A new approach to West Antarctic Ice Sheet evolution using blue-ice moraines on nunataks

西南极冰盖(WAIS)在上一次间冰期幸存下来了吗？我们建议使用双节肢作为冰盖海拔变化的标尺来帮助回答这个问题。目前有两种相互矛盾的假设。假设1：动态的WAIS。假设WAIS在大约125,000年前的最后一次间冰期条件下消失，当时气候和海洋条件比现在略热。假设2：一个稳定的WAIS。WAIS可能在海拔上有所不同，但在上一次间冰期，它作为一个连贯的冰盖持续存在。两种截然相反的假说的共存意味着，关于冰盖稳定性的主要控制因素，我们还有很多需要学习的地方。这种不确定性削弱了人们对我们预测WAIS未来及其对全球海平面变化影响的能力的信心。对WAIS的重要研究依赖于监测近几十年来速度和海拔变化的卫星观测，而对未来变化的预测依赖于冰盖模型。如果我们知道WAIS在上一次冰川周期中发生了什么，这两种方法都会得到加强。更长期的视角讲述了十年变化叠加在其上的变化轨迹。此外，冰川周期期间海拔变化的历史为约束和改进冰盖模型提供了数据。在这里，我们建议使用蓝色冰区双峰上形成的冰雹来检验这两个假设。蓝冰区是由强烈的下坡风造成的，这些风通常聚集在双峰附近，并侵蚀冰面。作为回应，冰流进了这样的消融区，有时会将底部碎片带到表面，然后沉积在冰缘。残留的冰雹出现在目前冰面上方的某些努纳塔克斜坡上，已有40万年以上的历史，这表明有可能获得冰海拔变化的长期记录。该项目汇集了冰川学家、地貌学家和地球物理学家在遗产范围内工作，这是一组从WAIS中央圆顶突出的努纳塔克峰。我们将首先检验这两个相互竞争的假说的预测，方法是利用野外调查和雷达研究当今蓝冰冰雹的形成过程，其次是确定冰雹的形态和沉积特征及其年龄。后者将使用暴露年龄测年，这是一种测量岩石在地表和暴露于宇宙射线的时间的技术。通过使用不止一种同位素，我们可以确定岩石表面可能被冰掩埋的时间，从而有可能重建丰富的冰海拔变化历史。通过这种方式，我们将评估WAIS在上一次间冰期是完好无损还是消失了。我们希望，这种方法可以扩展到南极洲的其他努阿特克，并提供广泛分布的海拔变化证据，以预测WAIS未来对气候变化的反应。

Did the West Antarctic Ice Sheet (WAIS) survive the last interglacial? We propose to use nunataks as dipsticks of ice-sheet elevation change to help answer this question. There are currently two conflicting hypotheses. Hypothesis 1: A dynamic WAIS. The hypothesis is that the WAIS disappeared under last-interglacial conditions ~125,000 years ago when climatic and oceanic conditions were slightly warmer than those of the present day. Hypothesis 2: A stable WAIS. The WAIS may have varied in elevation but that it persisted as a coherent ice sheet during the last interglacial. The co-existence of two opposing hypotheses implies that we have much to learn about the principal controls on ice-sheet stability. This uncertainty undermines confidence in our ability to predict the future of the WAIS and its effect on global sea-level change.Important research on the WAIS relies on satellite observations which monitor changes in velocity and elevation over recent decades, while predictions of future changes rely on ice-sheet models. Both approaches would be enhanced if we knew what happened to the WAIS during the last glacial cycle. The longer term perspective tells of the trajectory of change upon which decadal changes are superimposed. Further, a history of elevation changes during a glacial cycle provides data with which to constrain and improve ice-sheet models.Here we propose to test the two hypotheses using moraines that form on nunataks in blue-ice areas. Blue-ice areas result from strong downslope winds which are often funnelled in the vicinity of nunataks and ablate the ice surface. In response the ice flows into such ablation areas, sometimes bringing basal debris to the surface which is then deposited at the ice margin. Relict moraines occur on certain nunatak slopes above the present ice surfaces and are over 400,000 years old, suggesting that there is the potential to obtain a long record of ice elevation change.This project brings together glaciologists, geomorphologists and geophysicists to work in the Heritage Range, a group of nunataks which protrude through the central WAIS dome. We will test predictions of the two competing hypotheses firstly by examining the processes of blue-ice moraine formation today using field survey and radar, and secondly by establishing the form and sediment characteristics of the moraines and their age. The latter will employ exposure-age dating, a technique that measures the time a rock has been at the surface and exposed to cosmic rays. By using more than one isotope we can establish times when a rock surface may have been buried by ice and thus there is the potential to reconstruct a rich history of ice elevation changes. In this way we will assess if the WAIS remained intact, or disappeared during the last interglacial. Our hope is that the approach could be extended to other nunataks in Antarctica and provide widely dispersed evidence of elevation changes in predicting the future response of the WAIS to a changing climate.