Simulation of the Eemian Greenland ice sheet
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This thesis focuses on the simulation of the Greenland ice sheet (GrIS) during the Eemian interglacial period (~125,000 years ago). The warm Eemian summers on Greenland are used as a past analogue for future warmer conditions. The aim of this work is a contribution to the improvement of future sea level rise predictions and to better understand how model uncertainties propagate through the chain of models necessary to simulate ice sheet evolution in past climates. Firstly, the influence of surface mass balance (SMB) models and climate model resolution on the simulation of the Eemian SMB is investigated. The corresponding study shows that both, the selection of the SMB model as well as the climate model resolution are essential for simulating the Eemian SMB, and either of these two factors can have a dominating effect on the results. However, which factor dominates the results depends on the climate state (cold or warm) and particularly the prevailing insolation regime. It is shown that an inclusion of insolation in the selected SMB model is essential for the simulated warm early Eemian conditions. Secondly, the influence of SMB forcing on millennial time scale ice sheet modeling is tested. The simulations with two different SMB forcings reveal a large difference in the evolution of the ice sheet, while ice flow sensitivity tests with changed basal friction and changed ice flow approximation show small differences. Thirdly, regional climate simulations with a full surface energy balance model are analyzed focusing on Greenland surface melt. This analysis shows that all Greenland ice core locations, also GRIP near the summit of Greenland, are affected by surface melt during the Eemian interglacial period. Elevated levels of Eemian surface melt indicate that ice cores might be affected more strongly than previously considered. Therefore, caution needs to be applied when interpreting Greenland ice core records from warm periods such as the Eemian interglacial period. This thesis shows that forcing from a single climate model can lead to a wide range of SMBs and ice sheets. To quantify this large uncertainty, a systematic approach of model intercomparison, similar to what is used to constrain future climate projections, is advised. Climate and SMB model biases and uncertainties need to be explored and outliers rejected, to be able to provide a most likely range for the Eemian GrIS topography and its contribution to sea level.
Består avPaper I: Plach, A., Nisancioglu, K. H., Le clec’h, S., Born, A., Langebroek, P. M., Guo, C., Imhof, M., and Stocker, T. F., Eemian Greenland SMB strongly sensitive to model choice, Clim. Past 14, 1463-1485, https://doi.org/10.5194/cp-14-1463- 2018, 2018. The article is available at: http://hdl.handle.net/1956/19442
Paper II: Plach, A., Nisancioglu, K. H., Langebroek, P. M., and Born, A., Eemian Greenland ice sheet simulated with a higher-order model shows strong sensitivity to SMB forcing, The Cryosphere Discuss. The article is available in the main thesis. The article is also available at: https://doi.org/10.5194/tc-2018-225
Paper III: Plach, A., Vinther, B. M., Nisancioglu, K. H., Vudayagiri, S., and Blunier, T., Greenland climate simulations show high Eemian surface melt. Full text not available in BORA.