Mernild et al (2013) is a new paper that has authors from several countries that I am co-author on with Knudsen, Malmros in Denmark, Hanna from UK, Yde currently in Norway and Mernild in Chile. The key items here are using the snow line observed on any particular melt season day (transient snowline=TSL) as input for mass balance assessment. This paper examines how similar the migration of the TSL is from year to year, and how ablation rate can be determined using it, when field data can be used for validation. The first two images are figures from the paper of Lemon Creek Glacier and Mittivakkat Glacier illustrating the TSL at various dates. A second key is that if the progression is relatively repeatable towards the end of the melt season, than the equilibrium line altitude (ELA) can be determined, snowline at the end of the melt season, which is a key mass balance variable. Clouds often obscure the ELA from satellite image assessment, and this allows appropriate extrapolation. The figure below needs more data to determine the consistency and nature of the TSL variation at the end of the melt season, the ELA is the top of the parabola.
Base map of Lemon Creek Glacier in 2003 with colored lines indicating various dates of the TSL.
Base map of Miitivakkat Glacier in 2012 with colored lines indicating various dates of the TSL.
Progression of the TSL approximated with a second order Polynomial, to help derive the ELA.
A good example of the utility is an examination of the Landsat 8 imagery from this summer. Alaska had a warm and relatively clear weather period that provided a rare chance to examine the TSL in three consecutive satellite passes on June 14, June 21 and June 30. This period began with the glacier almost completely snow covered, red dots indicate TSL, red arrow indicates the 6/30 TSL. On June 14 the TSL was at 775 m within a couple of hundred meters of the terminus. By 6/21 the TSl had moved up the northwest side of the glacier 1.5 km to an altitude of 900m. On June 30th the TSL was at 975m two kilometers from the terminus. This progression up the northwest side of the glacier is typical. At the start of July the glacier is still 90% snowcovered. The Juneau Icefield Research Program is on this glacier in early July and field work will be critical to identifying snow depths above the TSL, that the TSL will transect later in the summer identifying ablation. The yellow arrow indicates the formation of Lake Linda, a meltwater lake that forms on the glacier, the expansion from June 14 to June 30 is evident. Pictures of the lake from JIRP during self arrest practice are gorgeous. More detailed examination of the longer term change of Lemon Creek Glacier and Mittivakkat Glacier has been completed.
June 14 2013 Landsat image
June 21 2013 Landsat image
June 30 2013 Landsat image
A paper by Mernild and others (2011) focusses on the Mittivakkat Glacier on the east coast of Greenland. The glacier is separate from the Greenland Ice Sheet and its climate response as a result more rapid and more similar to other alpine glaciers. Mernild and others (2011) observe that the glacier has retreated 1300 meters since 1931 and that it has had a considerable negative mass balance since 1995. Sebastian Mernild at the Climate, Ocean, and Sea Ice Modeling Group, Computational Physics and Methods, Los Alamos National Laboratory, Los Alamos, New Mexico has provided the pictures that document the terminus change. The field observations is completed in conjunction with Aarhus University and University of Copenhagen, both in Denmark. Notice the glacier ends just short of the coastline in 1931, but in 2006 is 1500 meters from the coastline. Mittivakkat Glacier has a mass balance record since 1995, that is reported to the World Glacier Monitoring Service. During the 1995-2010 period the glacier’s average balance has been -0.87 meters/year. The cumulative loss is -13 m, with the highest loss being in 2010 at -2.16 m. The 13 m loss in water equivalent snow-ice is equivalent to more than 14 m of ice thickness and 15% of the glaciers entire volume. The problem for the glacier is the loss of essentially all of its snow cover in four of the last ten years, this is not a recipe for long term glacier survival (Pelto, 2010). The image immediately below is a Digital Globe image from July 2005 indicating the snow covered area with six weeks left in the melt season is already limited, the glacier is in the center of the image and is the largest ice mass by far. The middle image from 2006 has areas of firn exposed indicated with blue arrows, this is not the end of the melt season yet. The lower image is from August 26 2010 and is a MODIS image catalogued by the Danish Meteorological Institute.The arrow indicates the glacier which has only 10% snow covered area, with a couple of weeks of melting left in the season. In 2010 air temperatures at Tasiilaq a few kilometers from the glacier were in the range of 1.5 C above average leading to twice the normal melt rate at the terminus, which will generate an even more rapid retreat for 2010 and 2011. The high temperatures in 2010 were not limited to this location as noted by Jason Box of Ohio State. The high melt rates were as a result not limited to the Mittivakkat Glacier as observed by the record melting reported in the Arctic Report Card. The recent large negative balances will generate ongoing retreat. Mernild observes that in 2011 the mass balance was even larger than -2.45 m An image provided by Sebastian Mernild indicates a whole in the glacier near the terminus, indicating rapid retreat in the near future.