TY - JOUR
T1 - Glacier algae accelerate melt rates on the south-western Greenland Ice Sheet
AU - Cook, Joseph
AU - Tedstone, Andrew
AU - Williamson, Christopher
AU - McCutcheon, Jenine
AU - Hodson, Andrew J.
AU - Dayal, Archana
AU - Skiles, McKenzie
AU - Hofer, Stefan
AU - Bryant, Robert
AU - McAree, Owen
AU - McGonigle, Andrew
AU - Ryan, Jonathan C.
AU - Anesio, Alexandre M.
AU - Irvine-Fynn, Tristram
AU - Hubbard, Alun
AU - Hanna, Edward
AU - Flanner, Mark
AU - Mayanna, Sathish
AU - Benning, Liane G.
AU - Van As, Dirk
AU - Yallop, Marian
AU - McQuaid, Jim
AU - Gribbin, Thomas
AU - Tranter, Martyn
N1 - Funding:
NE/M021025/1
NE/M020770/1
NE/S001034/1
Funding Information:
Acknowledgements. Joseph M. Cook, Andrew J. Tedstone, Andrew J. Hodson, Christopher Williamson, Archana Dayal, Stefan Hofer, Andrew McGonigle, Alexandre M. Anesio, Tristram D. L. Irvine-Fynn, Edward Hanna, Marian Yallop and Martyn Tranter acknowledge funding from UK National Environmental Research Council large grant “Black and Bloom”. Joseph M. Cook gratefully acknowledges the Rolex Awards for Enterprise, National Geographic and Microsoft (“AI for Earth”) and NERC Standard Grant “MicroMelt” . Liane G. Benning, Jenine McCutcheon and James B. McQuaid acknowledge funding from the UK National Environmental Research Council large grant “Black and Bloom”, and Liane G. Benning and Sathish Mayanna acknowledge funding from the German Helmholtz Recruiting Initiative. Thomas Gribbin acknowledges the Gino Watkins Memorial Fund and Nottingham Education Trust. Greenland Analogue Project (GAP) weather station data are made available through the Programme for Monitoring of the Greenland Ice Sheet (http://www.promice.dk/home.html, last access: January 2020). MAR v3.8.1 regional climate model outputs used to estimate mean snow depth were provided by Xavier Fettweis. We thank Stephen Warren his for helpful comments that improved the manuscript.
Funding Information:
Financial support. This research has been supported by the
Publisher Copyright:
© Author(s) 2020.
PY - 2020/1/29
Y1 - 2020/1/29
N2 - 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 26.15±3.77 % (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 km2 area around our field site, 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.
AB - 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 26.15±3.77 % (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 km2 area around our field site, 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.
UR - https://tc.copernicus.org/articles/14/309/2020/tc-14-309-2020-supplement.pdf
UR - http://www.scopus.com/inward/record.url?scp=85078945221&partnerID=8YFLogxK
U2 - 10.5194/tc-14-309-2020
DO - 10.5194/tc-14-309-2020
M3 - Article
SN - 1994-0416
VL - 14
SP - 309
EP - 330
JO - Cryosphere
JF - Cryosphere
IS - 1
ER -