~4.2ka.BP广西北海-英罗湾红树林“此消彼长”与相对海平面骤然下降求证

在我国，与~4.2 ka BP事件期间东亚冬季风（EAWM）的显著增强相对应，对相对海平面(RSL)变化更为敏感的海岸带发生了牡蛎（渤海湾）和珊瑚（雷州半岛）建礁停止和中断及红树林的再次发育（钦州湾和英罗湾）。这些事实自然地衍生一个值得探究的问题：显著增强的EAWM是否导致了区域RSL骤然下降，进而引发了此类生态系统的突变？针对这一问题，本项目拟通过广西北海白虎头出露、沙坝埋藏泥炭和英罗湾红树林沉积典型断面（高潮位—低潮位）各站位非连续沉积界面的精细AMS14C测年、花粉和硅藻鉴定、有机碳δ13C分析及两地~4.2 ka BP时的地形对比，查证：~4.2 ka BP时，两地红树林是否发生了“此消彼长”？区域RSL是否发生了显著下降？并基于气象观测事实，探讨EAWM增强事件导致区域RSL骤然下降的可能性。这一求证研究对于深入开展海-气相互作用的世纪尺度海平面效应研究具有促进作用。

Because it had seriously impacted the inland vegetation and human civilization, the ~4.2 ka BP event has aroused worldwide attentions both of academia and international climate organization, even though its cause is still unclear. In correspondence with strengthening of East Asian winter monsoon (EAWM) during the event, the reef constructions both of oyster in western Bohai Bay and coral in Leizhou separately stopped and halted, also grew mangrove again in Qinzhou and Yingluo Bays, Guangxi. These facts existing along Chinese coasts, where are more sensitive to regional relative sea-level (RSL) fluctuation, spontaneously derive an interesting question: whether had the obviously enhanced EAWM resulted in an abrupt RSL fall or not? Had the coastal ecosystems changed abruptly as a result of this fall? To answer the questions, two things will be further verified in this proposal for exposed and buried peats by sand bar at the Baihutou and current mangrove sediments in the Yingluo Bay through measurements of pollen, diatom, organic carbon stable isotope, and AMS14C dating for the peat and sediments along the short profiles across the phase transitions, combined with the comparison of landform difference between the two places during the event, that are: (a) Whether had the mangrove shifted from one place to another during the ~4.2 ka BP event or not, (b) At that time, whether had the regional RSL abruptly fell or not? Based on these verifications and meteorological observations, the probability of the abrupt fall of the regional RSL driven by enhanced EAWM will be discussed. This research focused on verifications will promote the study on the effect of the interaction between air and sea on regional sea level.