Diatom Response To Changes In Palaeoenvironments Of The South China Sea And The East Sea (Sea Of Japan) Since The Last Glacial Maximum

Diatom data of 192 surface sediment samples from the marginal seas in the western Pacific together with modern summer and winter sea surface temperature and salinity data were analysed.Canonical correspondence analysis seems to be suitable for diatom data and environmental variables.The results of canonical correspondence analysis show that summer sea-surface salinity(SSS) is highly positively correlated with winter SSS and so is summer sea-surface temperature(SST) with winter SST.The correlations between SSSs and SSTs are less positively correlated,which may be due to interaction of regional current pattern and monsoon climate.The correlations between diatom species and environmental variables on CCA biplot indicate that most of sample sites from the SCS and the Pacific represent the highest water temperatures and salinities,the sample sites from the coast of the SCS favor high water temperatures but relatively low salinity,almost all samples from the Sea of Japan(the East Sea) are characterised by high salinity but low water temperatures,the sample sites from the YS and the BS are located in the area with relatively low temperature and salinity and the sample sites from the ECS cover the largest salinity gradient.The correlations between diatom species,sample sites and environmental variables concur with known diatom ecology and regional oceanographic characters.Monte Carlo permutation tests demonstrate that all the results are statistically significant.Changes in palaeoenvironments through the last 15 000 years have been documented by a high-resolution diatom record of core 17940 from the northern slope of the South China Sea.Four diatom assemblage zones,each characterized by different diatom components,are distinguished by cluster analysis.The ratios of Thalassionema nitzschioides var.parva and the brackish-littoral species,used as the proxies for temperature and salinity,are compared with previously published sea-surface temperature(FP-12E-SSTw) and sea-surface salinity(SSS) data from the same core and with the Dongge Caveδ¹⁸O record.The B(?)lling-Aller(?)d warm phase, the Younger Dryas cold event,the Holocene Climate Optimum and three Holocene cooling events(7150-6250,4150-3450 and 1800-1350 cal.yr BP) are clearly distinguished by changes in the abundance of the brackish-littoral species and/or in the ratio of T.nitzschioides var.parva.A marked increase in abundance of the coastal species Paralia sulcata during the interval 11150-8050 cal.yr BP indicates a strong coastal water influence,probably due to the opening of the Taiwan Strait.During the late Pleistocene and the early Holocene,induced by sea-level changes may be the primarily controller of palaeogeographic variations,whereas,palaeoenvironmental changes appear to be mainly dominated by fluctuations of the East Asian summer monsoon during most of the Holocene.High-resolution diatom record of core UB-2 from the Ulleung Basin in the southern part of the East Sea(Sea of Japan) reveals palaeoenvironmental changes through the last 28000 years.Comparing withδ¹⁸O records of the East Sea(Sea of Japan) and the Greenland ice core(GRIP),the Marine Isotope Stages 3(MIS 3),the Last Glacial Maximum(LGM),the B(?)lling-Aller(?)d warm phase(B/A) and the Younger Dryas cold event(YD) are clearly distinguished by the percentage of warm water species and the abundance of fresh-littoral species.Increasing abundance of Paralia sulcata from 15200 cal.yr BP refers to the opening of the Tsushima Strait and the maximum abundance of P.sulcata during 11300 and 11100 cal.yr BP indicated a strong coastal water influence which corresponded to the melt-water pulse IB(mwp-IB).Climate-induced palaeogeographic variations may the main contributor to palaeoenvironmental changes.A similar diatom assemblage is found by comparing core 17940 of the South China Sea and core UB-2 of the East Sea(Sea of Japan).Planktonic species are the major components.There are little abundances of fresh,brackish,coastal and littoral species,but their varieties are obvious.The palaeoenvironmental changes can be indicated by some ecological important diatom species,although changes in absolute values of these species are relatively small.During the Younger Dryas cold event (YD),increasing of sea surface salinity is the main character,whereas,the East Sea (Sea of Japan) is dominated by lower temperature.The maximum abundance of P. sulcata during the early Holocene can be corresponded to the melt-water pulse IB (mwp-IB),and the increasing abundance of this species,which can be used as a proxy for the opening of straits,is due to sea level rising.