Long-term History of the West Antarctic Ice Sheet

最近的几项研究表明，有迹象表明南极洲西部的冰盖正在继续变薄。因此，地质证据表明，过去曾发生过规模大得多的冰川消融，这引起了人们对冰盖未来的担忧。该奖项支持一项暴露年代测定研究，该研究将有助于确定以前冰川消融的频率、范围和持续时间，并表明南极西部冰盖的现状是典型的，还是极不寻常的。该项目是基于宇宙射线产生的核素的测量，只有当岩石表面暴露在冰盖之上时，核素才会积聚。如果这些表面在冰期受到非侵蚀性冷基冰的保护，核素浓度的积累就可以记录暴露和冰盖的累积历史。虽然这种方法不能用于确定特定的先前冰期，但它可以用于获得过去暴露和冰期总持续时间的最小限度，以及晚第四纪（大约过去百万年）暴露的最大限度。作为一个例子，Al-26/Be-10对来自Marie Byrd Land的基岩样品进行了试验测量，揭示了其历史可以追溯到上新世，在此期间，采样表面经历了非常有限的暴露。结果表明，在350万年（非侵蚀性）冰盖中，累计暴露时间为~13万年，并将过去100万年的总暴露时间限制在~1万年以内。显然，这种特殊的表面很少露头，这表明与晚第四纪大多数间冰期相比，玛丽伯德地目前的消冰状态是不寻常的。该项目将通过对2000-01年野外季节收集的基岩样品进行进一步的Be-10/Al-26分析来探索这种可能性。如果出现一致的结果，就像上面描述的那样，科学家们将能够约束：(i)该地区冰盖的长期平均结构，（ii）在间冰期有多少当前地形通常暴露在外，（iii）早第四纪与晚第四纪冰消事件的比较频率和持续时间，以及（iv）晚第四纪冰消事件的持续时间，这可能与文献中报道的先前广泛的冰消事件有关。

Stone/0229915Several recent studies have shown indications of continued ice-sheet thinning in West Antarctica. Geological evidence of much larger-scale deglaciation in the past is therefore a cause for concern over the future of the ice sheet. This award supports an exposure-dating study that will help to determine the frequency, extent and duration of previous deglaciations, and show whether the present state of West Antarctic ice cover is typical, or highly unusual. The project is based on measurements of cosmic-ray-produced nuclides, which accumulate only when rock surfaces are exposed above the ice sheet. Provided these surfaces are protected during glaciation by non-erosive, cold-based ice, nuclide concentrations build up to record the cumulative history of exposure and ice cover. Although this method cannot be used to date specific prior glaciations, it can be used to obtain minimum limits on the total duration of past exposure and glaciation, and maximum limits on exposure within the late Quaternary (approximately the past million years). As an example of this, trial Al-26/Be-10 measurements on a sample of bedrock from Marie Byrd Land reveal a history extending back to the Pliocene, in which the sampled surface has experienced very limited exposure. The results indicate a cumulative exposure time of ~130,000 years, in 3.5 million years of (non-erosive) ice cover, and limit the total exposure time in the past million years to less than ~10,000 years. Evidently this particular surface seldom outcrops, suggesting that the current state of deglaciation in Marie Byrd Land is unusual compared to most interglacial periods in the late Quaternary. This project will explore this possibility with further, coupled Be-10/Al-26 analyses of bedrock samples collected during the 2000-01 field season. If consistent results emerge, like those described above, scientists will be able to constrain: (i) the long-term average configuration of the ice sheet in this region, (ii) how much of the current terrain is typically exposed during interglacial periods, (iii) the comparative frequency and duration of deglaciation in the early Quaternary vs the late Quaternary, and (iv) the duration of late-Quaternary deglaciation events, which may be linked to previous episodes of extensive deglaciation reported in the literature.