Stability of Landscapes and Ice Sheets in Dry Valleys, Antarctica: A Systematic Study of Exposure Ages of Soils and Surface Deposits

这项工作将研究南极洲干谷岩石和沉积物的宇宙成因同位素剖面，以了解其起源。研究结果将对东南极冰盖的历史提供重要的制约。火山灰和上覆沉积物近乎完美的保存表明，极度干旱的寒冷条件已经在干旱山谷盛行了1000万年以上。这些沉积物的幸存也表明，温暖的冰还没有进入山谷系统，冰盖的扩张一直很小。然而，其他证据表明，干河谷经历了比通常认为的更多的沉积物侵蚀：1）山谷中巨砾和基岩的宇宙成因暴露年龄通常都比用于确定冰碛和冰碛物最小年龄的火山灰沉积物的年龄小，2）松散斜坡沉积物（1000万年）的极端保存与已侵蚀2.6- 2.5万年的相邻基岩之间似乎存在差异。在同一时间间隔内，6米。冰碛和冰碛暴露年龄通常晚于上覆火山灰沉积物的年龄，这一事实可能反映了大陆冰盖向干谷扩张的冷基冰，从而既保护了景观，又保护了表面免受宇宙辐射的影响。另一个可能的解释是年轻的宇宙成因暴露年龄是侵蚀的沉积物和逐渐挖出以前埋在地表的巨石。宇宙成因同位素系统学特别适合解决这些问题。我们将测量岩石和沉积物剖面中的多种宇宙成因同位素，以确定最小暴露年龄、土壤稳定性或混合程度以及冷基冰对地表的屏蔽历史。我们期望得到明确的矿床最低年龄。此外，我们应该能够确定受冰缘活动干扰的地区，限制这种活动的时间，并解释火山灰等重要地层标志的零星保存。该项目的更广泛的影响包括研究生和本科生教育，并提高我们对数百万年时间尺度上南半球气候动态的理解，这对理解全球气候变化的控制和影响具有重大意义。

This work will study cosmogenic isotope profiles of rock and sediment in the Dry Valleys of Antarctica to understand their origin. The results will provide important constraints on the history of the East Antarctic Ice Sheet. The near-perfect preservation of volcanic ash and overlying sediments suggests that hyperarid cold conditions have prevailed in the Dry Valleys for over 10 Myr. The survival of these sediments also suggests that warm-based ice has not entered the valley system and ice sheet expansion has been minimal. Other evidence, however, suggests that the Dry Valleys have experienced considerably more sediment erosion than generally believed: 1) the cosmogenic exposure ages of boulders and bedrock in the Valleys all show generally younger ages than volcanic ash deposits used to determine minimum ages of moraines and drifts, 2) there appears to be a discrepancy between the suggested extreme preservation of unconsolidated slope deposits (10 Myr) and adjacent bedrock that has eroded 2.6-6 m during the same time interval. The fact that the till and moraine exposure ages generally post date the overlying volcanic ash deposits could reflect expansion of continental ice sheet into the Dry Valleys with cold-based ice, thus both preserving the landscape and shielding the surfaces from cosmic radiation. Another plausible explanation of the young cosmogenic exposure ages is erosion of the sediments and gradual exhumation of formerly buried boulders to the surface. Cosmogenic isotope systematics are especially well suited to address these questions. We will measure multiple cosmogenic isotopes in profiles of rock and sediment to determine the minimum exposure ages, the degree of soil stability or mixing, and the shielding history of surfaces by cold based ice. We expect to obtain unambiguous minimum ages for deposits. In addition, we should be able to identify areas disturbed by periglacial activity, constrain the timing of such activity, and account for the patchy preservation of important stratigraphic markers such as volcanic ash. The broader impacts of this project include graduate and undergraduate education, and improving our understanding of the dynamics of Southern Hemisphere climate on timescales of millions of years, which has major implications for understanding the controls and impacts of global climate change.