南海颗粒物质的通量、组成及其与沉积物积累率的关系初探

Fluxes and Constituents of Particulate Matter in the South China Sea in Comparison with Sediment Accumulation Rates

通过大孔径时间系列沉积物捕获器的多年测量及对样品的多学科综合分析表明：南海北部与中部深海区１０００ｍ左右水深颗粒通量大约为９０ｍｇ·ｍ－２·ｄ－１，在多数情况下，季风期间的颗粒通量有比较明显的增高。颗粒物主要组成为钙质生物来源的ＣａＣＯ３、生物硅、岩源物质及海洋生物来源的有机质。颗粒通量与组成在水柱中的垂向变化表明，生源组分中ＣａＣＯ３及有机质随深度具有较为明显的减少。颗粒物侧向运动可能是造成某些时段南海中部深层颗粒通量增加的主要原因。颗粒物质在进入深海沉积物之前，ＣａＣＯ３、生物硅均在深层水与沉积物界面之间发生大量的溶解作用。有机质在沉降过程中的减少，一方面是由于硅质与钙质壳体的溶解而使结合在壳体内部的有机质随之溶解造成；另一方面可能与生物及生物地球化学作用有关。岩源物质除水柱沉降之外，还可以通过浊流等底层搬运机制进入南海北部及中部海盆，其中在南海北部这种搬运作用更为明显。

Time-series sediment trap experiments covering the periods from September 1987 to October 1988 in the northern South China Sea and from December 1990 to April 1995 in the central South China Sea were carried out in order to measure the fluxes and constituents of particulate matter. Particle fluxes in northern and central South China Sea are about 90 mg·m -2 ·day -1 and 85～90 mg·m -2 ·day -1 ,respectively. Significant increases of the fluxes are observed during the periods of northeast and southwest monsoons. The main components of the particulate matter in the central South China Sea are carbonate (25.3%～61.0%), opal (15.3%～49.9%), organic matter (1.6%～12.5%) and lithogenic matter (12.2%～42.0%). Interestingly, in the northern South China Sea,opal only comprised 0.4%～2.5% of the total fluxes while lithogenic matter occupied 33.0～67.0%.Carbonate,opal and organic matter are mainly derived from recent calcareous and siliceous plankton,and as for lithogenic matter,besides fluvial sediment discharge,aeolian transportation may also play an important role to increase lithogenic flux. The decreases of total flux as well as carbonate,opal,organic matter fluxes with depth are mainly caused by dissolution of carbonate and opal in water column.Organic matter loss with depth is attributed to dissolution of plankton shells which contain abundant organic matter as well as their biogeochemical degradation processes in water column. The much higher fluxes recorded in deep traps than in shallow traps in some sampling intervals suggest that advect of particulate matter in the water column is very frequent. In comparison with sediments in the deep basin of the South China Sea, it shows that most of the marine biogenic constituents such as carbonate, opal and organic matter dissolved before their reaching at the bottom. So it is obviously that the decreases of organic matter in sediments are not only result of decomposition of these organic matter,but also caused by dissolution of carbonate and opal. Lithogenic accumulation rates in sediment are much higher than its fluxes in the deep water column suggest that about 30%～60% of the deep basin sediments are contributed by near bottom sediment transportation mechanisms such as turbidites, especially in the northern part of the deep South China Sea.