Master Thesis defence – Niels Bohr Institute - University of Copenhagen

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Master Thesis defence

Master Thesis defence by Peter Riddersholm Wang
Supervisor: Peter L. Langen, CIC.
Censor: Peter Aakjær, DMI. 

Seasonality over Greenland during the Holocene and possible explanations of the 8.2 kyr event. A study based on the circulation model ECBilt-CLIO


Using an Earth Model of Intermediate Complexity, experiments are performed during the Holocene to study a) the seasonality of precipitation in Greenland and the effect on the interpretation of ice-core signals, and b) possible mechanisms that can account for the sudden decrease in temperature seen in ice cores from Greenland 8.2 kyr ago.

a) Throughout the Holocene orbital parameters have changed resulting in a 5 W/m2 drop and a 0.9 W/m2 rise in annually averaged insolation at 80 and 20°N, respectively. It has been speculated that this increase in the meridional gradient of the annual mean solar forcing can lead to changes in the seasonality of Greenland precipitation. The isotope signal in ice cores are precipitation weighted, meaning that a signal is only recorded when it snows, and a change in the seasonality of precipitation will thus cause a bias in the signal. If, for instance, the amount of summer precipitation drops, this will appear as a cooling in the signal, even if the temperature is constant.

b) δ18O records from Greenland ice cores show a large excursion of ~2‰, found at 8.2 kyr ago. This cooling has been detected in many other indicators in the Greenland ice cores, and in cores from many other locations, indicating that the 8.2 kyr event was not restricted to the North Atlantic region. It is believed, that the event is caused by freshwater discharges, originating from the melting of the Laurentide ice sheet.

Orbital and freshwater forcings are built into the model, and the results will give an indication of the effects on regional and global climate.