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贡献存在很大的不确定性。这些冰盖排放到周围海洋中的大部分冰是通过快速流动的“海洋冰流”排出的，这些冰流的基地低于目前的海平面，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，其形式是变薄和边缘退缩。这些冰流是当前冰川学研究的主要焦点，但到目前为止，这些研究主要集中在冰流退缩的理论研究和/或现代冰流的观测上。这样的研究通常只能提供冰流生命周期的快照，仅限于过去几十年。目前，人们试图确定是什么控制了这些冰流的消退，但仍没有定论。在“政府间气候变化专门委员会”2007年的报告中用于预测未来海平面的现有大规模冰盖模型无法将冰流的这种快速变化纳入其中，这一事实使问题更加复杂。如果科学界打算以某种程度的确定性量化未来的海平面上升，那么了解冰流退缩的控制因素并预测它们未来的行为将是至关重要的。本研究旨在通过数值模拟与海洋地球物理观测相结合，确定海冰流退缩的控制因素。我们将使用对南极三个有充分记录的古冰流（即地质和地球物理证据记录的古冰流）的观测结果，这些冰流在末次极大期之后经历了不同的退缩风格和速度，从快速到间歇性再到缓慢。我们将使用的数值模型是专门为模拟冰流退缩而开发的。海洋地球物理和地质观测将为数值模型提供物理背景，更重要的是，将不同冰流的退缩历史与模型模拟进行比较。据我们所知，以前从未尝试过使用这些数据对海洋冰流数值模型进行可靠的比较和验证。本项目采用的跨学科方法提供了冰流退缩观测记录与数值模拟之间迫切需要的联系。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关键的见解，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.