Impact of deep subglacial groundwater on ice stream flow in West Antarctica (IGIS)

我们的项目将检验“冰下深层地下水地下水（包含在沉积岩的地壳盆地内）控制着南极洲西部冰流的流动”这一假设，并对南极洲西部冰盖（WAIS）威德尔海中部的研究所冰流（IIS）及其冷基邻居Bungenstock冰隆（BIR）进行实地测量和数值模拟。南极洲冰流是南极洲冰流的快速流动通道，它将90%的大陆冰排入海洋，需要一个膨胀的底质，因为它被水很好地润滑。冰碛物通常由冰流提供，这些冰流覆盖在WAIS冰流之下的地壳盆地内高度易蚀的沉积岩上，深达数万至数千米。冰碛层可以变形，当冰下水文源驱动软化它们的水时，促进快速的基底滑动和冰流。相反的效果是观察到当水流出到水文汇硬化的直到，减少基底滑动。无论当前的数值模型如何参数化基底滑移，对水和热源或汇的空间或时间变化的错误认识将直接转化为对这种滑移的不正确模拟，从而对冰流流动的不正确模拟。水通常被认为是在冰-冰碛界面的水文系统中产生和流动的，并且下面的沉积岩是不可渗透的。现在越来越多的证据表明，这一假设实际上是错误的，因为这些岩石的渗透性可能比以前认为的更强，并且拥有移动的地下水水库，这些地下水与界面水系统在水文学上相互作用。WAIS的Siple Coast流域、东南极冰盖、冰岛的Vatnajökull冰帽以及以前的冰川对沉积盆地中当代地下水库的水文影响的数值模型模拟，所有这些都模拟了冰盖和地下水之间剧烈的水和热的传递，因此，在模型中可能忽略了一个主要的水和热的来源冰流流动，现在迫切需要我们的理解冰流地下水的相互作用是transformed.We将确定解剖的IIS下的地壳地下水库，水和热传递的空间和时间性质之间的界面水系统，IIS的基础润滑的内在影响，并量化其脆弱性未来地下水调制的动态变化。我们将通过一个现场数据采集程序来实现这一点，该程序将提供约束地下水-冰流耦合的数值模型模拟所需的基本数据集。地震地球物理数据将诊断冰下冰碛物的内部结构和整体孔隙度以及IIS下方沉积盆地中的地下水库-重要的是整体含水层和弱透水层以及隧道山谷-并描绘目标冰下湖泊和BIR剖面捕获的任何冰下永久冻土。MT数据将描绘水库结构内的液态地下水，并确认BIR下方存在任何永久冻土。如果这一假设得到证实，那么我们将（1）改变我们对WAIS中冰流流动的理解，（2）形成并传播改进冰盖模型及其对未来WAIS变化的模拟所需的知识，（3）通过将其嵌入到群落冰盖模式CISM-2中来举例说明和分享这一点。

Our project will test the hypothesis that 'deep subglacial groundwater groundwater (contained within crustal basins of sedimentary rock) controls the flow of ice streams in West Antarctica' with an integrated programme of field measurements and numerical modelling of the Institute Ice Stream (IIS) and its cold-based neighbour the Bungenstock Ice Rise (BIR), in the central Weddell Sea sector of the West Antarctic Ice Sheet (WAIS). The IIS is particularly vulnerable to dynamic change and one of the largest sources of uncertainty in predictions of sea level change from Antarctica, and therefore an urgent priority for further scientific investigation.Ice streams are the fast-flowing conduits of the WAIS that discharge some 90% of continental ice into the ocean, requiring a substrate of basal till that dilates because it is lubricated well by water. Till is commonly supplied by ice flow over highly erodible sedimentary rocks contained within crustal basins beneath ice streams in the WAIS, tens to thousands of metres deep. Till layers can deform, facilitating fast basal slip and ice streaming when subglacial hydrological sources drive in water that softens them. The opposite effect is observed when water outflow into hydrological sinks stiffens the till, reducing basal slip. Irrespective of how current numerical models parameterise basal slip, a misrecognition of spatial or temporal variability in water and heat sources or sinks will translate directly into incorrect simulations of such slip and therefore of ice stream flow. The water is usually assumed to be produced and flow in a hydrological system at the ice-till interface, and the underlying sedimentary rocks to be impermeable. Evidence is now growing that this assumption is in fact wrong because these rocks can be more permeable than previously thought, and host to reservoirs of mobile groundwater that interacts hydrologically with the interfacial water system. Numerical model simulations of the WAIS's Siple Coast catchment, the East Antarctic Ice Sheet, the Vatnajökull Ice Cap in Iceland and the hydrological impacts of previous glaciations on contemporary groundwater reservoirs in sedimentary basins, all simulate vigorous transfers of water and heat between ice sheets and the underlying groundwater reservoirs.A major source of water and heat available for basal lubrication may therefore have been overlooked in models of ice stream flow, and it is now urgent that our understanding of ice-stream - groundwater interactions is transformed.We will identify the anatomy of the crustal groundwater reservoir beneath the IIS, the spatial and temporal nature of water and heat transfer between it and the interfacial water system, the inherent effects on the basal lubrication of the IIS, and quantify its vulnerability to future groundwater-modulated dynamic change. We will do this with a field data acquisiton programme that will deliver the essential datasets required to constrain numerical model simulations of groundwater-ice stream coupling. Seismic geophysical data will diagnose internal structures and bulk porosities of subglacial till and the groundwater reservoir in the sedimentary basin beneath the IIS - importantly bulk aquifer and aquitard layers as well as tunnel valleys - and delineate target subglacial lakes and any subglacial permafrost captured by the BIR profiles. MT data will delineate liquid groundwater within the reservoir structures and affirm the presence of any permafrost beneath the BIR.If the hypothesis is confirmed then we will have (1) transformed our understanding of ice stream flow in the WAIS, (2) formed and disseminated the knowledge required to improve ice-sheet models and their simulations of future WAIS change, and (3) exemplified and shared this by embedding it within the community ice sheet model CISM-2.