Distribution and oceanographic relationships of modern planktonic foraminifera in the Ryukyu Arc region, northwest Pacific Ocean

Recent planktonic foraminifera were analyzed in 52 surface sediment samples collected from the Ryukyu Are region in the northwestern Pacific Ocean and adjacent East China Sea with the goals of establishing relationships betwe en species distributions and oceanographic features with emphasis on the Ku roshio Current. Thirty-nine species of planktonic foraminifera were identif ied and grouped into 27 species and species groups based upon taxonomic and ecologic criteria. Calculation of a correlation matrix in the form of a si milarity index allowed for a comparison of the relative abundances of the 2 7 species and species groups within and among all sample sites. Q-mode clus ter analysis was subsequently applied using the UPGMA method, and five majo r site clusters A to E were distinguished. The geographic distribution of s amples in site cluster A coincides well with the distribution of higher loa ding values of factor 2, identified by Q-mode factor analysis carried out u sing the same coefficient matrix. Similar associations were established for site cluster C-l with those of factor 1, and site clusters C-2, D and E wi th those of factor 3, These associations suggest that site cluster A reflec ts the main path of the Kuroshio Current, cluster C-l represents the open w aters of the Pacific Ocean, and clusters C-2, D and E express susceptibilit y to carbonate dissolution at depths greater than 3000 m on the Ryukyu Tren ch slope. R-mode factor analysis using different loadings of factors 1 to 3 allows the 27 species and species groups to be classified into four groups A through D as follow: (1) Group A consists of taxa susceptible to carbona te dissolution such as the Globigerinoides ruber species group, G, sacculif er, etc. against group B which includes the Pulleniatina group, Neogloboqua drina dutertrei, Globorotalia tumida and G, menardii. Group B is dissolutio n resistant and also characterizes the Kuroshio Current. (2) Group C consis ts of Neogloboquadrina pachyderma (dextral), N, incompta and Turborotalia i nflata, all indicative of "relatively cold" water. (3) Group D composed of Globigerina bulloides and Globigerinella calida suggests influence of coast al water invasion.