Magnetic recordings of millennium-scale climate events in the northern Japan Sea since the early MIS 3
The Japan Sea is the largest marginal sea in the northwestern Pacific Ocean.For a long time,it has been widely believed that the sediments are deposited in strongly reducing environment,which results in extremely weak magnetic signals and then restricts the application of frequently-used magnetic method in this region.To investig-ate deeply the availability of magnetic indicators in paleoenvironmental and paleoceanographic studiesin the Japan Sea,we conducted systematic rock magnetic analyses,high-resolution accelerator mass spectrometer(AMS)14C dating,and grain-size analysis on a 626-cm-long sediment core(LV87-2-3,water depth 740 m)recovered from the northern Japan Sea that has been studied in relatively low level.The results indicate that the studied core corres-ponds to a sedimentary record since approximately 48.3 ka BP.The majority of primary ferrimagnetic minerals,mainly magnetite,in the sediments below 55 cm,had been reduced into pyrite,which caused weakly magnetic in-tensity.This is associated closely with the intensified stratification of water body and the increase in surface pro-ductivity during interstadials in the Dansgaard-Oeschger(D-O)cycles.Nevertheless,there are still four strong mag-neticlayers characterized by elevated percentages of high-coercivity minerals(i.e.,hematite and goethite),which are termed as'hard-magnetic abnormal'layers and correspond well with the Heinrich Events.This indicatesrelat-ively weak reducing conditions that were resulted from the enhanced East Asian Winter Monsoon(EAWM)and in-jection of high salinity Tsushima Warm Current(TWC).These changes,however,are not reflected by the grain-size of sediment.Our study therefore not only indicates that the role of magnetic parameters in the paleoenvironmental and palaeoceanographic reconstructions of the Japan Sea during the last glacial,but also provides new perspectives and ideasfor relevant investigations in the future.
sediments of the Japan Seamagnetic mineralsrock magnetismpaleoenvironmentthe Heinrich Events
NETL
NSTL
万方数据
