Sediment records of environmental changes in the south end of the Zhejiang-Fujian coastal mud area during the past 100 years

Previous studies carried out in the East China Sea （ECS） mud area focused on long-term environmental changes in sedimentary records during the Holoeene, especially during the mid-Holocene high-stand water levels period. These results indicate that sensitive grain size groups can be used as a sedimentary proxy to reconstruct the evolution of the East Asian Winter Monsoon （EAWM）. The studies have been carried out mainly in the northern and middle portions of the Zhejiang-Fujian coastal mud, however, similar research in the southern portion and the comparison between sedimentary proxy and modern measured data of EAWM are lacking. In this paper, we focused on a sedimentary record of the past 100 years with an enhanced resolution of 1.8 years. Investigations of the southern end of the Zhejiang-Fujian coastal mud area were conducted on the basis of 21~Pb chronology, grain-size analysis and chemical element analysis. The correspondence between the mean grain size （Mz） of sediment sensitive grain size and the measured EAWM was confirmed for the first time. We found that during the recent 100 years, the variation of the mean grain size of the sensitive population in the southern portion of the Zhejiang-Fujian mud was mainly controlled by the EAWM intensity changes; and not directly related to changes in the sediment discharge from Datong station of the Changjiang River （DTSD）. Finally, recent changes in the content of heavy metals in study area reflect the impact of human activities on the environment.     

南极罗斯海氧化还原敏感元素沉积地球化学特征及其古海洋意义

大洋深部氧化还原环境与深部水体流通状况以及表层水体生产力密切相关。表层生产力与深部流通性变化影响着有机碳-呼吸CO_2的转化及其在海洋-大气中的转移,最终与大气CO_2分压(pCO_2)变化密切相关。故探明大洋深部氧化还原环境的变化对于解决大气pCO_2冰期旋回机制具有重要意义。本次研究以中国第31和32次南极科考获得的南极罗斯海柱状岩心ANT31-R23及表层样为研究材料。通过元素钙、钛,以及氧化还原敏感元素(RSE)锰、钼、镍、钴、镉的测试分析,以表层样中RSE与Ti的比值作为判断ANT31-R23孔中相应RSE富集程度的背景值。结果显示,Mn在沉积期均表现出富集,表明罗斯海深部在该孔沉积期为氧化环境。根据Mn在不同层位出现的富集峰识别出4次强氧化脉冲事件,可能由南大洋底层水流通性增强和/或生产力降低导致。4次氧化脉冲事件层位中Mo、Ni、Co的明显富集,是由于锰(氢)氧化物对其捕获或吸附所致。此外,推测分析认为罗斯海对冰期大气pCO_2降低似乎没有明显贡献,但很可能对冰消期大气pCO_2迅速升高起重要作用。然而这些有关南极罗斯海深部氧化还原环境与大气pCO_2变化之间关联的推测,有待后续该孔精确年代模式的构建,方可进一步验证。     

黄海与东海泥质区高分辨率沉积记录研究新进展

陆架区沉积物季风代用指标在不同的地区可能具有不同意义,东海陆架泥质区的高分辨率古气候研究率先开始,有一大批成果通过提取敏感粒度指标进行东亚冬季风重建,并讨论了其与全球气候变化之间的驱动和响应关系;但有研究者指出,陆架沉积物的粒度指标更多的代表东亚夏季风信息,因此黄海地区更多的高分辨率沉积物古气候研究对此进行机制解释很有必要;古海洋学研究方面,最初依据有孔虫组合变化规律和AMS14 C年代学结合进行古海洋环境重建,后来不断有学者提供高分辨率古海水温度记录,近期沉积记录中古生态系统信息的提取为古海洋环境演化的研究提供了新的参考;工业革命以来,有机污染物、重金属污染在陆架区泥质沉积记录中变化明显,反映出人类活动对海洋沉积记录的影响。