Greenland-wide inventory of ice marginal lakes published in Scientific Reports

This month we published findings from our work on Greenland's ice marginal lakes. This work are part of the ESA Glaciers CCI (Climate Change Initiative), focused on producing a Greenland-wide inventory of ice marginal lakes as a benchmark dataset; also referred to as an Essential Climate Variable. The publication is the culmination of a lot of dedicated work from individuals in the project, pooling together specialist knowledge on classifying ice marginal lakes through various remote sensing approaches.

Ice marginal lakes form at the terrestrial margins of the Greenland Ice Sheet, ice caps, and mountain glaciers, where the outflow is dammed or restricted. Ice marginal lakes can buffer the contribution of glacial melt to the sea level budget, forming a significant store of meltwater. These lakes are also understood to burst due to dam failure and breaching, causing catastropic releases of water to the ocean known as GLOFs (Glacial Lake Outburst Floods). Ice marginal lake dynamics are generally ignored in current predictions of future sea level rise, where glacial runoff assumed to contribute directly to sea level once it leaves the glacial system.

A false colour satellite image of Kangaarssuup Tasersua in South-West Greenland. Kangaarssuup Tasersua is one of the largest ice-marginal lakes of the south-west region of the ice sheet margin, as mapped subsequently ('KT' in Figure 2 from How et al., 2021). Melt runoff from the outlet glacier to the east drains into the basin, but outflow is damed by the glacier in the west; forming the ice marginal lake. Source: SnapPlanet

We assessed and evaluated the significance of this terrestrial store of meltwater in Greenland, using three independent and established remote sensing classification techniques to classify ice marginal lakes over the entirety of the ice margin:

1. Backscatter classification from Sentinel-1 SAR (Synthetic Aperture Radar) satellite imagery
2. Multi-spectral classification from Sentinel-2 optical satellite imagery
3. Hydrological sink detection from the ArcticDEM (Digital Elevation Model)

Figure 1 from How et al. (2021) showing the overview of the 2017 ice marginal lake inventory of Greenland. Each point represents a lake - blue points indicate a lake adjacent to the ice sheet margin, and orange points are lakes that share a margin with either an ice cap or mountain glacier.

The inventory revealed 3347 ice marginal lakes (above 0.05 km²) across Greenland in 2017, with the highest number of lakes adjacent to the southwest ice sheet margin and Greenland's ice caps and mountain glaciers.

Comparison to previous work by Carrivick and Quincey (2014) suggests a 75% increase in the number of lakes along the west margin of the ice sheet over the past three decades. This trend is largely related to marked variations in the presence of smaller lakes (i.e. 0.05-0.15 km²), with future lake formation likely to be concentrated in regions where the terrestrial ice margin length will increase (e.g. where marine-terminating outlets retreat onto land).

Figure 2 from How et al. (2021) showing ice marginal lakes over a selected region of the southwestern sector of the ice sheet margin. Panel A shows lake area, B shows lake shape, and C shows the detection method. The largest lake of this region is Kangaarssuup Tasersua, which is labelled 'KT' in Panel B.

By evaluating the performance of the three methodologies used to derived the inventory, we uncovered that detecting ice marginal lakes is especially challenging in Greenland given its large latitudinal range. Water classification studies relying on a single detection method over large regions could be at risk to under-representation.

A false colour satellite image of Inderhytten lake in North-East Greenland. Inderhytten is the second largest lake in our ice marginal lake inventory, at 112 km². This was a particuarly interesting lake as its classification from satellite imagery is somewhat tricky - it is ice-covered throughout the majority of the year and its near-fjord margin lies at a low elevation. Source: SnapPlanet

As we were writing the paper, a really nice complementary study came out by Shugar et al., (2020) presenting a new global glacial lake inventory that included Greenland. This global inventory was derived solely from optical satellite imagery, which we found only captured 44% of the lakes present in our Greenland inventory. This reflects how multi-sensor and multi-method classification are time-consuming and require powerful processing capabilities that are not feasible in global studies at present; highlighting the need to continue this research and incorporate new and innovative approaches to classifying ice marginal lakes.

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Our publication is available to read (with open access) through Scientific Reports:

How, P., Messerli, A., Matzler, E., Santoro, M., Wiesmann, A., Caduff, R., Langley, K., Bojesen, M.H., Paul, F., Kaab, A. and Carrivick, J.L. Greenland-wide inventory of ice marginal lakes using a multi-method approach. Scientific Reports. doi:10.1038/s41598-021-83509-1

And the inventory can be freely accessed and downloaded through the CEDA archive.