海南东部小海潟湖沉积物地球化学特征及对古台风活动的指示

Geochemical characteristics of sediments in the Xiaohai lagoon( Eastern Hainan) and implications for the paleo-typhoon activities

为探讨海南东部历史时期的气候环境变化,2015年于海南岛东海岸小海潟湖中采集了一根长73 cm的柱状样(XH15-02),在年代学(210Pb和AMS14C)测试的基础上,开展了多环境代用指标(总有机碳(TOC)、总氮(TN)、有机碳稳定同位素、干密度等)的测试和分析.结果表明,XH15-02柱状样TOC与TN含量有很好的相关性,C/N比值在10.41~23.33之间变化,有机碳稳定同位素(δ13Corg)值在-25.14‰^-23.29‰之间.通过对多气候环境代用指标的分析,以及与历史文献资料和其他自然代用指标的综合比对,认为XH15-02孔岩芯沉积记录了研究区过去1100多年来较为丰富的气候环境、台风活动以及人类活动影响等信息.近千年来,小海潟湖沉积有机物主要以陆源输入为主,据估算该岩芯有机碳陆生来源约占47.00%~73.43%,但在不同时期变化幅度较大,该陆源有机碳含量变化可能主要反映了历史时期海南东部地区的干湿变化历史;自1850年以来,XH15-02孔岩芯沉积通量的显著增加与当地人口的快速增长历史一致,反映了研究区近二百年来可能受到的人类对自然界的开发活动影响强烈;多个具有显著偏正δ13Corg记录的时期同史料记载以及周边区域地质记录中的"大风"、"海溢"、"风暴"等事件发生时间较为相近,可能揭示了历史时期的台风或高海平面事件,进而认为小海潟湖沉积在重建历史时期海南地区台风活动等方面具有很大潜力.

Coastal lagoons with small catchment influenced both by seawater and river inflow, are highly sensitive to natural processes and anthropogenic activities, which make it ideal regions to study the paleo-environmental and paleo-climatic changes. To better understand the past climatic and environmental changes of the eastern Hainan Island, a 73 cm-long sediment core (XH15-02 core) was collected from the Xiaohai Lagoon, eastern Hainan Island in January, 2015. 210Pb and AMS14C dates were determined, respectively, and multiple proxies including the total organic carbon (TOC), total nitrogen (TN), organic carbon stable isotopes (δ13Corg), and dry density, were analyzed. In addition, based on the data mentioned above, deposition rate and flux of sediment and organic carbon were calculated, respectively. The results show that there is a good correlation between the content of TOC and TN;the ratios of C/N show remarkable variations ranging from 10.41-23.33, and δ13Corg values vary between -25.14‰ and -23.29‰;and the proportion of terrestrial organic carbon sources vary from 47.00% to 73.43% with some obvious low values during the last 1100 years, the terrestrial organic carbon content may record the precipitation changes in the eastern Hainan during the last millennium. Deposition rate and flux of sediment and organic carbon were relatively steady before 1850s, however, it increased rapidly after 1850s, especially since 1950s. The significant accelerated sedimentation process during the last two hundred years was probably related to the population growth and intensified anthropogenic activities in the Hainan Island at the same period. Based on the analysis of multi-proxies and comparison with the historical literature records and other climatic records from other regions, we assume that the XH15-02 core sediment drilled from the Xiaohai Lagoon may record some high sea level and/or strong typhoon events during the historical period. Especially, our results suggest that the δ13Corg records of XH15-02 core may be a valuable proxy to reconstruct the paleo-typhoon activities during the last millennium.