RAPID: Impact of Large Scale Greenland Ice Sheet Melting on Glacier Hydrology and Meltwater Geochemistry

In 2012, multiple lines of evidence suggest a record release of freshwater from the Greenland ice sheet (GrIS), the largest expanse of glacial ice in the Northern Hemisphere and a major source of meltwater and associated material to the surrounding North Atlantic and Arctic Oceans. Between July 8 and 12, satellite-derived estimates of surface melt increased from 40% to 97% of the ice sheet. This warming received widespread media attention and public interest, yet the scientific community lacks direct observations of meltwater controls on ice sheet movement and meltwater geochemistry for such a large-scale melting event. The overarching goal of this RAPID proposal is to quantify, in short order, the impact of a large-scale melting event on the ice sheet dynamics and meltwater biogeochemistry of a large, land-terminating glacier on the western Greenland margin. RAPID funds will enable the analysis and synthesis of a unique sample set collected during other fieldwork from the Leverett Glacier catchment, a large outlet glacier that discharges through a single proglacial river. Though the focus is on the 2012 episode, the investigators will also analyze samples and GrIS dynamics data from two field seasons (2011- 12), which will aid in interpretation of changes driven by the historic melting event owing to the highly contrasting annual freshwater discharge rates. The investigators will use time-series radiogenic (beryllium-7 and radon-222) and stable isotopes (oxygen and hydrogen), each with unique sources and constant production rates, from the Leverett glacier watershed to differentiate the fractions of meltwater sourced from recent surface snow, glacial ice and delayed flow meltwater. They will also investigate the composition and magnitude of nutrient and metal fluxes released from the subglacial environment and study how these fluxes evolved during July 2012. From 2011-12, parallel ice sheet geophysical data (GPS, satellite imagery) and meltwater biogeochemistry samples (carbon, macro- and micro-nutrients) have been collected by the PI and colleagues from universities in the United Kingdom. The proposed project will fully fund a Ph.D. student, and high school students and undergraduate interns will be recruited to assist with the laboratory aspect of the research. In order to increase the visibility of this project among the general public, the PI and student will co-author an article for the WHOI magazine Oceanus. This publication reaches a wide audience through both print- and web-based editions. Finally, the Ph.D. student will continue to report on the results of this study via an Expedition Blog called "Following the Ice" on Scientific American (http://blogs.scientificamerican.com/expeditions/tag/following-the-ice/). The radon dataset is complete and available for download immediately. The beryllium-7 and water isotope data will be uploaded by August 2015.2012年，多项证据表明格陵兰冰盖（Greenland Ice Sheet, GrIS）发生了有记录以来规模最大的淡水释放事件。格陵兰冰盖是北半球最大的冰川冰体，也是周边北大西洋与北冰洋融水及相关物质的主要来源。2012年7月8日至12日期间，卫星观测估算的冰盖表面融冰范围从40%升至97%。此次融冰事件引发了媒体的广泛报道与公众关注，但科学界尚缺乏针对此类大规模融冰事件中，融水对冰盖运动的控制作用以及融水地球化学特征的直接观测数据。 本RAPID专项资助项目的核心目标是，快速量化大规模融冰事件对格陵兰西部边缘大型陆终止冰川的冰盖动力学以及融水生物地球化学过程的影响。RAPID项目经费将支持对莱弗雷特冰川（Leverett Glacier）流域其他野外考察中采集的独特样本集进行分析与综合研究——该冰川为大型出口冰川，通过单一冰前河流向外排放融水。 尽管本研究聚焦2012年的融冰事件，研究团队还将分析2011至2012年两个野外季采集的样本与格陵兰冰盖动力学数据，借助两年间淡水排放量的显著差异，辅助解释此次历史性融冰事件驱动的变化。 研究团队将利用莱弗雷特冰川流域的时间序列放射性同位素（铍-7与氡-222）以及稳定同位素（氧、氢）数据——这些同位素各自具有独特的来源与恒定的生成速率——以区分近期地表积雪、冰川冰以及延迟径流融水的占比。同时，他们将探究冰下环境释放的营养盐与金属通量的组成与规模，并分析2012年7月期间这些通量的演化过程。 2011至2012年期间，首席研究员及其英国各高校的同事已采集了同步的冰盖地球物理数据（GPS、卫星影像）以及融水生物地球化学样本（碳、大量与微量营养盐）。 本资助项目将全额资助一名博士生，同时招募高中生与本科生实习生协助完成实验室研究工作。为提升本项目在公众中的知名度，首席研究员与博士生将共同为伍兹霍尔海洋研究所（WHOI）的《Oceanus》杂志撰写文章，该刊物通过印刷版与网络版覆盖广泛受众。此外，博士生将通过《科学美国人》（Scientific American）旗下名为“跟随冰川”（Following the Ice）的探险博客（http://blogs.scientificamerican.com/expeditions/tag/following-the-ice/）持续发布本研究的相关成果。 氡同位素数据集已完整完成，可立即下载；铍-7与水同位素数据将于2015年8月前上传至公开平台。