Magnitude of the Carbonate Dissolution Recycling Flux from Shallow Marine Carbonate Sediments: Evaluation from Pore Fluid and Sediment Geochemistry

该项目将研究佛罗里达州海湾浅海碳酸盐沉积物的孔隙流体和沉积物的地球化学，以评估它们作为碳酸钙和有机质再循环地点的意义。一项初步研究的结果表明，与先前的假设相反，沉积物孔隙流体中发生了显著的碳酸盐溶解，这是由硫酸盐还原过程中有机质氧化释放出来的碳酸推动的。扩大的调查将在比试点研究更广泛的环境和水深范围内对这一过程进行评估。将测定孔隙流体化学(重点是Ca/Cl、硫酸盐还原程度和碳酸体系参数)，并通过实验测量硫酸盐还原速率。将测定沉积物有机碳含量和孔隙流体的碳同位素组成，以更好地约束硫酸盐还原的控制和后果。这些结果将对浅层碳酸盐陆架沉积在碳酸钙和有机质海洋循环中所起的作用进行严格的评估。长期以来，碳酸钙的溶解一直被认为发生在深水中。然而，试点项目的结果证明，许多溶解发生在浅水中。该项目将从佛罗里达州海湾收集沉积岩心，并在收集后立即开始对沉积物进行地球化学分析。这项研究将把这一重要的地球化学过程的知识更深入地扩展到一个新的环境中，以考察其他环境参数对该过程的作用。

This project will investigate pore fluid and sediment geochemistry of shallow marine carbonate sediments from Florida Bay in order to assess their significance as recycling sites for calcium carbonate and organic matter. Results of a pilot study suggest that, contrary to prior assumptions, significant carbonate dissolution occurs in sediment pore fluids, driven by carbonic acid liberated from organic matter oxidation during sulfate reduction. The expanded investigation will evaluate this process across a wider range of environments and water depths than were accessible in the pilot study. The pore fluid chemistry (emphasis on Ca/Cl, degree of sulfate reduction, and carbonic acid system parameters) will be determined and sulfate reduction rates measured experimentally. Sediment organic carbon contents and carbon isotopic compositions of pore fluids will be determined to better constrain controls and consequences of sulfate reduction. Results will provide a rigorous assessment of the role shallow carbonate shelf deposits play in the oceanic cycles of calcium carbonate and organic matter. %%% The dissolution of calcium carbonate has long been thought to occur in deep water. The results of the pilot project, however, prove that much dissolution occurs in shallow water. This project will collect sedimentary cores from Florida Bay and begin geochemical analyses of the sediments immediately after their collection. This study will expand the knowledge of this important geochemical process to a new environment at greater depth to examine the role of other environmental parameters on the process.