【作者】 任景玲；

【导师】 张经；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2010， 博士

【摘要】 铝是海洋中的痕量元素,主要来源于陆地岩石风化产物的溶解并通过河流和大气沉降输送到海洋,海洋中溶解态铝的含量可用于示踪陆源物质输送、大气沉降及不同水团的混合,其海洋生物地球化学行为的研究受到广泛重视。黄、东海是世界上最宽广的陆架边缘海之一,接受大量来自黄河、长江等大河流域及东亚沙尘输送的陆源物质,同时受季风气候和太平洋西边界强流——黑潮入侵陆架的影响形成复杂的环流体系,是研究铝的生物地球化学循环的理想场所,其来源、通量、内部循环及其埋藏的研究对于丰富铝的生物地球化学研究具有重要的科学意义。本论文以长江流域和黄、东海为研究对象,系统地认识了长江流域和黄、东海铝的分布特征、时空变化及其影响因素,获得的主要认识如下：2009年秋季调查期间长江主流溶解态铝的含量范围为146-1263 nmol/L,上游浓度显著地高于下游。长江主流溶解态铝的平均含量为548±354 nmol/L,与三峡截流前1997年调查的结果相比含量显著降低。长江北方支流溶解态铝的含量高于南方支流。三峡截流前后,长江上游及其主要北方支流溶解态铝的浓度年际变化不大,而长江下游及主要南方支流溶解态铝的浓度则较截流前显著降低。长江流域南、北支流溶解态铝的含量主要受两方面因素的影响：一、流域盆地岩石土壤组成、风化特点、气候条件、径流量等因素是造成南、北支流溶解态铝含量差异的主要原因；二、人为活动对溶解态铝含量有重大影响,部分支流如牛拦江由于受到人为活动的影响使得溶解态铝含量较1997年明显升高。人为活动的影响还体现在三峡大坝的建设上,长江截流使得上游流速减缓、坝区前水体存留时间延长、下游含沙量明显降低,这些均对南、北支流铝的分布和迁移转化产生明显的影响。长江流域溶解态铝的含量与我国及世界其它河流相比仍处于中等偏下水平,没有受到人为活动的明显扰动。我国主要河流中溶解态铝的含量随流域化学风化率增加而显著降低,主要受气候变化控制。黄海海域溶解态铝的分布受黄海沿岸流、朝鲜沿岸流及黄海暖流的共同影响,基本呈现出山东半岛以南近岸区域含量较高,黄海中部含量最低的平面分布特征。季节变化上,黄海溶解态铝的含量冬季略高于春季。影响黄海铝的生物地球化学循环的主要因素有：一、春季沙尘气溶胶在海洋表层的溶解释放,沙尘过镜后黄海表层溶解态铝的含量显著升高,随深度增加含量逐渐下降。2007年春季航次开始阶段受到沙尘暴的影响,根据现场采集的沙尘气溶胶样品计算了沙尘输送通量和大气沙尘沉降带来的溶解态铝的沉降通量,估算了沙尘沉降对黄海表层溶解态铝含量的影响,估算结果与实测结果较好地吻合。二、浮游植物水华对黄海溶解态铝生物地球化学循环的调控作用。黄海水华发生过程中溶解态铝与硅酸盐的垂直分布剖面一致,且随着水华的发生、发展过程黄海中部表层溶解态铝的含量明显降低,水华过程中采集的悬浮颗粒物样品中HAc-Al提取态铝含量较非水华期明显升高,这些结果均说明浮游植物的生长对黄海海域铝的生物地球化学循环具有重要的影响。通量计算结果表明,黄海大气沙尘沉降带来的溶解态铝的输送通量与长江、鸭绿江等河流输送的通量相当,黄海溶解态铝的存留时间约为87±9天。东海中陆架溶解态铝的分布主要受长江及浙闽沿岸径流、台湾暖流、黑潮等水团的共同影响,基本呈现出沿岸区域含量较高,随离岸距离增加含量逐渐降低的平面分布特征。季节变化特征上,受陆源径流的季节变化影响东海中陆架溶解态铝的含量秋季高于冬季。通量计算结果表明,黑潮和台湾暖流的入侵对东海溶解态铝的分布影响非常显著,而河流输送通量则与大气干、湿沉降通量相当。东海中陆架溶解态铝的存留时间约为337±154天。以溶解态铝含量作为长江陆源输送的示踪因子,根据三端员模型计算自长江口向西南琉球群岛方向延伸的PN断面上长江冲淡水、黑潮和台湾暖流的混合情况,估算春、秋季长江冲淡水在PN断面的影响程度。结果表明,长江冲淡水对陆架的影响程度秋季强于春季。长江冲淡水的影响主要集中在距河口150 km范围以内,至距河口300 km处长江冲淡水的影响小于2%,主要受黑潮次表层水入侵的影响。黄海中部海域现场和实验室的铝加富培养实验结果均表明,浮游植物生长过程中会有效地清除海水中的溶解态铝。Al的加富会使培养初期浮游植物的比生长率降低,且降低的程度随铝加富浓度的增加而加大。Al的加富虽然会延缓培养初期浮游植物的生长,但对最终的浮游植物生物量不产生影响。2007-2009年间在黄、东海用20μm浮游植物网现场采集浮游植物样品,用草酸盐淋洗试剂淋洗以区分浮游植物细胞内结合态铝和细胞外吸附态铝。浮游植物总铝的含量范围为4.4-48.6mg/g内,其中细胞内结合态铝的含量范围为2.2-48.0mg/g。浮游植物总铝的含量在黄、东海的沿岸区域较高,随离岸距离的增加含量逐渐下降。而细胞内结合态铝占总铝比值则在黄海中部较高,长江口海域比较低。初步分析结果表明,硅藻样品中铝主要以细胞内结合态形式存在,而甲藻样品中铝则主要以细胞表面吸附态形式存在。硅藻水华发生初期浮游植物细胞内铝主要以结合态形式存在,而在水华衰退期则表面吸附态含量开始升高。分析了黄海中部E2站、长江口A13站、浙闽沿岸E5站、东海中陆架E6站和东海陆坡P4站重力管及沉积物多管样品中的Al/Ti的平均比值变化情况,结果发现,E2站、E5站和P4站重力管沉积物样品中Al/Ti比值高于黄河、长江沉积物及黄土、土壤背景值中Al/Ti比值,表明黄、东海陆架边缘海海区沉积物中存在“过剩铝”信号。过剩铝占沉积物总铝的比例在黄海中部最高,达到11.8%,且与生物硅含量正相关,在浙闽沿岸和东海陆坡海区过剩铝含量约为5%,表明沉积物中的过剩铝含量与海洋生源的自生沉积有关。更多还原

【Abstract】 Aluminum is the trace metal in the ocean, mainly comes from the dissolution of weathering products and can be used as the tracer of terrestrial input, atmospheric deposition and mixing of different water masses. The study of marine biogeochemical cycles of aluminum in natural waters gets more and more attentions these years. The Yellow Sea (YS) and East China Sea (ECS) is the most extensive continental shelf in the world. It receives huge amounts of terrestrial materials from large rivers (e.g., Changjiang, Huanghe etc.) and from East Asia dust storms. The current systems in the YS and ECS are regulated by the seasonal variability of monsoons and incursion of Kuroshio and Taiwan Warm Current. Therefore, the YS and ECS is an ideal place to study the source, sink, internal cycles of aluminum in the continental shelf region. The knowledge of biogeochemical cycles of aluminum in the shelf region can help scientist to deeply understand its behavior in the ocean. This thesis presents the results of biogeochemical cycles of aluminum in the Changjiang drainage basin, the YS and the ECS shelf. The distributions, seasonal variations and its effect factors are mainly discussed. The main results are listed below.Water samples were collected from river mouth upstream over a distance of 3500-4000 km in Changjiang and its 15 northern and southern tributaries during September-October in 2009. The concentrations of dissolved aluminum in the main stream of Changjiang range from 146 to 1263 nmol/L, with an average of 548±354 nmol/L. The concentrations of dissolved aluminum are higher in the upstream than the downstream, and are also higher in the northern tributaries than the southern tributaries. Compared with the results obtained at April-May 1997 before the construction of Three Gorges Dam (TGD), the concentrations of dissolved aluminum in the upstream of Changjiang and major northern tributaries show little annual variations. However, the concentrations of dissolved aluminum in the downstream of Changjiang and southern tributaries decrease dramatically after the construction of TGD. Source rocks in the drainage basin and weathering characteristics are the first control factor on the concentrations of dissolved aluminum in the northern and southern tributaries. Several tributaries are contaminated by human activity (e.g. Nulanjiang). Construction of TGD in the main stream at the Yichang brings several influences, for example, decreasing the water flow and increasing the water residence time before the dam, decreasing the suspended particle contents after the dam etc. All of these influences will change the concentrations and transportations of dissolved aluminum in the Changjiang. Compared with the other Chinese and world rivers, the concentrations of dissolved aluminum remain at the lower level. The concentrations of dissolved aluminum in different drainage basins in China are mainly controlled by the weather characteristics.Three cruises were carried out aboard R/V Beidou in March-April 2007, February 2009 and March-April 2009, respectively, to understand the biogeochemical behaviors of aluminum in the YS. The distributions of dissolved aluminum in the YS are influenced by the mixing of Yellow Sea Coastal Current, Korean Coastal Current and the Yellow Sea Warm Current. The concentrations of dissolved aluminum are high in the coastal area of Shandong peninsula and relative low in the central YS. The concentrations of dissolved aluminum in winter are higher than the average concentrations in spring. Strong East Asia dust storms in spring have important impacts on the distributions of dissolved aluminum in the YS. The concentrations of dissolved aluminum show surface maximum profiles after the dust deposition, which are quite different with the normal profiles in the shelf. The impact of one dust deposition on the increment of dissolved aluminum in the top mix layer of YS is estimated. The estimation matches with the real measured results very well. The concentrations of dissolved aluminum in the top mixed layer of the central YS decrease sharply during the spring bloom. The vertical profiles of dissolved Al are similar with that of silicate during the bloom, which shed light on the biological mediation of dissolved Al in the YS. The HAc-Al fractions in the suspended particles increase during the bloom. Input fluxes of dissolved Al from atmospheric deposition, riverine input and exchanges with the East China Sea and Bohai are estimated, in which the atmospheric deposition is the major source of dissolved Al in the SYS. Combined the dissolved Al inventory with the total input flux, a 87±9 days’residence time of dissolved Al in the SYS is inferred.Two cruises were carried out aboard R/V Beidou in November-December 2006 and February 2007, respectively, to understand the biogeochemical behaviors of aluminum in the ECS shelf. The distributions of aluminum in the YS and ECS show the effects of land-source inputs from the Changjiang and the adjacent rivers in the Zhejiang and Fujian Province and also from water masses mixing from Kuroshio and Taiwan Warm Current, with obvious seasonal variations. The concentrations of dissolved aluminum are high in the coastal area of the ECS shelf and decrease with the distance from the coast. The distributions and seasonal variations of dissolved aluminum in a southeast transect from the Changjiang Estuary to the Ryukyu Islands (i.e. PN section) in the ECS shelf are mainly discussed in the thesis. Combining the different inputs from the Changjiang, atmospheric deposition, Kuroshio waters and Taiwan Warm Current with the total amount of Al, a simple budget was established for the ECS Shelf. The incursion of Kuroshio Subsurface Water and Taiwan Warm Current has significant impact on the distribution of dissolved aluminum in the ECS Shelf. The input flux from atmospheric deposition is similar with that of river. The results reveal an average residence time of 337±154 days for dissolved Al. The impact of Changjiang terrestrial materials over the continental shelf (PN section) is discussed. Using three distinct aluminum-salinity end-members, it is determined that the contribution of the Changjiang in the autumn is significant than the spring. The impact of Changjiang is highest at the station nearest the Changjiang Estuary, and decreased seaward along the PN section within a distance of 150 km. At a distance of 300 km from the Changjiang mouth, the freshwater input was hardly seen and the incursion of Kuroshio waters became dominant. Results of aluminum enrichment incubation experiments both in situ during the cruise in the YS and in lab show that phytoplankton can scavenge the dissolved aluminum from the water column effectively. The enrichment of aluminum will decrease the specific growth rate of phytoplankton in the initial stage, and this effect become serious with the increasing aluminum enrichments. However, the enrichment of Al in the incubation system doesn’t affect the total phytoplankton biomass compared with the control group. Several phytoplankton samples were collected during 2007 and 2009 in the YS and ECS by the 20μm phytoplankton sieves. The phytoplankton samples were dealt with the trace metal clean reagent to differentiate the intra-cellular Al and extra-cellular Al contents. The total contents of aluminum in phytoplankton collected in the YS and ECS shelf range in 4.4-48.6 mg/g, with the intra-cellular Al contents of 2.2-48.0 mg/g. Total aluminum contents in phytoplankton are high in the coastal area and decrease with the increasing of distance from the coast. However, the ratio of intra-cellular to total Al contents in phytoplankton is high in the central YS and low in the Changjiang Estuary. Aluminum exists in the intra-cellular pool for the diatom, while in the extra-cellular pool for the dinoflagellates. During the diatom bloom in the YS, Al exists in the interior pool at the early stage of bloom and change to surface associate phase during the decay of bloom.Gravity core sediments were collected in the central YS (E2), Changjiang Estuary (A13), coastal area of Zhejiang and Fujian (E5), mid ECS shelf (E6) and ECS edge (P4) aboard the R/V Dong Fang Hong 2 in September 2002. The average ratios of Al to Ti in the gravity core sediments collected in stations E2, E5 and P4 are higher than the source terrestrial materials from Huanghe, Changjiang, loess and soil, which indicate the existence of excess aluminum in the continental shelf. The average contents of excess aluminum at stations E2, E5 and P4 are 11.8%,5.4% and 5.1%, respectively, which shed light on the biogenic deposition of aluminum in the YS and ECS Shelf.更多还原