Research On Asian Eolian Input To The West Philippine Sea Over The Last One Million Years

The eolian is playing a more and more important role in paleoclimatic andpaleoenvironmental research. The eolian component in ocean sediments has beenrecognized as providing a direct link between the continental loess and marine δ~18Oclimate records. Previous studies had suggested significant influx of eolian dust fromthe Asian mainland into this area. Here we utilized grain size, scanning electronmicroscope combined with energy dispersive X-ray spectrometer (SEM-EDS) andhigh-resolution clay mineral stratigraphies based on δ~18O chronology in sedimentsfrom the International Marine Past Global Change (IMAGES) Core MD06-3050inthe West Philippine Sea in order to trace the sources of clay minerals and reconstructproxy records of past changes in the Asian eolian input to the basin and the evolutionhistory of East Asia winter monsoon (EAWM) since1.0Ma.The clay mineral assemblage in Core MD06-3050mainly consists of smectite(~65%) and illite (~25%), with minor kaolinite (~5%) and chlorite (~5%). Provenanceanalysis suggests that smectite was derived mainly from the weathering of volcanicrocks on Luzon island, whereas illite, chlorite and kaolinite were mainly transportedas eolian dust by the EAWM from the central Asia. Spectral analysis further revealsthe close link between the extent of high latitude glaciation, East Asian wintermonsoon intensity and eolian input to the West Philippine Sea at eccentricity (100ka),obliquity (41ka) and precession (23ka) bands since1.0Ma. Three grain-sizepopulations with high variability through time were defined as2.4-4.6μm,14-22μmand45-75μm. Provenance analysis by the accumulation rates and percentagecomposition of three grain-size populations indicates that2.4-4.6μm particles were mainly from the river input of Luzon Island,14-22μm was dominated by eoliandeposition transported by the EAWM from Central Asia, while36-50μm wereconstituted by tephra and coarse granules from island river input. Further analysis ofclay minerals using SEM-EDS shows that the illite particles in Core MD06-3050arerich in Na and K and appear with good abrasion, possibly suggesting an eolian origin.However, the smectite in Core MD06-3050is often cauliflower-like erinite and itsmain source is the Luzon Island.The mass accumulation rate of14-22μm terrigenous materials and illite/smectitevalues of sediments in Core MD06-3050were used as proxies of the EAWM intensity.Both proxies generally show higher and more variable values during glacial periodsand lower during interglacials, suggesting that higher eolian input to the WestPhilippine Sea generally co-varied with EAWM intensity and more aridity incontinental Asia since1.0Ma. Multiple indices analysis further reveals the evolutionhistory of EAWM intensity since1.0Ma could be roughly divided into two mainstages: a weaker EAWM between1.0-0.6Ma and a significantly increased EAWMsince0.6Ma.