(Appendix A) Radiolarian abundance in ODP Hole 202-1241A

• Main Authors: Kamikuri, Shin-Ichi, Motoyama, Isao, Nishi, Hiroshi, Iwai, Masao
• Format: Dataset
• Language: English
• Published: PANGAEA 2009
• Subjects: 202-1241A; Acanthodesmia vinculata; Acanthosphaera circopora; Acrobotrys tritubus; Acrocubus octopylus; Acrosphaera murrayana; Acrosphaera spinosa; Actinomma antarcticum; Actinomma boreale; Actinomma delicatulum; Actinomma leptodermum; Actinomma medianum; Actinomma popofskii; Actinomma sp.; Actinomma spp.; Actinosphaera haeckeli; AGE; Albatrossidium spp.; Amphiplecta sp.; Amphirhopalum straussii; Amphirhopalum ypsilon; Amphispyris costata; Amphispyris sternalis; Amphispyris subquadrata; Amphistylus angelinus; Amphistylus sp.; Amphymenium amphistylium; Anomalacantha dentata; Anomalacantha sp.; Anthocyrtidium adiaphorum; Anthocyrtidium angulare; Anthocyrtidium ehrenbergi; Anthocyrtidium jenghisi; Anthocyrtidium nosicaae; Anthocyrtidium ophirense; Anthocyrtidium pliocenica; Anthocyrtidium zanguebaricum; Axoprunum bispiculum; Axoprunum spp.; Axoprunum stauraxonium; Bathropyramis woodringi; Botryocyrtis scutum; Botryostrobus aquilonaris; Botryostrobus auritus/australis; Botryostrobus bramlettei; Botryostrobus miralestensis; Calculated; Calculated after Shannon (1948); Calocyclas monumentum; Calocycletta caepa; Pacific; Antarc*
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.776080; https://doi.org/10.1594/PANGAEA.776080

A quantitative radiolarian study at Ocean Drilling Program Site 1241 in the eastern tropical Pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle Miocene. Today, this site is located just under the Eastern Pacific Warm Pool (EPWP). Based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes, it is suggested that three notable changes occurred at 10.6, 9.8, and 4.2 Ma in the region. Four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following: (1) stratified seawater (12.0 to 10.6 Ma); (2) a shallowing of the thermocline and an increasing of upwelling (10.6 to 9.8 Ma); (3) significant inflow of warm water to the eastern tropical Pacific caused by an intensified Northern Equatorial Countercurrent (NECC), resulting in the formation of EPWP (9.8 to 4.2 Ma); and (4) the reduction of the EPWP and the NECC, and an increase in upwelling (4.2 to 0 Ma). The timing of these paleoceanographic events indicated the strong relations with the opening and closing of the Indonesian and Central American (Panama) Seaways. The reduction of the EPWP (this study) and the deepening of the thermocline in western Pacific at about 4.2 Ma (Cannariato and Ravelo, 1997; Chaisson and Ravelo, 2000) indicated a change from a state resembling El Niño in the late Miocene and the early Pliocene time to a state resembling La Niña by the late Pliocene