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

该项目结合气候系统模拟和野外数据收集，研究南美洲南部全新世气候变化的原因和表现。这是唯一一个延伸到地球上最具活力的风系统--南西风带风场核心的重要陆地。该项目从Lago Sarmiento收集过去气候变化的信息，Lago Sarmiento是一个位于51°S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量平衡明显受风场强度的控制。存在丰富的碳酸盐沉积物，它们与湖泊沃茨平衡沉淀。这些沉积物进行了分析，使用稳定同位素和微量元素的方法来重建过去的水分平衡的变化。利用AMS放射性碳、现有的火山灰年代学和U/Th的组合，可以建立一个很好的年代学。Lago Sarmiento毗邻Lago del Toro，一个类似但开放系统的湖泊，以及西南智利群岛的海洋峡湾。正在从这些系统中收集更多的岩心样本，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站点的西风变率。第一种方法利用湖泊水文和生物碳酸盐相的氧同位素分馏之间的密切联系。第二个使用碳同位素来限制湖泊分层的时间，因为风对湖泊的压力减少了。第三个是对受风浪驱动的再沉积影响地区的沉积物进行粒度分析。通过结合地球化学沉积学方法，该项目开发了高分辨率的古气候记录，为全新世气候变化提供了重要信息。这项研究还包括一个实质性的模拟部分，使用一个大气环流模式和一个嵌入式高分辨率区域气候模式来确定气候强迫和反馈，并进行模式数据的相互比较。该项目提供了一个很好的全新世年表过去的降雨量，水平衡和温度的变化从太平洋边缘的巴塔哥尼亚西南部。该记录具有很高的内在价值，因为从南部西风风场的核心可以获得的高质量气候重建很少。然而，最大的优点来自于模型数据的相互比较和模拟实验，在这些实验中，研究了东南太平洋数百年至数千年时间尺度上气候变化的原因。研究结果有助于南美洲最南端的气候预测，特别是在水的供应方面。全新世西风的重建也应该在整个南大洋的气候研究提供了一个有用的约束。其中一个好处可能是更好地了解南大洋吸收人为二氧化碳的能力。对社会的好处包括更好地了解气候对水平衡的影响（对智利和阿根廷的农民、牧场主和土地使用规划者直接重要），以及更好地了解大气流动如何与全球气候变化有关，以及它如何与大气CO2水平的持续上升相互作用。在该项目期间，为南北美洲研究生、博士后研究员和新教员举办了两个为期一周的讲习班，内容涉及：1）大湖湖沼学、沉积学和地层学，2）正在组织研究水文循环过去变化的工具。

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.