latitude temperature warmer than today and global sea level likely higher by at least 6 meters. Considering the transient nature of the Earth system, the LIG climate and ice-sheets 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 PAGES-PMIP working group on Quaternary Interglacials, 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.

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

“…The GHG data can be found at https://doi.org/10.1594/PANGAEA.871273 (Köhler et al, 2017b). The combined ice sheet as well as the separate Northern Hemispheric and Greenland ice sheets are also publicly available on the Research Data Australia repository at https://doi.org/10.26190/5d0c0c0bd1f26 (Menviel et al, 2019). In addition, all the forcing files as well as the paleo-data described in the paper are available on the PMIP4 wiki: https://pmip4.lsce.ipsl.…”

The Onset of the Last Interglacial and Fingerprints of Transient Atlantic Meridional Overturning Circulation

“…The uncertainty represents spatially averaged 1σ standard error based upon 17 locations. The same records show anomalies of +0.4‰ ± 0.3‰ δ 18 O c vs. PDB in planktic foraminifera, and -0.5‰ ± 0.6‰ δ 18 O sw vs. SMOW. The calculation of δ 18 O sw is based upon temperature and calcite reconstructions (for further details, see the Supplementary Material).…”

“…The same records show anomalies of +0.4‰ ± 0.3‰ δ 18 O c vs. PDB in planktic foraminifera, and -0.5‰ ± 0.6‰ δ 18 O sw vs. SMOW. The calculation of δ 18 O sw is based upon temperature and calcite reconstructions (for further details, see the Supplementary Material). We compare these reconstructions against fully coupled, stable oxygen isotope enabled ECHAM5/MPIOM-wiso simulations 21 forced by changes in atmospheric GHG concentrations [22][23][24] and orbital values 25 at 130 ka.…”

“…To test this hypothesis, we mimic a transition from glacial to interglacial by initializing our model from a cold ocean state, which is an idealized representation of T-II (this experiment runs for a total of 2000 years, see Methods for further details). The simulated North Atlantic exhibits lower surface temperatures compared to PI, depleted δ 18 O values, and enriched δ 18 O c values, along with a weaker AMOC state. This scenario offers a unique characteristic, which is not possible with the typical snapshot experiments described earlier.…”

“…The proxy reconstructions cover a time span of 131 to 129 ka BP, and maintaining the injection for the entire period would imply a sea level increase of 9.3 meters; which is at the upper limit of the reconstructed sea level changes for the entire LIG period spanning from 130 to 115 ka BP 31,32 . Furthermore, the dilution effect described above would be continuously active during these 2000 years, leading to increasingly depleted δ 18 O seawater values as the freshwater forcing is maintained. Therefore, although the 0.05 Sv injection scenario provides a possible explanation and yields the smallest model/data mismatch based upon the RMSE values, we also explore an alternative mechanism to explain the ocean state reconstructed in the proxy data.…”