Revealing the former bed of Thwaites Glacier using sea-floor bathymetry: implications for warm-water routing and bed controls on ice flow and buttressing
Revealing the former bed of Thwaites Glacier using sea-floor bathymetry: implications for warm-water routing and bed controls on ice flow and buttressing
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DOI：
10.5194/tc-14-2883-2020
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发表时间：
2020-09-09
期刊：
影响因子：
5.2
通讯作者：
Wellner, Julia
中科院分区：
文献类型：
--
作者：
Hogan, Kelly A.;Larter, Robert D.;Wellner, Julia
紧接南极海洋冰川的海底几何形状是对暖水路径的基本控制，但它也描述了以前的地形固定点，这些固定点对冰架支撑起了重要作用。不幸的是，由于无法进入这些地区进行调查，这些信息往往缺乏，导致在数值模拟模拟中使用模拟或插值的水深测量作为边界条件。在斯韦茨冰川（TG），这一关键数据缺口在2019年国际斯韦茨冰川合作（ITGC）项目的第一次巡航期间得到了解决。我们展示了在TG近海特殊海冰条件下获得的超过2000公里(2)的新多波束回声测深仪（MBES）数据，并更新了现有的水深测量汇编。在缺少MBES数据的地方，海底槽的横截面积被低估了高达40%，或者根本没有得到解决，这表明槽容量的计算以及因此产生的海洋热通量可能被大大低估了。地形高点形态的空间变化，已知是TG浮冰架的前固定点，表明了地形证据支持的床成分的差异。我们讨论了覆冰体与冰动力学的联系，包括潜在的正反馈机制，其中软可蚀高地的侵蚀可能导致冰架不接地，即使冰很少或没有变薄。对海床粗糙度和基底阻力贡献的分析表明，TG前的海底测深与现有的海床区域相似。海底沟槽和山脊上的冰流可能受到与今天在搁浅区类似的高基底阻力的影响。我们的结论是，从这些三维水深数据集可以收集到更多关于热重下床层粗糙度和床层成分类型可能的空间变异性的信息。这项工作还解决了最近的数值冰盖和海洋模拟研究的要求，这些研究已经认识到需要精确和高分辨率的水深测量来确定通往接地区的温水路线，并最终预测冰川退缩行为。
The geometry of the sea floor immediately beyond Antarctica's marine-terminating glaciers is a fundamental control on warm-water routing, but it also describes former topographic pinning points that have been important for ice-shelf buttressing. Unfortunately, this information is often lacking due to the inaccessibility of these areas for survey, leading to modelled or interpolated bathymetries being used as boundary conditions in numerical modelling simulations. At Thwaites Glacier (TG) this critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project. We present more than 2000 km(2) of new multibeam echo-sounder (MBES) data acquired in exceptional sea-ice conditions immediately offshore TG, and we update existing bathymetric compilations. The cross-sectional areas of sea-floor troughs are under-predicted by up to 40% or are not resolved at all where MBES data are missing, suggesting that calculations of trough capacity, and thus oceanic heat flux, may be significantly underestimated. Spatial variations in the morphology of topographic highs, known to be former pinning points for the floating ice shelf of TG, indicate differences in bed composition that are supported by landform evidence. We discuss links to ice dynamics for an overriding ice mass including a potential positive feedback mechanism where erosion of soft erodible highs may lead to ice-shelf ungrounding even with little or no ice thinning. Analyses of bed roughnesses and basal drag contributions show that the sea-floor bathymetry in front of TG is an analogue for extant bed areas. Ice flow over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting at the grounding zone today. We conclude that more can certainly be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. This work also addresses the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm-water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.