【作者】 秦亚超；

【导师】 翁焕新；

【作者基本信息】 浙江大学 ， 环境科学， 2006， 博士

【摘要】 硅不仅是岩石圈的主要组成元素(占27％)，它也是海洋系统中重要的生源要素。海洋中80％的溶解态硅源于河流的输入。在河口三角洲环境中，溶解态硅在咸、淡水混合过程中的移出和生物硅的沉积使得河口陆架边缘成为活动性硅埋藏的潜在区域。然而，大多数分析技术的测试结果表明，与深海沉积环境(比如，南大洋、北太平洋等)相比，河口陆架沉积物中蛋白石质硅的含量很低，是生物硅埋藏较少的地区。这一方面是由于河口三角洲高的陆源颗粒物沉积通量所产生的稀释作用显著降低了生物硅的含量，另一方面还在于在热带、亚热带浅水环境中广泛存在的生物硅反向风化作用。在高浑浊度的河口环境中，埋藏在还原态、弱氧化态的三角洲沉积物中的生源蛋白石颗粒可以只发生部分溶解、甚至不溶解，而由铝硅酸盐或富含金属的皮膜所快速覆盖，在早期成岩过程中逐步转变为富含钾、铁的自生铝硅酸盐矿物，并在河口活动层沉积物的反复运动中重新散布。本项研究通过模拟实验定量研究了珠江口沉积硅在振荡时间、pH值、盐度等不同环境参数条件下的释放及其环境影响因素，并采用连续提取法(Tessier et al．，1979．Analytical Chemistry 51(7)，844-851)对沉积硅的形态进行了全面分析。对于珠江口三角洲沉积物中生物硅的提取，本项研究对采用铝校正的碱液提取法(Ragueneau et al．，2005．Continental Shelf Research 25(5-6)，697-710)进行了改进，以去除沉积颗粒物表面的金属氧化物皮膜；同时，采用温和酸—温和碱连续淋滤法(Michalopoulos and Aller，2004．Geochimiea et Cosmochimica Acta 68(5)，1061-1085)对沉积物中反应性硅进行了提取和分析。研究结果表明，珠江口沉积颗粒物表面皮膜中与Fe，Al氧化物相结合的硅绝大多数源于河流溶解态硅酸的移出过程，其含量约占反应性沉积硅总量的30％。生物硅在早期成岩作用过程中约有60％转化为自生铝硅酸盐矿物。生物硅和Fe，Al氧化物的供给是控制生物硅成岩转化的重要因素。将生源蛋白石的自生转化产物归入反应性硅的埋藏量将显著提高河流源溶解态硅在三角洲的储量。三角洲是硅石的汇，由于对三角洲环境中的反向风化过程缺乏考虑，以往的估算显著低估了该区域沉积硅的埋藏以及常量元素的吸收，进而对硅石及相关元素的全球收支平衡的估算也是不充分的。更多还原

【Abstract】 Silicon, which represents 27% of the lithosphere, is an important component in the marine ecosystem. About 80% inputs of silicic acid to the world ocean come from rivers. Estuarine environments are potential locations for labile silica burial due to removal of dissolved silica during mixing processes of fresh and brackish water and deposition of biogenic opal, where commonly supporting abundant diatom blooms. However, small quantities of opaline silica detected by most operational analytical techniques exhibit that deltaic environments are relatively minor sites of biogenic silica burial, compared to abyssal sedimentary environments (e.g., the South Ocean, the northern Pacific Ocean). On the one hand, it lies in that high terrigenous debris flux dilutes biogenic silica content; on the other hand, it is due to reverse weathering of opaline silica, which is wildly present in tropical, subtropical deltaic environments. In high-turbidity shallow estuaries, the surfaces of biogenic silica particles are often quickly coated with aluminosilicate or Fe, Al-rich coatings, dramatically affecting solubilities and dissolution behavior of Si in both the oceanic water column and sedimentary deposits. These particles buried in reductive or suboxic delta deposits may be gradually altered into authigenic K-Fe-rich aluminosilicate minerals during the early diagenetic processes and be disseminated in the seasonally reworked sediment.In this thesis, the silicon release from the surficial sediments of the Pearl River estuary is quantitatively studied that are exposed in vitro under different environmental conditions of agitation time, pH value, and salinity. The consequent speciation distributions of silicon in the leached sediments are also analyzed using a sequential extraction method (Tessier et al., 1979. Analytical Chemistry 51(7), 844-851) through comparing with the silicon speciation in the initial (unleached) sediments. As to biogenic silica buried in the sediment cores, a wet-alkaline extraction method (Al correction) proposed by Ragueneau et al. (2005) (Continental Shelf Research 25(5-6), 697-710) is modified to remove metal-rich coatings on sedimentary particulates and then is performed; meanwhile, a mild acid-mild alkaline sequential extraction (Michalopoulos and Aller, 2004. Geochimica et Cosmochimica Acta 68(5), 1061-1085) is also adopted to analyze reactive silica. Results show that, silicon bound to Fe, Al oxides in the coatings of sedimentary particles, accounting for 30% of total reactive silica, derives from the removal of riverine dissolved silica. About 60% of biogenic silica is altered into authigenic aluminosilicates during the early diagenetic processes. The supply of biogenic silica and the presence of Fe, Al-oxide rich debris derived from the drainage basin are major controls on the amount of clay formed. Inclusion of authigenic alteration products of biogenic silica in estimates of reactive Si burial will markedly increase the deltaic storage of riverine Si. Deltaic environments are important sinks for silica. The lack of consideration for reverse weathering processes in deltas implies that the burial of biogenic silica and uptake of major elements therein may be substantially underestimated, and further suggests that global budgets for silica and associated elements are inadequate.更多还原