西菲律宾海硅藻席沉积中的多囊虫类放射虫记录及其环境意义

为了多角度理解海洋纹层沉积物的形成过程，利用在西菲律宾海采集到的含纹层硅藻席的XT47孔岩心样品，进行多囊虫类放射虫的组合变化与环境意义分析.研究表明XT47孔岩心上段260 cm厚硅藻席沉积中含有丰富的放射虫、丰度高于2×104个/克；中段260~460 cm出现5次放射虫丰度高峰与红粘土的交替旋回沉积；下段460~630 cm红粘土沉积层中放射虫稀少.依据放射虫地层种的初现生物事件，470 cm以深的年龄大于0.34 Ma，表明西菲律宾海硅藻质沉积形成于中更新世以来.此外，受暖水影响控制的Tetrapyle group和Didymocyrtis tetrathalamus tetrathalamus相对丰度在末次冰盛期（LGM）呈现显著的低值期，推测在LGM期西菲律宾海北赤道暖流的影响强度是变弱的.值得注意的是，多囊虫类放射虫的丰度与生物硅含量的变化趋势出现明显的不同步现象，推测4次生物硅含量高峰是由大型硅藻（盘筛藻）的急剧增加导致的，即西菲律宾海LGM期盘筛藻的勃发呈现明显的阶段性强弱变化；进一步发现盘筛藻的4次勃发强盛期对应着胶体虫相对丰度变化的低谷期和中深层冷水种相对丰度变化的高峰期，前者指示上层水体成层化减弱、后者指示中深层水体中营养物增多.据此，认为西菲律宾海LGM期盘筛藻勃发的4次强盛期是由于上层水体成层化减弱、下层水体中丰富的营养物上涌引起.研究结果可为菲律宾海盘筛藻勃发在LGM长时间持续并最终在海底形成厚达近3 m的硅藻席沉积提供了一种可能的解释. 

Records of Polycystine Radiolaria in the Diatom Mats Sediments from the Western Philippine Sea and Their Environmental Significance

In order to understand the formation process of marine laminar sediments from multiple perspectives, this paper studied the changes of polycystine radiolarian assemblages and their environmental significance by using the XT47 core samples with laminar diatom mats collected in the western Philippine Sea. Results show that there were abundant radiolarians, generally higher than 2×104 inds. g-1in the upper 260 cm depth; five times of alternating deposition of maximum radiolarian abundances and red clay occurred at the middle 260-460 cm depth; radiolarians in the bottom 460-630 cm depth were rare. According to the early occurrence of radiolarian species, the sediment age of > 470 cm depth was older than 0.34 Ma, suggesting the diatom sediments in the western Philippine Sea were formed since the Middle Pleistocene. The relative abundances of Tetrapyle group and Didymocyrtis tetrathalamus tetrathalamus, which are controlled by warm currents, significantly decreased during the last glacial maximum (LGM) period, indicating that the influence of North Equatorial warm current on the studied areas weakened during the LGM period. Interestingly, the variation of radiolarian abundance shows a different pattern, compared to the change of biogenic silica content, suggesting that the four peaks of biogenic silica content may be caused by the rapid increase of diatom, that is to say, the bloom of Ethmodiscus rex in the western Philippine Sea had a strong-weak fluctuation during the LGM period. Furthermore, four strong blooms of Ethmodiscus rex were found to be good correspondence to the low relative abundances of collodarians, and the high relative abundances of mediate-deep cold species. The former indicates that the stratification of upper water became weakened, and the latter reflects the increase of nutrients in mediate-deep water. Therefore, we believe that four strong blooms of Ethmodiscus rex during the LGM period may be caused by the weak stratification in the upper water and the upwelling of lower water with the abundant nutrients. Our results may provide a possible explanation for the long-term occurrence of the large diatom bloom and the formation of diatom mats with thickness up to three meters on the seafloor in the Phillippine Sea.