暖池区1.53Ma以来上层海水变化的颗石藻证据

Coccolith Evidence of Upper Ocean Water Variations for Past 1.53 Ma in Western Pacific Warm Pool

对位于西太平洋暖池区核心的大洋钻探计划(ODP)807站1.53 Ma以来深海沉积样品进行了颗石藻化石分析,通过Florisphaera profunda数量百分比讨论了营养跃层深度变化的趋势,并计算了初级生产力.结果表明1.53Ma以来暖池核心区海水营养跃层经历了明显变化:从1.53～0.9 Ma,营养跃层深度逐渐变浅;自0.9 Ma起营养跃层开始变深并保持到0.48 Ma;0.48～0.28 Ma之间是营养跃层深度明显变浅的一个时期,在这以后营养跃层逐渐变深.根据颗石藻得出的海水营养跃层变化与初级生产力变化基本一致,也与根据浮游有孔虫转换函数得出的温跃层深度变化趋势基本一致.对比ODP 807站和南海ODP 1143站F.profunda数量百分比和初级生产力变化曲线,两站在0.9 Ma以前变化的趋势相反,而0.9 Ma以后基本一致.说明0.9 Ma以前暖池核心地区与边缘区上层海水的变化有差异,而0.9 Ma以后两者则趋同.

Florisphaera profunda is one of the lower euphotic zone species of coccolithophores. Using its percentage, we can reconstruct the variations in the upper ocean water such as the depth of nutricline and the primary productivity. Coccolith analysis has been carried out for the past 1.53 Ma sediment from ODP Site 807 which is located in the center of the Western Pacific Warm Pool. The results show that the depth of nutricline experienced significant changes, mainly at 0.9,0.48 and 0.28Ma respectively, enabling the recognition of four stages of changes for the last 1.53 Ma. From 1.53 Ma to 0.9 Ma,the depth of nutricline shoaled gradually. At about 0.9 Ma, nutricline abruptly deepened and remained stable until 0.48 Ma. The nutricline became very shallower during the time interval between 0.48 to 0.28 Ma. At 0.28 Ma, it deepened again and increased gradually up to present. Variations in the primary productivity are similar to that of nutricline and also the depth of thermocline devived from planktonic foraminifera. Comparison between the percentage of F. profuuda and primary productivityfrom ODP Site 807 and ODP Site 1143 in the southern South China Sea indicates opposite changes before 0.9 Ma but similar changes after 0.9 Ma . This implies that variations in the upper ocean water are different between the center and the margin of the Western Pacific Warm Pool before 0.9 Ma,but after 0.9 Ma they have the same trends.