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

本项目结合气候系统建模和实地数据收集，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南方西风场核心的重要陆地，西风场是地球上能量最高的风系统。该项目收集了位于南纬51度的大型封闭碱性湖泊Lago sammiento过去气候变化的信息。该地区的降水以及湖泊的水文和水量平衡明显受风场强度的控制。碳酸盐岩沉积物丰富，与湖水平衡沉淀。利用稳定同位素和微量元素方法对这些沉积物进行了分析，以重建过去的水分平衡变化。利用AMS放射性碳测年法、现有的温度测年法和U/Th测年法的结合，可以开发出一种优秀的年表。Lago sammiento位于Lago del Toro附近，Lago del Toro是一个类似的开放式湖泊，也是智利西南部群岛的一个海洋峡湾。正在从这些系统中收集更多的岩心样本，这将使该项目能够反卷积温度变化、降水和蒸发的影响。该项目将使用三种方法重建该站点的西风变异性。第一种方法利用了湖泊水文与生物碳酸盐相氧同位素分馏之间的紧密联系。第二种方法使用碳同位素来限制湖泊分层的周期，因为湖泊上的风应力减少了。三是风浪再沉积影响区沉积物粒度分析。通过结合地球化学和沉积学方法，该项目开发了高分辨率的古气候记录，提供了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组成部分，使用一个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。更广泛的影响和意义。该项目提供了一个完整的全新世年表，记录了巴塔哥尼亚西南部太平洋边缘地区过去降雨、水平衡和温度的变化。这一记录具有很高的内在价值，因为在南方西风场的核心地区很少有高质量的气候重建。然而，最大的优点来自模式数据的相互比较和模拟实验，在这些实验中，研究了几个世纪到几千年时间尺度上东太平洋气候变化的原因。研究结果有助于预测南美洲最南端的气候，特别是关于水资源的可用性。全新世西风重建也将为整个南大洋的气候研究提供有用的约束。其中一个好处可能是提高对南大洋吸收人为二氧化碳能力的认识。对社会的好处包括对气候对水平衡的影响有更多的了解（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），以及对大气流量如何与全球气候变化相关以及它如何与持续上升的大气二氧化碳水平相互作用有更好的了解。在项目期间，为南北美洲的研究生、博士后研究员和新教员组织了两个为期一周的讲习班，内容包括：1)大湖湖沼学、沉积学和地层学；2)检查过去水文循环变化的工具。

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.