Phosphorous Geochemistry in Marine Sediments

到目前为止，研究已经产生了一些重要的发现。(1)通过改进的选择性萃取技术，在许多地点的沉积物中区分了不同的固体形态磷，并测定了它们的浓度，重点是亚马逊三角洲。结果表明，以前不为人知的从海水中去除磷的机制(如分散的自生磷灰石和与水合三氧化二铁有关的磷)在全球范围内可能是重要的。此外，不同地区含磷相相对比例的差异符合独立的地质推理，这对该方法起到了检查作用。(2)用~(31)P核磁共振研究了海洋沉积物中有机磷的C/P比及其化学性质。主要形式是磷酸单酯和双酯，以及磷酸盐化合物，后者是首次在海洋沉积物中发现的。磷酸盐是C与P直接键合的地方，它特别重要，因为它能抵抗细菌腐烂。(3)对氟磷灰石在类海水溶液中的成核和晶体生长动力学进行了实验研究，提出了上升流区磷矿形成的假说，认为上升流区的磷矿是在浅部堆积很高浓度(400um)的间隙溶解磷酸盐的结果。较高的浓度可以使亚稳的钙磷酸盐析出，这是氟磷灰石析出所必需的成核剂。本研究将通过(1)详细分析亚马逊河、长江(长江)和黄河(黄河)三条主要河流及其海洋三角洲沉积物中不同形态的固体磷。(2)扩大实验室沉淀研究，包括特定成核剂的作用，如胶原蛋白，以及改变溶解碳酸盐水平对磷灰石沉淀的影响。

Research to date has resulted in a number of significant findings. (1) By means of a modified selective extraction technique, separate solid forms of phosphorus have been distinguished, and their concentrations determined, in sediments from a number of locations, with emphasis on the Amazon Delta. Results indicate that previously unrecognized mechanisms for the removal of P from seawater (as dispersed authigenic apatite and P associated with hydrous ferric oxides) may be important on a global basis. Also, differences in relative proportions of P- containing phases from place to place agree with independent geological reasoning which serves as a check on the method. (2) Organic phosphorus in marine sediments has been investigated in terms of C/P ratios and its chemical nature using 31P NMR. Principal forms are phosphate monoesters and diesters, and phosphonate compounds, the latter having been identified in marine sediments for the first time. Phosphonate, where C is directly bonded to P, is especially important because of its resistance to bacterial decay. (3) An experimental study of the kinetics of nucleation and crystal growth of fluorapatite from seawater-like solution has resulted in the hypothesis that phosphorite in upwelling areas forms as the consequence of the buildup of very high concentrations (400 uM) of interstitial dissolved phosphate at shallow depths. The high concentrations enable the precipitation of metastable Ca-phosphate phases which serve as necessary nucleating agents for fluorapatite precipitation. This study will be continued by (1) analyzing in detail for different forms of solid phosphorus in sediments from three major rivers and their marine deltas: the Amazon, the Yangtze (Chang- jiang) and the Yellow (Huang-he). (2) Extending laboratory precipitation studies to include the role of specific nucleating agents, such as collagen, and the effect of changing dissolved carbonate levels on apatite precipitation.