Did Variations in the Total Solar Irradiance affect the Greenland Ice Sheet during the Holocene? - A Model Study

Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years. It has been suggested that these events were caused by reductions in solar activity, indicating that an external forcing that is considered small, could have a potential impact on climate due to feedback mechanisms. These proposed interactions between climate and solar irradiance have been investigated using numerical models, but so far without dynamically computing the Greenland ice sheet and iceberg calving.

We therefore use the earth system model iLOVECLIM coupled to the ice sheet/ice shelf model GRISLI and to a dynamic-thermodynamic iceberg module to investigate the effect of variations in total solar irradiance (TSI) on the Greenland ice sheet, as well as on iceberg calving and transport. We have performed fifteen different transient ensemble experiments of the last 6000 years, applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads and orbital parameters as forcing. In ten of these fifteen experiments, we additionally apply reconstructed variations of the TSI that differ in amplitude (weak or strong).

The resulting transient evolution of the Greenland ice sheet fits well to observations and we do find strong fluctuations in the calving flux as computed by GRISLI. But these fluctuations occur in all the experiments performed, independent of the use of TSI forcing, indicating that internal ice sheet variability causes the simulated variations. Thus, we cannot confirm the impact of the total solar irradiance on the ice rafted debris in our coupled climate – ice-sheet – iceberg model, but our experiments do suggest that internal ice sheet variability may be a possible alternative explanation for the Holocene ice rafting events that have been observed in Atlantic sediment cores.