P2C2: Amazonian Tree-Ring Chronologies for Climate and Streamflow Reconstruction

该项目旨在开发亚马逊盆地长达200-400年的树木年轮年表，以延长短暂的降水和径流仪器记录。亚马逊河流量是地球上最大的流量，部分受到来自热带大西洋和太平洋的海气强迫的调制。亚马逊流量自1902年以来一直受到监测，似乎进入了一个水文变异性放大的新区域。最近在最小和最大流量方面的分歧在短期的仪器记录中是没有先例的。亚马逊地区这种加强的水文循环的原因尚不清楚，但可能是由于与观测到的热带北大西洋变暖有关的森林砍伐或水汽平流变化。根据CMIP5气候模式集合模拟，在一切照常的温室气体排放和土地覆盖变化下，预测21世纪中期亚马逊大部分地区的年降水量将严重下降。在全新世晚期自然气候变异性的背景下，最近和预测的水文气候变化可能是多么史无前例，无法通过亚马逊盆地为数不多的短期和空间不连续的仪器观测来确定经验。树轮重建提供了对过去特大干旱和暴雨的准确的空间分布估计，这是验证北美和亚洲十年湿度制度动态的模型模拟所需的。然而，世界上生物多样性最丰富的森林生态系统--亚马逊森林--并没有免费提供可用于准确测年或气候重建的多世纪年轮年表。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上独特的年轮，因此不能用于常规的树干年代学。然而，在一些热带森林中确实存在强烈的环境节律，并可以在少数本地物种中诱导一年生树轮的形成。这些年度变化包括亚马逊中部、东部和南部低地森林深刻的降水季节性和延长的洪水脉冲。研究小组的同事们已经证明，在这些淹没的森林中，大叶藻中存在年轮，并证明了它们在水文气候应用中的潜在价值。在巴西和玻利维亚东部季节性干旱的高地森林中发现的年轮也被证实存在于Bertholletia Exelsa、Cedrella fisilis、C.odorata和Centrolobium microchaete中，由它们得出的年轮宽度和氧同位素年表与大尺度气候变异性有关。该项目将使用新的树轮年表来开发网格区域水分重建，使用过去千年和21世纪的CMIP5集合模拟来框定气候变化背景下最极端的仪器前和现代干旱，并探索亚马逊地区气候的海洋-大气强迫的稳定性。该项目还将利用研究资源，联合来自美国、巴西、玻利维亚和阿根廷的学生和研究人员应用树状气候学来选择亚马逊地区的热带硬木。一个由气候学家、树木年代学家和森林科学家组成的国际合作组织了所需的专业知识，以解决热带硬木精确年轮测年所涉及的复杂性。

This project aims to develop 200-400 year-long tree-ring chronologies from the Amazon Basin to extend the short instrumental record of precipitation and streamflow.Amazon River discharge, the largest on Earth, is modulated in part by ocean-atmospheric forcing from the tropical Atlantic and Pacific. Amazon discharge has been monitored since 1902 and appears to have entered a new regime of amplified hydrological variability. The recent divergence in minimum and maximum flows has no precedent in the short instrumental record. The cause of this intensified hydrological cycle over Amazonia is not known, but may arise from deforestation or moisture advection changes associated with the observed warming of the tropical North Atlantic.A severe decline in annual precipitation is predicted for the mid-21st century over most of Amazonia based on CMIP5 climate model ensemble simulations under business-as-usual greenhouse gas emissions and land cover changes. How unprecedented the recent and predicted hydroclimatic changes might be in the context of natural climate variability during the late Holocene cannot be determined empirically from the few short and spatially discontinuous instrumental observations from the Amazon Basin.Tree-ring reconstructions have provided well-dated spatially distributed estimates of past megadroughts and pluvials needed for verifying model simulations of the dynamics responsible for decadal moisture regimes over North America and Asia. However, the most biodiverse forest ecosystems in the world, the forests of Amazonia, have not produced freely available multi-century tree-ring chronologies 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 tree-ring formation in a few native species. These annual changes include the profound precipitation seasonality and prolonged flood pulse of lowland forests in the central, eastern, and southern Amazon. Colleagues on the research team have proven that annual rings exist in Macrolobium acaciifolium in these inundation forests and have demonstrated their potential value for hydroclimatic applications. Annual rings have also been proven in Bertholletia excelsa, Cedrella fissilis, C. odorata, and Centrolobium microchaete from seasonally dry upland forests of Brazil and eastern Bolivia, and ring width and oxygen isotope chronologies derived from them are related to large-scale climate variability. This project will use new tree-ring chronologies to develop gridded regional moisture reconstructions, to frame the most extreme pre-instrumental and modern droughts in the context of climate change using CMIP5 ensemble simulations of the past millennium and the 21st century, and to explore the stability of ocean-atmospheric forcing of climate over Amazonia.The project will also leverage research resources and unite students and investigators from the United States, Brazil, Bolivia, and Argentina in the application of dendroclimatology to select tropical hardwoods in Amazonia. An international collaboration of climatologists, dendrochronologists, and forest scientists has been organized with the expertise required to solve the complexities involved in the exact tree-ring dating of tropical hardwoods.