Dating and modelling fast ice-sheet grounding-line retreat over the last 4000 years in the SW Weddell Sea, Antarctica

南极洲威德尔海西南部过去 4000 年来冰盖接地线快速退缩的年代测定和建模

基本信息

批准号：
NE/J008087/1
负责人：
Richard Hindmarsh
金额：
$ 42.9万
依托单位：
British Antarctic Survey
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FJ008087%2F1
关键词：
Dating modelling fast ice sheet

项目摘要

The threat the West Antarctic ice-sheet poses to sea-level is largely through retreat of the grounding line, the line that separates floating ice, whose effects on sea-level are negligible, and grounded ice, which can affect sea-level. A concern is that theoretical models suggest grounding-line retreat may be unstable.Geological evidence for the grounding line retreat under the Antarctic ice shelves, where the most substantial retreat took place, is scarce owing to poor accessibility. We will use a new technique that dates ice-flow changes from stratigraphic anomalies in the small ice-rises lying within the Ronne ice shelf. This will provide information about retreat of the grounding line there. Firstly, an established technique which looks at anticline geometry will be applied. A new feature is the application of a technique (the BAS-developed pRES) for the direct measurement of deformation in the ice, which will allow us to quantitatively constrain the development of the anticlines, rather than having to make assumptions about ice viscosity. Our project will therefore investigate both the retreat and rheology (flow) of the Antarctic ice-sheet. We will visit several ice divides in the SW Ronne area - the Korff, Henry, Skytrain and Fowler - to apply these techniques and date the most recent flow changes associated with the passage of the grounding line past the ice-rise. These will give information about the retreat of the Ronne grounding line between Berkner Island and the Ellsworth Mountains. There are many indications that this has happened in the past 4000 years, representing some of the most recent response of the Antarctic ice-sheet to deglaciation following the last glacial maximum.Measurements of ice rheology have general relevance to ice-sheet modelling. The rate at which ice flows into the sea from the large ice-sheets directly affects sea-level. The forces which drive this flow are controlled by the largely well-known geometry of the the ice-sheets, but the resistance to flow depends upon the viscous (rheological) properties of ice. Ice has the property that the the viscosity depends upon the rate at which the ice is deforming. This sensitivity is usually described with the Glen index. The Glen index can be measured in the laboratory or the field. Laboratory measurements diverge from field measurements, and are very difficult to make at the low strain-rates observed in the field. In many field measurements it is difficult to characterise the stresses sufficiently well to quantify the viscosity.By going to divide locations, where the stress field can be characterised and ice provenance is well constrained, we will be able to measure the Glen index. The technique is based on the fact that radar layers provide markers within the ice, and their vertical displacement over relatively short time periods can be measured using interferometric phase-sensitive radar techniques. These provide instantaneous strain-rate fields in the upper third to a half of the ice field. The technique has been proven at Summit in Greenland.Once we have obtained the data, we will have an idea of how quickly the grounding line retreated. We will then run ice-sheet models, to see what kind of situations could have caused this. Grounding line retreat rates are ultimately fixed by several variables; how the ocean pumps warm water under shelves, how sea-level is rising, how the land surface recovers as ice unloads, and how ice softens as it warms. The mathematical model will be able to assess the influence of all of these factors. Our team has also collected a lot of other data about ice-sheet extent in the area, and we will be able to see if the model can predict ice-sheet geometry that matches all of these.At the end of the project, with our new dates for grounding line retreat and our model that represents the past, we will have a much clearer idea of how and why the ice-sheet retreated as it did in the Weddell Sea area.

南极西部冰页面对海平面构成的威胁主要是通过接地线的撤退，该线将浮冰分开，其对海平面的影响可忽略不计，并且会影响海平面。一个令人担忧的是，理论模型表明地面撤退可能是不稳定的。由于可及性不佳，因此在南极冰架下的地面撤退的地质证据（在南极冰架上的撤退（在那里发生的最实质性撤退）之后，它是稀缺的。我们将使用一种新技术，该技术与罗恩冰架内的小冰层中的地层异常发生了冰流的变化。这将提供有关那里的接地线撤退的信息。首先，将应用一种既定的技术，该技术将应用于背叛的几何形状。一项新功能是将技术（BAS开发的PRES）应用于冰中变形的直接测量，这将使我们能够定量限制反线的发展，而不必对冰粘度进行假设。因此，我们的项目将研究南极冰盖的撤退和流变学（流）。我们将访问SW Ronne地区的几个ICE鸿沟 - Korff，Henry，Skytrain和Fowler-应用这些技术，并日期日期与接地线经过冰山的最新流动变化。这些将提供有关伯克纳岛和埃尔斯沃思山之间罗恩接地线的撤退的信息。有许多迹象表明这发生在过去的4000年中，这代表了在最后一次冰川最大值之后对南极冰淇淋的一些最新响应。冰流变性的测量与冰形建模有关。冰从大冰块流入大海的速度直接影响海平面。驱动该流动的力是由冰盖的主要众所周知的几何形状控制的，但是对流的阻力取决于冰的粘性（流变）特性。冰具有粘度取决于冰变形的速率的特性。这种灵敏度通常用GLEN指数描述。可以在实验室或田地中测量GLEN指数。实验室测量与现场测量相差，并且在现场观察到的低应变率很难进行。在许多野外测量中，很难很好地表征应力以量化粘度。通过划分位置，可以表征应力场，而冰的出处受到很好的约束，我们将能够测量Glen指数。该技术基于以下事实：雷达层在冰中提供标记，并且可以使用干涉相敏感雷达技术在相对较短的时间段内进行垂直位移。这些提供了冰场上部三分之一至一半的瞬时应变率场。该技术已在格陵兰峰的Summit证明。一旦我们获得了数据，我们将了解接地线撤退的速度。然后，我们将运行冰盖模型，以了解可能导致的情况。接地线的撤退率最终由几个变量固定；海洋如何在货架下泵送温水，如何上升，土地表面如何恢复为冰卸下，以及冰如何变暖。数学模型将能够评估所有这些因素的影响。我们的团队还收集了有关该地区冰上范围的许多其他数据，我们将能够查看该模型是否可以预测与所有这些相匹配的冰片几何形状。