Glacier algae accelerate melt rates on the south-western Greenland Ice Sheet
Glacier algae accelerate melt rates on the south-western Greenland Ice Sheet
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DOI：
10.5194/tc-14-309-2020
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发表时间：
2020-01-29
期刊：
影响因子：
5.2
通讯作者：
Tranter, Martyn
中科院分区：
文献类型：
--
作者：
Cook, Joseph M.;Tedstone, Andrew J.;Tranter, Martyn
格陵兰冰盖（GrIS）的融化是海平面上升的最大单一因素，并且由于冰面上色素藻类的生长而被放大，这增加了太阳辐射的吸收。这种生物反照率降低效应及其对海平面上升的影响以前没有被量化。在这里，我们将场光谱与辐射传输模型、无人机（UAV）和卫星遥感数据的监督分类以及径流模型相结合，以计算生物驱动的冰面消融。研究表明，2017年夏季，冰川的增长导致GrIS西南地区裸冰径流量增加4.4-6.0 Gt，占总径流量的10% - 13%。在具有高生物量积累的局部斑块中，藻类加速融化高达26.15 +/- 3.77%（标准误差，SE）。2017年是高反照率的一年，因此我们也将分析扩展到特别低反照率的2016年融化季节。2016年，西南赤冰区由藻类贡献的径流量要高得多，为8.8-12.2 Gt，尽管藻类贡献的径流量占总径流量的比例相似，为9% - 13%。在我们现场周围10000公里(2)的区域内，藻类在这两年覆盖了相似比例的裸露冰区（2016年为57.99%，2017年为58.89%），但2016年被归类为“高生物量”的藻冰（8.35%）比2017年（2.54%）更多。这一年际比较显示了一种正反馈，在高融化年份，冬季积雪退得更远、更早，预计会形成更广泛、更高生物量的藻华，为藻华的发展提供更大的面积，也增加了从融化的冰中释放出来的营养物质和液态水的供应。我们的分析证实了这种生物反照率反馈的重要性，并且预测模型中对其的遗漏导致了对格陵兰岛未来海平面贡献的系统性低估，特别是因为可供藻类定居的裸冰带和生物生长季节的长度都将在未来扩大。
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 al- gal 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 km(2) 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.