Glacier algae accelerate melt rates on the south-western Greenland Ice Sheet
<p>Melting of the Greenland Ice Sheet (GrIS) is the largest single contributor to eustatic sea level and is amplified by the growth of pigmented algae on the ice surface, which increases solar radiation absorption. This biological albedo-reducing effect and its impact upon sea level rise has n...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-01-01
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| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/14/309/2020/tc-14-309-2020.pdf |
| Summary: | <p>Melting of the Greenland Ice Sheet (GrIS) is the largest
single contributor to eustatic sea level and is amplified by the growth
of pigmented algae on the ice surface, which increases solar radiation
absorption. This biological albedo-reducing effect and its impact upon sea
level rise has not previously been quantified. Here, we combine field
spectroscopy with a radiative-transfer model, supervised classification of
unmanned aerial vehicle (UAV) and satellite remote-sensing data, and runoff modelling to calculate
biologically driven ice surface ablation. We demonstrate that algal growth
led to an additional 4.4–6.0 Gt of runoff from bare ice in the
south-western sector of the GrIS in summer 2017, representing 10 %–13 %
of the total. In localized patches with high biomass accumulation, algae
accelerated melting by up to <span class="inline-formula">26.15±3.77</span> % (standard error, SE). The year 2017
was a high-albedo year, so we also extended our analysis to the particularly low-albedo 2016 melt season. The runoff from the south-western bare-ice zone attributed to algae was much higher in 2016 at 8.8–12.2 Gt, although the
proportion of the total runoff contributed by algae was similar at 9 %–13 %. Across a 10 000 km<span class="inline-formula"><sup>2</sup></span> area around our field site,<span id="page310"/> algae covered
similar proportions of the exposed bare ice zone in both years (57.99 %
in 2016 and 58.89 % in 2017), but more of the algal ice was classed as
“high biomass” in 2016 (8.35 %) than 2017 (2.54 %). This interannual
comparison demonstrates a positive feedback where more widespread, higher-biomass algal blooms are expected to form in high-melt years where the
winter snowpack retreats further and earlier, providing a larger area for bloom
development and also enhancing the provision of nutrients and liquid water
liberated from melting ice. Our analysis confirms the importance of this
biological albedo feedback and that its omission from predictive models
leads to the systematic underestimation of Greenland's future sea level
contribution, especially because both the bare-ice zones available for algal
colonization and the length of the biological growth season are set to
expand in the future.</p> |
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| ISSN: | 1994-0416 1994-0424 |