A PRELIMINARY EVALUATION ON B/CA OF PLANKTIC FORAMINIFERA AS A PROXY FOR SEAWATER PH: VITAL EFFECTS AND DISSOLUTION

B/Ca in the planktic foraminifera is mainly controlled by seawater pH,and thus could be used as ageochemical proxy for seawater pH.In order to explore the significance of ocean on the pCO₂ in the atmosphere in glacial cycles,the proxy has received wide concerns among researchers.However,its reliability may be influenced by various factors,such as temperature,CO₃^2-,dissolution,vital effects(such as symbiont photosynthesis,respiration and calcification)as well as interspecies effects.To evaluate the influence of vital effects and dissolution on B/Ca of planktic foraminifera,we measured the B/Ca for Globigerinoides ruber and Neogloboquadrina dutertrei with different size and shell thickness from the core MD06-3052 in the western Pacific Warm Pool.Except for two cases,the B/Ca of G.ruber generally increases with increasing shell size,which is supposed to be controlled by increasing calcification rate.For the two special kinds of cases,the B/Ca of G.ruberfrom one sampling layer shows little change with the increase inshell size,and the figure from the other layer does not vary in the beginning and then increases with shell size.It is believed that these characteristics are caused by the opposite effect of calcification,respiration and symbiosis photosynthesis on the B/Ca of G.ruber.The B/Ca of N.dutertrei,however,generally decreases with increasing shell size which is probably controlled by respiration.In addition,the B/Ca of G.ruber and N.dutertrei are also different for same size shells in same sample layer.The differences in B/Ca insame species with different shell size and in different species with same shell size suggest that vital effects have important influence on foraminifera B/Ca through specific processes.However,that the B/Ca of G.ruber and N.dutertrei in the same sample layer do not show obvious discrepancy between the species with different shell thickness and same shell size suggests that dissolution has little effect on B/Ca.In summary,from the perspective of vital effects and dissolution,the B/Ca of planktic foraminifera is a valid proxy for seawater pH,as long as the dominant shell size is chosen to reduce the influence of vital effects on its B/Ca.