| Summary: | Meridional heat transport of the western Pacific boundary current(the Kuroshio Current)is one of the key factors in global climate change.This current is important because it controls the temperature gradient between low latitudes and the North Pacific and so significantly influences mid-latitude atmosphere-ocean interactions.Here we reconstruct changes in hydrological conditions within the mid-latitude mainstream of the Kuroshio Current based on faunal analysis of planktonic foraminifera in core DSDP 296 from the Northwest Pacific Ocean.This approach enabled us to deduce evolutionary processes within the Kuroshio Current since the Pliocene.A total of 57 species in the coarser section(>150 μm)were identified;results indicate that planktonic foraminiferal faunal evolution has mainly been characterized by three major stages,the first of which comprised mixed-layer warm-water species of Globigerinoides ruber which first appeared between 3.5 and 2.7 Ma and then gradually increased in content.Percentages of another warm-water species of G.conglobatus also gradually increased in number over this interval.Variations in warm-water species indicate a gradual rise in sea surface temperature(SST)and imply initiation of Kuroshio Current impact on the Northwest Pacific Ocean since at least 3.5 Ma.Secondly,over the period between 2.7 and 2.0 Ma,thermocline species of Globigerina calida,Neogloboquadrina humersa,Neogloboquadrina dutertrei,and Pulleniatina obliquiloculata started to appear in the section.This fauna was dominated by G.ruber as well as increasing G.conglobatus contents.These features imply a further rise in SST and its gradually enhanced influence on thermocline water,suggesting strengthening of the Kuroshio Current since 2.7 Ma.Thirdly,between 2.0 Ma and present,increasing contents of thermocline species(i.e.,G.calida,N.dutertrei and P.obliquiloculata)indicate a gradual rise in seawater temperature at this depth and also imply more intensive Kuroshio Current during this period.On the basis of comparative ...
|
|---|