Algal photophysiology drives darkening and melt of the Greenland Ice Sheet.
Algal photophysiology drives darkening and melt of the Greenland Ice Sheet.
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藻类光生理学导致格陵兰冰盖变暗和融化。
DOI：
10.1073/pnas.1918412117
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发表时间：
2020
影响因子：
11.1
通讯作者：
Williamson CJ
中科院分区：
文献类型：
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作者：
Williamson CJ
Zygnematophycean“冰川藻类”的大量繁殖降低了格陵兰冰盖(GRIS)的裸露冰的反照率，放大了夏季冰面的能量吸收，并增加了来自冰冻圈的融水径流，而冰冻圈是当代海平面上升的最大贡献因素。在这里，我们通过量化使冰川藻类在裸露的冰面上茁壮成长并使其变暗的光生理机制，提供了对藻类驱动的冰盖变暗的当前理解的一步改变。显著的次生酚类色素沉积(是叶绿素细胞含量的11倍)使冰川藻类能够耐受极端辐射(高达4,000微克分子光子数∼⋅m−2⋅S−1)，同时重新利用捕获的紫外线和短波辐射产生熔体。酚类色素使细胞的总能量吸收增加了50倍，而位于遮荫色素下的冰川藻叶绿体仍然对弱光适应(Ek∼46微摩尔光子⋅m−2⋅S−1)，并依赖于典型的非光化学猝灭机制进行光调节。在GRIS上，冰川藻类只将入射能量的∼1至2.4%用于光化学，而48%至65%用于冰面融化，在藻类丰度较高的地块(∼104∼⋅mL−1)中，冰川藻类每天额外贡献1.86厘米水当量的表面融化。在区域尺度上，地表变暗是由冰川藻类对冰反照率的直接和间接影响驱动的，宽带反照率(中分辨率成像光谱仪[MODIS])与冰川藻类生物量之间存在显著的负相关关系(R2=0.75，n=149)，这表明整个西南地区反照率的变化高达75%可能归因于冰川藻类的存在。
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 chlorophylla) 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 (∼104cells⋅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.