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

南极西部冰原（WAIS）在最后一次间冰期幸存下来了吗？我们建议使用冰原高度变化的标尺来帮助回答这个问题。一种假说认为，WAIS是在12.5万年前的末次间冰期消失的，当时的气候和海洋条件比现在稍微温暖一些（动力学）。另一种假说认为，西半球可能在海拔高度上有所变化，但在最后一次间冰期（稳定期），它一直是一个连贯的冰盖。两种相反假设的共存意味着我们对冰盖稳定性的主要控制因素还有很多要了解。这种不确定性削弱了我们预测WAIS未来及其对全球海平面变化影响的能力的信心。关于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。如果我们知道在最后一次冰期循环中WAIS发生了什么，这两种方法都将得到加强。从长期的角度来看，十年变化叠加在变化的轨迹上。此外，冰期循环期间海拔变化的历史提供了约束和改进冰盖模型的数据。在这里，我们建议使用在蓝冰地区的冰凌上形成的冰碛来测试这两个假设。蓝冰区是由强烈的下坡风形成的，这些风通常在冰暴附近形成漏斗状，并烧毁冰面。作为回应，冰流入这样的消融区，有时将基底碎屑带到地表，然后沉积在冰缘。残存的冰碛出现在当前冰表面上方的某些冰凌斜坡上，其历史超过40万年，这表明有可能获得冰高度变化的长期记录。该项目汇集了冰川学家、地貌学家和地球物理学家，在遗产山脉工作，这是一组突出穿过WAIS中央圆顶的冰峰。我们将测试这两个相互竞争的假设的预测，首先是通过实地调查和雷达检查今天的蓝冰冰碛形成过程，其次是通过建立冰碛的形式和沉积物特征及其年龄。后者将采用暴露年龄测定法，一种测量岩石在地表暴露在宇宙射线中的时间的技术。通过使用多种同位素，我们可以确定岩石表面可能被冰掩埋的时间，从而有可能重建冰高程变化的丰富历史。我们希望这种方法可以推广到南极洲的其他冰峰，并提供广泛分散的海拔变化证据。

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. One 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 (Dynamic). Another hypothesis suggests the WAIS may have varied in elevation but that it persisted as a coherent ice sheet during the last interglacial (Stable). 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. Our hope is that the approach could be extended to other nunataks in Antarctica and provide widely dispersed evidence of elevation changes.