Sensitivity of the results of Northern Hemisphere ice sheet model simulations to millennium-scale forcing variations in the last glacial cycle

Abstract

Ensemble simulations with the Northern Hemisphere ice sheets model are performed for the last glacial cycle (last 123 kyr). The time dependence of the atmospheric forcing is reconstructed based on two sets of borehole data — EPICA (The European Project for Ice Coring in Antarctica; the data exhibit weak millennium-scale variabilitу) and NGRIP (North Greenland Ice Core Project; the data show strong temperature variability at the indicated timescale). The time dependence is combined with the long-term means from theERA5 reanalysis(for the present-day state) and with the IPSL-CM4-V1-MR model output for the Last Glacial Maximum. We found that the simulated trajectory in MIS3 (Marine Isotope Stage 3; ~60–30 kyr before present) is very sensitive to the relatively small perturbation of thus constructed paleoscenarios. This sensitivity is exhibited both for EPICA(after perturbing the data by the stochastic autoregressive processes with decorrelation timescale up to 2 kyr) and NGRIP data (after removing the millenium-scale variability from the data by applying the Savitzky– Golay filter). In particular, depending on the existence of such variability in the forcing dataset and provided that this variability is strong enough, an artificial interglacial is developed during MIS3. The physical reason for the development of this interglacial is the location of the system trajectory near the glacial termination threshold owing to the specific Earth orbit parameter configuration in the time interval indicated. We conclude that both the EPICA and NGRIP data can be used to force the Northern Hemisphere ice sheet model in the last glacial cycle. However, it is sensible to exclude the millennium-scale variability from the NGRIP data before applying them to paleoscenario reconstruction. In addition, high sensitivity of the model to the applied forcing during MIS3 might indicate the trajectory splitting in the vicinity of the attractor basin boundary in this time interval.