1991年皮纳图博火山灰沉降物对南海海洋环境及硅藻生长的影响

Impact of ash precipitation on marine environments and diatoms:A case of 1991 from the Pinatubo volcano in the South China Sea

通过对菲律宾皮纳图博(Pinatubo)火山1991年6月爆发前后南海表层沉积物及沉降颗粒物中的硅藻丰度及群落组成进行分析,试图揭示皮纳图博火山爆发对南海硅藻生长的影响。研究发现,火山爆发后南海沉积物中硅藻相对丰度显著减少,原因主要在于皮纳图博火山喷发物大量沉积于南海深海,显著提高了南海沉积速率,同时稀释了沉积物中生源物质的含量。进一步对火山爆发前后同期南海中部深海沉降颗粒物开展研究发现,火山爆发次年同期沉降颗粒物总通量以及生物硅通量明显增加,而硅藻及其他硅质生物相对丰度和通量均显著降低,其中硅藻相对丰度从2.20×10^(8)枚·g^(-1)降到5.48×10^(7)枚·g^(-1),通量从2.90×10^(7)枚·m^(-2)·d^(-1)降到8.57×10^(6)枚·m^(-2)·d^(-1)。1年后的南海中部深海沉降颗粒物中仍然有大量火山玻璃的存在,可能是导致湿化学法测量生物硅含量明显增加的主要原因,而硅藻乃至所有硅质生物通量及丰度的显著降低可能与火山灰沉降的负面影响有关,也可能与1991年厄尔尼诺对南海海洋环境的影响有关。总之,1991年6月皮纳图博火山爆发后南海的沉积物硅藻及沉降颗粒物硅藻丰度都出现了显著降低,但具体的环境调控机制仍有待进一步深入研究。

The abundance and species composition of diatoms and sinking particles in the surface sediments of the South China Sea(SCS)before and after the 1991 eruption of Pinatubo volcano are analyzed in this work,in order to better reveal the impact of ash precipitation on marine diatoms.It is found that the precipitation of volcanic ash apparently increases the sedimentation rate,and dilutes the other components of the surface sediments,as the result,the relative abundance of diatoms in the surface sediments is significantly decreased.The records of sinking particles further suggest that the ash precipitation has a long-term effect to the sea environment.Both the total sinking particle flux and biogenic silica(BSi)flux in the deep water of central SCS increased substantially one year after the eruption,as the relative abundance and flux of diatoms and other siliceous organisms decreased significantly.The relative abundance decreased from 2.20×10^(8)to 5.48×10^(7)individuals g^(-1),and the flux of diatoms decreased from 2.90×10^(7)to 8.57×10^(6)individuals m^(-2)d^(-1).The apparent decrease in siliceous organism fluxes is attributed to the depressed productivity in the central SCS,that might be related to Pinatubo ash falling,or the impact of the El Ni?o in 1991.On the other hand,the increase in“BSi”flux one year after the eruption is more likely resulted from the dissolution of volcanic glass during measurement of BSi in the lab,but not from the increase of biogenic siliceous organism frustules or skeletons.It is found that there is a large amount of volcanic glass in the sinking particles.Further works are necessary to clarify the change in the BSi flux before and after the Pinatubo eruption,the decrease of siliceous organisms,and the impact of volcanic eruption on biogeochemistry and sedimentation dynamics in the SCS.