17:15 〜 19:15
[MIS14-P26] Calcareous nannofossil assemblages and paleo-oceanography of the Middle-Late Pleistocene in Marion Plateau, NE Australia
キーワード：オーストラリア、グレートバリアリーフ、石灰質ナンノ化石、古海洋環境
Calcareous nannofossils are the most important producers of calcareous sediment in the ocean (e.g. Young, 1994) and are sensitive to changes in the vertical structure of surface water (Chiyonobu et al, 2012). Calcareous nannofossil assemblages and abundances are controlled by environmental changes in surface water, and thus these fossils records are useful tools in reconstructing paleoceanographic conditions and vertical water-mass structure.
The Marion Plateau, located under the Eastern Australian Current (EAC) of the southwestern Pacific Ocean, influences the Great Barrier Reef. Previous studies have illustrated that shifting between pelagic carbonates and terrestrial drift sediments in the Quaternary significantly affected conditions in this region (e.g. Dumbar et al., 2003).
This study examines the relationship between calcareous nannofossil assemblages and paleoceanographic conditions through analysis of sediment recovered from Ocean Drilling Program (ODP) Site 1198 Hole A located Marion Plateau. The calcareous nannofossil events indicate the age of core 1H to 11H corresponds to approximately 1.6 to 0.1 Ma. Calcareous nannofossil assemblages and abundance patterns illustrated three successive surface water-mass states, one 1.6 to 1.05 Ma (Phase 3), second 1.05 to 0.3 Ma (Phase 2), and third that existed after 0.3 Ma (Phase 1).
The relative abundance of very small Gephyrocapsa spp. (<0.2μm) and absolute abundance of the upper photic zone (UPZ) coccolith species decreased abruptly at approximately 1.05 Ma. The relative abundance of lower photic zone species Florisphaera profunda greatly increased after 0.3 Ma. These assemblage and abundance changes suggest significant modifications to the surface water-mass structure.
Surface water was strongly mixed and nutrient were supplied to the UPZ prior to 1.05 Ma (Phase 3), but weakly stratified and changed to oligotrophic condition in the UPZ after 1.05 Ma (Phase 2). After Phase 2, the surface water-mass intensely stratified and decreased nutrient supply (Phase 3). Changes in the surface water-mass structure suggest intensification changes of the EAC for the past 1.6 Ma.
The Marion Plateau, located under the Eastern Australian Current (EAC) of the southwestern Pacific Ocean, influences the Great Barrier Reef. Previous studies have illustrated that shifting between pelagic carbonates and terrestrial drift sediments in the Quaternary significantly affected conditions in this region (e.g. Dumbar et al., 2003).
This study examines the relationship between calcareous nannofossil assemblages and paleoceanographic conditions through analysis of sediment recovered from Ocean Drilling Program (ODP) Site 1198 Hole A located Marion Plateau. The calcareous nannofossil events indicate the age of core 1H to 11H corresponds to approximately 1.6 to 0.1 Ma. Calcareous nannofossil assemblages and abundance patterns illustrated three successive surface water-mass states, one 1.6 to 1.05 Ma (Phase 3), second 1.05 to 0.3 Ma (Phase 2), and third that existed after 0.3 Ma (Phase 1).
The relative abundance of very small Gephyrocapsa spp. (<0.2μm) and absolute abundance of the upper photic zone (UPZ) coccolith species decreased abruptly at approximately 1.05 Ma. The relative abundance of lower photic zone species Florisphaera profunda greatly increased after 0.3 Ma. These assemblage and abundance changes suggest significant modifications to the surface water-mass structure.
Surface water was strongly mixed and nutrient were supplied to the UPZ prior to 1.05 Ma (Phase 3), but weakly stratified and changed to oligotrophic condition in the UPZ after 1.05 Ma (Phase 2). After Phase 2, the surface water-mass intensely stratified and decreased nutrient supply (Phase 3). Changes in the surface water-mass structure suggest intensification changes of the EAC for the past 1.6 Ma.