The Late Quaternary Paleo-environment Evolution And Sea Level Change In The Yellow Sea And The East China Sea

Benthic foraminifer fauna, AMS14C dating and acoustic sub-bottom profile was analyzed in the core EY02-2 and EY02-1 drilled from the muddy deposit in the middle Southern Yellow Sea and the mid-shelf of north East China Sea. Considering the results of core QC2?DZ4 and the standard oxygen isotope curves, we discussed the Late-Quaterenary paleo-environment evolution, benthic foraminifer fauna, paleo-climate, the climate events and water mass in postglacial period, average sedimentation rates, paleo-water depth, origin of sediments, average sea level rise rate in the shelf of South Yellow Sea and East China Sea. At last we discussed the condition of sea level rise in the East China, Green house effect and the protection of coastal zone.A total of 115 sediment samples was analyzed for benthic foraminifer in core EY02-2. The benthic foraminiferal fauna was dominated by hyaline foraminifera which ranged from 93.87% to 100%. The transgression and regression sequence since MIS6 was revealed in core EY02-2.Very few planktonic foraminifera were found in core EY02-2 showing little influence of the Yellow Sea Warm Current. The top sediment above 1.8m depth was referred to be the deposit under the cold water mass since 9.7kaBP. in the middle Southern Yellow Sea. Q-mode factor analysis was employed on 98 samples and 33 benthic foraminiferous species with relative abundance of more than 2% in at least 3 samples and 5 varimax factors had been recognized as follows: Factor 1 (Ammonia beccarii vars. assemblage) represented the coastal shallow-water environment; Factor 2 (Protelphidium tuberculatum assemblage) represented the alongshore cold-water current area or cold shallow sea environment; Factor 3 (Elphidium magellanicum assemblage) represented the shallow sea (<20-30m depth) deposit; Factor 4 (Ammonia ketienziensis assemblage) represented the shallow-sea water more than 50m depth; and Factor 5 (Buccella frigida assemblage) represented the colder-water sea environment; and the distribution of factor load accorded with the character of benthic foraminifer community. The transition function between the foraminifer content and paleo-water depth was locally limited and couldn't be used in any shelf area of Southern Yellow Sea.The carbonate content varied from 0 to 34.55% in the column of drilling core EY02-2, the higher carbonate content related to materials of modern and old Yellow River in postglacial period,while the peak carbonate content related to the shell fragment in the sediment, the dissolved cycle appeared to be the carbonate dissolved cycle of the Atlantic Mode. The muddy deposit took its shape at about 9.7kaBP. in middle Southern Yellow Sea. Average sediment rates were different in different epoch and region: In the edge area of cold-water cyclonic eddy in the middle Southern Yellow Sea, Sedimentation rate was calculated as 0.133mm/a for the period from the present to 7.9kaBP., and 0.426mm/a for the period from 7.9kaBP. to 10.16kaBP., which were far lower than sedimentation rate of the mid-eddy deposit area (0.1 cm/a) and the southeastern Yellow Sea (2.28 mm /a). In addition the average sedimentation rate was obviously higher in the interglacial period than in the glacial period in the drilling core EY02-1 in the north of mid-shelf.Many research such as clay minerals, suspend in the sea, the grain size trend analysis of surface sediment, POC 6 Cu and 8 C13 in bottom sediments etc. showed that: The Yellow Sea Warm Current divided the South Yellow Sea into two, the terrestrial material of modern sediment on the west shelf plain mainly came from the modem Yellow River suspend carried by the alongshore current, and the sediment difference between the west and east side of Yellow Sea Trough was represented by the sedimentation thickness in postglacial period, sedimentation stratum, and oxygen isotope record.The transgression and regression sequence since MIS6 was revealed in core EY02-l.Planktonic foraminifer was by far abundant in the surface sediment of core EY02-1 in the north mid-shelf of East Chin...