The Interactions Between Aluminum and Biogenic Silica in Marine Sediments: An Experimental Flow-Through Reactor Study

9633351货车Cappellen 铝在底栖生物再生营养酸和保存沉积记录中的生物蛋白石中起着重要作用。 根据先前对南大洋印度部分沉积物的研究结果，Al干预二氧化硅早期成岩作用的潜在机制包括：（1）生物硅质骨骼在生物成矿作用中对Al的初次吸收，（2）海底生物硅质微体化石对Al的二次吸收，（3）埋藏过程中生物硅质碎屑表层Al/Si比值的重新调整;（4）孔隙水硅铝同时沉淀。 这项研究将测试所提出的铝硅相互作用机制，并在这样做，建立一个定量的基础，预测其在不同的海洋沉积环境中的相对重要性。在实验中将使用搅拌流通反应器，因为它们允许在可重现的稳态条件下测量反应动力学。通过测量纯硅藻培养物的高铝和低铝样品的草酸生产的稳态速率，将研究生物硅化过程中初级铝吸收的影响。动力学将被确定为二氧化硅硅藻壳的饱和度，温度，pH和Al含量的函数。二氧化硅和可溶性铝之间的早期成岩相互作用将通过提供溶解的铝通过输入溶液，或通过添加固体源的活性铝悬浮在反应器中的生物二氧化硅进行研究。在后面的实验中，将给定量的生物二氧化硅与增加量的固体Al源混合。这将模拟海洋沉积物中碎屑物质对生物硅的稀释作用。实验结果将允许检查的假设，即在富含碎屑的沉积物中的渐近孔隙水二氧化硅水平代表一个动力学稳定状态之间的生物硅溶解和消耗的自生Al-Si相的沉淀生产草酸。 自生沉淀物的Al/Si化学计量将从反应器实验中Al沉淀和二氧化硅再沉淀的相对速率获得。批量吸附实验也将被用来限制铝吸附的水平，在该水平下，二次铝吸收生物硅质表面从吸附到沉淀物的形成。扫描电子显微镜和固态化学分析将补充基于反应堆的实验。

9633351 Van Cappellen Aluminum plays a major role in the benthic regeneration of nutrient silicic acid and the preservation of biogenic opal in the sedimentary record. Based on results of a previous study of sediments from the Indian sector of the Southern Ocean, potential mechanisms by which Al intervenes in the early diagenesis of silica include: (1) primary uptake of Al by biosiliceous skeletons during biomineralization, (2) secondary uptake of Al by biosiliceous microfossils at the seafloor, (3) readjustment of the Al/Si ratio of the surface layers of biosiliceous debris during burial, and (4) simultaneous precipitation of pore water silica and aluminum. This study will test the proposed Al-Si interaction mechanisms and, in doing so, build a quantitative basis for predicting their relative importance in different marine depositional environments. Stirred flow-through reactors will be used in the experiments, because they allow the measurement of reaction kinetics under reproducible, steady-state conditions. The effect of primary Al uptake during biosilicification will be studied by measuring the steady state rates of silicic acid production from high-Al and low-Al samples of pure diatom cultures. The kinetics will be determined as a function of the degree of saturation, temperature, pH and Al content of the silica frustules. The early diagenetic interactions between silica and soluble Al will be studied by supplying dissolved Al via the input solution, or by adding a solid source of reactive Al to biogenic silica suspended in the reactor. In the latter experiments, a given amount of biogenic silica will be mixed with increasing amounts of the solid Al source. This will mimic the increased dilution of biogenic silica by detrital material in marine sediments. The experimental results will allow to examine the hypothesis that the asymptotic pore water silica level in detrital-rich sediments represents a kinetic steady state between production of silicic acid by biogenic silica dissolution and consumption by precipitation of authigenic Al-Si phases. The Al/Si stoichiometry of the authigenic precipitates will be obtained from the relative rates of Al precipitation and silica reprecipitation in the reactor experiments. Batch adsorption experiments will also be used to constrain the levels of Al sorption at which secondary Al uptake by biosiliceous surfaces switches from adsorption to the formation of precipitates. Scanning electron microscopy and solid state chemical analyses will complement the reactor-based experiments.