Masters Thesis defense by Martin Vindbæk Madsen

Title: Quantifying Snow-Atmosphere Water Isotopic Exchange through Eddy Covariance Fluxes

Abstract: The project has been to study the interaction and exchange process between the snow surface and the vapour in the atmosphere at the EGRIP deep ice-core camp on the Greenland ice sheet.

Measurements of water stable isotopes in ice cores from Greenland and Antarctica are one of the cornerstones that we have in terms of the knowledge of atmospheric temperatures of more than the past 700,000 years. Our present interpretation of water stable isotopes in ice cores are made on the assumption of a perfect preservation of the isotopic composition within the snow-ice matrix on annual scales or larger. Steen-Larsen et al. [2014a] showed that post-depositional processes influence the isotopic composition of the snow in the time it resides on the surface. This fact questions our present knowledge of the climate of the past and the methods that isotope records from ice cores are being used in modern climate research.

In the summer 2016, as a part of the surface program related to the East Greenland Ice core Project (EastGRIP), a Picarro cavity ring-down spectrometer (CRDS) was installed for in-situ continuous water vapour measurements at four vertical levels: 0:5, 1, 2 and 8 metres above the snow surface. In parallel with this CRDS an eddy covariance system was installed to measure heat fluxes at the surface. The measurements from these instruments span the period between the 14th of June to the 4th of August 2016. By combining these measurements a series of hypotheses are addressed. These are for example: The isotopic composition of the snow is constant during a daily cycle, and snow does not fractionate during sublimation. These hypotheses have been commonly accepted as facts in the scientific community since the 1960s [Dansgaard, 1964].