Collaborative research: Coupled glacial and lacustrine evidence for decadal- to millennial-scale variability in the climatologic Aleutian low, southern Alaska

该项目的总体目标是重建气候阿留申低在十年至千年时间尺度上的低频行为，并评估其变化与全新世气候平均状态过去变化的关系。为了自信地重建过去的气候变化，必须很好地理解控制替代气候指标的相互关联的过程。该项目将继续对阿拉斯加南部的九个湖泊进行持续监测和湖芯调查，其双重目标是：(1)了解沉积变化的主要控制因素；(2)利用这一认识生成与夏季温度和冬季降水定量相关的最高质量的古气候指标时间序列。研究人员最近发现了两个湖泊，它们含有每年层叠(变化)的沉积物。这些是阿拉斯加目前已知的为数不多的各种湖泊之一，它们为开发过去气候变化的年度分辨时间序列提供了机会。这些冰川供养的湖泊的分层厚度和粒度变化的低频成分可能反映了集水区冰覆盖的程度，而年际和年内变化可能与融化季节的温度和水文因素，特别是大降雨事件有关。除了新的层状湖泊外，该项目还将从更适合于生态替代物的湖泊中产生补充记录，包括摇蚊和花粉/大型化石组合，以及对生长季温度做出反应的湖泊生产力指标。此外，将分析硅藻中的氧同位素比率，以重建水分来源的变化，并将使用地貌证据来评估湖泊集水区内全新世冰川的波动。这项研究的学术价值包括它的多代理方法，旨在探索北太平洋海洋-大气环流的一个关键特征：阿留申低压系统。这一重要的行动中心与太平洋地区的气候变异性指数有关。它在冬季表现得最强烈，因为它将西南部的风暴引向内陆，从而控制着北美西北部地表温度和降雪的空间格局。该项目包括冰川和冰湖记录，因为冰川的大小取决于冬季降水量，而冬季降水量随阿留申低气压而变化。冰川的大小也取决于夏季的温度，这就需要夏季温度的互补时间序列。基本的研究设计是将相距2100公里的三个研究区中的一个冰川补给湖(分层记录)与一个富含有机物质的湖泊(摇摆湖记录)配对：遥远西部的阿达克(阿留申群岛中部)、西南部的阿赫克伦山脉和阿拉斯加湾的丘加赫山脉。这三个地区横跨在阿留申低压影响下的突出偶极子上。当阿留申低压加强时，阿拉斯加湾冬季降水和气温增加，而西部减少。水分来源也会随着阿留申低点的变化而变化，这些都记录在湖水和生长在湖水中的硅藻的氧同位素比率中。多指标时间序列将延伸到全新世，在两个时期进行更高分辨率的分析，涵盖过去的暖期，即本世纪早期发生的全新世最热时期，以及包括所谓的中世纪暖期在内的最后2000年，这是20世纪变暖的关键基准。这项研究的更广泛的影响包括它与美国鱼类和野生动物管理局的资源经理(他们正在Togiak国家野生动物保护区制定一个主要的环境监测项目)、美国地质调查局阿拉斯加火山观测站的地球科学家(他们正在努力评估阿留申弧形火山的喷发频率并确定广泛的冰盖地层标志)以及更广泛的多学科和跨学科科学家社区的协同活动，这些科学家旨在了解北太平洋、北极和全球气候变化的原因和影响。该项目有助于理解气候变化，这是社会面临的一个关键挑战。美国气候变化科学计划将“北极和高纬度地区过去的气候变异性和变化”确定为其主要研究目标之一。该项目正在培训三名研究生和几名本科生进行全球变化研究，并支持一名研究助理教授的早期职业生涯。作为NSF PolarTREC计划的一部分，PI已经让高中科学教师参与了他们的实地研究。

The overall goal of this project is to reconstruct the low-frequency behavior of the climatological Aleutian Low on decadal to millennial time scales, and to assess how its variability has related to past shifts in the mean state of climate during the Holocene. To confidently reconstruct past climate change, the inter-related processes that control the proxy climate indicators must be well understood. This project will continue on-going monitoring and lake-core-based investigations at nine lakes in southern Alaska with the dual aims of (1) understanding the primary controls on the sedimentary changes, and (2) applying this understanding to generate the highest quality time series of paleoclimate proxies that relate quantitatively to summer temperature and winter precipitation. The investigators recently discovered two lakes that contain annually laminated (varved) sediment. These are among the few varved lakes currently known in Alaska, and they present an opportunity to develop annually resolved time series of past climate variability. The low-frequency component of lamination thickness and grain-size variability at these glacier-fed lakes probably reflects the extent of ice cover in the catchment, while inter- and intra-annual variability is likely related to melt-season temperature and hydrologic factors, particularly large rainfall events. In addition to the new laminated lakes, this project will generate complementary records from lakes more suitable for ecologically based proxies, including chironomid and pollen/macrofossil assemblages, and lake-productivity indicators that respond to growing-season temperature. In addition, oxygen-isotope ratios in diatoms will be analyzed to reconstruct moisture-source variations, and geomorphic evidence will be used to assess Holocene glacier fluctuations within the lake catchments. The intellectual merit of this study includes its multi-proxy approach designed to probe a key feature of ocean-atmospheric circulation in the North Pacific: the Aleutian Low pressure system. This prominent center of action is linked to indices of climate variability across the Pacific. It is most strongly expressed in winter when it steers southwesterly storms inland, thereby governing the spatial pattern of surface temperature and snowfall across northwestern North America. This project includes glacier and glacial-lacustrine records because glacier size depends on winter precipitation, which varies with the Aleutian Low. Glacier size also depends on summer temperature necessitating complementary time series of summer temperature. The basic study design is to pair a glacial-fed lake (lamination record) with an organic-rich lake (chironomid record) in each of three study areas separated by 2100 km: Adak (middle Aleutian Islands) in the far west, Ahklun Mountains in the southwest, and Chugach Range in the Gulf of Alaska. These three areas straddle the prominent dipole in the influence of the Aleutian Low. When the Aleutian Low strengthens, winter precipitation and temperature increase in the Gulf of Alaska, while it decreases in the west. Moisture sources also shift with the Aleutian Low, and these are recorded in the oxygen-isotope ratios of lake water and the diatoms that grow within it. The multi-proxy time series will extend through the Holocene, with higher-resolution analyses over two periods that encompass past warm intervals, namely the Holocene thermal maximum, which took place early during the current epoch, and the last 2000 years, which includes the so-called medieval warm period, a key benchmark for 20th century warmth. The broader impacts of this study involve its synergistic activities with resource managers at US Fish and Wildlife Service who are developing a premier environmental monitoring program in the Togiak National Wildlife Refuge, geoscientists at the US Geological Survey's Alaska Volcano Observatory who are striving to assess the frequency of eruptions of Aleutian Arc volcanoes and to identify widespread tephra-stratigraphic markers, and the broader community of multi- and inter-disciplinary scientists aiming to understand the causes and effects of climatic change around the North Pacific, the Arctic, and globally. This project contributes to understanding climatic variability, a key challenge facing society. The US Climate Change Science Program identifies "Past Climate Variability and Change in the Arctic and at High Latitudes" as one of its primary research objectives. The project is training three graduate and several undergraduate students in global-change research, and supports a Research Assistant Professor in her early career. The PIs have involved high school science teachers in their field research as part of NSF's PolarTREC program.