Neogene calcareous nannofossils in the Caribbean and the eastern equatorial Pacific

Principal components analysis of nannofossil assemblages in five ODP sites in the Caribbean and the eastern equatorial Pacific was used to monitor Neogene surface water circulation changes. In 15.83-10.71 Ma, floral distributions clearly show the existence of the Circum-tropical Current between the Caribbean and the eastern equatorial Pacific and no surface water communication between the northern and southern Caribbean. In 10.71-9.36 Ma, the Circum-tropical Current weakened and the northward intra-Caribbean current had been initiated. Northern and southern Caribbean surface waters again became separated in 8.35-3.65 Ma and the Circum-tropical Current was regenerated. After 2.76 Ma, the northward intra-Caribbean current has completely been established and the Circum-tropical Current disappeared. This suggests that a barrier to the Circum-tropical Current had formed, indicating the final closure of the Isthmus of Panama.

针对加勒比海及东赤道太平洋5个大洋钻探计划（Ocean Drilling Program, ODP）站位的钙质超微化石（nannofossil）组合开展主成分分析（Principal Components Analysis），以此监测新近纪（Neogene）表层环流的演化与变化。在15.83~10.71 Ma期间，该化石组合的分布特征清晰表明，加勒比海与东赤道太平洋之间存在环热带流（Circum-tropical Current），且加勒比海南北海域无表层水交换。在10.71~9.36 Ma期间，环热带流（Circum-tropical Current）逐渐减弱，加勒比海内部北向流开始形成。8.35~3.65 Ma期间，加勒比海南北表层海水再次出现分隔，环热带流（Circum-tropical Current）得以重建。2.76 Ma之后，加勒比海内部北向流完全形成，环热带流（Circum-tropical Current）就此消失。这表明环热带流的流通屏障已然形成，指示巴拿马地峡（Isthmus of Panama）最终完成闭合。