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The Cryosphere An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Oct 2019

Submitted as: research article | 28 Oct 2019

Review status
A revised version of this preprint is currently under review for the journal TC.

Quantifying spatiotemporal variability of ice algal blooms and the impact on surface albedo in southwest Greenland

Shujie Wang1, Marco Tedesco1,2, Patrick Alexander1,2, Min Xu3, and Xavier Fettweis4 Shujie Wang et al.
  • 1Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • 2NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • 3Department of Geography, University of Alabama, Tuscaloosa, AL 35401, USA
  • 4Department of Geography, University of Liège, Liège 4000, Belgium

Abstract. Albedo reduction due to light-absorbing impurities can substantially enhance ice sheet surface melt by increasing surface absorption of solar energy. Ice algae have been suggested to play a critical role in darkening the ablation zone in southwest Greenland. It was very recently found that the Sentinel-3 Ocean and Colour Instrument (OLCI) band ratio R709 nm/R673 nm can characterize the spatial patterns of ice algal blooms. However, Sentinel-3 was launched in 2016 and current data are only available over three melting seasons. Here, we demonstrate the capability of the MEdium Resolution Imaging Spectrometer (MERIS) for mapping ice algae from space and extend the quantification of ice algal blooms over southwest Greenland back to the period 2004–2011. Several band ratio indices (MERIS chlorophyll indices and impurity index) were computed and compared with each other and against field measurements. The results indicate that the MERIS two-band ratio index (2BDA) R709 nm/R665 nm is very effective in capturing the spatial distribution and temporal dynamics of ice algal growth on bare ice in July and August. We analyzed the interannual (2004–2011) and summer (July–August) trends of algal abundance and found significant increasing trends of ice algae close to the Jakobshavn Isbrae Glacier and along the middle dark zone between the altitudes of 1200 m and 1400 m. Using broadband albedo data from the Moderate Resolution Imaging Spectroradiometer (MODIS) we quantified the impact of ice algal growth on bare ice albedo, finding a 0.02∼0.04 reduction rate in albedo for each algal population doubling. Our analysis indicates the strong potential for the satellite algal index to be used to reduce bare ice albedo biases in regional climate model simulations.

Shujie Wang et al.

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Shujie Wang et al.

Shujie Wang et al.


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Publications Copernicus
Short summary
Ice algal blooms play a significant role in darkening the Greenland Ice Sheet during summertime. The dark pigments generated by ice algae could substantially reduce the bare ice albedo and thereby enhance surface melt. We used satellite data to map the spatial distribution of ice algae and characterized the seasonal growth pattern and interannual trends of ice algae in southwest Greenland. Our study is important for bridging the microbial activities with ice sheet mass balance.
Ice algal blooms play a significant role in darkening the Greenland Ice Sheet during summertime....