Impurities of glacier ice
Top image: West Greenland on the 21 August 2016. Photo: NASA Worldview.
The Greenland ice sheet is not entirely white. Parts of the ice sheet have darkened since 1996, leading to increased melting. PhD candidate Thomas Gölles has developed tools to study the interplay of particle accumulation, ice flow and ice melt. Gölles will defend his dissertation at UNIS on 29 September.
23 September 2016
Press release from the University Centre in Svalbard (UNIS) and NMBU
The Greenland ice sheet is the largest ice mass in the Northern Hemisphere and has experienced accelerating mass loss in recent decades. An increase in surface melt is the major cause for the loss of mass.
According to satellite data and ground observations, parts of the ice sheet are darkening since 1996 at a rate of about 2% per decade. The darker surface leads to more melt and ultimately to a rising sea level.
A darker surface absorbs more energy, a phenomena which can be experienced first-hand on a dark surface in a car on a sunny day. In ice the absorbed energy is used to heat up the ice and melt it.
The dark surface is caused by particles on the surface and is both natural and man-made. The darkest particles, the result of incomplete burning of biomass and fossil fuel, are called “black carbon” or in short BC. BC particles are light and small and can travel with the wind for days and over thousands of kilometres. Since BC is extremely dark a very small amount is sufficient to visibly darken snow or ice. Other dark particles are dust from erosion and particles associated to microbiological activity.
Not all particles are transported by wind or produced on the spot by microbes. Some particles are trapped inside the moving ice, where they can travel over long distances and many thousands of years before they are released when the ice melts.
Predicting future ice loss
The particles accumulate on the ice and snow surface. On snow the darkening effect of accumulated particles is short lived and takes place only until the next significant snowfall or melt event. However, on ice the particles can stay on the surface for decades before they are washed away.
The long residence time on ice leads to a high amount of accumulated particles, which darken the surface and amplifies melt. This causes more particles to melt-out, forming an accelerating feedback loop.
Thomas Gölles has developed tools to study the interplay of particle accumulation, ice flow and ice melt. Melt-out of particles depends strongly on air temperature; therefore under warmer climatic conditions the darkening effect is stronger.
The additional mass loss of the Greenland ice sheet, under a scenario of an eight degrees warmer climate in the year 2300, leads to 7% more mass loss in the year 3000 when the darkening effect is included.
Until now most studies treat ice reflectivity as constant and uniform over the whole ice sheet. The studies by Thomas Gölles emphasise the need to include ice reflectivity in projections of future sea level rise and introduce some of the necessary tools. In addition, recent decreases in BC production have a positive long-term effect on the Greenland ice sheet and glaciers in general.
Thomas Gölles will defend his PhD thesis, entitled “Impurities of glacier ice: accumulation, transport and albedo” at UNIS on Thursday 29 September 2016 at 09:15 in the auditorium “Lassegrotta”.
He will give a trial lecture entitled: “Feedback loops in the ice sheet-climate interaction and associated time scales” on Wednesday 28 September at 15:15 in Lassegrotta.
About the candidate:
Thomas Gölles (36) was born in Graz, Austria. He completed a MSc in Environmental Systems Sciences – Physics from the University of Graz, before starting his PhD studies at UNIS and NMBU in 2010.
Phone: +43 677 61132611/+46 73-817 02 91