A multi-model assessment of the early last deglaciation (PMIP4 LDv1): The meltwater paradox reigns supreme

• Main Authors: Snoll, Brooke, Ivanovic, Ruza, Gregoire, Lauren, Sherriff-Tadano, Sam, Menviel, Laurie, Obase, Takashi, Abe-Ouchi, Ayako, Bouttes, Nathaelle, He, Chengfei, He, Feng, Kapsch, Marie, Mikolajewicz, Uwe, Muglia, Juan, Valdes, Paul
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Ice Sheet; North Atlantic
• Online Access: https://doi.org/10.5194/egusphere-2023-1802; https://noa.gwlb.de/receive/cop_mods_00068117; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00066551/egusphere-2023-1802.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1802/egusphere-2023-1802.pdf

Transient simulations of the last deglaciation have been increasingly performed to better understand the processes leading to both the overall deglacial climate trajectory as well as the centennial- to decadal- scale climate variations prevalent during deglaciations. The Paleoclimate Modelling Intercomparison Project (PMIP) has provided a framework for an internationally coordinated effort in simulating the last deglaciation (~20 – 11 ka BP) whilst encompassing a broad range of models. Here, we present a multi-model intercomparison of 17 simulations of the early part of the last deglaciation (~20 – 15 ka BP) from nine different climate models spanning a range of model complexities and uncertain boundary conditions/forcings. A main contrasting element between the simulations is the method by which groups implement freshwater fluxes from the melting ice sheets and how this forcing then impacts ocean circulation and surface climate. We find that the choice of meltwater scenario heavily impacts the deglacial climate evolution, but the response of each model depends largely on the sensitivity of the model to the freshwater forcing as well as to other aspects of the experimental design (e.g., CO2 forcing or ice sheet reconstruction). There is agreement throughout the ensemble that warming begins in the high latitudes associated with increasing insolation and delayed warming in the tropics aligned with the later increases in atmospheric CO2 concentration. The delay in this warming in the tropics is dependent on the timescale of the CO2 reconstruction used by the modelling group. Simulations with freshwater forcings greater than 0.1 Sverdrup (Sv) after 18 ka BP experience delayed warming in the North Atlantic, whereas simulations with smaller freshwater forcings begin deglaciating sooner. All simulations show a strong correlation between North Atlantic temperatures, atmospheric CO2 concentrations, and the AMOC. In simulations with a freshwater forcing greater than 0.1 Sv, North Atlantic temperatures correlate strongly ...