Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The lower part from 29.79 to 13.35 m, called Unit A2, was deposited during the period from the post-glacial transgression to the middle Holocene (at about 6 14C ka BP) when the rising sea level reached its maximum, while the upper part above 13.35 m (called Unit A1) was deposited in a cold eddy associated with the formation of the Yellow Sea Warm Current just after the peak of post-glacial sea level rise. Rock-magnetic properties of the uppermost 29.79 m core were investigated in detail. The experimental results indicate that the magnetic mineralogy of the core is dominated by magnetite, maghemite and hematite and that, except for the uppermost 2.35 m, the magnetic minerals were subject to reductive diagenesis leading to significant decline of magnetic mineral content and the proportion of low-coercivity component. More importantly, ferrimagnetic iron sulphide (greigite) is found in Unit A2 but absent in Unit A1, suggesting the control of marine environmental conditions on the magnetic mineral diagenesis. Magnetic parameters show abrupt changes across the boundary between Units A1and A2, which reflects a co-effect of environmental conditions and primary magnetic components of the sediments on the diagenesis. Alternating zones of high and low magnetic parameters are observed in Unit A2, which is presumably due to periodic changes of the concentration and/or grain size of magnetic minerals carried into the study area.
Indexes of sediment grain size, sedimentation rates, geochemical composition, heavy minerals, benthic foraminiferal fauna, indicator species of the Kuroshio Cur-rent, paleo-SST and carbonate dissolution of core E017 con-formably suggest a great marine environmental change oc-curring at about 10.1—9.2 cal. kaBP in the southern Oki-nawa Trough, which may correspond to the strengthening of the Kuroshio Warm Current and re-entering the Okinawa Trough through the sea area off northeast Taiwan. The inva-sion of Kuroshio current has experienced a process of grad-ual strengthening and then weakening, and its intensity be-came more fluctuation during the last 5000 years. Compared to the transition of sediment grain size, geochemical compo-sition and heavy minerals, the foraminiferal faunas show a 900-year lag, which may indicate that the invasion of Ku-roshio Current and the consequent sea surface and deep-water environmental changes is a gradual process, and fauna has an obvious lag compared to environment altering. The carbonate dissolution of the Okinawa Trough has had an apparent strengthening since 9.2 cal. kaBP, and reached a maximum in the late 3000 years, which may be caused by the deep-water environmental changes due to the invasion of Kuroshio Current.
By reference of the d 18O and d 13C isotopic compositions of G.. sacculifer and accelerator mass spectrometry (AMS)14C dates, the, and Pr/Pn in core DGKS9603 have been used to characterize the changes of paleooceanographic environment occurring in the East China Sea (ECS) during the last 35000 years. The stratigraphic records of these proxies have shown that during the last 35 ka the Okinawa Trough has gone through 7 stronger cold-climate events (C1-C7) and 9 terrigenous matter-decreasing events (e1-e9), of which, the C1 corresponds to the cold episode occurring in the middle late Holocene, C2-C4 and C7 correspond to the H1-H4 events, respectively. e1 and e3-e8 correspond to the decrease of sea surface temperature (SST), respectively. The terrigenous inputs increased when Heinrich events occurred. Climate colding resulted in the decrease of terrigenous matter transported by rivers, and the increase of that transported by winter monsoon. Heinrich events are closely related to East Asia monsoon. During the Last Glacial Maximum (LGM, 15.5-25.8 Cal ka BP), reduction environment fluctuated strongly, bringing forth three stronger reduction events (R1-R3) and one weaker reduction event (O), of which, R1-R3 correspond to the decrease of SST and increase of terrigenous nutrient and O corresponds to the decrease of terrigenous nutrient. The fluctuation of reduction condition must be related to the change of sea surface productivity.
