HR: 0800h
AN: PP41D-0777    [Abstracts]
TI: The silicoflagellates and ebridians from the central Arctic Ocean in the early middle Eocene
AU: Onodera, J
EM: jm-jo@kochi-u.ac.jp
AF: Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, 783-8502, Japan
AU: * Takahashi, K
EM: kozo@geo.kyushu-u.ac.jp
AF: Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Hakozaki 6-10-1, Fukukoka, 812-8581, Japan
AB: The early middle Eocene sediments from the central Arctic Ocean obtained by IODP Expedition 302 (ACEX) were studied for the siliceous microfossils of silicoflagellates and ebridians in order to establish the biostratigraphy and to decipher the paleoceanographic changes of the upper water column. Seven silicoflagellate taxa of the total of 56 taxa and three ebridian taxa of the total of 30 taxa were previously unknown and they were newly described as new species. Silicoflagellate and ebridian assemblages in lower part of Lithologic Unit 2 are endemic compared to the assemblages of the outside of the Eocene Arctic Ocean. Temporal intervals of the silicoflagellate and ebridian assemblages were categorized to several assemblage groups according to the variation in the assemblage characteristics. Changes in characteristic assemblage is probably due to the habitat modulation governed by the extent of mixing of significantly different water masses between the low salinity waters derived from the Arctic region and relatively high salinity waters supplied from the outside of the Arctic Ocean. The low salinity water in the Eocene Arctic is suggested from the co-occurrence of freshwater and blackish water microfossils. The origin of the freshwater is attributed to the rainfall and river influx during the rainy Eocene Arctic summer. The circulation of the Arctic Ocean in the early middle Eocene probably corresponds to an estuarine type, which includes the Black and the Baltic Seas today. The high abundance of ebridians may reflect the presence of hypoxic waters in or near the euphotic layer based on the extant ebridian ecology of Hermesinum adriaticum with symbiotic algae, which is present in the Black Sea today.
DE: 3036 Ocean drilling
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4944 Micropaleontology (0459, 3030)
DE: 9315 Arctic region (0718, 4207)
DE: 9606 Paleogene
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting