北大西洋45°N区氧同位素3期以来上层水体性质的变化  

Changes of the upper water column at the 45°N North Atlantic since marine isotope stage 3

作　　者：叶孝贤 HarunurRashid YE Xiaoxian;Rashid Harunur(College of Marine Sciences,Shanghai Ocean University,Shanghai,CHINA 201306)

机构地区：[1]上海海洋大学海洋科学学院,上海201306

出　　处：《海洋地质与第四纪地质》2021年第3期114-123,共10页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金项目“浮游有孔虫δ18O和Mg/Ca比值示踪过去45万年以来西北大西洋混合层和温跃层的温度和密度梯度在千年尺度上的变化”(41776064)。

摘　　要：北大西洋45°N区是北大西洋冰筏碎屑(IRD)带的中心区,其海洋沉积物包含高分辨率沉积环境和气候变化信息,对45°N区沉积记录的研究有利于反演末次冰期以来古海洋环境的变化。通过对岩心Hu71-377中IRD含量的统计、浮游有孔虫组合及氧和碳同位素(δ18O和δ^(13)C)分析,重建了北大西洋45°N上层水体水团性质演化历史。结合AMS14C数据和氧同位素地层学,在氧同位素3期(MIS3)和2期(MIS2)中识别出5个Heinrich层,其中Heinrich 1、2和4层具有明显IRD峰值、Neogloboquadrina pachyderma高丰度和轻δ18O值特征,而Heinrich 3和5层的δ18O值未明显变轻。Heinrich 3和5层与Heinrich 1、2和4层的δ18O差异可能反映了上层水体受融水输入的影响不同。δ^(13)CN.incompta和δ^(13)CN.pachyderma差值也反映了Heinrich事件期间混合层和温跃层的变化,它们的δ^(13)C差值在Heinrich 1和2期间接近零,归因于强风驱动的海水垂向混合。而δ^(13)CN.incompta和δ^(13)CN.pachyderma差值在Heinrich 4和5期间增大,反映了季节性温跃层变浅,推测与北大西洋暖流增强有关。浮游有孔虫组合进一步反映了海洋上层水团性质,特别是N.pachyderma和Neogloboquadrina incompta的相对丰度反映了MIS3期以来海表温度(SST)变化。The 45°N of North Atlantic is located at the central zone of the ice-rafted detritus(IRD)belt of the North Atlantic,where the marine sediments contain rich environmental and climatic information of high-resolution.The sedimentary records there are used for reconstruction of the pale-oceanic environment since the last glacial in this study.IRD contents,planktonic foraminiferal assemblages and their oxygen and carbon isotopes(δ18O andδ^(13)C)from the core Hu71-377,are used as major tools.Combined with AMS14C dating and oxygen isotope stratigraphy,five Heinrich layers are identified in the MIS3 and MIS2,in which the Heinrich layer 1,2 and 4 have obvious IRD peaks,high relative abundance of Neogloboquadrina pachyderma and lightδ18O values,but no obvious lightδ18O are observed in the Heinrich layer 3 and 5.The difference inδ18O between the Heinrich layers 3 and 5 and the Heinrich layers 1,2 and 4 may suggest the impacts of melt water on the upper water column.Further,the offsets betweenδ^(13)CN.incompta andδ^(13)CN.pachyderma may also reflect the changes in the mixed layer and thermocline during the Heinrich events.Theδ^(13)C offsets were close to zero during Heinrich 1 and Heinrich 2,attributing to the vertical mixing of seawater driven by strong winds.And theδ^(13)C offsets became larger during Heinrich 4 and Heinrich 5,indicating that the seasonal thermocline became shallower,which supports the inference of the penetration of the North Atlantic Current.What’s more,the planktonic foraminiferal assemblages may reflect the properties of the water masses in the upper water column,especially the relative abundance of N.pachyderma and Neogloboquadrina incompta may indicate the sea surface temperature(SST)changes during MIS3.

关 键 词：HEINRICH事件 浮游有孔虫组合 碳氧同位素 上层水团变化 北大西洋 

分 类 号：P736.4[天文地球—海洋地质]