Oxygen- and carbon-isotopes of Globigerina bulloides and Neogloboquadrina pachyderma at DSDP Holes 80-548 and 80-549A

Oxygen- and carbon-isotope analyses have been performed on the Quaternary planktonic foraminifers of Sites 548 and 549 (DSDP Leg 80) to investigate major water mass changes that occurred in the northeastern Atlantic at different glacial-interglacial cycles and to compare them with the well-defined picture of 18,000 yr. ago. Oxygen-isotope stratigraphy also provides a chronological framework for the more important data on the fauna and flora. Although bioturbation and sedimentary gaps obliterate the climatic and stratigraphic record, general trends in the oceanographic history can be deduced from the isotopic data. Isotopic stratigraphy has tentatively been delineated down to isotopic Stage 16 at Site 548 and in Hole 549A. This stratigraphy fits well with that deduced from benthic foraminiferal d18O changes and with bioclimatic zonations based on foraminiferal associations at Site 549. Variations in the geographic extension and in the flux of the Gulf Stream subtropical waters are inferred from both d18O and d13C changes. Maximal fluxes occurred during the late Pliocene. Northward extension of subtropical waters increased through the various interglacial phases of the early Pleistocene and decreased through the late Pleistocene interglacial phases. Conversely, glacial maxima were more intense after Stage 16. Isotopic Stages 12 and 16 mark times of important change in water mass circulation. Oxygen- and carbon-isotope analyses have been performed on the Quaternary planktonic foraminifers of Sites 548 and 549 (DSDP Leg 80) to investigate major water mass changes that occurred in the northeastern Atlantic at different glacial-interglacial cycles and to compare them with the well-defined picture of 18,000 yr. ago. Oxygen-isotope stratigraphy also provides a chronological framework for the more important data on the fauna and flora. Although bioturbation and sedimentary gaps obliterate the climatic and stratigraphic record, general trends in the oceanographic history can be deduced from the isotopic data. Isotopic stratigraphy has tentatively been delineated down to isotopic Stage 16 at Site 548 and in Hole 549A. This stratigraphy fits well with that deduced from benthic foraminiferal d18O changes and with bioclimatic zonations based on foraminiferal associations at Site 549. Variations in the geographic extension and in the flux of the Gulf Stream subtropical waters are inferred from both d18O and d13C changes. Maximal fluxes occurred during the late Pliocene. Northward extension of subtropical waters increased through the various interglacial phases of the early Pleistocene and decreased through the late Pleistocene interglacial phases. Conversely, glacial maxima were more intense after Stage 16. Isotopic Stages 12 and 16 mark times of important change in water mass circulation.本研究对深海钻探计划(Deep Sea Drilling Project, DSDP)第80航次548与549站位的第四纪(Quaternary)浮游有孔虫(planktonic foraminifers)开展了氧碳同位素分析，旨在探究东北大西洋不同冰期-间冰期旋回中发生的主要水团变化，并将其与距今18000年的明确古环境记录进行对比。氧同位素地层学(Oxygen-isotope stratigraphy)同时为动植物群的关键数据提供了年代学框架。尽管生物扰动(bioturbation)与沉积间断(sedimentary gaps)抹去了气候与地层记录，但海洋演化史的总体趋势可通过同位素数据推导得出。研究已在548站位及549A钻孔中初步划分出可追溯至同位素第16期(isotopic Stage 16)的同位素地层。该地层与底栖有孔虫(benthic foraminiferal)δ¹⁸O变化推导的地层结果，以及549站位基于有孔虫组合(foraminiferal associations)的生物气候分带(bioclimatic zonations)结果高度吻合。墨西哥湾流(Gulf Stream)亚热带水体(subtropical waters)的地理分布范围与通量变化，可通过δ¹⁸O与δ¹³C的变化共同推断。其通量峰值出现于上新世晚期(late Pliocene)。在早更新世(early Pleistocene)的各间冰期阶段，亚热带水体的北扩范围逐渐扩大；而在晚更新世(late Pleistocene)的间冰期阶段，北扩范围则逐渐缩小。与之相反，同位素第16期之后的冰期盛期(glacial maxima)更为显著。同位素第12期与同位素第16期标志着水团环流(water mass circulation)发生重大转变的时期。