Characteristics Of Marine Paleoenvironment Evolution In The Northern Okinawa Trough Since 7500aBP

Cores DOC024, retrieved from the Okinawa Trough in the East China Sea, are used to reconstruct marine environmental conditions during the Holocene (~7.5-0ka BP) in the northern part of the Okinawa Trough based on a multi-proxy approach including geochemical and micropaleontological proxies, combined with detailed AMS 14C dates, stable isotope and other data acquired by previous studies,. In addition, the evolution of productivity, upwellings and Kuroshio Warm Current are discussed to study their significance on regional marine environment.The productivity of calcareous microfossils (including foraminifera and coccolith) was higher markedly before 7ka BP than that of 6.4-0ka BP in the northern part of the Okinawa Trough, suggested by the data recovered from core DOC024; but the peak fluxes of silicious microfossils (including radiolaria and silicoflagellate) occurred at around 3.0ka BP, it increased before 3.0ka BP and declined from 3.0 to 0ka BP. The primary productivity was high at around 7kaBP, then it decreased with more fluctuations after 7kaBP, obvious peak fluxes also appeared at about 0.9kaBP. The variation pattern of productivity and the difference between various paleoproductivity proxies during the Holocene may reflect the variability of the Kuroshio Warm Current, and the cold eddies and upwellings associated with it.In the northern part of the Okinawa Trough,at about 7.5-7.0kaBP of the early Holocene, this studied region was controlled by the continental shelf water, and at about 7.0aBP Kuroshio water combined with continental shelf water intensively, then the region was controlled by the intensified Kuroshio water with upwellings during 7.0-6.0kaBP; from 6.0-2.0ka BP the upwellings developed stably and the thermocline gradually declined: from 6.0-5.0 kaBP the impact of the upwellings mainly focused on the thermocline and much less on the sea surface, from 5.0-4.0kaBP the SST decreased because the sea surface was influenced by the cool water brought by the intensified upwellings; from 2.0-1.2kaBP, the upwelling declined and the SST increased consequently; since 1.2 kaBP the upwelling increased and the thermocline declined obviously. In the studied region of the northern Okinawa Trough, the variation of the thermocline was controlled evidently by the upwellings closely related to the Kuroshio, and the intensity of the upwellsings varied linearly with that of the Kuroshio; The paleoenvironmental variation around the cold eddy also show obvious regional characteristics.Due to the disturbance of volcanic ash layers in core DOC024 around 7.5ka BP, few detailed conclusion could be made on the evolution of the Kuroshio Warm Current during the Holocene, especially in the complicated marine environmental conditions in the northern Okinawa Trough. Around 7.5kaBP the intensity of Kuroshio declined obviously and the Kuroshio almost did not influenced the studied region; from 7.0-2.0kaBP the upwelling developed stably near the studied region which proved the stability of the Kuroshio with less fluctuations; from 2.0-1.2kaBP the upwelling declined with the Kuroshio; around 1.2kaBP, the Kuroshio increased intensively with the climate's warming; since 0.3kaBP the Kuroshio declined with climate's cooling. Since about 7.0kaBP the Kuroshio always influenced the region, and since 6.6kaBP the influences of the bottom water of the Kuroshio were quite stable.