Airborne geophysical investigations of conditions at the bed of fast-flowing outlet glaciers of large Canadian Arctic ice caps

最近的工作表明，在评估高山冰川和冰盖对当代全球海平面上升的影响时，最大的未知因素是北极大型冰盖的冰山崩解造成的质量损失率（Radic和Hock，2011年，《自然地球科学》）。北极最大的冰盖，事实上是南极和格陵兰冰盖之外最大的冰块，是加拿大北极岛屿的冰盖。重要的是，新的研究结果表明，2004-2009年，质量损失率的急剧增加也使加拿大北极群岛成为格陵兰岛和南极洲以外全球海平面上升的最大贡献者（Gardner等人，2011，Nature）。这些加拿大的大冰帽中的每一个都被分成一系列的流域，这些流域通过狭窄的、裂缝严重的快速流动的出口冰川流入峡湾，这些冰川将岛屿的边缘山脉分开。因此，科学家和政策制定者面临的一个主要问题是，这些冰盖将如何继续对21世纪预测的气温上升作出反应，并注意到大气环流模型预测北极的气温上升将明显高于低纬度地区。然而，由于缺乏对这些出口冰川床的几何形状和性质的了解，大型冰团的数值模拟受到限制。我们将利用机载探冰雷达、激光测高仪、重力仪、磁力仪和全球定位系统仪器，从加拿大北极地区埃尔斯米尔岛和德文郡岛的大冰帽的冰帽出口冰川获取地球物理数据。我们将重点关注每个流域的三个关键领域：严重裂缝快速流动的出口冰川本身，冰帽内部和狭窄的出口冰川之间的上部过渡区;和接地区标志着过渡到漂浮的冰舌在一些加拿大高北极峡湾的头部。我们的科学目标是：（a）确定冰面和冰下河床的高度;（B）确定底质的特性，特别是它是基岩还是可变形的沉积物;（c）确定冰下融化的分布;（d）揭示内陆冰、流出冰川和接地区之间过渡区的基底特性变化;（e）对出口冰川崩解通量及其在长达十年的时间尺度上的变化提供新的估计。这些信息，结合卫星数据集的出口冰川表面运动和我们以前的观察，这些冰盖的区域规模的几何形状，将提供基本的边界条件，这些冰盖的数值模拟，从而，他们如何应对大气和海洋变暖在未来几十年，海平面上升的影响。

Recent work has shown that the single largest unknown in assessing the contribution of mountain glaciers and ice caps to contemporary global sea-level rise is the rate of mass loss by iceberg calving from large Arctic ice caps (Radic and Hock, 2011, Nature Geoscience). The largest ice caps in the Arctic, and indeed the largest ice masses outside the Antarctic and Greenland ice sheets, are those of the Canadian Arctic islands. Importantly, new findings indicate that, for 2004-2009, a sharp increase in the rate of mass loss also makes the Canadian Arctic Archipelago the single largest contributor to global sea-level rise outside Greenland and Antarctica (Gardner et al., 2011, Nature). Each of these large Canadian ice caps is divided into a series of drainage basins that flow into fjords via narrow, heavily crevassed fast-flowing outlet glaciers which dissect the islands' fringing mountains. A major question for scientists and policymakers is, therefore, how these ice caps will continue to react to the temperature rises that are predicted for the 21st century, noting that Atmospheric General Circulation Models predict that temperature rise will be significantly greater in the Arctic than at lower latitudes. Numerical modelling of large ice masses is constrained, however, by a lack of knowledge of the geometry and nature of the bed of these outlet glaciers. We will acquire geophysical data from ice-cap outlet glaciers draining the large ice caps on Ellesmere and Devon islands in the Canadian Arctic using an airborne ice-penetrating radar, laser altimeter, gravimeter, magnetometer and GPS instruments. We will focus on three key areas of each drainage basin: the heavily crevassed fast-flowing outlet glaciers themselves, an upper transition zone between the ice-cap interior and the narrow outlet glaciers; and the grounding zone marking the transition to floating ice tongues at the head of some Canadian High-Arctic fjords. Our scientific objectives are: (a) to determine ice-surface and subglacial-bed elevation; (b) to characterize the substrate, in particular whether it is bedrock or deformable sediment; (c) to establish the distribution of subglacial melting; (d) to reveal basal character changes at the transition zones between inland ice, outlet glaciers and the grounding zone; (e) to provide new estimates of outlet glacier calving fluxes and their variability on up to decadal timescales. This information, integrated with satellite datasets on outlet-glacier surface motion and our earlier observations of the regional-scale geometry of these ice caps, will provide fundamental boundary conditions for the numerical modelling of these ice caps and, thus, how they may respond to atmospheric and ocean warming over the coming decades, with implications for sea-level rise.