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

P2C2：气候和水流重建的亚马逊树轮年表

• 批准号: 1501321
• 负责人: David Stahle
• 金额: $ 41.87万
• 依托单位: University of Arkansas
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1501321&HistoricalAwards=false
• 关键词: P2C2; Amazonian; Tree; Ring; Chronologies

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.

该项目旨在开发亚马逊流域200-400年的树木年轮年表，以扩展降水和水流的短仪器记录。亚马逊河的流量是地球上最大的，它部分受到来自热带大西洋和太平洋的海洋-大气作用力的调节。亚马逊河流域的流量自1902年以来一直受到监测，似乎已经进入了一个放大水文变化的新制度。最近在最小和最大流量上的分歧在短期仪器记录中是没有先例的。亚马逊流域水循环加剧的原因尚不清楚，但可能是由森林砍伐或与观测到的热带北大西洋变暖相关的水汽平流变化引起的。在常规温室气体排放和土地覆盖变化条件下，基于CMIP5气候模式集合模拟，预计21世纪中叶亚马逊大部分地区的年降水量将严重减少。在全新世晚期自然气候变率的背景下，最近的和预测的水文气候变化是多么史无前例，不能从亚马逊盆地的几次短暂和空间不连续的仪器观测中经验地确定。树木年轮重建提供了对过去特大干旱和雨淋的准确的空间分布估计，这些估计需要用于验证对北美和亚洲的年代际湿度状况负责的动力学模式模拟。然而，世界上最具生物多样性的森林生态系统——亚马逊河流域的森林，并没有产生免费的、可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，在一些热带森林中确实存在强烈的环境节奏，并且可以诱导一些本地物种的年轮形成。这些年度变化包括深远的降水季节性和亚马孙中部、东部和南部低地森林的洪水脉冲延长。研究小组的同事已经证明，在这些淹没森林中，大叶阔叶草（Macrolobium acaciifolium）存在年轮，并证明了它们在水文气候应用方面的潜在价值。在巴西和玻利维亚东部的季节性旱地森林中也发现了年轮，其中的年轮宽度和氧同位素年轮与大尺度气候变率有关。该项目将使用新的树木年轮年表进行网格化区域湿度重建，利用CMIP5过去一千年和21世纪的整体模拟，在气候变化背景下构建仪器前和现代最极端的干旱，并探索亚马逊地区海洋-大气气候强迫的稳定性。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调查人员，应用树木气候学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已经组织起来，他们拥有解决热带硬木年轮准确测年所涉及的复杂问题所需的专业知识。