GCM SIMULATIONS OF THE LAST GLACIAL MAXIMUM SURFACE CLIMATE OF GREENLAND AND ANTARCTICA

The LMDz variable grid GCM was used to simulate the Last Glacial Maxim um (LGM, 21 ky Bp.) climate of Greenland and Antarctica at a spatial r esolution of about 100 km. The high spatial resolution allows to inves tigate the spatial variability of surface climate change signals, and thus to address the question whether the sparse ice core data can be v iewed as representative for the regional scale climate change. This st udy addresses primarily surface climate parameters because these can b e checked against the, limited, ice core record. The changes are gener ally stronger for Greenland than for Antarctica, as the imposed change s of the forcing boundary conditions (e.g., sea surface temperatures) are more important in the vicinity of Greenland. Over Greenland, and t o a limited extent also in Antarctica, the climate shows stronger chan ges in winter than in summer. The model suggests that the linear relat ionship between the surface temperature and inversion strength is modi fied during the LGM. The temperature dependency of the moisture holdin g capacity of the atmosphere alone cannot explain the strong reduction in snowfall over central Greenland; atmospheric circulation changes a lso play a crucial role. Changes in the high frequency variability of snowfall, atmospheric pressure and temperature are investigated and po ssible consequences for the interpretation of ice core records are dis cussed. Using an objective cyclone tracking scheme, the importance of changes of the atmospheric dynamics off the coasts of the ice sheets, especially for the high frequency variability of surface climate param eters, is illustrated. The importance of the choice of the LGM ice she et topography is illustrated for Greenland, where two different topogr aphies have been used, yielding results that differ quite strongly in certain nontrivial respects. This means that the paleo-topography is a significant source of uncertainty for the modelled paleoclimate. The sensitivity of the Greenland LGM climate to the prescribed sea surface conditions is examined by using two different LGM North Atlantic data sets.