秋、夏季珠江口、南海北部陆坡溶解态铝的分布及其影响因素

于2014年10月和2015年6月对珠江口、南海北部陆坡区域溶解态铝的分布进行观测,探讨影响其分布及季节差异的主要因素,并以其作为示踪因子探讨潜在的陆源物质跨陆架输送途径。研究结果显示,夏、秋季珠江口盐度为0时溶解态铝的浓度分别为690.0 nmol/L和360.0 nmol/L,在淡咸水混合初期溶解态铝迅速自水体清除,夏季的清除率(55.8%)大于秋季(29.7%)。在南海北部陆坡区域,夏季表层溶解态铝浓度表现为沿纬线方向西高东低的分布特点,秋季则相反;夏、秋季底层溶解态铝浓度均呈现出随着离岸距离增加逐渐降低的分布趋势。秋季溶解态铝浓度的分布与盐度呈现显著的负相关关系,表明其行为近乎保守,陆架混合水及黑潮次表层水等水团混合是影响南海北部陆坡区域溶解态铝分布的主要因素。并且以溶解态铝作为示踪因子发现,在21.6~22.2 kg/m^3密度面区间存在自陆架向陆坡方向的跨陆架输送。而夏季陆坡中部受到珠江冲淡水的影响出现低盐水舌,但溶解态铝的浓度相对较低,表现出明显的不保守行为。浮游植物的清除作用是导致夏季陆坡区域溶解态铝分布异常的重要因素。

Distributions and influencing factors of dissolved aluminum in the Zhujiang River Estuary,continental slope of the northern South China Sea in autumn and summer

Distributions of dissolved aluminum in the Zhujiang River Estuary and slope of the northern South China Sea (NSCS) were observed in October 2014 and June 2015, respectively. We discuss the main factors affecting its distribution and seasonal variation, and use dissolved aluminum as a tracer to explore the potential cross-shelf transport of terrestrial materials. The concentrations of dissolved aluminum in the Zhujiang River were 690 nmol/L and 360 nmol/L in summer and autumn, respectively. Dissolved aluminum were significantly removed from the water column in the initial mixing of fresh and saline water in the Zhujiang River Estuary, with scavenging rate of 55.8% and 29.7% in summer and autumn, respectively. In the slope of the NSCS, the concentration of dissolved aluminum in the surface decreased from east to west along the latitude in summer and was completely opposite in autumn. The concentrations of dissolved aluminum in the bottom were gradually decreased across the NSCS shelf with the increasing distance from the coast both in summer and autumn. The negative correlation between dissolved aluminum and salinity in autumn indicated that the behavior of dissolved aluminum was nearly conservative and the mixing of different water masses including shelf mixed water and kuroshio subsurface water was the main influencing factor. Dissolved aluminum showed decreasing trend from the continental shelf to the middle of NSCS along the isopycnal surfaces of 21.6 to 22.2 kg/m³, indicating the potential cross-shelf transport path in the NSCS. In summer, there was a water tough with lower salinity appeared in the middle of the study area, indicating the influence of the Zhujiang diluted water. However, the concentration of dissolved aluminum was relatively low corresponding to the water mass with low salinity. Scavenging by phytoplankton bloom in the top mixed layer was the major influencing factor of semi-conservative behavior of dissolved aluminum in summer.