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在年代际到千年的时间尺度上重建气候阿留申低的低频行为，并评估其变化与全新世期间平均气候状态的过去变化之间的关系。为了自信地重建过去的气候变化，必须充分了解控制代理气候指标的相互关联的过程。该项目将继续在阿拉斯加南部的九个湖泊进行持续监测和基于湖核的调查，其双重目标是：(1)了解沉积变化的主要控制因素，(2)应用这种理解来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代用指标时间序列。调查人员最近发现了两个湖泊，其中每年都有层压沉积物。这些是阿拉斯加目前已知的少数几个变异湖泊之一，它们为发展过去气候变化的年度解决时间序列提供了机会。这些冰川湖泊层压厚度和粒度变率的低频分量可能反映了集水区的冰覆盖范围，而年际和年内变率可能与融季温度和水文因素有关，特别是与大降雨事件有关。除了新的叠层湖泊外，该项目还将从湖泊中获得更适合生态指标的补充记录，包括chironomid和花粉/大型化石组合，以及响应生长季节温度的湖泊生产力指标。此外，还将分析硅藻中的氧同位素比率，以重建湿源变化，并利用地貌证据评估湖泊集水区全新世冰川波动。这项研究的智力价值包括其设计用于探测北太平洋海洋-大气环流的一个关键特征的多代理方法：阿留申低压系统。这个突出的行动中心与整个太平洋的气候变率指数有关。它在冬季表现得最为强烈，此时它将西南风暴引向内陆，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川湖泊记录，因为冰川的大小取决于冬季降水，而冬季降水随阿留申低地而变化。冰川的大小还取决于夏季温度，因此需要夏季温度的补充时间序列。基本的研究设计是在三个研究区域（相距2100公里）中的每个区域配对一个冰川湖泊（层压记录）和一个富含有机物的湖泊（chironomid记录）：最西部的Adak（阿留申群岛中部），西南部的Ahklun山脉和阿拉斯加湾的Chugach山脉。这三个地区在阿留申低地的影响下跨越了突出的偶极子。当阿留申低压增强时，阿拉斯加湾冬季降水和温度增加，而西部则减少。水分来源也随着阿留申低地的变化而变化，这些变化记录在湖水的氧同位素比率和生长在其中的硅藻中。多代理时间序列将延伸到整个全新世，对两个时期进行更高分辨率的分析，包括过去的温暖间隔，即全新世热最大值，发生在当前时代的早期，以及过去2000年，其中包括所谓的中世纪温暖期，这是20世纪温暖的关键基准。这项研究的更广泛影响包括与美国鱼类和野生动物管理局的资源管理人员的协同活动，他们正在托贾克国家野生动物保护区制定一个首要的环境监测计划，美国地质调查局阿拉斯加火山观测站的地球科学家正在努力评估阿留申弧火山爆发的频率，并确定广泛的火山层地层标志，以及旨在了解北太平洋、北极和全球气候变化的原因和影响的多学科和跨学科科学家组成的更广泛的社区。该项目有助于了解气候变化，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率和变化”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。作为美国国家科学基金会PolarTREC项目的一部分，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.