Scheick Jessica, Enderlin Ellyn M, Miller Emily E, Hamilton Gordon
School of Earth and Climate Sciences, University of Maine, Orono, ME 04469, USA.
Climate Change Institute, University of Maine, Orono, ME 04469, USA.
Remote Sens (Basel). 2019;11(8). doi: 10.3390/rs11080935. Epub 2019 Apr 18.
Warm water masses circulating at depth off the coast of Greenland play an important role in controlling rates of mass loss from the Greenland Ice Sheet through feedbacks associated with the melting of marine glacier termini. The ability of these warm waters to reach glacier termini is strongly controlled by fjord bathymetry, which was unmapped for the majority of Greenland's fjords until recently. In response to the need for bathymetric measurements in previously uncharted areas, we developed two companion methods to infer fjord bathymetry using icebergs as depth sounders. The main premise of our methods centers around the idea that deep-drafted icebergs will become stranded in shallow water such that estimates of iceberg surface elevation can be used to infer draft, and thus water depth, under the assumption of hydrostatic equilibrium. When and where available, surface elevations of icebergs stranded on bathymetric highs were extracted from digital elevation models (DEMs) and converted to estimates of iceberg draft. To expand the spatial coverage of our inferred water depths beyond the DEM footprints, we used the DEMs to construct characteristic depth-width ratios and then inferred depths from satellite imagery-derived iceberg widths. We tested and applied the methods in two fjord systems in western Greenland with partially constrained bathymetry, Ilulissat Isfjord and Naajarsuit Fjord, to demonstrate their utility for inferring bathymetry using remote sensing datasets. Our results show that while the uncertainties associated with the methods are high (up to ±93 m), they provide critical first-order constraints on fjord bathymetry.
在格陵兰岛海岸附近深处循环的暖水体，通过与海洋冰川末端融化相关的反馈机制，在控制格陵兰冰盖的质量损失速率方面发挥着重要作用。这些暖水到达冰川末端的能力受到峡湾地形的强烈控制，直到最近，格陵兰岛大部分峡湾的地形仍未被测绘。为了满足在以前未测绘地区进行水深测量的需求，我们开发了两种配套方法，利用冰山作为深度探测器来推断峡湾水深。我们方法的主要前提围绕这样一个观点，即吃水较深的冰山会搁浅在浅水区，这样在静水压力平衡的假设下，冰山表面海拔的估计值可用于推断吃水深度，进而推断水深。当有可用数据时，从数字高程模型（DEM）中提取搁浅在地形高点上的冰山的表面海拔，并将其转换为冰山吃水深度的估计值。为了将我们推断的水深空间覆盖范围扩展到DEM覆盖范围之外，我们利用DEM构建特征深度-宽度比，然后从卫星图像得出的冰山宽度推断深度。我们在格陵兰岛西部两个水深部分受限的峡湾系统，伊卢利萨特冰峡湾和纳亚尔苏伊特峡湾，测试并应用了这些方法，以证明它们在利用遥感数据集推断水深方面的实用性。我们的结果表明，虽然与这些方法相关的不确定性很高（高达±93米），但它们为峡湾水深提供了关键的一阶约束。
