Collaborative Research: Climate as a Principal Control on Monsoon-Dominated Deltas: Late Quaternary Records from the Ganges-Brahmaputra System

摘要：本项目旨在重建恒河-雅鲁藏布江（G-B）三角洲系统气候影响和河流沉积响应的40-ky地层记录，为期两年。这项研究的主要目标是确定在季风变化的控制下，变化的源区、风化模式和沉积物的输送如何影响孟加拉盆地的发展。以前由国家科学基金会支持的由PIs对孟加拉盆地的研究表明，它包含了喜马拉雅流域晚第四纪河流沉积信号的高分辨率记录，提供了一个无与伦比的机会来了解南亚气候的剧烈变化是如何影响沉积物和主要三角洲序列的特征的。G-B沉积物扩散系统特别适合本研究的关键特征包括：(1)强烈的气候响应和从流域到边缘的快速信号传播；(2)一套与印度-喜马拉雅流域内的过程和区域相关的地球化学和矿物学特征；(3)在边缘保存了厚的、高分辨率的、多样化的地层记录。此外，G-B系统将为河流系统行为和地层对气候变化的响应提供重要的见解，特别是对喜马拉雅/西藏隆起的7个主要河流系统。本研究的主要方法包括：(1)钻孔样品的地球化学、地层学和古环境研究；(2)季风影响沉积物扩散系统的概念模型开发；(3)利用最先进的数值模型测试流域对气候变化和沉积物输送的响应。从恒河、雅鲁藏布江、混合输入以及细粒和粗粒结构的区域采集钻孔样品，提供各种沉积信号和序列。锶和钕同位素，连同矿物学，将被用来追踪最近间冰期、冰期和间冰期沉积物的产生和扩散。风化模式将利用粘土矿物学和稳定的O和H同位素进行追踪。放射性碳和光激发发光定年法将用于建立年表和确定变化的吸积速率。这些数据将进一步与有机d13C值和协同孢粉学研究相关联，以推断植物群落的变化。总之，这种多代理方法将使我们能够确定孟加拉盆地的诊断性地球化学和地层特征，这些特征可能与晚第四纪气候条件的变化有关。最后，使用水文和地层学模型的数值模拟实验将使我们能够测试我们关于晚第四纪气候变化对河流行为和盆地地层学影响的概念。更广泛的社会影响：了解气候对河流沉积物向孟加拉边缘输送的影响，将有助于我们预测受季风影响的河流三角洲环境中气候变化的环境后果。特别是，孟加拉国1.3亿居民的生计在很大程度上依赖于农业实践，而农业实践对沉积物输送、洪水模式以及低地和沿海地区侵蚀/增加周期的变化非常敏感。此外，调解该国目前的地下水砷危机可能取决于更全面地了解地下含水层的矿物学和地球化学，本研究将对此作出贡献。此外，ppi与发展中东道国的科学家/学生之间的大量科学交流将扩大我们的成果在当地和国际上的影响。与达卡大学和孟加拉国地质调查局的合作安排将确保孟加拉国科学家和资源管理人员的充分参与。两名来自美国的研究生，一名来自威廉玛丽大学，一名来自石溪大学，他们将参与这项工作的各个方面，他们的论文将决定这项研究的结果。该项目也将包括本科生通过独立和/或高级研究学习。最后，两位pi都是各自机构的教学人员，本研究的进展和结果将纳入相关课程。

ABSTRACTFunds are requested for a two-year study to reconstruct a 40-ky stratigraphic record of climate impacts and fluviosedimentary responses in the Ganges-Brahmaputra (G-B) delta system. The study's main objectives are to determine how changing source areas, weathering patterns, and delivery of sediment have influenced development of the Bengal basin under the control of shifting monsoon regimes. Previous NSF-supported studies of the Bengal Basin by the PIs demonstrate that it contains a high-resolution record of Late Quaternary fluviosedimentary signals from the Himalayan catchment, presenting an unparalleled opportunity to understand how dramatic changes in South Asian climate have impacted the sediments and character of a major deltaic sequence. Key features of the G-B sediment dispersal system that make it particularly appropriate for this study include: (1) strong climatic responses and rapid signal propagation from the catchment to margin, (2) a suite of geochemical and mineralogical signatures that can be related to processes and regions within the Indo-Himalayan catchment, and (3) the preservation of thick, high-resolution, and diverse stratigraphic records at the margin.Furthermore, the G-B system will provide important insight for river system behavior andstratigraphic responses to climate change, especially for the seven major fluvial systems fed by the Himalayan/Tibetan uplift.The main approaches for this study involve: (1) geochemical, stratigraphic, andpaleoenvironmental studies of borehole samples, (2) conceptual model development for monsoon-affected sediment dispersal systems and, (3) testing of basin response to changing climate and sediment delivery using state-of-art numerical models. Borehole samples will be collected from areas dominated by Ganges, Brahmaputra, and mixed inputs, as well as those of fine- and coarse-grained textures, providing a variety of sedimentary signals and sequences. Strontium and neodymium isotopes, along with mineralogy, will be used to trace the production and dispersal of sediment over recent interglacial, glacial, and interstadial periods. Weathering patterns will be traced using clay mineralogy and stable O and H isotopes. Radiocarbon and optically-stimulated luminescence dating will be used to establish a chronology and determine changing accretion rates. These data will be further correlated with organic d13C values and a collaborative palynology study to infer shifting floral communities. Altogether, this multi-proxy approach will allow us to identify diagnostic geochemical and stratigraphic signatures in the Bengal Basin that can be related to changing climatic conditions during the Late Quaternary. Finally, numerical-modeling experiments using both hydrologic and stratigraphic models will allow us to test our conceptual ideas regarding the influence of Late Quaternary climate change on river behavior and basin stratigraphy.Broader societal impacts: Understanding the influence of climate on the delivery of river sediment to the Bengal margin will contribute to our ability to predict the environmental consequences of climate change in monsoon-influenced fluviodeltaic settings. In particular, the subsistence livelihood of Bangladesh's 130 million inhabitants depends largely on agricultural practices that are sensitive to changes in sediment delivery, flooding patterns, and erosion/accretion cycles of lowland and coastal areas. In addition, mediation of the country's current groundwater arsenic crisis may hinge on a more complete understanding of the mineralogy and geochemistry of subsurface aquifers, to which this study will contribute. Furthermore, substantial scientific exchanges between the PIs and scientists/students in the developing host country will broaden the local and international impact of our results. Collaborative arrangements with Dhaka University and the Geological Survey of Bangladesh will assure the full involvement of Bangladesh scientists and resource managers. Two graduate students from the U.S., one at William & Mary and one at Stony Brook, will participate in all aspects of this work, and their theses/dissertations will shape the outcome of this study. The project will also involve undergraduate students through independent and/or senior research studies. Finally, both PIs are teaching faculty at their respective institutions, and the progress and results of this study will be incorporated into relevant courses.