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.

冰山崩解占格陵兰岛和南极冰盖排放量的一半，这些排放量在过去二十年急剧增加。通过移动和逐渐融化，这些冰山通过影响其分层、营养物和碳循环来影响区域海洋及其生态系统。冰山融化造成的淡水输入有可能影响区域海冰分布和全球翻转环流。此外，它们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有限，而且它们在海洋和气候模型中的表示过于简单化，部分原因是只有少数观察结果。因此，基于模型对冰山融化速率、融化水的命运及其对海洋影响的预测具有高度不确定性。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影响的不确定性。鉴于预计两个冰盖的冰山排放量都会增加，这是一个紧迫的问题。虽然现场实验将在格陵兰岛进行，但预计结果将适用于南极洲的板状冰山。受该项目支持的一名学生将接触到前沿问题和多学科研究人员团队。作为该项目的一部分，将开发由具有教育/环境材料经验的专业制作人制作的视频包，以说明用于解决复杂科学问题并吸引广泛受众的不同方法。这里制作的包将包括一个类似的视频纪录片、一个 360 度虚拟现实视频和剪辑，将分发到包括社交媒体在内的各种媒体场所。总的来说，参与该项目的多元化科学团队在通过媒体参与进行公众宣传方面拥有广泛的记录。当前海洋模型中冰山运动和融化的参数化通常仅利用表面海洋速度和特性。这与大部分冰山质量通量集中在吃水深度达数百米的大型冰山的观点不一致。事实上，研究人员和其他人最近基于观察、理论和实验室实验的工作表明，以垂直剪切流为特征的分层海洋中深龙骨冰山的运动和融化并不能很好地用当前的参数化来表示。虽然将剪切流对冰山运动参数化的影响相当简单，但剪切流对冰山融化的影响却并非如此。特别是，初步实验室实验表明，剪切流与冰山边缘上升的熔体羽流的相互作用非常复杂，从而产生非线性熔体响应。同样，对分层海洋中冰川融化的观测和模型表明，融化动力学受到周围分层的强烈影响。基于这些最近的研究，将检验以下假设：冰山融化和冰山附近融水的分布受到周围分层和垂直剪切的强烈影响。通过包括格陵兰岛现场测量和实验室建模在内的多方面方法，该项目旨在确定影响冰山地下融化分布以及融水释放到周围海洋的主要参数。自主水面车辆、喷气艇和无人机将用于量化冰山融化并绘制冰山周围融水的循环和分布图。理想化的实验室实验将补充现场测量，并提供熔体的定量和全面的描述。这些结果将共同用于改进海洋和气候模型中使用的冰山参数化。