Collaborative Research: A field and laboratory study of the melting processes of icebergs in a Greenland fjord

合作研究：格陵兰峡湾冰山融化过程的现场和实验室研究

• 批准号: 1657938
• 负责人: Hanumant Singh
• 金额: $ 4.31万
• 依托单位: Northeastern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-03-15 至 2020-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657938&HistoricalAwards=false
• 关键词: Collaborative; Research; field; laboratory; study

Iceberg calving accounts for half of the mass discharge from the Greenland and Antarctic ice sheets, which has increased dramatically over the last two decades. Through their displacement and progressive melt, these icebergs impact the regional ocean and its ecosystem by affecting its stratification, nutrient and carbon cycling. Freshwater input due to iceberg melt has the potential to impact regional sea-ice distribution and the global overturning circulation. In addition, they pose a threat to local infrastructure and navigation. Notwithstanding their importance, our understanding of where and how icebergs melt is limited and their representation in ocean and climate models is over-simplistic, in part because informed by only a handful of observations. As a result, model-based predictions of iceberg melt rates, of the fate of the melt water, and of its impact on the ocean are highly uncertain. Improved iceberg parameterizations will reduce uncertainties in model-based predictions of the impact of shrinking polar ice caps on the large-scale ocean circulation and marine ecosystems. This is an urgent issue given the projected increase in iceberg discharge from both ice sheets. While the field experiment will take place in Greenland, it is expected that the results will be applicable to Antarctica?s tabular icebergs. One student supported by this project will be exposed to a cutting-edge problem and a multidisciplinary team of researchers. A video package, created by professional producers with experience in educational/environmental material, will be developed as part of this project to illustrate the different methodologies used to address a complex scientific problem and engage a broad audience. The package produced here will include a similar video-documentary, a 360-degree virtual reality video and clips to be distributed to various media venues including social media. In general, the diverse scientific team engaged in this project has an extensive track record of public outreach through media engagement.Current parameterizations of iceberg motion and melt in ocean models typically utilize only surface ocean velocities and properties. This is inconsistent with the notion that much of the iceberg mass flux is concentrated in large icebergs with drafts of several hundred meters. Indeed, recent work by the investigators and others, based on observations, theory and laboratory experiments, has shown that both the motion and the melting of deep-keeled icebergs in a stratified ocean characterized by a vertically sheared flow are not well represented by current parameterizations. While incorporating the impact of sheared flows on parameterizations of iceberg motion is fairly straightforward, the impact of sheared flows on iceberg melt is not. In particular, preliminary laboratory experiments show that the interaction of the sheared flow with the melt plumes that rise at the edge of icebergs is complex - giving rise to non-linear melt responses. Similarly, observations and models of glaciers melting in a stratified ocean have shown that the melt dynamics is strongly affected by the ambient stratification. Based on these recent studies, the hypothesis that melting of icebergs and the distribution of melt water, in the vicinity of the iceberg, are strongly affected by the ambient stratification and vertical shear will be tested. Through a multi-faceted approach that includes field measurements in Greenland and laboratory modeling, this project seeks to identify the leading parameters that impact the distribution of subsurface melt of an iceberg and the release of melt water into the surrounding ocean. An autonomous surface vehicle, the jetyak, and an unmanned aerial vehicle will be used to quantify iceberg melt and map the circulation and distribution of melt water around the iceberg. Idealized laboratory experiments will complement the field measurements and provide quantitative and comprehensive descriptions of the melt. Together, these results will be used to improve iceberg parameterizations to be used in ocean and climate models.

冰山崩解占格陵兰和南极冰盖大量排放的一半，在过去20年里，这一数字急剧增加。这些冰山通过移位和逐渐融化，影响了区域海洋及其生态系统，影响了其分层、营养和碳循环。冰山融化的淡水输入有可能影响区域海冰分布和全球颠覆环流。此外，它们还对当地基础设施和导航构成威胁。尽管冰山很重要，但我们对冰山融化的地点和方式的了解是有限的，它们在海洋和气候模型中的表现过于简单化，部分原因是只有少数几个观测数据。因此，对冰山融化速度、融化水的命运及其对海洋影响的基于模型的预测是高度不确定的。改进的冰山参数化将减少基于模型预测极地冰盖缩小对大规模海洋环流和海洋生态系统的影响的不确定性。这是一个紧迫的问题，因为预计两个冰盖的冰山排放量都会增加。虽然野外实验将在格陵兰岛进行，但预计结果将适用于南极S板状冰山。由该项目资助的一名学生将接触到一个前沿问题和一个多学科的研究团队。作为该项目的一部分，将制作一个由在教育/环境材料方面有经验的专业制片人制作的录像带，以说明用于解决复杂科学问题和吸引广大受众的不同方法。这里制作的套餐将包括一部类似的视频纪录片、一部360度虚拟现实视频和将分发到包括社交媒体在内的各种媒体场所的剪辑。总体而言，参与这一项目的各种科学团队在通过媒体参与进行公众宣传方面有着广泛的记录。目前冰山运动和海洋融化模型的参数通常只利用表面海洋速度和特性。这与冰山质量流量大部分集中在吃水几百米的大型冰山中的观点不一致。事实上，研究人员和其他人最近基于观察、理论和实验室实验所做的工作表明，在以垂直切变流动为特征的分层海洋中，深龙骨冰山的运动和融化都不能很好地用目前的参数表示。虽然包含切变流动对冰山运动参数的影响是相当直接的，但切变流动对冰山融化的影响却不是这样。特别是，初步的实验室实验表明，剪切流动与上升在冰山边缘的熔融羽流之间的相互作用是复杂的--导致了非线性的熔融反应。同样，冰川在分层海洋中融化的观测和模型表明，冰川融化的动力学受到环境层化的强烈影响。根据最近的这些研究，冰山的融化和冰山附近的融水分布受到环境层化和垂直切变的强烈影响的假设将得到检验。通过多方面的方法，包括格陵兰岛的实地测量和实验室建模，该项目试图确定影响冰山次表层熔体分布和向周围海洋释放融化水的主要参数。自主水面飞行器Jetyak和无人驾驶飞行器将用于量化冰山融化，并绘制冰山周围融化水的循环和分布图。理想化的实验室实验将补充现场测量，并提供对熔体的定量和全面描述。总而言之，这些结果将用于改进海洋和气候模型中使用的冰山参数。