北冰洋中部阿尔法脊晚第四纪介形虫化石群与古海洋环境变迁

Late Quaternary paleoceanographic history of the Alpha Ridge, central Arctic Ocean based on ostracode records

基于北冰洋中部阿尔法脊ARC3-B84A岩芯(水深2 280 m)中的介形虫化石群记录,重建了MIS 13期以来该海域的古海洋环境变迁。从该岩芯获取的介形虫壳瓣逾7 000枚,包含8属11种。由介形虫丰度所代表的底栖生物古生产力在MIS13–10期很低,进入MIS 9期之后显著升高。海冰指示种Acetabulastoma arcticum显示常年海冰很可能是在MIS 9期之后出现的。在所有属种中,北冰洋中层水(AIW)指示种Polycope spp.和北冰洋深层水(AODW)指示种Cytheropteron sedovi的个体数量最多,二者在岩芯中的百分含量呈负相关,它们与其他属种(Microcythere medistriatum, Pseudocythere caudata, Pedicythere spp., Cytheropteron scoresbyi, Cytheropteron higashikawai, Henryhowella asperrima)一起,揭示该岩芯站位经历了如下的水团变迁历史:最初处于AODW上部(MIS 13–12),之后被上涌的AODW下部所取代(MIS 11–10);尔后,上方的AIW大幅下潜,取代了AODW(MIS 9期–MIS 5早期);在MIS 5中–晚期,AODW下部快速上涌,取代了AIW;最终在MIS 4之后,水团定格在AODW上部。

The paleoceanographic history of the central Arctic Ocean since Marine Isotope Stage(MIS) 13 was reconstructed based on ostracode assemblages in a gravity core from the Alpha Ridge(modern water depth 2 280 m). Over 7 000 ostracode valves, including 8 genera and 11species, were obtained from the core. The biological productivity, as represented by ostracode abundance, is low during MIS 13-10 but is markedly high throughout MIS 9-1. The distribution of Acetabulastoma arcticum, a sea ice-dwelling species, indicates that perennial sea ice was probably absent during MIS 13-9. The ostracode assemblages are predominated by Polycope spp.(an indicator of Arctic Intermediate Water,AIW) and Cytheropteron sedovi(an indicator of Arctic Ocean Deep Water, AODW), and are accompanied by Microcythere medistriatum,Pseudocythere caudata, Pedicythere spp., Cytheropteron scoresbyi, Cytheropteron higashikawai, and Henryhowella asperrima. The relative frequencies(%) of Polycope spp. and Cytheropteron sedovi show inverse correlation throughout the core. The reconstructed paleo-watermass history is as follows: initially, the core site was occupied by the upper part of AODW(MIS 13-12) and lower part of AODW(MIS 11-10);after then, the overlying AIW shifted downward and took the place of AODW(MIS 9-early MIS 5);later, the lower part of AODW shifted up rapidly(middle to late MIS 5) and finally the upper part of AODW came to settle down at the site(MIS 4-1).