Supra-glacial melt lakes form in the Greenland ice sheet ablation region in response to surface melt. The Jakobshavn Ablation Region (JAR) in west – central Greenland (68.2 – 68.8°N) is an area with a high areal concentration of melt lakes, providing an ideal region to study melt lake development. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are acquired for the 2000 – 2008 melt seasons (days 150 – 274) to observe the spatial and temporal melt lake characteristics. Knowing that melt rates vary with elevation, JAR is divided into five elevation zones of 250 m intervals, between 585 – 1835 m above sea level. An empirically-derived depth function, based on MODIS optical reflectance, is applied to classified melt lake pixels at JAR, yielding depth, area and volume statistics.
There is a strong correlation between melt lake area and volume quantities, regardless of elevation. Peak zonal fractional melt area, volume maxima and peak mean melt lake depth are reached at the mid-ablation zone (1035 – 1334 m). Melt intensity is determined from a Positive Degree Day (PDD) model. A correlation is found between melt lake area and volume anomalies and PDD anomalies that decrease with elevation.
The melt season at the uppermost elevation (1585 – 1834 m) begins five weeks after the onset at the lowest elevation (585 – 834 m). The date of maximum area and volume also increase with time, with a difference of 50 - 60 days. Average melt season at JAR lasts 70 – 85 days below 1584 m and decreases to 30 days at the uppermost zone (1585 – 1834 m).
To verify MODIS-derived lake area accuracy, three IKONOS 1 m resolution images are compared for a single lake, Lake Disco (67.23°N, 48.61°W). Uncertainty in MODIS estimates of area are 20±2%. Such differences confirm the difficulty of identifying depth values between 0 and ~2.5 m from the Box and Ski (2007) lake depth-retrieval classification. Shallow depths prevent the MODIS sensor’s coarse resolution from identifying lake perimeter in area estimation.
Sixteen melt lakes are identified on an elevation-basis to describe melt lake behavior at JAR lakes individually. Melt lakes reappear in the same basin year after year and lakes that form more frequently are found at lower elevations, while lakes at higher elevations form less frequently.
Overall, supra-glacial melt lakes in west-central Greenland show evidence of melt lake formation and evolution based on elevation and topography, as suggested by Lüthje et al. (2006) and McMillan et al. (2007). The highest rates of melt intensity occur at intermediate ablation zone elevations (835 – 1584 m), coinciding with larger area and volume quantities and a longer melt season duration. Anticipating continuing climate warming, it seems likely that the high ablation and lake formation in the mid-elevations (835 – 1584 m) will continue migrate towards the ice sheet interior.