15:31 〜 15:48
[MIS03-02] Paleoceanographic interpretation of environmental magnetic and XRF core scanning data from sediment cores in the Western Pacific Warm Pool
★Invited Papers
キーワード：XRFコアスキャナー、岩石磁気学、西部太平洋暖水塊
The Western Pacific Warm Pool plays a significant role in large-scale atmospheric circulation and global hydrology. In order to better constrain climatic and oceanographic variability, we conducted an environmental magnetic study of two late Pleistocene sediment cores (KR0515-PC2, PC4) from the western equatorial Pacific Ocean offshore of New Guinea, which was published as Yamazaki and Horiuchi (2016). Geochemical data obtained afterward using an XRF core scanner (ITRAX) in 2019 have urged us to reconsider the previous magnetic interpretation.
Magnetic property measurements and transmission electron microscopy revealed that the magnetic mineral assemblages in the studied sediments are a mixture of biogenic and terrigenous magnetite, and the terrigenous component carries about 70% of the magnetization. Variations of magnetic mineral concentration and the proportion of terrigenous to biogenic magnetite are in-phase with local summer insolation at New Guinea. Variations of Fe/Ca ratio, a proxy of terrigenous input, are in accord with the proportion of terrigenous magnetite. Increased precipitation on New Guinea is considered to be the cause of the increased terrigenous input. Precessional frequencies in magnetic mineral concentration variations are suppressed after correction for carbonate dilution, whereas cyclic changes with a ~100 kyr periodicity remain in carbonate-free magnetic concentration variations. Ba/Ti ratio variations contain a ~100 kyr periodicity component, which suggests higher biological productivity in interglacials. Glacial-interglacial changes in bottom water currents may have influenced transportation and deposition of magnetic minerals and also productivity of this region.
Magnetic property measurements and transmission electron microscopy revealed that the magnetic mineral assemblages in the studied sediments are a mixture of biogenic and terrigenous magnetite, and the terrigenous component carries about 70% of the magnetization. Variations of magnetic mineral concentration and the proportion of terrigenous to biogenic magnetite are in-phase with local summer insolation at New Guinea. Variations of Fe/Ca ratio, a proxy of terrigenous input, are in accord with the proportion of terrigenous magnetite. Increased precipitation on New Guinea is considered to be the cause of the increased terrigenous input. Precessional frequencies in magnetic mineral concentration variations are suppressed after correction for carbonate dilution, whereas cyclic changes with a ~100 kyr periodicity remain in carbonate-free magnetic concentration variations. Ba/Ti ratio variations contain a ~100 kyr periodicity component, which suggests higher biological productivity in interglacials. Glacial-interglacial changes in bottom water currents may have influenced transportation and deposition of magnetic minerals and also productivity of this region.