At present, the East Asian Monsoon (EAM) influences water availability for nearly one third of the global population. The intensity and position of the EAM has varied considerably since its onset, but disagreement still exists related to the precise latitudinal and intensity shifts of the Westerly Jet and associated storm fronts, which mark the northern extent of the monsoon. Paleoclimate research can assist in improved assessment and prediction of EAM intensity, radiative forcing, and biogeochemical cycles in the Japan Sea and North Pacific, especially under the currently changing climate. My research primarily focuses on using major-, trace- and rare earth elements in sediments from International Ocean Drilling Program Expedition 346 in the Japan (Ulleung Basin) and East China Seas (Okinawa Trough) to track variability in the EAM on millennial time scales. Using geochemical and multivariate statistical techniques (Q-Mode Factor analysis and Constrained Least Squares multiple linear regressions), I differentiated compositionally similar terrigenous aluminosilicate materials (continental crust components, eolian dusts, volcanic ash) from these sediment archives. I successfully constructed a robust record of aluminosilicate provenance, which enables more precise determinations of EAM position and intensity than previously possible. Most of my research focused on the interpretation of aluminosilicate records over several different timescales from three sites from Expedition 346. In tandem with this research, I also refined values of the well-known, and widely used, Standard Reference Material (SRM) Hawaiian Volcano Observatory Basalt (BHVO-2). In the Okinawa trough (Sites U1428/U1429), I identified and tracked the increase in flux of five continental crust materials, loesses, and volcanic ashes during glacial cycles, continental shelf exposure, and the migration of paleo-rivers in the last 400 kyr. Additionally, I constructed a 12 Myr record, which identified and quantified the dust fluxes to Ulleung Basin (Site U1430), and emphasized the importance of the Taklimakan and Gobi Deserts as main sources of dust to the Japan Sea and Pacific through the Cenozoic. Collectively, these aluminosilicate flux reconstructions are first to identify multiple specific Asian source regions through the Cenozoic, and highlight the complexity of accurately reconstructing monsoons and other aspects of paleoclimate from sediment in dynamic environments.

The Miocene climate evolution in North China is preliminarily discussed by means of comparisons in seven climate parameters quantitatively reconstructed by the Coexistence Approach on 34 selected macro- and microfloras over North China. The Miocene temperatures show no great difference in the western and eastern part of North China. Temperature fluctuations, particularly in mean annual temperature, are found within floras from several sites. The fluctuation pattern, from a climate optimum in the Mid Miocene to cooling decline in the Late Miocene, is generally consistent with the global trend of Miocene temperature change. The reconstructed precipitation from all the sites studied shows much wetter conditions in North China during the Miocene than at present, which corroborates the results from paleoprecipitation proxy of fossil mammals. Like the situation in paleo-temperature, the Miocene precipitation from North China shows no distinct difference between the western and eastern regions. It is suggested that North China, particularly in the western part, was by no means under an arid or semi-arid environment during the Miocene. North China is an ideal region for study of the impact of the East Asian monsoon system, however, the pattern of precipitation change derived from the monsoon index (MSH) and mean annual precipitation (MAP) shows contradictory results. Therefore, there appears no definite conclusion on when the East Asian summer monsoon intensified. Possible reasons for inconsistency in temperature and precipitation changes are discussed. Directions of future work to improve the resolution of climate evolution are also pointed out.

This study contributes to developing terrestrial and marine palynological indicators of winter or summer monsoon signals as well as oceanographic environments of the South China Sea (SCS). The high-resolution reconstructions of Holocene East Asian Monsoon (EAM) climate and oceanographic condition of the northern SCS provide insights into regional climate events in the western low-latitude Pacific Ocean and their impacts on local oceanography and ecology. Sediment trap samples from the southwest Taiwan waters of the SCS in winter monsoon (March-April) and summer monsoon (July-August) seasons identify abundances of Pinus and Ulmus pollen as indicators of the winter monsoon whereas fern spores appeared to be indicators of the summer monsoon. The increased fluxes of dinoflagellate cyst (DC) taxa during summer are correlated with decreased sea-surface salinity (SSS) associated with nutrient-rich river inputs. DC distributions across the SCS show that some taxa are good indicators of changes in sea-surface temperature (SST), SSS, water depth and chlorophyll-a (chl-a) concentrations associated with EAM and oceanographic conditions. In particular, the concenrations of Brigantedinium spp. and cysts of Protoperidinium together with Echinidinium spp. are positively correlatd with SST in January and SST in July, and chl-a concentrations, respectively, which are linked to past monsoon strength and primary productivity. In total, four high cyst concentration regions have been observed off southern Vietnam, Borneo, Hainan, and South China. High-resolution palynological records from a sediment core in the northern SCS reflect several EAM climatic and oceanographic events over the last 12.5 kyr. A short-term Impagidinium decrease implied that the Taiwan Strait opened at ~11.7–11.0 cal kyr BP, with reduced Kuroshio Current influence when the East China Sea waters entered through the strait. Three Holocene relative sea-level stages were identified in the palynomorph records. The highest herb pollen abundances were observed before ~10.4 cal kyr BP, reflecting the shortest distance from the grassland sources on the exposed shelf at the low sea-level stand. High Brigantedinium and cysts of Protoperidinium abundances also indicate a near-shore environment. During ~10.4- ~6.8-6.0 cal kyr BP at the rising sea-level stage, fern spore abundances increased and DC abundances decreased. Consistently low total DC concentrations and high fern spore abundance were observed after ~6.8-6.0 cal kyr BP when the present oceanographic conditions were formed. Increased abundances of Pinus pollen reflected three strengthened winter monsoon intervals at ~5.5, 4.0 and 2.5 cal kyr BP under the present oceanographic conditions. The highest Dapsilidinium pastielsii abundances reflected the warmest interval at ~6.8-5.5 cal kyr BP of the northern SCS. / Graduate / 2019-12-13