The Analysis Of Millennial-scale Climate Changes In North Atlantic Ice-rafted Debris Belt Since The Pleiocene

Hole IODP306-U1312B is located in northeast of the Azores (42°50.2150′N,23°5.2652′W; water depth:3523m). Site U1312plays an important role in IODP306because the region between40°and50°N is considered to have been sensitive tosea-surface temperature changes in the North Atlantic through geologic time, andduring the Quaternary there were several glacial–interglacial oscillations with thesea-surface temperatures (SST) that was higher than10°C.According to the analysis of planktonic foraminifers oxygen and carbon stableisotope of IODP306-U1312B core, combined with the study of planktonicforaminiferal assemblage and the SST&SSS estimated by MAT, the results show that:The Changes of the δ18Oand δ13C of planktonic foraminifera and SST&SSS (SurfaceSea Salinity) are broadly consistent with glacial-interglacial cycles in U1312B core,and the range of variation was relative small before MIS17(Marine Isotope Stage，MIS), and turn to wide after MIS17. Although there was a relatively warminterglacial period between two glacial periods, with the further expansion of Arcticice sheet, the glaciers widely covered mainland in most of the time since MIS17,correspond to the climate changes of Mid-Pleistocene Transition(MPT). In this study,MPT started from696ka, and the main cycles that dominated the climate transform41ka (obliquity) to100ka (eccentricity) since that time.The marine environment nearby the ice-rafted debris belt of north Atlantic iscomplicated, mainly influenced by the control of Mexico-North Atlantic Current (withhigh temperature and high salt but lack of nutrition) and Canary Current (with lowtemperature and low salt and but high productivity). In the warmer period,Mexico-North Atlantic Current was dominated, and in the cooler time, CanaryCurrent played a dominant role in the study areas.The Ice-rafted debris (IRD) Mainly appeared in MIS24～23、22～21、20～19、16～15、10～9and the deglacial period MIS4～3. As lots of IRD poured intoresearch area in these stages, SST and SST both gradually transformed low to high. The change trend of the curve that size>0.25mm and the curve that size<0.25mm(0.25>IRD>0.15mm) was roughly the same, but the size <0.25mm played adominant role. According to grading analysis, the quantitative of IRD were mostlyeffected by the transport of sea ice in the area. Besides, the thermohaline circulationwas reinforce during the interglacial periods, and became weaken during glaciations,moreover, it would became more weaker during episodes of dramatic ice sheetscalving which occured on millennial time-scales. Thermohaline circulation of northAtlantic is sensitive to the climate of the area and the quantity of the runoff glacier,and its influence could be expanded, even to exhibition on the global oceanatmosphere system. When excessive ice sheet calving drifted into the sea or ice meltflowed into the ocean, SST and SSS were both lowered, which prevented thegeneration of North Atlantic Deep Water (NADW), and to be formed some briefevents that was similar to the Glacial return.