Krinner_et_al-2000-Journal_of_Geophysical_Research__Atmospheres_(1984-2012).pdf (original) (raw)

This paper reports on ana. lyses of the surface pressure, surface wind, and seasonality of temperature and precipitation in the central parts of Greenland a, nd Antarctica. a.s simulated by different general circulation models (GCMs) for the present and for the Last Glacial Maximum (LGM) climates. These parameters, in addition to the mean surface temperature, influence the air content of the ice either directly or through their influence on the pore volume. To correctly interpret the air content of the ice in terms of past ice sheet elevation changes, the wria, tions of these parameters must therefore be known. Most of the simulaUons discussed here have been ca. rried out within the framework of the Paleoclimate Modeling Intercomparison Project. Moreover, a stretched grid GCM has been used with a. high resolution over the ice sheets. We show that not [aking into account changes of surface pressure at constant altitude between the LGM a. nd today leads to an overestimation of pa, st ice sheet elevation up to 150 m, while wind speed changes are too weak to have a significant influence on ice core air content. The results concerning changes of the amplitude or phase of the seasonal variations of precipitation and tempera. ture are somewhat a. mbiguous. Most, but not all, of the models suggest an intensification of the seasonal cycle of surface temperatures over central Greenla. nd, and, to a lesser extent, over central East Antarctica. Neglecting these changes might lead to an underestimation of past eleva. tion by up to 140 m for the Greenland ice sheet, but this number is subject to large uncerta. inties. come isolated) [Raynaud and Lebel, 1979; Martinerie et al., 1992]. Because of the strong dependence on at-•nospheric pressure it has been proposed to use t, he air content A as an indicator of past ice sheet surface elevation [Lorius et al., 1968]. Nevertheless, the use of such a "paleobarometer" requires knowledge of the past. evolution of the at. mospheric pressure fields at. the surface of the ice sheet.. Moreover, past wind speed as well as temperature and precipitation seasonality must. be known because these surface climate parameters influence the ice porosity [Martinerie et al., 1994; Ra!tnaud et al., 1997]. The air content A (in cm 3 g-l) of ice is a function of the atmospheric pressure Pi, of the temperature of the site at, the close-off time interval, and of the porous volume 2Now at. Program for Climat. e Model Diagnosis and Inter-of the ice • at. close off. If the close-off pore volume and comparison, Lawrence Livermore National Laboratory, air temperature are known, one can thus theoretically Livermore, California. retrieve the paleosurface pressure Pi by measuring the air content of old ice [e.g., Martinerie et al., 1992]'