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
Ryder Glacier drains from the northern margin of the Greenland Ice Sheet into Sherard Osborn Fjord. The glacier was first surveyed by Lauge Koch in 1917. By 1956 the glacier had lost 75% of its floating tongue. Since 1990 the glacier front has advanced slightly with much of this change beginning in a mini-surge in 1995. As noted in the Arctic Report Card 2010 since 2000, the net area change of the 35 widest marine-terminating glaciers is -1535 km2. This is an effective average glacier length change of -1.7 km since year 2000. While the overall area change indicates the largest observed retreat, 7 of 35 glaciers did advance in 2010 relative to 2009. The largest glacier advances were at Ryder and Storstrømmen glacier, each advancing 4.6 and 4.2 km2, respectively.The shelf front of Ryder Gletscher advanced has advanced recently at about the
rate of flow, but it is thin <200 m and fractured in the floating region. This does not appear to be an advance driven by increased mass balance. In the last decade particularly since 2003 the transient snowline observable in satellite images has in most years reached 1000 m. The floating tongue has to date managed to avoid the large losses on Petermann Glacier. Both glaciers have experienced enhanced surface melt, the key has been greater basal melt to date at Petermann Glacier. This is in contrast to the 800 m level reported in the Satellite image Atlas of Greenland. The transient snowline (TSL) on the outlet glaciers of the local ice caps provides a crucial measure of annual balance and the extent of significant melting on the Ice Sheet. The number of satellite images available has increased dramatically providing the capability for TSL identification daily if clouds permit using MODIS. MODIS, Landsat 7, NOAA Microwave imagery and ENVISAT images below indicate the transient snowline for the Ryder Glacier area. Note that many of images from late June indicate a TSL in the 1000 m range even early in the melt season. To the west of Ryder Glacier (R), Steensby Glacier (S) and sometime Petermann Glacier (P) are evident n the outlet glaciers of Steensby Gletscher and Ryder Gletscher, where
it reaches an altitude of approximately 800 m. Ryder Glacier’s TSL lies very close to the southern boundary of the processed images from the Danish Meteorological Institute. The first slide is the topgraphy of the Ryder Glacier near the TSL, the second is a 1976 satellite image from the USGS Greenland Satellite Image Atlas 1386-c. The rest are annotated images downloaded from DMI or from the USGS for the Landsat images which are false color images. The TSL tends to rise from 975 m to the east of the glacier outlet to 1100 m south of and west of the fjord entrance.