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

摘要为重建恒河-雅鲁藏布江三角洲（G-B）系统中气候影响和河流沉积响应的40-ky地层记录，需要一项为期两年的研究资金。这项研究的主要目标是确定如何改变源区，风化模式和沉积物的输送影响了孟加拉盆地的发展下，不断变化的季风制度的控制。先前NSF支持的PIs对孟加拉盆地的研究表明，它包含来自喜马拉雅流域的晚第四纪河流沉积信号的高分辨率记录，为了解南亚气候的剧烈变化如何影响沉积物和主要三角洲序列的特征提供了无与伦比的机会。G-B沉积物扩散系统的主要特征使其特别适合于本研究，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有关的地球化学和矿物学特征，以及（3）保存厚，高分辨率，G-B系统将为研究河流系统行为和地层对气候变化的响应提供重要的信息，特别是对喜马拉雅/青藏高原隆起的七大河流系统。（1）钻孔样品的地球化学、地层学和古环境研究，（2）季风影响的沉积物扩散系统的概念模型开发，（3）使用最先进的数值模型测试盆地对气候变化和沉积物输送的响应。将从恒河、雅鲁藏布江和混合输入地区以及细粒和粗粒结构地区采集钻孔样品，提供各种沉积信号和序列。锶和钕同位素，沿着矿物学，将被用来追踪最近的间冰期，冰期和间冰期沉积物的生产和分散。将使用粘土矿物学和稳定的O和H同位素来追踪风化模式。放射性碳和光激发光测年法将用于确定年代学和确定不断变化的吸积速率。这些数据将进一步与有机d13 C值和一个合作的孢粉学研究，以推断转移花群落。总之，这种多代理的方法将使我们能够识别诊断地球化学和地层签名在孟加拉盆地，可以在第四纪晚期气候条件的变化。最后，使用水文和地层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影响的概念性想法。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季风气候变化的环境后果的能力。影响河流三角洲的环境。特别是，孟加拉国1.3亿居民的基本生计主要依赖于对沉积物输送、洪水模式以及低地和沿海地区侵蚀/增生周期变化敏感的农业做法。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，这项研究将作出贡献。此外，发展中东道国的专业研究员和科学家/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。两个来自美国的研究生，一个在威廉玛丽和一个在斯托尼布鲁克，将参与这项工作的各个方面，他们的论文/学位论文将塑造这项研究的结果。该项目还将通过独立和/或高级研究涉及本科生。最后，这两个PI都是各自机构的教学人员，这项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.