Impact of surface melt and ponding on ice shelf dynamics and stability

冰架环绕着南极一半的海岸线，对南极冰原的冰流起着根本的控制作用。它们可以通过与海洋和大气的相互作用来增加或减少质量。从长期来看，它们的演变和对冰盖的影响是由海洋控制的，但在短期内，大气变暖的影响可能占主导地位，因为它为冰架突然崩塌提供了条件和机制。南极半岛是冰架最近变化最大的地方，其大气变暖的速度比地球上任何地方都要快。大气变暖导致南极半岛冰架的崩塌已经涉及到表面融化和池塘——2002年拉森B冰架的消失导致了显著的持续冰川加速，内陆的地面冰减少，并导致海平面上升。毫无疑问，气候变暖将导致更多的冰架在相当长的一段时间内受制于高于冰点的温度。Larsen B冰架更大的南部邻居Larsen C冰架每年都会经历表面融化和淤积的时期，并且部分地区的冰层密度似乎正在接近Larsen B冰架崩塌之前的水平。然而，人们对熔体和固体致密化的时空格局、池塘的分布和大小，以及这些因素对流动和断裂的影响知之甚少。因此，对冰盖质量平衡的关键控制还没有充分了解。我们的项目将通过实地考察、遥感和数值模拟相结合的方案来解决这个问题。我们将把重点放在拉森C冰架上，作为一个理想的例子，一个大型冰架经历了各种各样的表面融化和池塘条件，并且很容易进行实地测量。利用钻孔相机测量和监测仪器，以及地面地球物理，我们将获得关于冰柱上半部分冰架密度和温度的急需的新数据。我们将探索数百年前的冰层，以了解拉森C冰架融化和淤积的历史。为了了解过去和未来的融水和池塘对冰架的影响，我们将开发一个耦合模拟，使用区域气候模型来预测表面融水和池塘，使用冰架数值模型来测试融水对流动和断裂的影响。这些模型将通过我们将收集的实地调查和遥感数据进行优化。结果将是迄今为止最精确的冰架模型，这将使我们充分了解融化和积水对冰架的影响，并预测拉森C冰架在下个世纪的未来演变。

Ice shelves fringe around half of the Antarctic coastline and exert a fundamental control on the discharge of ice from the Antarctic ice sheets. They can gain and lose mass through interactions with both the ocean and the atmosphere. In the long term their evolution and impact on the ice sheets is controlled by the ocean, but the effect of a warming atmosphere may dominate in the shorter term by providing the conditions and mechanisms for abrupt ice shelf collapse. The atmosphere on the Antarctic Peninsula, where ice shelves have recently undergone most change, is warming faster than anywhere else on Earth.Atmospheric warming leading to surface melt and ponding has already been implicated in the collapse of ice shelves of the Antarctic Peninsula - the loss of the Larsen B ice shelf in 2002 led to significant and ongoing glacier acceleration, draw-down of grounded ice from the interior, and contribution to sea level rise. There is no doubt that climate warming will lead to more ice shelves being subject to temperatures above freezing for significant periods. The much larger southerly neighbour of the Larsen B ice shelf, Larsen C, annually experiences periods of surface melt and ponding, and appears in parts to be approaching the level of firn densification that preceded the Larsen B collapse. Very little is known, however, about the spatial and temporal pattern of melt and firn densification, the distribution and size of ponds, or the impact of these factors on flow and fracture. A key control on ice sheet mass balance is therefore inadequately understood.Our project will address this issue through a combined program of fieldwork, remote sensing and numerical modelling. We will focus on the Larsen C Ice Shelf as an ideal example of a large ice shelf experiencing a wide variety of surface melt and ponding conditions, and which is readily accessible for field measurements. Using borehole camera survey and monitoring instrumentation, and surface geophysics, we will acquire much needed new data about the density and temperature across the ice shelf in the upper half of the ice column. We will probe layers of ice going back hundreds of years to understand the history of melt and ponding on Larsen C Ice Shelf. To understand the impact on the ice shelf of past and future melt and ponding, we will develop a coupled simulation which will use a regional climate model to predict surface melt and ponding and an ice shelf numerical model to test the impact of this meltwater on flow and fracture. These models will be optimised by data from fieldwork and remote sensing that we will collect. The outcome will be the most accurate model of an ice shelf to date which will allow us fully understand impact of melt and ponding on ice shelves and to predict the future evolution of Larsen C Ice Shelf over the next century.