Tropical Climate Reconstruction with Tree-Ring Chronologies from the Central Amazon and Eastern Highlands of Brazil

该合作项目将涉及阿肯色大学（David Stahle）、巴西国家亚马逊研究所/马克斯普朗克研究所（Jochen Schongart）和巴西拉夫拉斯联邦大学（Ana Carolina Barbosa）。严格的树木年代学方法将用于培训这两个机构的学生和教师，并开发几个精确的年代，很好地复制环宽年表，涵盖亚马逊盆地中部季节性洪水淹没的洼地森林和巴西东部季节性干旱的高地森林的过去300年。准确确定年代的树木年轮年表为全球变暖提供了一个重要的工业化前视角，并产生了对过去特大干旱和雨淋的唯一空间分布估计，这些估计需要用于测试气候模式对北美年代际湿度状况的动态模拟。全世界现有的绝大多数树木年轮年表都是从温带和北方森林发展而来的。然而，世界上最具生物多样性的森林生态系统，即巴西亚马逊盆地的森林，还没有产生一种可免费获得的、用于精确测年或气候重建的多世纪树木年轮年表。在没有寒冷的冬季休眠季节的情况下，大多数热带树种不会产生解剖学上独特的年轮，因此不能用于常规的树木年代学。然而，在一些热带森林中，强烈的环境节奏确实存在，并且可以诱导一些本地物种的年轮形成。这包括深远的降水季节性和亚马孙中部低地森林的长期洪水脉冲。初步研究表明，这些淹没林中的小檗属植物存在年轮，具有潜在的水文气候应用价值。在巴西和玻利维亚东部的季节性旱地森林中也发现了年环，它们的环宽度和氧同位素年代学与大尺度气候变率有关。在亚马逊地区发展对气候敏感的树木年轮年表的一个主要障碍是缺乏严格应用树木年表的专门知识，树木年表是地质年表中最准确和精确的测年方法。通过该项目将开发300年的树木生长和气候历史的主年表，预计将利用广泛的跨学科研究，包括气候动力学，同位素古气候学和森林生态学。一旦这一研究概念得到证实，美国和巴西科学家将参与进一步的合作研究，以模拟得出的年表的气候和水流响应，开发年度水文气候条件的校准重建，并研究南美洲热带地区湿度制度的大尺度海洋-大气强迫。

This collaborative project will involve the University of Arkansas (David Stahle), the Brazilian National Institute for Amazonian Research/Max Planck Institute (Jochen Schongart), and the Federal University at Lavras, Brazil (Ana Carolina Barbosa). Rigorous dendrochronological methods will be used to train students and faculty at both institutions and to develop several exactly dated, well replicated ring-width chronologies covering the last 300-years in the seasonally flooded bottomland forests of the central Amazon basin and in seasonally dry upland forests of eastern Brazil. Exactly dated tree-ring chronologies provide a vital preindustrial perspective on global warming and have produced the only spatially distributed estimates of past megadroughts and pluvials needed for testing climate model simulations of the dynamics responsible for decadal moisture regimes over North America. The vast majority of tree-ring chronologies available worldwide have been developed from temperate and boreal forests. However, the most biodiverse forest ecosystems in the world, the forests of the Amazon Basin in Brazil, have not produced a single freely available multi-century tree-ring chronology useful for exact dating or climate reconstruction. In the absence of a cold winter dormant season, most tropical tree species do not produce anatomically distinctive annual growth rings and therefore cannot be used for routine dendrochronology. However, strong environmental rhythms do exist in some tropical forests and can induce annual ring formation in a few native species. This includes the profound precipitation seasonality and the prolonged flood pulse of lowland forests in the central Amazon. Preliminary research has proven that annual rings exist in Macrolobium acacifolium in these inundation forests and their potential value for hydroclimatic applications has been demonstrated. Annual rings have also been proven in Cedrella fissilis and C. odorata from seasonally dry upland forests of Brazil and eastern Bolivia, and ring width and oxygen isotope chronologies from both are related to large-scale climate variability. A major impediment to the development of long climate sensitive tree ring chronologies in Amazonia has been the lack of expertise with the rigorous application of dendrochronology, the most accurate and precise dating method in geochronology. The 300-year long master chronologies of tree growth and climate history that will be developed through this project are expected to leverage a wide range of interdisciplinary research, including climate dynamics, isotope paleoclimatology, and forest ecology. Once this research concept is proven, further collaborative investigations are envisioned that involve US and Brazilian scientists, in order to model the climate and stream flow response of the derived chronologies, develop calibrated reconstructions of annual hydroclimatic conditions, and investigate the large scale ocean-atmospheric forcing of moisture regimes over tropical South America.