Meltwater retention in polar firn - A new method to estimate refrozen meltwater by the means of radioscopic imaging and its application to firn cores drilled in 2012 in southern Greenland


Contact
Johannes.Freitag [ at ] awi.de

Abstract

The reported warming trend of global mean temperatures during the last three decades has a high influence on polar ice caps and associated sea level changes. In Greenland wide spread melt events associated with these temperature changes have been inferred from satellite data. As melt layers in deep ice cores have previously been used as a temperature proxy for past summer climate a melt layer analysis of firn cores should provide climatic information of the last decades. In this work a method is developed to determine the amount of refrozen meltwater in firn cores by analysing radioscopic images of the firn and using the density contrast between regular firn and refrozen meltwater for the separation. 3D computer tomography on selected firn samples is used to verify the developed automatic melt percentage determination procedure which allows for a quantification of refrozen meltwater content of firn cores in an unprecedented accuracy, resolution and speed. By applying the developed method to two southern Greenland firn cores drilled in 2012 at Dye3 and South Dome a melt history for both cores is developed using d18O measurements performed on the Dye3 core and grain size stratigraphy as dating tools. A significant increase in melting during the last decade can be inferred from the resulting annual melt percentage profiles of both cores. This increase however is not exceptional if compared to melt records extending more than 2000 years back in time. While a comparison with the d18O signal often used as a proxy parameter for paleo-temperatures hardly shows any correlation, a good correlation is found between the melt record and mean summer (especially mean July) air temperatures at the South Dome site. Significant differences are found between the annual melt record found in the firn cores and the surface melt events inferred from passive microwave data gathered by satellites.



Item Type
Thesis (Master)
Authors
Divisions
Primary Division
Programs
Primary Topic
Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
39662
Cite as
Eling, L. (2014): Meltwater retention in polar firn - A new method to estimate refrozen meltwater by the means of radioscopic imaging and its application to firn cores drilled in 2012 in southern Greenland , Master thesis, University of Bremen.


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