New Planktic Foraminiferal Transfer Functions for the Kuroshio : Oyashio Current Region off Japan

抄録

Factor analysis of planktic foraminiferal assemblages analyzed in sediment samples from the Northwest Pacific Ocean near Japan defines five major factors including the Kuroshio, Transitional Water, Oyashio, Kuroshio Gyre Margin and Coastal Water factors which, when mapped, show distinctive distributions. These factors account for over 94% of the total variance. Each of the factors can be treated as an independent variable in a regression analysis. Equations relating factors to winter and summer sea-surface temperatures (SSTs) show a high degree of accuracy. The standard errors of estimate for the transfer function equations PFJ-125 established in this study average about ±1.75°C for estimated winter temperatures, and about ±1.17°C for summer temperatures. Transfer functions PFJ-125 were applied to assemblages representing the last 12K yrs. in piston core C-1 collected in the area off Joban, northeast Honshu, Japan. The lowest estimated winter SST is 4.1°C and 18.5°C for the summer SST at 10, 500 yrs. B. P. whereas at 6, 300 yrs. B. P. the winter highest SST is 12.8°C and 23.9°C in the summer. Based on down-core variations in estimated winter and summer SST and fluctuations of the five identified factor loadings, the C-1 core site was alternatively under the influence of the Oyashio and Kuroshio Fronts through the last 12 K yrs. Marine conditions at core site C-1 at 10, 500 yrs. B. P. are comparable with those recorded in the same area for the last glacial maximum.