Simulation of the climate of the last glacial maximum with an interactive ice sheet model.

A northern hemisphere version of the ice sheet model mPISM (20 km resolution) has been coupled to the coarse resolution of the MPI climate model (resolution atmosphere: T31 corresponding to 3.75 degree, ocean: 3 degree with poles located on Greenland and Antarctica). No bias correction was applied in the coupling between the model components. To save computer time, asynchronous coupling was used with the climate model accelerated relative to the ice sheet model by a factor of 10.

The model has been exposed to preindustrial (1850 A.D.) and last glacial maximum (LGM, 21 kyears ago) insolation and greenhouse gas concentrations. The simulated ice sheet distributions are shown in Fig. 1.



For preindustrial conditions, the model simulates an ice sheet on Greenland and some smaller ones around Baffin Bay and in the Arctic, which compare well with observation. The only major discrepancy to the present ice sheets is a small ice sheet in Alaska. Here, a cold bias in the atmosphere model causes several smaller glaciers to grow together and form an ice sheet.

For the last glacial maximum the model is capable of simulating both, the Fennoscandian (located over Scandinavia) and the Laurentide (located over North America) ice sheets, in a realistic way. The model also produces an extensive glaciation over northern Siberia. This model artefact is likely to be the consequence of using steady state forcing rather than a transient forcing.

The ice sheet model has the capability to generate surges. In the eastern part of the Laurentide ice sheet the model produces Heinrich event-like multi-millennial  variability under glacial external forcing with accumulation phases and discharge through Hudson Strait (Fig. 2). There are also several other ice streams that show strong millennial variability of the discharge. This effect is an additional driving mechanism for  long-term climate variability in the model. 



A detailed description of the model and the results can be found in Ziemen 2013 and Ziemen et al. 2014.



Ziemen, F., Rodehacke, C., & Mikolajewicz, U. (2014). Coupled ice sheet–climate modeling under glacial and pre-industrial boundary conditions. Climate of the Past, 10, 1817-1836. (link) 

Ziemen, F. (2013). Glacial climate variability. PhD Thesis, Universität Hamburg, Hamburg. (link)