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

9633351范卡普伦铝在营养硅酸的底栖生物再生和生物蛋白石在沉积记录中的保存中发挥着重要作用。根据以前对南大洋印度段沉积物的研究结果，铝参与硅质早期成岩作用的潜在机制包括：(1)生物成矿过程中生物硅质骨架对铝的初级吸收，(2)海底生物硅质微化石对铝的二次吸收，(3)埋藏过程中生物硅质碎屑表层铝硅比的调整，以及(4)孔隙水和硅铝的同时沉淀。这项研究将检验所提出的Al-Si相互作用机制，并以此建立一个定量基础，以预测它们在不同海洋沉积环境中的相对重要性。实验中将使用搅拌流通式反应器，因为它们允许在可重复的、稳定的条件下测量反应动力学。通过测量纯硅藻培养的高铝和低铝硅酸的稳态产酸速率，研究生物硅化过程中原生铝吸收的影响。动力学将被确定为饱和度、温度、pH和硅石小锥的铝含量的函数。通过输入溶液提供溶解的铝，或在反应器中悬浮的生物硅中加入固体源的活性铝，可以研究二氧化硅和可溶铝之间的早期成岩作用。在后面的实验中，一定数量的生物成因二氧化硅将与增加数量的固体铝源混合。这将模拟海洋沉积物中碎屑物质对生物源二氧化硅的日益稀释。实验结果验证了富碎屑沉积物中的渐近孔隙水SiO_2水平代表了生物SiO_2溶解产生硅酸和自生Al-Si相沉淀消耗硅酸之间的动力学稳定状态的假说。在反应堆实验中，自生沉淀物的Al/Si化学计量比将由Al沉淀物和二氧化硅再沉淀物的相对速率得到。批量吸附实验也将被用来限制铝的吸附水平，在这个水平上，生物硅表面的二次铝吸收从吸附转变为沉淀的形成。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.