Collaborative Research: Holocene Drought in the North American Interior

摘要本研究将在北美大陆内部的两个干旱易发地区：北方大平原和北方落基山脉，在几十年到千年的时间尺度上检验几个关于主要干旱的原因和空间格局的假设。第一次定量重建降水变化的年代际分辨率，跨越整个全新世将产生北方大平原保存在区域湖泊沉积物中的无机和有机地球化学记录。此外，该研究将开发一个相对较新的地球化学指标，为大陆设置，特别是使用烯酮，以重建温度变化的盐湖。智力MeritHigh-resolution古气候数据表明，在过去的两千年，北美西部大部分地区经历了广泛的严重干旱，比干旱的持续时间更长的世纪。目前还不清楚是什么造成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。拟议中的研究将比较从北方大平原延伸到整个全新世的高分辨率（十年）记录与北方落基山脉的记录。跨越数千年的记录的生成将能够评估数十年干旱的频率如何受到大规模边界条件变化的影响，例如作为全新世早期与晚期特征的季节性日照差异。将对中部大陆主要干旱的长期重建时间序列与太平洋和北大西洋海面温度记录进行比较，以评估1）北方落基山脉和北方大平原是否对大西洋与太平洋的变化敏感，以及2）干旱与潜在海洋强迫之间的关系是否随时间而稳定。该研究还将开发和应用一种相对较新的、功能强大的地球化学代用指标，用于大陆环境中的温度重建，这有可能极大地提高我们解释过去气候和水文响应的能力。因为它能够评估目前的水管理计划是否基于对气候自然长期变异性的正确理解。为了提高公众和直接受干旱影响的人的科学认识，该研究将在蒙大拿州东部的一个新的州立公园创建一个展览，该公园位于本项目研究的主要湖泊岸边。该展览将描述湖泊沉积物如何用于生成气候和景观演变的历史，以及对该湖泊进行的研究所提出的干旱历史的见解。此外，三名研究生将接受社会相关性跨学科研究的培训。

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.