중기플라이스토세 전환기 동안 적도수렴대의 위도변화에 따른 중앙태평양 적도해역의 대기순환 및 해양 표층순환 변화 연구

Abstract

We investigated temporal changes in dust provenance, regional hydrology, and surface productivity in a deep-sea sediment core retrieved from the central equatorial Pacific (5°53N, 177°26W, 4,136 m depth) in order to determine the cause of a brief, but prominent, cooling event (1.1 - 0.8 Ma) occurred in the equatorial upwelling regions of the Atlantic and Pacific during the Mid-Pleistocene Transition (MPT). The radiogenic isotope composition (i.e., 87Sr/86Sr and εNd) and flux of the inorganic silicate fraction indicate that eolian dust was mainly derived from Southern Hemisphere to the study site before 0.8 Ma, but a gradual increase in the proportion of Asian dust deposition after 0.8 Ma. This shift in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity. These changes can be best explained by the southward movement of the Intertropical Convergence Zone (ITCZ) and North Equatorial Counter Current (NECC) at the study site. Our results, together with previously published Atlantic data, suggest the northward displacement of the ITCZ between 1.1 and 0.9 Ma, and the southward displacement thereafter. Such meridional movement of the ITCZ during the MPT was in phase with the cooling and then warming trend in upwelling regions in the equatorial Pacific and Atlantic, which suggests ITCZ movement as a plausible cause of this brief cooling event.e of a brief, but prominent, cooling event (1.1 - 0.8 Ma) occurred in the equatorial upwelling regions of the Atlantic and Pacific during the Mid-Pleistocene Transition (MPT). The radiogenic isotope composition (i.e., 87Sr/86Sr and εNd) and flux of the inorganic silicate fraction indicate that eolian dust was mainly derived from Southern Hemisphere to the study site before 0.8 Ma, but a gradual increase in the proportion of Asian dust deposition after 0.8 Ma. This shift in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity. These changes can be best explained by the southward movement of the Intertropical Convergence Zone (ITCZ) and North Equatorial Counter Current (NECC) at the study site. Our results, together with previously published Atlantic data, suggest the northward displacement of the ITCZ between 1.1 and 0.9 Ma, and the southward displacement thereafter. Such meridional movement of the ITCZ during the MPT was in phase with the cooling and then warming trend in upwelling regions in the equatorial Pacific and Atlantic, which suggests ITCZ movement as a plausible cause of this brief cooling event.