Expansion and diversification of high-latitude radiolarian a

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TitleExpansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the southwest PacificAbstractThe long-term cooling trend from middle to late Eocene was punctuated by several large-scale climate perturbations that culminated in a shift to 'icehouse' climates at the Eocene-Oligocene transition. We present radiolarian micro-fossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) sites 277, 280, 281, and 283 and Ocean Drilling Project (ODP) Site 1172 to identify significant oceanographic changes in the southwest Pacific through this climate transition (âˆ¼ 40-30 Ma). We find that the Middle Eocene Climatic Optimum at âˆ¼ 40 Ma, which is truncated but identified by a negative shift in foraminiferal Î´18O values at Site 277, is associated with a small increase in radiolarian taxa with low-latitude affinities (5 % of total fauna). In the early late Eocene at âˆ¼ 37 Ma, a positive oxygen isotope shift at Site 277 is correlated with the Priabonian Oxygen Isotope Maximum (PrOM). Radiolarian abundance, diversity, and preservation increase within this cooling event at Site 277 at the same time as diatom abundance. A negative Î´18O excursion above the PrOM is correlated with a late Eocene warming event (âˆ¼ 36.4 Ma). Radiolarian abundance and diversity decline within this event and taxa with low-latitude affinities reappear. Apart from this short-lived warming event, the PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and early Oligocene (âˆ¼ 38-30 Ma) at DSDP sites 280, 281, 283 and 1172 and are associated with very high diatom abundance. We therefore infer a northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau in the latest Eocene. In the early Oligocene there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are scarce. These data indicate that, once the Antarctic Circumpolar Current was established in the early Oligocene (âˆ¼ 30 Ma), a frontal system similar to present day developed, with nutrient-depleted Subantarctic waters bathing the area around DSDP Site 277, resulting in a more restricted siliceous plankton assemblage. Â© 2015 Author(s).Funding DetailsNE/L007452/1, NERC, Natural Environment Research Council

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1st AuthorPascher, K. AuthorPascher, K.Hollis, C.Bohaty, S.Cortese, G.McKay, R.Seebeck, H.Suzuki, N.Chiba, K.Year2015JournalClimate of the PastVolume11Number12Pages1599-1620DOI10.5194/cp-11-1599-2015URLhttps://www.scopus.com/inward/recor.....f8adbe10684d388c0e8666c3bPublisherCopernicus GmbHKeywordsAntarctic Circumpolar Wavearctic environmentcircumpolar currentcoolingdepositional environmentEoceneEocene-Oligocene boundaryfossil assemblageisotopic ratioOligocenepaleoclimateplanktonic foraminiferaradiolariataxonomy, Campbell PlateauPacific OceanPacific Ocean (Southwest), Bacillariophyta

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CitationPascher, K., Hollis, C., Bohaty, S., Cortese, G., McKay, R., Seebeck, H., Suzuki, N. and Chiba, K. (2015). Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the southwest Pacific. Climate of the Past, 11(12):1599-1620