Holocene Climate Change in Southwestern Patagonia: New Insights from Large Lake Paleolimnology

巴塔哥尼亚西南部全新世气候变化：大湖古湖泊学的新见解

• 批准号: 1103550
• 负责人: Robert Dunbar
• 金额: $ 59.23万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-15 至 2015-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1103550&HistoricalAwards=false
• 关键词: Holocene; Climate; Change; Southwestern; Patagonia

This project combines climate system modeling and field data collection to examine causes and expressions of Holocene climate change in Southern South America. This is the only significant land mass that extends into the core of the southern westerly wind field, the most energetic wind system on Earth. The project is collects information on past climate change from Lago Sarmiento, a large closed-basin alkaline lake located at 51°S. Precipitation in the area, and therefore the hydrology and water balance of the lake, is demonstrably controlled by the intensity of the wind field. Abundant carbonate sediments are present and they precipitate in equilibrium with lake waters. These sediments are analyzed using stable isotope and trace element methods to reconstruct past variations in moisture balance. An excellent chronology can be developed using a combination of AMS radiocarbon, an existing tephrochronology, and U/Th. Lago Sarmiento is located adjacent to Lago del Toro, a similar but open-system lake, as well as a marine fjord of the SW Chilean archipelago. Additional core samples from these systems are being collected and will enable the project to deconvolve the effects of changing temperature, precipitation, and evaporation. The project will use three methods to reconstruct westerly wind variability at this site. The 1st method exploits the strong connection between lake hydrology and oxygen isotope fractionation of biogenic carbonate phases. The 2nd uses carbon isotopes to constrain periods of lake stratification due to reduced wind stress on the lake. The 3rd involves grain size analysis of sediments in areas affected by wind wave-driven redeposition. By combining geochemical & sedimentological methods the project develops high resolution paleoclimate records that provide important information on Holocene climate variability. The study also includes a substantial modeling component, using a General Circulation Model and an embedded high resolution regional climate model to identify climate forcings and feedbacks and for model-data intercomparison.Broader Impacts and Significance. The project delivers a well-dated Holocene chronology of past variability in rainfall, water balance, and temperature from the Pacific margin of southwestern Patagonia. The record is of high intrinsic value as few high quality climate reconstructions are available from the core of the southern westerly wind field. However, the greatest merit comes from model-data intercomparisons and modeling experiments where the causes of climate change in the SE Pacific over timescales of centuries to millennia are examined. Results aid in climate forecasting for southernmost South America, particularly with regard to water availability. The Holocene westerly wind reconstructions should also provide a useful constraint in climate studies throughout the Southern Ocean. One benefit is likely to be an improved understanding of the capacity of the Southern Ocean to take up anthropogenic carbon dioxide. Benefits to society include greater knowledge of climatic influences on water balance (directly important to farmers, ranchers, & land-use planners in Chile & Argentina) as well as better understanding of how atmospheric flow may be related to global climate change and how it interacts with the ongoing rise in atmospheric CO2 levels. During the project two 1-week workshops for North & South American graduate students, post-doctoral fellows, and new faculty members on: 1) Large lake limnology, sedimentology and stratigraphy, & 2) Tools for examining past variability in the hydrologic cycle are being organized.

该项目结合了气候系统建模和实地数据收集，以研究南美洲南部全新世气候变化的原因和表现。这是唯一延伸到南西风场核心的重要陆地，南西风场是地球上最活跃的风系统。该项目从萨米恩托湖（Lago Sarmiento）收集有关过去气候变化的信息，萨米恩托湖是一个位于南纬 51° 的大型封闭盆地碱性湖。该地区的降水量以及湖泊的水文和水平衡显然是受风场强度控制的。存在丰富的碳酸盐沉积物，它们与湖水平衡沉淀。使用稳定同位素和微量元素方法对这些沉积物进行分析，以重建过去的水分平衡变化。使用 AMS 放射性碳、现有的热年代学和 U/Th 的组合可以开发出出色的年代学。萨米恩托湖 (Lago Sarmiento) 毗邻德尔托罗湖 (Lago del Toro)，这是一个类似但开放系统的湖泊，也是智利西南部群岛的一个海洋峡湾。正在收集来自这些系统的更多岩心样本，这将使该项目能够对温度变化、降水和蒸发的影响进行解卷积。该项目将使用三种方法来重建该地点的西风变化。第一种方法利用了湖泊水文学与生物碳酸盐相的氧同位素分馏之间的紧密联系。第二个使用碳同位素来限制湖泊分层的周期，因为减少了湖泊的风应力。第三个涉及对受风浪驱动的再沉积影响的地区的沉积物进行粒度分析。通过结合地球化学和沉积学方法，该项目开发了高分辨率古气候记录，提供有关全新世气候变化的重要信息。该研究还包括一个重要的建模部分，使用大气环流模型和嵌入式高分辨率区域气候模型来识别气候强迫和反馈以及模型数据相互比较。更广泛的影响和意义。该项目提供了巴塔哥尼亚西南部太平洋边缘过去降雨量、水平衡和温度变化的全新世年表。该记录具有很高的内在价值，因为从南西风场的核心可以获得高质量的气候重建数据。然而，最大的优点来自于模型数据比较和建模实验，其中研究了东南太平洋在几个世纪到几千年的时间尺度上气候变化的原因。结果有助于南美洲最南端的气候预测，特别是在水资源供应方面。全新世西风重建也应该为整个南大洋的气候研究提供有用的约束。好处之一可能是加深对南大洋吸收人为二氧化碳的能力的了解。对社会的好处包括更多地了解气候对水平衡的影响（对智利和阿根廷的农民、牧场主和土地利用规划者直接重要），以及更好地了解大气流量与全球气候变化的关系以及它如何与大气中二氧化碳水平持续上升的相互作用。在该项目期间，为北美和南美研究生、博士后研究员和新教员举办了两次为期 1 周的研讨会，内容涉及：1）大型湖泊湖沼学、沉积学和地层学，以及 2）用于检查水文循环过去变化的工具。