Millennial-scale Variability Of Paleoproductivity And Terrigenous Matter Supply In The Subarctic Pacific Since MIS 6

The Subarctic Pacific,which contains the North Pacific and the Bering Sea et al.,is located between the Pacific and the Arctic.It is influenced by the poor ventilation condition,and stores abundant of dissolved inorganic cabon due to the presence of the permanent thermocline.As one of the three carbon sink area in the world,it plays a vital role in regulating the concentration of the carbon dioxide of the atmosphere.Researches on the revolution of the past changes of the Subarctic Pacific contribute to the comprehension of it's response to the global climate changes in the glacial/interglacial cycles,and have great significance of predicting the future climate changes.The two gravity cores Lv63-4-2 and B11 recovered from the Subarctic Pacific?Northwest Pacific and Bering Sea Slope,repectively?were dated by the?¹⁸O value and AMS¹⁴C data of the planktonic foraminifera.Based on the geochemical producticity index,grain size and clay mineral analysis et al.,the results indicat that the general pattern,the productivity is high during the deglaciation and low during the glaciation,did't occur in the Subarctic Pacific area.There are no regular changes of the paleoproductivity indexes.The sources of the TOC were complex,and the peak of the TOC content preceded to the other indexes during the last deglaciation,which may induced by the supply of the terrigenious organic matter.When compared with the Bering Sea,the occurance of the TOC content peaks in the Northwest Pacific sediments delayed,this may because that the distance between the Bering sea and the continent is shorter,and the influence of the sea-ice and sea-level changes are more notable.The Ca/Ti value and biogenic CaCO₃ contents show that there were two calcium carbonate content peaks during the MIS 5.5 and last deglaciation,and the biogenic CaCO₃ contents of the Northwest Pacific are high in relation to the Bering sea,but the peaks of it are late.The mechnism of the MIS 5.5 calcium peaks has not been ascertained,it may be related to the rising global temperature and also the nutrients from the sea-ice melting.While the mechnisms of the last deglaciation one are different in the diverse sea areas,the Bering Slope area is mainly influenced by the expanded CCD,while the Northwest Pacific is related to the favorable storage condition which is induced by the upwelling water that causes the release of the CO₂from seawater,and also the enhanced productivity that aroused by the strengthened Alaskan Current.Si/Al value and Opal content indicate that there are siliceous productivity peaks during all the stages,but the most obvious is during MIS 4.The high nutrients utilization induced by the terrigenous nutrients from the loess,in particular,Fe element,may the main causes of this peak,but this mechanism is subject to the latitute.Campared the paleoproductivity data between the Northwest Pacific and the Bering sea,it points out that the productivity modes of the two area are quiet different,the Northwest Pacific is dominated by the calcareous planktons,while the Bering Sea is dominated by the silicon planktons.The ice rafted detritus?IRD?contents show clearly that the sea-ice effect was enhanced during the MIS 6-5 stages,and reduced since the last glaciation,but when it comes to the Heinrich stadial 1 period?HS 1?,the continental shelf was covered by the perennial sea-ice,and the IRD contents were scarce.The main clay minerals of the Subarctic Pacific sediments contain the chlorite and illite,the two minerals comprise80%of the clay mineral,while the illite accounts for nearly 50%.Smectite contains the lowest amount of the clay minerals,no more than 10%.The variation of the clay mineral component was dominated by the evolution of the continental shelf ice influenced by the glaciation/deglaciation cycle,and the current circulation which is controlled by the sea-level changes.