Collaborative Research: Assessing climate-biosphere linkages using Late Holocene records of climate variability and vegetation dynamics from the Brazilian Amazon and Savanna

这一合作项目旨在调查南美夏季风强度的变化对全新世晚期发生的森林-稀树草原生物群转变的作用。来自季风区核心和附近的古气候记录的发展使评估整个区域的古季风信号的强度成为可能。研究人员希望从巴西亚马逊和塞拉多(稀树草原)产生独立的、但共同定位的过去气候(洞穴)和植被(土壤剖面)动态记录，现有记录尚不存在。古气候和生态解释将通过洞穴监测和代理系统模型来验证。研究人员打算评估以下问题：i)洞穴三角洲18-氧值是否反映了SASM强度的变化，ii)SASM强度的变化是否驱动了当地湿度条件的相应变化，iii)SASM强度和当地湿度条件的变化的性质和驱动因素是什么，以及iv)营养过渡带的生物群对SASM强度和当地水分条件的变化的敏感性如何。该项目涉及监测现代洞穴环境，以评估洞穴三角洲18氧值作为SASM强度和洞穴微量元素浓度的替代指标，以及锶同位素组成作为当地水分条件的替代指标。这项研究将把亚马逊和塞拉多过去一千年已有的洞穴三角洲18-氧记录进一步向前延伸，并开发相应的洞穴三角洲微量元素和87-锶/86-锶和土壤有机质三角洲13-碳的记录，以评估区域季风强度、当地湿度条件和生物群迁移之间的协变性。该项目有助于促进对SASM的更好了解，并与巴西科学家密切合作。SASM是该区域最重要的降雨来源，具有重大的社会经济和环境意义，包括确定当前的生态系统分布和稳定性、水电生产和农业。

This collaborative project aims to investigate the role of changes in the South American Summer Monsoon (SASM) intensity on forest-savanna biome shifts that occurred during the Late Holocene. Development of paleoclimate records from in and near the core of the monsoon region enables an assessment of the strength of the paleo-monsoon signal across the region.The researchers look to generate independent, yet co-located, records of past climate (speleothems) and vegetation (soil profiles) dynamics from the Brazilian Amazon and Cerrado (savanna), for which existing records are absent. Paleoclimate and ecological interpretations will be validated using cave monitoring and proxy system modeling.The researchers intend to evaluate the following questions: i) Do speleothem delta 18-Oxygen values reflect variations in SASM intensity, ii) Do variations in SASM intensity drive corresponding variation in local moisture conditions, iii) What was the nature and driver of Late Holocene variability in SASM intensity and local moisture conditions, and iv) how sensitive were biomes in vegetative transition zones to variability in SASM intensity and local moisture conditions. The project involves the monitoring of modern cave environments to evaluate speleothem delta 18-Oxygen values as a proxy of SASM intensity and speleothem trace element concentrations and Strontium isotope compositions as a proxy of local moisture conditions. The research will extend existing speleothem delta 18-Oxygen records of the last millennium from the Amazon and Cerrado further back in time and develop corresponding records of speleothem trace element and 87- Strontium /86-Strontium and soil organic matter delta 13-Carbon to assess the co-variability between regional monsoon intensity, local moisture conditions, and biome shifts.The project helps promote greater understanding of the SASM and strong collaboration with Brazilian scientists. The SASM is the most important source of rainfall to the region with great socio-economic and environmental relevance, including defining current ecosystem distribution and stability, hydroelectric production, and agriculture.