| Based on the Size-Normalized Weight(SNW) of planktonic foraminifer from the sediment core MD06-3052, we discussed the carbonate concentration changes in the past 150 ka. We also discussed the vertical distribution and affecting of surrounding environmental factors in the modern western Pacific based on the plankton tow sample selected from western Pacific and southern South China Sea.Planktonic foraminifera Globigerinoides ruber shell weight of sediment samples from SCS located in the South China Sea and MD06-3052 located in the western Pacific has been tested using Size-Normalized Weight(SNW) method and Shell Weight method. Contrasting to traditional shell weight method, SCS data indicated that the SNW method for G. ruber can significantly reduce the influence of test size on foraminifera shell weight in this study area. As showed the same trend with pCO2 variation recorded in Vostok ice core, MD06-3052 G. ruber data showed that SNW has the potential to indicate the change of sea surface water [CO32-]. The SNW method provides a reliable and rapid proxy for the weight analyses in the paleoceanographic study, and a potential proxy in studying the surface sea water’s important influence in global carbon cycle since Late Pleistocene.Tropical western Pacific is a vast global diverge center of water and vapour, and plays an important role in the global climate change. The thermocline located here is deeper than other areas, reduced the primary productivity in this area, and induced the equilibrium condition between surface water pCO2 and atmosphere pCO2. This area is suitable for studying for planktonic foraminifer SNW and the influence of atmosphere pCO2, as the carbonate concentration in surface water is directly decided byatmosphere pCO2. SNW of G. ruber is varied following the changes of pCO2 recorded in the Vostok ice core, during 150 ka, except MIS 5e. The result shows that the carbonate concentration in the surface water of western Pacific is consistent with the global atmosphere pCO2 changes. Unlike G. ruber, the SNW of P. obliquiloculata is not so correlative with the pCO2 change recorded in the Vostok ice core, but showed strong relativity with thermocline/nutricline in this location. The environmental condition in tropical western Pacific is dominated by ENSO and Asian Monsoon, and the thermocline/nutricline has long term changes. SNW of P. obliquiloculata is lighter when thermocline is shallower will cause the upwelling of deeper waters with lower nutrients and carbonate, vice versa. Therefore, the changes of P. obliquiloculata’s SNW here is displayed the carbonate concentration changes of the subsurface water which related with the structure of upper water column.Though the planktonic foraminiferal shells from sediment cores were widely used to reconstruct the paleoceanographic changes of the quaternary by the analyze of their assemblage and shell chemical composition in South China Sea and Western Pacific, the vertical distribution of living planktonic foraminifera in modern ocean is still few in this area. In this study, 90 plankton tows at 18 stations were conducted in SCS and WP in 2010 and 2011. The total planktonic foraminifera showed high abundance in Kuroshio source region and Mindanao current system, and low abundance in NEC area and South China Sea. The assemblage is dominated by G.sacculifer and G. ruber which showed relative abundance of 44.87% and 24.89%. G.sacculifer and G. ruber showed alike distribution patterns in our research, but G.ruber showed more abundant in warmer periods. P. obliquiloculata was mainly distributed in the upper 50-150 m of water column in Kuroshio source region and Mindanao current system. |
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