Collaborative Research: P2C2--Reconstructing Atmospheric 14C across the Inter Tropical Convergence Zone Using Tropical Tree Rings from South America and Central Africa

该项目旨在利用热带辐合带(ITCZ)的树木年轮建立1950年后大气放射性碳(14C)数据的观测记录。年轮地点位于南美洲(厄瓜多尔、秘鲁、玻利维亚、巴西)和中部非洲(喀麦隆)，横跨ITCZ频段。这些新的14C数据将被用来约束南半球大气14C的空间格局，目前南半球大气14C的空间格局主要依赖于在南半球东部采集的样本。研究人员还将测量年轮宽度和年轮中氧和碳的稳定同位素组成，以调查可能导致14C变化的空间和时间变化的因素。这些指标包括树木生长的季节性和反映大气环流动态的雨水来源。这些联合指标旨在改进：1)ITCZ环流和半球间交换的区域和局部特征；2)对ITCZ变化的预测；3)赤道南半球的14C校准曲线。潜在的更广泛的影响包括更好地定义低纬地区的半球内14C纬向划分，以及南半球的14C时间尺度，这将有利于古气候界对全新世的年代学约束(放射性碳法的准确性)和ITCZ的气候动力学。该项目的成果将惠及其他领域，包括：放射性碳校准学、天体物理学、生态学、生物地球化学、地球科学和考古学。该项目将为两名本科生和一名博士生提供培训。加州大学欧文分校将组织一个放射性碳短期课程，研究人员、学生和国际合作者将参与其中。这些项目的数据将被整合到大气放射性碳的国际相互校准曲线中。这一奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project aims to develop an observational record of atmospheric radiocarbon (14C) data post-1950 by using calendrically dated tree rings across the intertropical convergence zone (ITCZ). The tree-ring sites are located in South America (Ecuador, Peru, Bolivia, Brazil) and central Africa (Cameroon) across the ITCZ band. These new 14C data will be used to constrain the spatial pattern of atmospheric 14C in the southern hemisphere, which currently relies on samples collected mostly in the eastern part of the southern hemisphere. The researchers will additionally measure the ring width and the stable isotope compositions of Oxygen and Carbon from the tree rings to investigate factors that can cause spatial and temporal variations of 14C variations. These include the seasonality of tree growth and the source of rainwater which reflects atmospheric circulation dynamics. The combined proxies aim to improve: 1) regional and local features of ITCZ circulation and inter-hemispheric exchange; 2) prediction of the ITCZ shifts in response to anthropogenic forcings; 3) the 14C calibration curve for the equatorial southern hemisphere.The potential Broader Impacts include a better definition of the intra-hemispheric 14C zonal division at lower latitudes, and the 14C timescale in Southern hemisphere which will benefit the paleoclimate community for chronology constraints (accuracy of the radiocarbon method) of the Holocene and climate dynamics of the ITCZ. Results of this project will benefit other fields including: radiocarbon calibration, astrophysics, ecology, biogeochemical and Earth science and archeology. The project will provide training for two undergraduate students and one PhD student. A radiocarbon short course will be organized at University of California Irvine where researchers, students and international collaborators will participate. The data of these project will be integrated in the International intercalibration curve of atmospheric radiocarbon.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.