Interstitial-water chemistry and stable isotope record of Prydz Bay sediments

Leg 119 of the Ocean Drilling Program (ODP) provided the first opportunity to study the interstitial-water chemistry of the eastern Antarctic continental margin. Five sites were cored in a northwest-southeast transect of Prydz Bay that extended from the top of the continental slope to within 30 km of the coastline. Geological studies of the cores reveal a continental margin that has evolved through terrestrial, glacial, and glacial-marine environments. Chemical and stable isotopic analyses of the interstitial-waters were performed to determine the types of depositional environments and the diagenetic and hydrologic processes that are operating in this unusual marine environment.
Highly compacted glacial sediments provide an effective barrier to the vertical diffusion of interstitial-water solutes. Meteoric water from the Antarctic continent appears to be flowing into Prydz Bay sediments through the sequence of terrestrial sediments that lie underneath the glacial sediments. The large amounts of erosion associated with glacial advances appear to have had the effect of limiting the amount of marine organic matter that is incorporated into the sediments on the continental shelf. Although all of the sites cored in Prydz Bay exhibit depletions in dissolved sulfate with increasing depth, the greatest bacterial activity is associated with a thin layer of diatom ooze that coats the seafloor of the inner bay. Results of alkalinity modeling, thermodynamic calculations, and strontium analyses indicate that (1) ocean bottom waters seaward of Site 740 are undersaturated with respect to both calcite and aragonite, (2) interstitial waters at each site become saturated or supersaturated with respect to calcite and aragonite with increasing depth, (3) precipitation of calcium carbonate reduces the alkalinity of the pore waters with increasing depth, and (4) recrystallization of aragonite to calcite accounts for 24% of the pore-water strontium. Weathering of unstable terrestrial debris and cation exchange between clay minerals and pore fluids are the most probable chemical processes affecting interstitial water cation gradients.

大洋钻探计划（Ocean Drilling Program, ODP）第119航次首次提供了研究南极东部大陆边缘孔隙水（interstitial water）化学特征的契机。研究团队在普里兹湾（Prydz Bay）沿西北-东南向布设了5个取芯站位，取样范围从大陆坡顶部延伸至距海岸线30公里以内区域。对岩芯的地质研究表明，该大陆边缘经历了陆相、冰川相以及冰海相的演化过程。研究人员通过孔隙水化学与稳定同位素分析，旨在明确该特殊海洋环境中的沉积环境类型，以及正在发生的成岩与水文过程。
高度压实的冰川沉积物可有效阻隔孔隙水溶质的垂向扩散。源自南极大陆的大气水似乎通过冰川沉积物下方的陆相沉积序列，流入普里兹湾的沉积物中。冰川进积伴随的强烈侵蚀作用，似乎限制了大陆架沉积物中海洋有机质的富集量。尽管普里兹湾所有取芯站位的溶解硫酸盐浓度均随深度增加而降低，但湾内海底覆盖的薄层硅藻软泥（diatom ooze）区域，细菌活动最为活跃。碱度模拟、热力学计算以及锶分析的结果表明：（1）740站位外侧的海底底层水对于方解石与文石均呈欠饱和状态；（2）各站位的孔隙水随深度增加，对方解石与文石逐渐达到饱和乃至过饱和；（3）碳酸钙的沉淀作用随深度增加会降低孔隙水的碱度；（4）文石向方解石的重结晶作用贡献了孔隙水中24%的锶元素。不稳定陆源碎屑的风化作用，以及粘土矿物与孔隙流体间的阳离子交换，是影响孔隙水阳离子分布梯度的最主要化学过程。