Evolution of ditaom plankton provinces and surface water circulation systems in the Pacific Ocean

点击翻译按钮获取中文摘要

Three varieties in a single species (Thalassionema nitzschioides var. incurvata, var. inflata and var. parva) of Family Thalassionemataceae were found to be characteristic of a surface water mass formed in the surface water circulation system of the modem North Pacific Ocean. Thalassionema nitzschioides var. incurvata, var. inflata and var. parva, which should be bundled into a single variety with their morphological continuity, dominate in wann saline water masses in the Subtropical Gyre.Temporal and spacial distribution of the three varieties in DSDP-ODP cores in the western Pacific, together with two known hypotheses in evolution of surface water circulation systems (the gyral circulation system was weakly developed in the Early Miocene, and became stronger by the Late Miocene in association with closure of the Indonesian Seaway and intensification of the Kuroshio Current in the Middle Miocene, and prior to 2.5Ma the modern subarctic water mass did not exist at least in the western Pacific), suggest that changes in surface water circulation systems caused differentiations of plankton provinces, including temporal and spacial distribution of the three varieties. The three T. nitzschioides varieties, including T. hirosakiensis being in synonymy with T. nitzschioides var. inflata and var. parva, have been continuously present in both the northwestern Pacific and the eastern equatorial Pacific Ocean since a strong subtropical gyre formed in the Middle to Late Miocene. The three varieties continuously occurred in the early Late Miocene to Early Pliocene sequence which lie in the modern subarctic water mass, and the these varieties have been barren in the upper horizons of the sequences. The modern subarctic water mass formed after middle Pliocene might have acted as a barrier to northward migration of the three varieties.