叶孝贤, HarunurRashid. 北大西洋45°N区氧同位素3期以来上层水体性质的变化[J]. 海洋地质与第四纪地质, 2021, 41(3): 114-123. DOI: 10.16562/j.cnki.0256-1492.2020073102
引用本文: 叶孝贤, HarunurRashid. 北大西洋45°N区氧同位素3期以来上层水体性质的变化[J]. 海洋地质与第四纪地质, 2021, 41(3): 114-123. DOI: 10.16562/j.cnki.0256-1492.2020073102
YE Xiaoxian, Harunur Rashid. Changes of the upper water column at the 45°N North Atlantic since marine isotope stage 3[J]. Marine Geology & Quaternary Geology, 2021, 41(3): 114-123. DOI: 10.16562/j.cnki.0256-1492.2020073102
Citation: YE Xiaoxian, Harunur Rashid. Changes of the upper water column at the 45°N North Atlantic since marine isotope stage 3[J]. Marine Geology & Quaternary Geology, 2021, 41(3): 114-123. DOI: 10.16562/j.cnki.0256-1492.2020073102

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

  • 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δ13C)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。δ13CN.incompta和δ13CN.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δ13C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δ13CN.incompta和δ13CN.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. pachydermaNeogloboquadrina incompta的相对丰度反映了MIS3期以来海表温度(SST)变化。

     

    Abstract: 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 and δ13C) 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 light δ18O values, but no obvious light δ18O are observed in the Heinrich layer 3 and 5. The difference in δ18O 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 between δ13CN.incompta and δ13CN.pachyderma may also reflect the changes in the mixed layer and thermocline during the Heinrich events. The δ13C offsets were close to zero during Heinrich 1 and Heinrich 2, attributing to the vertical mixing of seawater driven by strong winds. And the δ13C 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.

     

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