THE GREENLAND ICE SHEET: RECONSTRUCTION UNDER MODERN-DAY CONDITIONS AND SENSITIVITY TO THE NORTH ATLANTIC OSCILLATION

THE GREENLAND ICE SHEET: RECONSTRUCTION

UNDER MODERN-DAY CONDITIONS AND

SENSITIVITY TO THE NORTH

ATLANTIC OSCILLATION

By Katherine Pingree

Thesis Advisor: Dr. Peter O. Koons

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Earth Sciences)

August 2010

The Greenland Ice Sheet is considerably exposed to the North Atlantic Oscillation (NAO), a well-known atmospheric fluctuation in sea level pressure between the Icelandic Low and Bermuda-Azores High. Persistence of a single phase of the NAO is known to cause significant changes in mass balance trends over the Greenland Ice Sheet that result in similar changes to the ice sheet. Quantitative estimates of these changes in ice thickness and volume, however, are lacking. NAO is chosen as a characteristic climate driver because it is an identifiable major modern atmospheric oscillation influencing temperature and precipitation over Greenland and may aid in predicting the future response of the Greenland Ice Sheet as well as improving the interpretation of its past.

The University of Maine Ice Sheet Model (UMISM) is used to develop a reconstruction of the present-day Greenland Ice Sheet driven with modern-day atmospheric conditions. These mass balance conditions and reconstructed ice sheet are then used to investigate the Greenland Ice Sheet’s sensitivity to persistent NAO phase conditions. Average surface temperature and total precipitation data from six distinctive years in the NAO record are used to drive persistent positive and negative NAO phase UMISM model runs. Comparisons to the reference mass balance conditions and ice sheet identify the resulting changes to the ice sheet. Model runs are compared at temporally relevant intervals, representing observed average and extreme persistence of NAO phases.

Very long-term persistence of the positive NAO phase during the Medieval Warm Period (MWP) is linked to the settlement and establishment of farming communities by the Norse people in southwest Greenland. The disappearance of the Norse ~500 years later correlates with the subsequent weakening of the NAO signal and reestablishment of the negative NAO phase. The depression of the local bedrock due to increased ice load during the reestablishment of the negative NAO phase occurs within a few decades. The resulting submergence and flooding of large sections of cultivatable land greatly affected the terrestrial resources available to the Norse and ultimately played a key role in their eventual disappearance.