OCE-PRF: Towards Quantifying Calcium Carbonate Sediment Dissolution During Marine Diagenesis

海洋成岩过程中碳酸钙沉积物溶解的定量研究该项目的目标是研究海底沉积物中碳酸钙(CaCO3)的溶解，并确定其对海水化学的重要性。该项目使用了过去50年来通过科学海洋钻探计划从海洋不同部分收集的沉积物样本和化学数据。碳酸盐的沉积物溶解可以减轻海洋酸化的影响，海洋酸化是由于从大气中吸收二氧化碳(CO2)而导致海洋pH值下降的过程。海洋酸化威胁着牡蛎、文蛤和珊瑚礁等海洋生物的生存，这可能会改变海洋食物链和人类的食物供应。通过改善对海洋中碳酸盐溶解的了解，该项目的结果将能够更好地预测海洋酸化对海洋生物的影响。这将推动科学的进步，促进能够为公共政策提供信息的知识。此外，了解碳酸盐沉积物的溶解作用还有其他重要的目的。例如，溶解可能在沉积物之间创造出很小的空间，一旦沉积物在数百万年后转化为岩石，这些空间可能会被地下水填满。因此，了解岩石中空间的存在和空间分布可能有助于确定地下水在地下含水层中的体积和运动。该项目为一名博士后研究员提供支持，并通过伍兹霍尔海洋研究所的暑期学生奖学金和伍兹霍尔全伙伴关系教育计划为学生提供研究培训机会。碳酸盐矿物溶解是海洋碱度和碳循环的一个组成部分，随着大气中二氧化碳的持续上升，碳酸盐矿物溶解预计将在调节海洋化学变化方面发挥越来越重要的作用。该项目的目标是为量化海洋成岩环境中碳酸盐沉积物的溶解作用提供必要的热力学约束。具体地说，将使用专门开发的Pitzer离子活动模型在全球分布的365个地点计算孔隙流体的CaCO3饱和状态，该模型特别适用于计算高离子强度溶液中的活度系数，例如那些表征大多数成岩环境的溶液。这些计算将通过对四个代表性地点的沉积物样本进行的地球化学和结构分析来证实，以确定具体的成岩过程(例如，溶解、沉淀和重结晶)，并记录导致这些过程发生和流行的条件。计算孔隙流体饱和状态的直接好处是，这种数据可用于估计海底以下碳酸盐沉积物的溶解情况，并量化其对碱度和碳循环的贡献，从而能够更准确地预测海洋酸化的后果。全球饱和状态数据集的另一个好处是，它将提高我们对自生碳酸盐降水及其与地球历史上的碳循环的联系的理解，地球历史上的碳循环被认为是一个重要的碳汇。此外，通过用结构和地球化学分析补充热力学计算，该项目将分析各种成岩过程，并确定导致这些过程发生的沉积学和地球化学条件。这些知识对于评估成岩作用对碳酸盐赋存的古环境指标的影响至关重要。总体而言，该项目将为从机制上理解碳酸盐成岩作用铺平道路。这将对海洋碱度循环、碳埋藏率和地球化学指标提供重要的限制，最终帮助我们更好地了解气候变化背景下我们海洋系统的未来。这一奖项反映了NSF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。

OCE-PRF Towards Quantifying Calcium Carbonate Sediment Dissolution During Marine DiagenesisThe goal of the project is to investigate dissolution of calcium carbonate (CaCO3) in sediments below the seafloor and determine its importance to the chemistry of seawater. This project uses sediment samples and chemical data collected from different parts of the ocean during the past five decades by scientific ocean drilling programs. Sediment dissolution of carbonate can lessen the impact of ocean acidification, the process that causes the pH of the ocean to decrease due to the uptake of carbon dioxide (CO2) from the atmosphere. Ocean acidification threatens the survival of marine organisms, such as oysters, clams, and coral reefs, which could alter marine food chains and food supply to humans. By improving understanding of carbonate dissolution in the ocean, results from this project will enable better predictions of the effects of ocean acidification on marine organisms. This will advance the progress of science and contribute to the knowledge that can inform public policy. In addition, understanding carbonate sediment dissolution serves other important purposes. For example, dissolution can create small spaces between sediments that may get filled with groundwater once sediments convert to rocks over millions of years. Thus, understanding the occurrence and spatial distribution of spaces within rocks may help determine the volume and movement of groundwater in subsurface aquifers. This project provides support for a postdoctoral research fellow and research training opportunities for students through the Summer Student Fellowship and Woods Hole-wide Partnership Education Programs at the Woods Hole Oceanographic Institution. Carbonate mineral dissolution is an integral part of the alkalinity and carbon cycles in the ocean and is expected to play an increasingly significant role in mediating changes in ocean chemistry as atmospheric CO2 continues to rise. The goal of this project is to provide thermodynamic constraints necessary for quantifying carbonate sediment dissolution in marine diagenetic environments. Specifically, the CaCO3 saturation state of pore fluids will be calculated in 365 globally distributed sites from previous scientific ocean drilling expeditions using a specially developed Pitzer ion activity model which is particularly useful for calculating activity coefficients in high ionic strength solutions such as those that characterize most diagenetic environments. These calculations will be substantiated with geochemical and textural analyses of sediment samples from four representative sites to identify the specific diagenetic processes (e.g., dissolution, precipitation, and recrystallization) and document the conditions responsible for their occurrence and prevalence. The immediate advantage of calculating the saturation state of pore fluids is that such data can be used to estimate carbonate sediment dissolution below the seafloor and quantify its contribution to the alkalinity and carbon cycles, which will lead to more accurate predictions of the consequences of ocean acidification. Another benefit of the global saturation state dataset is that it will improve our understanding of authigenic carbonate precipitation and its link to the carbon cycle over Earth history, which has been proposed as a significant sink for carbon. Furthermore, by complementing the thermodynamic calculations with textural and geochemical analyses, this project will parse out various diagenetic processes and identify the sedimentological and geochemical conditions responsible for their occurrence. Such knowledge is crucial for evaluating the impact of diagenesis on the carbonate-hosted paleoenvironmental proxies. Collectively, this project will pave the way towards a mechanistic understanding of carbonate diagenesis. This will provide important constraints on the oceanic alkalinity cycle, carbon burial rates, and geochemical proxies, which ultimately help us better understand the future of our ocean system in the context of climate change.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.