Doctoral Dissertation Research: A Holocene Chronology of Alpine Glaciation for the Western United States

由于世界山区发现的小型高山冰川对气候变化的响应时间较短(10‘S年)，其波动记录提供了过去气候变化的杰出代表。这项研究将基于对美国西部几个地点冰川峰顶巨石的表面暴露年代测定来开发全新世冰川年代学。年表将讨论冰川在空间和时间上的变化，以响应假定的全新世气候强迫。许多研究解释了美国西部的几次全新世冰川进步，但年龄控制主要基于相对测年技术，已被证明误差长达1万年。这项研究中使用的宇宙源核素对地表暴露的测年，为重新评估年代不佳的冰川年代学和开发美国西部全新世的高精度冰川记录提供了一种可靠的方法。这一年表的发展将为主要全新世气候强迫的范围及其对北美西部高山冰川物质平衡的影响提供新的限制，并为理解全新世期间的气候强迫提供更好的框架。这类信息直接适用于帮助理解未来气候变化的性质和后果。本研究将具体回答四个地质和气候学问题：1)发生在高山冰川和冰川斜坡下的冰雹的年龄是多少？所谓的小冰期是否代表着全新世冰川推进的顶峰？使用区域气候模式(RegCM)和Genesis大气环流模式模拟，气候情景是否符合已知的冰川年代学？如果是，最有可能使冰川在这些过去的位置保持平衡的气候情景是什么？这种改进的冰川年代学与全新世时期的其他古气候指标相比如何？利用模型输出和新的冰川年代学，根据过去的气候强迫和未来的预测，北美西部冰川物质平衡在应对全球变暖方面可以预期到什么？该项目将向更广泛的公众提供有关冰川变化的原因和方式、导致这些变化的机制以及当前的变化如何影响未来的高山生态系统、山脉水文学、森林野火和自然游乐区的信息。这些调查结果将通过与国家公园和林业官员(如大盆地和约塞米蒂国家公园解释护林员)共同编制的指南和宣传手册部分传播。

Because the small alpine glaciers found in the mountains of the world have short response times (10's years) to climate change, records of their fluctuations provide outstanding proxies of past climate changes. This research will develop a Holocene glacial chronology based on surface exposure dating of boulders from moraine crests at several sites across the western United States. The chronology will address spatial and temporal glacier variability in response to postulated Holocene climate forcings. A number of studies have interpreted several Holocene glacial advances in the western U.S., but age control is based largely on relative dating techniques, which have been shown to be in error by up to 10,000 yrs. The dating of surface exposures using cosmogenic nuclides, as used in this study, provides a robust method to reevaluate poorly dated glacial chronologies and to develop a high-precision glacial record across the western U.S. for the Holocene epoch. Development of this chronology will provide new constraints on the extent of major Holocene climate forcings and their effects on the mass balance of western North America alpine glaciers as well as providing a better framework for understanding climate forcing during the Holocene. This kind of information is directly applicable for helping to understand the nature and consequences of future climate change. This research will specifically answer four geological and climatological questions: 1.) What are the ages of the moraines that occur immediately down slope of the high, alpine cirques and glaciers and does the so-called Little Ice Age represent the culmination of the glacial advances during the Holocene? 2.) Using a regional climate model (RegCM) and the GENESIS atmospheric general circulation model simulations, do the climate scenarios agree with known glacial chronology and if so, what were the most likely climatic scenarios that allowed the glaciers to be in equilibrium at these past positions? 3.) How does this refined glacial chronology compare with other paleoclimate proxies during the Holocene epoch? 4.) Utilizing the modeling outputs and new glacial chronology, what can be expected in terms of western North American glacier mass balances in respond to global warming based on past climate forcings and future projections? This project will provide information to the greater public about why and how glaciers change, the mechanisms that induce those changes, and how current changes could affect future alpine ecosystems, mountain hydrology, forest wildfires, and natural recreation areas. Such findings will be disseminated in part through guides and informational brochures developed with national park and forestry officials (e.g. Great Basin and Yosemite National Park interpretive rangers).