Following on from the previous post, the second glacier analysed was the Humboldt Glacier (HG) shown in Fig. 1; the largest in Greenland. This was used to provide method validation with Box et al (2012), which encompassed the whole of the Greenland Ice Sheet (GrIS), as well as a more detailed and localised analysis of individual glacier albedo behaviour. A small yearly discrepancy of 0.0006 was seen which provides confidence in the methods to replicate both short and long – term albedo variability.
Figure 1: Study site map for Humboldt Glacier. Coordinates refer to UTM (Universal Trans Mercator)
zone 20N. Contour spacing is marked at 200 m and AWS refers to the automatic weather station from which
data was collected. The inset shows shows the location of Humboldt Glacier within Greenland and the
Canadian Archipelago with coordinates referring to the NSIDC sea ice polar stereographic north system.
The results were broken down into three sections. Firstly, daily albedo measurements provide an overview of the behaviour of albedo throughout the melt season and allow short term fluctuations from the norm to be quantified (Fig. 2).
Figure 2: Seasonal evolution of daily albedo on HG.
Secondly, yearly averages were calculated including maximum and minimums (Fig. 3).
Figure 3: Yearly evolution of albedo on HG.
Finally, regional maps were created highlighting the spatial relationship of albedo fluctuations throughout the time series (Fig. 4).
Figure 4: Regional evolution of albedo on HG.
Key points from these figures are as follows:
- Average albedo across the glacier (αyearly) is decreasing at a rate of 0.0042 ± 0.0011 year-1 with minimum and maximum trends following suit.
- Analysing average monthly albedo shows that June and July were largely responsible for yearly declines with July albedo decreasing at rate twice that of αyearly (0.0086 ± 0.0023 year.-1). Almost no trend existed for August and September.
- Regionally 87% of the glacier has seen a decline in albedo.
- Two seasons saw significant deviations (σ) from daily average albedo (αdaily) with mid-June to early-August 2008 measuring 1 σ below, and early-June to mid-August 2012 measuring 2 σ below at peak melt.
- Daily melt season anomalies, defined as > 1 σ below αdaily, were five times more common in the period 2008 – 2013 than 2001 – 2007.
- Albedo standard deviations are at their largest during times of higher melt.
References: Box, J. E., Fettweis, X., Stroeve, J., Tedesco, M., Hall, D., Ste en, K., 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. The Cryosphere 6 (4), 821 – 839.