Master thesis defence by Anne W. Petersen – Niels Bohr Institute - University of Copenhagen

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Master thesis defence by Anne W. Petersen

Response of stable water isotopes in Greenland precipitation to varying Eemian ice sheet configurations - a general circulation model study

Climate change is a highly political debated subject because of the consequences on the life of humans. One of the direct effects is sea level change, which can be estimated from climate modelling. Information about changes in the extent and volume of the Greenland Ice Sheet can be used to estimate global and local sea level changes linked to changes in the Greenland Ice Sheet. The previous interglacial, the Eemian, has been found to have been 3-5C warmer than present, and are therefore often suggested as an analogue to the expected climate of the following century with estimated global mean temperature change of 2-4C. The extent and height of the Greenland ice sheet during the Eemian are poorly constrained, and thus not very useful as an analogue for the future climate, yet.

In this study an attempt to constrain the Eemian Greenland Ice Sheet to isotope measurements of Eemian ice in several Greenland ice cores was made. The Greenland Ice Sheet was investigated under Eemian optimum conditions. Three Eemian experiments with variants of the Greenland Ice Sheet were carried out with the Community Atmosphere Model, CAM3, with an isotope module. An unchanged present-day ice sheet, an ice sheet having retreated mainly in northeastern Greenland and one having retreated mainly in southwestern Greenland constituted the ice sheet variants. The ice sheets limited to the north and south were represented by configurations from Born and Nisancioglu (2011) and Solgaard and Langen (2012), respectively.

None of the three ice sheet configurations for which atmospheric simulations was computed succeeded in producing isotopic composition changes (with respect to a pre-industrial control) with a similar signal as those observed from ice core measurements. It was found that a more uniform response than those produced with the applied ice sheet configurations was required for a better agreement with the observations. Finally It was concluded, that a uniform warming response in combination with a lowering of the southern part of the Greenland Ice Sheet and possibly marginal changes may constitute Eemian conditions in agreement with isotopic composition from the ice cores.

Peter L. Langen, Post doc, DMI
Bo M. Vinther, Ass. Professor, Center for Ice and Climate
Jesper Sjolte, Post doc.