Deglacial history of the West Antarctic Ice Sheet in the Weddell Sea embayment: Constraints on past ice volume change: REPLY
Deglacial history of the West Antarctic Ice Sheet in the Weddell Sea embayment: Constraints on past ice volume change: REPLY
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威德尔海海湾西南极冰盖的消冰历史：对过去冰量变化的限制：回复
作者：
Bentley M
我们欢迎克拉克（Clark，2011）对西南极洲埃尔斯沃斯山脉冰消历史的兴趣。他的评论的本质是问为什么我们没有考虑另一种解释，即我们确定的冰盖极限代表了上一次冰河周期结束时的衰退位置，而不是其最大位置。在这个替代模型中，极限是在较早且较厚的冷基冰盖变薄期间形成的。下面我们概述了我们的建议背后的理由，即日期限制是最大头寸，以及为什么衰退模型似乎不太可能发生。在这样做之前，我们应该清楚地注意到，我们确实同意冰已经高于极限高度，但我们不同意这个较厚冰盖的年龄（Bentley等人，2010）。首先，我们在论文中注意到低于和高于极限的碎屑之间存在强烈的风化对比。克拉克对北极关于风化、古老表面上是否存在新鲜冰川物质沉积的争论提供了精彩的总结。事实上，同样的情况也发生在南极洲西部玛丽伯德地的萨尔诺夫山脉（Sugden et al., 2005）。埃尔斯沃斯的工作和克拉克提到的北极工作之间的一个关键区别是，我们没有发现超过极限的新的不稳定因素。尽管我们在所有海拔高度寻找新的不稳定因素，包括 480 m 极限以上，因为我们最初怀疑较高的 Denton 等人 (1992) 修剪线是末次盛冰期 (LGM) 极限 (Bentley 和 Anderson, 1998)。此外，我们测年的高于极限的不稳定因素以及托德等人（2004）测年的不稳定因素都给出了老年，基本上早于全球末次盛冰期，与北极形成鲜明对比的是，北极的不稳定因素的宇宙成因核素（CN）年龄显示存在较年轻的覆盖冰（例如，戴维斯等人，2006年；布林纳等人，2006年）。在埃尔斯沃斯山脉，那些经过配对 Al 和 Be 分析的样品显示连续暴露了数百公里
We welcome Clark's (2011) interest in our deglacial history of the Ellsworth Mountains, West Antarctica. The essence of his Comment is to ask why we did not consider an alternative interpretation that the ice sheet limit we dated represents a recessional position during the end of the last glacial cycle, rather than its maximum position. In this alternative model, the limit would have formed during thinning from an earlier and thicker cold-based ice sheet. Below we outline the reasoning behind our suggestion that the dated limit is a maximum position and why the recessional model appears less likely to have occurred. Before doing so, we should note clearly that we do agree that ice has been above the altitude of the limit, but it is the age of this thicker ice sheet that we disagree upon (Bentley et al., 2010).First, we noted in the paper the strong weathering contrast between clasts below and above the limit. Clark provides an excellent summary of the debate in the Arctic regarding the presence of fresh glacial material deposited over weathered, older surfaces. Indeed, the same situation also occurs in the Sarnoff Mountains of Marie Byrd Land, West Antarctica (Sugden et al., 2005). One key difference between the Ellsworth work and the Arctic work to which Clark refers is that we found no fresh erratics above the limit. This is in spite of looking for fresh erratics at all altitudes, including above the 480 m limit because we initially suspected that the higher Denton et al.(1992) trimline was the Last Glacial Maximum (LGM) limit (Bentley and Anderson, 1998). Furthermore, the erratics we dated above the limit, and those dated by Todd et al.(2004) all gave old ages, substantially predating the global LGM, contrasting to the Arctic where cosmogenic nuclide (CN) ages of erratics showed the presence of younger over-riding ice (eg, Davis et al., 2006; Briner et al., 2006). In the Ellsworth Mountains, those samples with paired Al and Be analysis showed continuous exposure for several 100 ky