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

该项目旨在编制亚马逊河流域200-400年的树木年轮年表，以扩大降水和流量的短仪器记录，亚马逊河是地球上最大的河流，其流量部分受到热带大西洋和太平洋的海洋-大气作用力的影响。自1902年以来一直监测亚马逊河流量，似乎已进入一个水文变异性扩大的新制度。最近最小和最大流量的分歧在短期仪器记录中没有先例。目前尚不清楚亚马逊河流域水文循环加剧的原因，但可能是由于森林砍伐或与观测到的热带北大西洋变暖相关的水分平流变化。基于CMIP 5气候模式集合模拟，在温室气体排放和土地覆盖变化的情况下，预测21世纪中期亚马逊河流域大部分地区年降水量将严重减少。 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史无前例的，无法根据亚马逊盆地的少数短暂且空间不连续的仪器观测来凭经验确定。树木年轮重建提供了良好的-对过去特大干旱和多雨的空间分布估算，需要验证负责十年湿度状况的动力学模型模拟飞越北美和亚洲。 然而，世界上生物多样性最丰富的森林生态系统-亚马逊河流域的森林-并没有免费提供可用于精确测年或气候重建的多世纪树木年轮年表。由于没有寒冷的冬季休眠季节，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，在一些热带森林中确实存在强烈的环境节律，并能诱导少数本地物种形成年轮。 这些年度变化包括深刻的降水季节性和延长洪水脉冲的低地森林在中部，东部和南部亚马逊。研究小组的同事已经证明，年轮存在于这些淹没森林中的Macrolobium acaciifolium中，并证明了它们在水文气候应用中的潜在价值。Bertholletia excelsa、Cedrella fissilis、C. odorata和Centrolobium microchaete的年轮宽度和氧同位素年代学与大尺度气候变率有关。该项目将使用新的树木年轮年表来开发网格化的区域水分重建，使用CMIP 5对上千年和21世纪的集合模拟，在气候变化的背景下框定最极端的仪器前和现代干旱，探索海洋的稳定性该项目还将利用研究资源，联合来自美国，巴西，玻利维亚和阿根廷应用树木气候学在亚马逊河流域选择热带硬木。气候学家、树木年代学家和森林科学家的国际合作已经组织起来，他们拥有解决热带硬木精确树木年轮年代测定所涉及的复杂问题所需的专业知识。

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.