Three cores （ZY-1, ZY-2 and ZY-3） retrieved from the Central Yellow Sea mud （CYSM） were analyzed in sensitive grain size and AMS J4C dating to reconstruct the history of the East Asian Winter Monsoon （EAWM） since the Middle Holocene in the study area. The results show that these data provide a continuous history of the EAWM over the past 7.2 ka and that the EAWM can be divided into three periods： strong and highly fluctuating during 7.2-4.2 ka BP; moderate and relatively stable during 4.2-1.8 ka BP; and weakened during 1.8-0 ka BP. Compared with the East Asian Summer Monsoon （EASM） recorded in the previous studies, the evolutionary history of the EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the EASM. At the centennial scale, however, the EAWM intensified events correlate well with the EASM weakened events and the North Atlantic climatic variations （Bond events 0 to 5） within the dating error, most likely forced by the reduction of solar irradiance through changes in the oceanic-atmospheric circulation patterns.
HU BangQiYANG ZuoShengZHAO MeiXunYoshiki SAITOFAN DeJiangWANG LiBo
Biomarkers have been widely used to reconstruct phytoplankton productivity and community structure changes, and this method has been applied for the first time in the middle Okinawa Trough during the transition from the last deglaciation to the Holocene. The total content of all marine phytoplankton biomarkers, used as a total productivity indicator, reveals higher productivity during the deglaciation. The ratios of the biomarkers are used as community structure indicators which show that, compared with the Holocene, the contribution from haptophytes decreased while the contributions from diatoms and dinoflagellates increased during the deglaciation. The increased productivity during the deglacia- tion was likely caused by the stronger winter monsoon. Also increased nutrient supply from terrestrial sources contributes to the higher productivity due to lower sea-level, which is consistent with higher terrestrial biomarker (long-chain n-alkanols) content. These changes in the nutrient supply also con- tributed to the community structure changes in the Okinawa Trough.
This paper reports high-resolution biomarker records of the last 260 ka for core MD05-2904 from the northern South China Sea (SCS). The sea surface temperature (SST) record using the U k3’7 index re-veals a minimum of 21.5℃ (MIS 2) and a maximum of 28.3℃ (MIS 5.5), for a temperature difference of almost 7℃, and provides the longest high-resolution U k3’7 SST record in northern SCS. The content of odd-number long chain n-alkanes and several n-alkanes indexes such as the CPI, ACL and the C31/C27 ratio, all reveal generally higher values during the glacials and lower values during the interglacials. Terrestrial input as indicated by n-alkane content was mostly controlled by sea-level changes: During the glacials, lower sea-level exposed the continental shelf to enable rivers to transport more terrestrial materials to the slope; and the situation reverses during the interglacials. The n-alkane indexes changes reveal more n-alkanes from contemporary vegetation during glacials as a result of the prox-imity of the core site to the source region, while the increases in ACL and C31/C27 ratio during glacials indicate a change to more grassy vegetation. However, the highest values for CPI, ACL and the C31/C27 ratio all occurred during late MIS 3, and it was suggested that this period was characterized by a strong summer monsoon-dominated humid climate which resulted in a denser vegetation for the exposed continental shelf region.
HE Juan ZHAO MeiXun LI Li WANG PinXian GE HuangMin
