The drill sites of Ocean Drilling Program (ODP) Leg 170 are located on the lower continental slope and the bottom of the Middle American Trench off the Nicoya Peninsula, Costa Rica (Fig. F1) (Kimura, Silver, Blum, et al., 1997). Based on planktonic foraminiferal analyses, the sediments of Cores 170-1039B-18X through 1H are assignable to Zones N19-N23, which are Pliocene to Pleistocene in age, and those of Cores 170-1043A-30X through 18X are included in Zones N17-N23, which are late Miocene to Pleistocene in age. As areas off Costa Rica are located in low latitudes (~9°N), planktonic foraminiferal components typically are assemblages rich in warm-water species.
In this article, biostratigraphic and chronostratigraphic analyses and quantitative examinations of planktonic foraminifers on ODP samples are made and paleoceanographic changes during the Pliocene-Pleistocene are suggested.