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压在十年到千年时间尺度上的低频行为，并评估其变化如何与全新世平均气候状态的过去变化相关。为了有信心地重建过去的气候变化，必须很好地理解控制代用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芯的调查，其双重目标是（1）了解沉积变化的主要控制因素，以及（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理时间序列。研究人员最近发现了两个湖泊，其中含有每年层压（纹）沉积物。这些是阿拉斯加目前已知的为数不多的多纹湖泊之一，它们提供了一个机会，每年解决过去气候变化的时间序列。在这些冰川湖泊的层厚度和粒度变化的低频分量可能反映了在集水区的冰盖的程度，而年内和年间的变化可能与融化季节的温度和水文因素，特别是大的降雨事件。除了新的层状湖泊，该项目将产生补充记录的湖泊更适合生态为基础的代理，包括摇蚊和花粉/宏化石组合，湖泊生产力指标，生长季节的温度。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的全新世冰川波动。这项研究的智力价值包括其多代理方法，旨在探测北太平洋海洋大气环流的一个关键特征：阿留申低压系统。这个重要的行动中心与整个太平洋的气候变化指数有关。在冬季，当它将西南风暴引向内陆时，它的表达最为强烈，从而控制了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，因为冰川大小取决于冬季降水量，而冬季降水量随阿留申低压而变化。冰川的大小还取决于夏季温度，因此需要补充夏季温度的时间序列。基本研究设计是在相距2100公里的三个研究区域中的每个区域将冰川湖泊（层压记录）与富含有机物的湖泊（摇蚊记录）配对：遥远西部的阿达克（阿留申群岛中部）、西南部的阿克伦山脉和阿拉斯加湾的丘加奇山脉。这三个地区在阿留申低压的影响下横跨显著的偶极子。当阿留申低压加强时，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压的变化而变化，这些变化记录在湖水和生长在其中的硅藻的氧同位素比率中。多代理时间序列将贯穿全新世，在两个时期进行更高分辨率的分析，包括过去的温暖间隔，即全新世热最大期，发生在当前时代的早期，以及过去的2000年，其中包括所谓的中世纪温暖期，这是20世纪世纪温暖的一个关键基准。这项研究的更广泛的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Togiak国家野生动物保护区开发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，并确定广泛的火山岩地层标志，以及更广泛的多学科和跨学科科学家社区，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。该项目正在对三名研究生和几名本科生进行全球变化研究方面的培训，并为一名研究助理教授的早期职业生涯提供支助。作为NSF PolarTREC计划的一部分，PI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.