Collaborative Research: Holocene Drought in the North American Interior

摘要本研究将对北美大陆内部两个干旱易发地区（大平原北部和落基山脉北部）在多年代际至千年时间尺度上关于大旱成因和空间格局的若干假设进行检验。利用区域湖泊沉积物中保存的无机和有机地球化学记录，首次定量重建了大平原北部整个全新世的年代际降水变化。此外，这项研究将为大陆环境开发一种相对新的地球化学指标，特别是利用烯酮来重建盐湖的温度变化。高分辨率的古气候数据表明，在过去的两千年里，北美西部的大部分地区经历了大面积的严重干旱，这种干旱比20世纪的干旱更持久。目前还不清楚是什么导致了这些所谓的特大干旱，因为只有少数高分辨率的大陆古气候记录跨越了过去1000到2000年。拟议的研究将比较从大平原北部延伸到整个全新世的高分辨率（年代际）记录与从落基山脉北部的记录。跨越数千年的记录的生成将使我们能够评估多年代际干旱的频率如何受到大尺度边界条件变化的影响，例如作为全新世早期与晚全新世特征的季节性日照差异。将重建的中部大陆大干旱的长时间序列与太平洋和北大西洋海表温度记录进行比较，以评估1)落基山脉北部和大平原北部对大西洋和太平洋变率的敏感性是否存在差异；2)干旱与潜在海洋强迫之间的关系是否随时间而平稳。这项研究还将开发和应用一种相对较新的、强大的地球化学代理，用于大陆环境中的温度重建，这有可能大大提高我们解释过去气候和水文响应的能力。更广泛的影响了解过去与严重持续干旱有关的因素具有社会效益，因为它使我们能够评估当前的水资源管理计划是否基于对气候自然长期变化的合理理解。为了加强对公众和直接受干旱影响的人们的科学理解，这项研究将为蒙大拿州东部的一个新的州立公园创建一个展览，该公园位于本项目要研究的主要湖泊的岸边。该展览将描述湖泊沉积物如何被用来生成气候和景观演变的历史，以及在这个湖上进行的研究所提出的关于干旱历史的见解。此外，三名研究生将接受与社会相关的跨学科研究培训。

ABSTRACTThis research will test several hypotheses about the causes and spatial pattern of major drought at multi-decadal to millennial time scales in two drought prone regions of the North American continental interior: the northern Great Plains and northern Rocky Mountains. The first quantitative reconstruction of precipitation variation at decadal resolution that spans the entire Holocene will be generated for the northern Great Plains from inorganic and organic geochemical records preserved in regional lake sediments. In addition, the research will develop a relatively new geochemical indicator for continental settings, specifically the use of alkenones to reconstruct temperature variation in saline lakes.Intellectual MeritHigh-resolution paleoclimatic data suggest that, during the last two millennia, much of western North America experienced widespread severe drought that was more persistent than the droughts of the 20th century. It is unclear what produces these so-called megadroughts, because only a handful of high-resolution continental paleoclimatic records span more than the last 1000 to 2000 years. The proposed research will compare high resolution (decadal) records that extend through the entire Holocene from the northern Great Plains with records from the northern Rocky Mountains. The generation of records that span many millennia will enable an assessment of how the frequency of multi-decadal drought is influenced by changes in large-scale boundary conditions, such as the seasonal insolation differences that characterize the early versus late-Holocene. The long reconstructed time series of major drought in the mid continent will be compared with Pacific and North Atlantic sea-surface temperature records to evaluate 1) whether the northern Rockies and northern Great Plains are differentially sensitive to Atlantic versus Pacific variability, and 2) whether the relationship between drought and potential oceanic forcing is stationary through time. The research also will develop and apply a relatively new and powerful geochemical proxy for temperature reconstruction in continental settings, which has the potential to greatly improve our ability to interpret past climates and hydrologic responses.Broader ImpactsUnderstanding the factors associated with severe persistent drought in the past is of societal benefit, because it enables an assessment of whether or not current water management plans are based on a sound understanding of the natural long-term variability of climate. To enhance the scientific understanding of the public and the people directly impacted by drought, the research will create an exhibit for a new state park in eastern Montana, located on the shores of the primary lake to be studied in this project. The exhibit will describe how lake sediments can be used to generate a history of climate and landscape evolution and the insights about drought history suggested by research carried out on this lake. In addition, three graduate students will receive training in interdisciplinary research of societal relevance.