Phosphorous Geochemistry in Marine Sediments

迄今为止的研究已经产生了一些重要的发现。通过一种改良的选择性萃取技术，已经在许多地点，特别是亚马逊三角洲的沉积物中区分出了磷的不同固体形式，并确定了它们的浓度。结果表明，以前未被认识到的从海水中去除磷的机制（如分散的自生磷灰石和与含水氧化铁相关的磷）可能在全球范围内是重要的。此外，各地含P相相对比例的差异与独立的地质推理一致，这是对该方法的检验。(2)利用31P核磁共振对海洋沉积物中有机磷的C/P比值及其化学性质进行了研究。主要形式是磷酸盐单酯和二酯，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，其中C直接与P结合，特别重要，因为它对细菌腐烂具有抵抗力。(3)一项对类海水溶液中氟磷灰石成核和晶体生长动力学的实验研究提出了这样一种假设：上升流区域的磷矿是在浅层深处形成非常高浓度（400 μ m）的间隙溶解磷酸盐的结果。高浓度使亚稳钙磷酸盐相的沉淀成为氟磷灰石沉淀的必要成核剂。本研究将继续：(1)详细分析亚马逊河、长江和黄河三条主要河流及其海洋三角洲沉积物中不同形式的固体磷。(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，以及改变溶解的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.