Diatom And Reconstruction Of The Winter Sea-surface Temperature In The Southern Okinawa Trough Since7000cal.yr BP

In addition to cores of ODP893and ODP1202, core MD05-2908is another high deposition core in the southern Okinawa Trough, which provides basic materials for palaeoceanographic research since the mid-Holocene in the area.A total of69taxa were identified from176sediment samples of core MD05-2908. The main species include Azpeitia africana、Azpeitia neocrenulata、 Azpeitia nodulifer、Cyclotella striata、Cyclotella stylorum、Diploneis bombus、 Diploneis suborbicularis、Nitzschia marina、Nitzschia interruptestriata、Paralia sulcata、Rhizosolenia bergonii、Thalassiothrix frauenfeldii、Thalassiosira eccentrica、 Thalassionema nitzschioides and Thalassionema nitzschioides var. parva. Of which the typical tropic planktonic species are Azpeitia africana、Azpeitia neocrenulata、 Azpeitia nodulifer、Heminodiscus cuneiformis、Rhizosolenia bergonii and Nitzschia marina. After quantitative analysis on relationship bwteen abundance of these diatoms and winter sea-surface temperature (SSTW), the results show that they live the water with the high temperature, influenced by the Kuroshio. So they can be regarded as the Kuroshio indicator species.The research has demonstrated that SSSS and SSTW are the main impact factors which controll the distribution of the surface sediment diatoms of the West Pacific. The diatom-temperature transfer function is established based on the diatom-environment data base of the West Pacific maginal seas. The C2Software, with five mathematical reconstruction methods, is use to calculate process of the transfer function. Then root mean squared error (RMSE), root mean squared error of prediction based on the leave-one out jackknifing (RMSEP(Jack)) test and coefficient of determination between observed and predicted values (R2(Jack)) are used to evaluate the five mathematical reconstruction methods, which is to choose the most suitable transfer function model. The results show that WA-PLS with4components has the lowest RMSEP(Jack)(1.6209) and higher R2(Jack)(0.97502), and it is appropriate for the reconstruction of the SSTW.No dramatical trend has been found in the reconstructed SSTW since7000cal. yr BP, based on the diatom-temperature transfer function. The SSTW record can generally be divided into four stages and two sub-stages, including three high temperature stages (6800-5700cal. yr BP、4700～3800cal. yr BP and1600～0cal. yr BP) and two low temperature stages (5700-4700cal. yr BP and3800-1600cal. yr BP). Besides, there are three cold events, at about5700cal. yr BP,5000cal. yr BP and2100cal.yr BP.The study also reveals that the Kuroshio largely influenced the winter sea-surface temperature of the southern Okinawa Trough between7000and3800cal. yr BP. After3800cal. yr BP, the Kuroshio has become weakened, and other factors may affect winter sea-surface temperature changes in the southern Okinawa Trough. In addition, the cold periods (5890～5400cal. yr BP、4700-4500cal. yr BP、3500-3200cal. yr BP、1900-1600cal. yr BP and600-550cal. yr BP) found in core MD05-2908corresponds well with the Ice-raft-events in north Atlantic, which shows the globality of the climate and the correlation of climate change between the high and low latitude.