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

南极西部冰盖对海平面的威胁主要是通过接地线的退缩，这条线将浮冰和接地冰分开，前者对海平面的影响已经消失，后者可能影响海平面。南极大冰架下的接地线退缩的地质证据很少，因为那里发生了最大幅度的退缩。我们将使用一种新技术，根据伦讷冰架内小冰丘的地层异常来确定冰流变化的日期。这将提供有关接地线撤退的信息。首先，一个既定的技术，着眼于背斜几何形状将被应用。一个新的特点是应用的技术（BAS开发的pRES）的直接测量的应变率在冰，这将使我们能够定量约束的发展的背斜，而不是作出假设冰流变。因此，我们的项目将调查南极冰盖的退缩和流变（流动）。我们将前往西南部伦讷地区的几个冰分水岭--科尔夫、亨利、空中列车和福勒，应用这些技术并确定与分水岭相关的最新流量变化的日期。这些将提供有关伯克纳岛和埃尔斯沃思山之间的伦讷接地线撤退的信息。有许多迹象表明，这已经发生在过去的4000年，并代表了一些最近的南极冰盖的最后一次冰期最大的冰川消退的反应。冰流变学的测量有一个普遍的相关性冰盖建模。冰从大冰原流入大海的速度直接影响海平面。驱动这种流动的力是由日益众所周知的冰盖几何形状控制的，但流动阻力取决于冰的粘性（流变学）特性。冰有一种特殊的性质，即粘性取决于冰变形的速度。这种敏感性通常用Glen指数来描述。格伦指数可以在实验室或现场测量。实验室测量偏离现场测量，并且在现场观察到的低应变率下非常难以进行。在许多野外测量中，很难很好地测量应力，也很难知道冰的来源如何影响测量。通过划分位置，在那里应力场可以很好地表征，冰的来源受到很好的限制，我们将能够测量格伦指数。该技术是基于这样一个事实，即雷达层提供的标志内的冰，和他们的垂直位移在相对较短的时间内可以使用干涉相位敏感雷达技术测量。这将提供瞬时的垂直速度场和应变率场在上三分之一到一半的冰领域。这项技术已经在格陵兰岛的Summit得到了验证。一旦我们获得了数据，我们就可以知道接地线后退的速度有多快。然后我们将运行冰盖模型，看看什么样的情况可能导致这种情况。接地线撤退率最终由几个变量决定：海洋如何将温暖的水泵入洞穴，海平面如何上升，陆地表面如何随着冰卸载而恢复，以及冰如何随着变暖而软化。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大量有关该地区冰盖范围的其他数据，我们将能够看到该模型是否能够预测与所有这些数据相匹配的冰盖几何形状。在项目结束时，我们的新的接地线撤退日期和我们代表过去的模型，我们将更清楚地了解冰盖如何以及为什么会像威德尔海地区那样退缩。

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 played out, and grounded ice, which can affect sea-level. Geological evidence for the retreat of grounding line under the great Antarctic ice shelves, where the most substantial retreat took place, is scarce owing to poor accessibility. We are going to use a new technique which dates ice flow changes from stratigraphic anomalies in the small ice-rises which reside 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 strain-rates in the ice, which will allow us to quantitatively constrain the development of the anticlines, rather than make assumptions about ice rheology. Our project will therefore investigate both the retreat and rheology (flow) of the Antarctic ice-sheet. We will go to 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 divide. 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, and represents some of the most recent response of the Antarctic ice-sheet to the deglaciation following the last glacial maximum.Measurements of ice rheology have a 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 increasingly well-known geometry of the the ice-sheets, but the resistance to flow depends upon the viscous (rheological) properties of ice. Ice has the peculiar 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 very well and to know how the provenance of the ice has affected measurements. By going to divide locations, where the stress field can be characterised well and ice provenance is very 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. This will provide instantaneous vertical velocity fields and 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 cavities, how sea-level is rising, how the land surface recovers as ice unloads, and how the 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.