Understanding marine ice stream retreat using numerical modelling and geophysical data

目前，格陵兰和南极冰盖对未来海平面上升的影响存在很大的不确定性。这些冰盖排入周围海洋的大部分冰是通过快速流动的“海洋冰流”排出的，这些冰流的底部低于现在的海平面，每年以几百米到几公里的速度流动。最近的卫星观测表明，其中一些海洋冰流正在经历迅速的变化，其形式是边缘变薄和退缩。这些冰流是当前冰川学研究的主要焦点，但到目前为止，这项研究主要集中在冰流退缩的理论研究和/或现代冰流的观测。这些研究通常只提供了冰流生命周期的快照，仅限于过去几十年。目前试图确定是什么控制了这些冰流的撤退仍然没有结果。这个问题是复杂的事实，现有的大规模冰盖模型，用于未来海平面的预测在“政府间气候变化专门委员会”2007年的报告，是不能够纳入这种快速变化的冰流。如果科学界打算以任何确定性程度量化未来海平面上升，了解冰流退缩的控制因素并预测其未来行为将至关重要。本研究的目的是通过数值模拟和海洋地球物理观测相结合来确定海洋冰流退缩的控制因素。我们将使用来自南极洲三个有据可查的古冰流（即地质和地球物理证据记录的古冰流）的观测结果，这些冰流在末次冰期最大期之后经历了对比鲜明的风格和退缩速度，从快速到缓慢。我们将使用的数值模型是专门开发的，使我们能够模拟冰流撤退。海洋地球物理和地质观测将为数值模型提供物理环境，至关重要的是，还将提供不同冰流的消退历史，以便与模型模拟进行比较。据我们所知，一个强大的比较和验证的数值海洋冰流模型使用这样的数据从来没有尝试过。在这个项目中采取的跨学科的方法提供了迫切需要的冰流撤退的观测记录和数值模拟之间的联系。它将促进我们对控制这种退缩的因素的理解，并为开发冰盖模型提供重要的见解，从而有助于提高科学界预测未来海平面上升的能力。

Currently there is major uncertainty surrounding the contributions of the Greenland and Antarctic ice sheets to future sea level rise. The majority of the ice discharged by these ice sheets into the surrounding oceans is by drainage of fast flowing 'marine ice streams' which have their bases below present sea level and which flow at speeds of a few hundred metres to several kilometres per year. Recent satellite observations show that some of these marine ice streams are experiencing rapid change in the form of thinning and retreat of their margins. These ice streams are a major focus for current glaciological research, but up until now this research has mostly concentrated on either theoretical studies of ice stream retreat and/or observations of modern ice streams. Such studies typically only provide a snapshot of an ice stream's life-cycle, limited to the last few decades. Current attempts to determine what controls the retreat of these ice streams remain inconclusive. This problem is compounded by the fact that existing large-scale ice sheet models, used for future sea level predictions in the 'Intergovernmental Panel on Climate Change' 2007 report, are not able to incorporate such rapid changes in ice streams. Understanding the controls of ice stream retreat and predicting their future behaviour will be crucial, if the scientific community intends to quantify future sea level rise with any degree of certainty. This study aims to determine the controlling factors on marine ice stream retreat by combining numerical modelling with marine-geophysical observations of ice stream retreat. We will use observations from three well documented palaeo-ice streams in Antarctica (i.e. ancient ice streams recorded by geological and geophysical evidence) that underwent contrasting styles and rates of retreat following the last glacial maximum and ranging from rapid through episodic to slow. The numerical model that we will use is specifically developed to allow us to simulate ice stream retreat. The marine geophysical and geological observations will provide the physical setting for the numerical model and, crucially, the retreat history of the different ice streams for comparison to the model simulations. To our knowledge, a robust comparison and validation of a numerical marine ice stream model using such data has never before been attempted. The inter-disciplinary approach taken in this project provides the urgently needed link between observational records of ice stream retreat and numerical modelling. It will advance our understanding of the factors that control such retreat and also provide crucial insights for developing ice sheet models, and thus contribute to improving the ability of the scientific community to predict future sea level rise.