The Ca isotope geochemistry of chemical weathering in the New Zealand Southern Alps

新西兰南阿尔卑斯山化学风化的钙同位素地球化学

• 批准号: 0643317
• 负责人: Andrew Jacobson
• 金额: $ 6万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0643317&HistoricalAwards=false
• 关键词: Ca; isotope; geochemistry; chemical; weathering

Over geologic timescales, the chemical weathering of continental silicate rocks regulates atmospheric CO2 levels and thereby global climate. Quantifying this mechanism and its controls is crucial for understanding how Earth became and remains habitable. Calcium (Ca) is coupled to the long-term carbon cycle because as rocks weather, Ca is released in dissolved form, transported by rivers to the oceans, and sequestered during carbonate precipitation from seawater. The Ca isotope composition (delta 44Ca) of marine carbonate thus reflects the history of continental weathering and related changes in atmospheric CO2 concentrations. However, development of the marine Ca isotope record has outpaced understanding of processes eliciting Ca isotope variation during mineral weathering and subsequent transport of aqueous Ca. By analyzing the Ca isotope composition of rivers draining the New Zealand Southern Alps, the goal of this project is to help resolve questions concerning if, how, and the extent to which tectonic and climatic processes influence the Ca isotope budget of seawater. The mountain range has a uniform lithology but large gradients in tectonics and climate. The western side experiences a wet climate, rapid uplift, and high rates of physical erosion, whereas the eastern side experiences an arid climate, low uplift, and low rates of physical erosion. The PI has worked previously in the New Zealand Southern Alps to quantify mineral weathering reactions, atmospheric CO2 consumption rates, and riverine Sr isotope fluxes. Using this framework, the PI will test specific hypotheses concerning controls on the Ca isotope geochemistry of rivers. Sample collection will include waters, suspended sediments, rocks, and vegetation. The PI will measure delta 44Ca values by thermal ionization mass spectrometry and synthesize data using mass-balance modeling, carbonate equilibria calculations, hydrograph separations, and elemental and isotope mixing equations. The intellectual merit of the project is to improve knowledge about the Ca isotope geochemistry of weathering and thereby aid reconstructions of past atmospheric CO2 levels using the marine Ca isotope record. Broader impacts include the teaching and training of a post-doctoral research fellow.

在地质时间尺度上，大陆硅酸盐岩石的化学风化调节了大气中的二氧化碳水平，从而调节了全球气候。量化这种机制及其控制对于理解地球如何变得并保持可居住至关重要。钙（Ca）与长期碳循环相关联，因为随着岩石风化，Ca以溶解形式释放，通过河流运输到海洋，并在海水中的碳酸盐沉淀过程中被隔离。因此，海洋碳酸盐的Ca同位素组成（δ 44 Ca）反映了大陆风化的历史和大气CO2浓度的相关变化。然而，海洋钙同位素记录的发展已经超过了对矿物风化过程中钙同位素变化和随后的水钙运输过程的理解。通过分析新西兰南阿尔卑斯山脉河流的钙同位素组成，该项目的目标是帮助解决有关问题，如果，如何，以及在何种程度上构造和气候过程影响海水的钙同位素收支。该山脉具有统一的岩性，但在构造和气候的大梯度。西侧气候潮湿，隆起迅速，物理侵蚀率高，而东侧气候干旱，隆起低，物理侵蚀率低。PI以前曾在新西兰南阿尔卑斯山量化矿物风化反应，大气CO2消耗率，河流Sr同位素通量。使用这个框架，PI将测试有关控制河流的钙同位素地球化学的具体假设。样本采集将包括沃茨、悬浮沉积物、岩石和植被。PI将通过热电离质谱法测量δ 44 Ca值，并使用质量平衡建模、碳酸盐平衡计算、水文分离以及元素和同位素混合方程合成数据。该项目的智力价值是提高有关风化的钙同位素地球化学的知识，从而有助于利用海洋钙同位素记录重建过去的大气CO2水平。更广泛的影响包括博士后研究员的教学和培训。