Algal photophysiology drives darkening and melt of the Greenland Ice Sheet

Christopher James Williamson, Joseph Cook, Andrew Tedstone, Marian Yallop, Jenine McCutcheon, Ewa Poniecka, Douglas Campbell, Tristram Irvine-Fynn, James B. Mcquaid, Martyn Tranter, Rupert Perkins, Alexandre Magno Anesio

Allbwn ymchwil: Cyfraniad at gyfnodolynErthygladolygiad gan gymheiriaid

66 Wedi eu Llwytho i Lawr (Pure)


Blooms of Zygnematophycean “glacier algae” lower the bare ice albedo of the Greenland Ice Sheet (GrIS), amplifying summer energy absorption at the ice surface and enhancing meltwater runoff from the largest cryospheric contributor to contemporary sea-level rise. Here, we provide a step change in current understanding of algal-driven ice sheet darkening through quantification of the photophysiological mechanisms that allow glacier algae to thrive on and darken the bare ice surface. Significant secondary phenolic pigmentation (11 times the cellular content of chlorophyll a) enables glacier algae to tolerate extreme irradiance (up to ∼4,000 µmol photons⋅m−2⋅s−1) while simultaneously repurposing captured ultraviolet and short-wave radiation for melt generation. Total cellular energy absorption is increased 50-fold by phenolic pigmentation, while glacier algal chloroplasts positioned beneath shading pigments remain low-light–adapted (Ek ∼46 µmol photons⋅m−2⋅s−1) and dependent upon typical nonphotochemical quenching mechanisms for photoregulation. On the GrIS, glacier algae direct only ∼1 to 2.4% of incident energy to photochemistry versus 48 to 65% to ice surface melting, contributing an additional ∼1.86 cm water equivalent surface melt per day in patches of high algal abundance (∼104 cells⋅mL−1). At the regional scale, surface darkening is driven by the direct and indirect impacts of glacier algae on ice albedo, with a significant negative relationship between broadband albedo (Moderate Resolution Imaging Spectroradiometer [MODIS]) and glacier algal biomass (R2 = 0.75, n = 149), indicating that up to 75% of the variability in albedo across the southwestern GrIS may be attributable to the presence of glacier algae.
Iaith wreiddiolSaesneg
Rhif yr erthygl1918412117
Tudalennau (o-i)5694–5705
Nifer y tudalennau12
CyfnodolynProceedings of the National Academy of Sciences of the United States of America
Rhif cyhoeddi11
Dyddiad ar-lein cynnar24 Chwef 2020
Dynodwyr Gwrthrych Digidol (DOIs)
StatwsCyhoeddwyd - 17 Maw 2020

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