15 Aug 2023
 | 15 Aug 2023
Status: this preprint is currently under review for the journal CP.

Surface mass balance and climate of the Last Glacial Maximum northern hemisphere ice sheets: simulations with CESM2.1

Sarah Louise Bradley, Raymond Sellevold, Michele Petrini, Miren Vizcaino, Sotiria Georgiou, Jiang Zhu, Bette L. Otto-Bliesner, and Marcus Lofverstrom

Abstract. The Last Glacial Maximum (LGM, from ~26 to 20 ka BP) was the most recent period with large ice sheets in Eurasia and North America. At that time, global temperatures were 5–7 °C colder than today, and sea level ~125 m lower. LGM simulations are useful to understand Earth System dynamics including climate-ice sheet interactions, and to evaluate and improve the models representing those. Here, we present two simulations of the Northern Hemisphere ice sheet climate and surface mass balance with the CESM2.1(CAM5) with prescribed ice sheets for two time periods that bracket the LGM period: 26 ka and 21 ka BP. CESM2.1 includes explicit simulation of snow/firn compaction, albedo, refreezing, and direct coupling of ice sheet surface energy fluxes with the atmosphere. The simulated mean snowfall accumulation is lowest for the Greenland and Barents-Kara Sea Ice Sheets (GrIS, BKIS) and highest for British and Irish (BIIS) and Icelandic (IcIS) ice sheets. Melt rates are negligible for the dry BKIS and GrIS, and relatively large for the BIIS, NAISC, SIS and IcIS, and are reduced by almost a third in the colder 26 ka BP climate compared with 21 ka BP. The surface mass balance (SMB) is positive for the GrIS, BKIS, SIS and IcIS during the LGM (26 ka and 21 ka BP), and negative for the NAISC and BIIS. Relatively wide ablation areas are simulated along the southern (terrestrial), Pacific and Atlantic margins of the NAISC, across all of the BIIS surface, and along the terrestrial southern margin of the SIS. For 26 ka BP climate the integrated SMB substantially increases for the NAISC and BIIS, but it does not reverse the negative sign. Summer incoming solar radiation at the surface is largest over the high interior of the NAISC and GrIS, and minimum over the BIIS and southern margin of NAISC. Summer net radiation is maximum over the ablation areas and minimum where the albedo is highest, namely in the interior of the GrIS, northern NAISC and all of the BKIS. Summer sensible and latent heat fluxes are highest over the ablation areas, positively contributing to melt energy. Refreezing is largest along the equilibrium line for all ice sheets, and prevents 40–50 % of meltwater entering the ocean. Our SMB results are in qualitative agreement with the climatic variability across the different northern hemisphere ice sheets. The large, simulated melt for the NAISC suggests potential biases in the climate simulation, ice sheet reconstruction, and/or highly non-equilibrated climate and ice sheet at the LGM time.

Sarah Louise Bradley et al.

Status: open (until 10 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-62', Anonymous Referee #1, 31 Aug 2023 reply
  • RC2: 'Comment on cp-2023-62', Sam Sherriff-Tadano, 16 Sep 2023 reply
  • RC3: 'Comment on cp-2023-62', Anonymous Referee #3, 17 Sep 2023 reply

Sarah Louise Bradley et al.

Sarah Louise Bradley et al.


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Short summary
The Last Glacial Maximum was the most recent period with large ice sheets in the Europe and North America. We provide a detailed analysis of surface mass and energy components for two time periods the bracket the LGM: 26 ka and 21 ka. We use an earth system model which has been adopted for modern ice sheets. We find that all northern hemisphere ice sheets have a positive surface mass balance apart from the British and Irish ice sheet and the North American ice sheet complex.