【作者】 张振虎；

【导师】 陈志华； 姚政权；

【作者基本信息】 自然资源部第一海洋研究所 ， 海洋地质， 2023， 硕士

【摘要】 北极作为近百年来全球增暖最显着的区域,正在以两倍于全球的速度快速升温,北极快速气候变化及其环境效应已经成为当前极地研究的热点,而北极东西伯利亚陆架是开展北极地区大陆边缘海冰-海洋-河流综合控制的沉积过程和环境变化的理想区域。气温升高、海冰退缩、冻土融化、径流增大、海岸侵蚀加剧以及生产力提高等北极快速变化引起了一系列大气、海洋、冰雪和陆地等多圈层间相互作用的变化,对北极地区汞的生物地球化学循环过程具有重要的影响。为了深入认识北极快速气候变化背景下沉积汞的变化特征,本论文基于2016年、2018年和2020年三次中俄北极联合考察航次在楚科奇海、东西伯利亚海和拉普捷夫海取得的表层沉积物和多管沉积短柱等样品资料,在利用²¹⁰Pb和¹³⁷Cs建立的年代框架的基础上,对沉积物样品进行了粒度、沉积汞含量、常微量元素、有机碳、氮及同位素、生物硅等测试和分析,初步探讨了北极东西伯利亚陆架沉积汞的分布特征、控制因素及污染水平,揭示了百年来沉积汞的变化及其对北极快速气候变化的响应,主要认识如下:本文对北极东西伯利亚陆架87个表层沉积物的汞进行测试,发现表层沉积物中汞含量的分布呈现出明显的空间差异性,根据沉积汞含量的分布特征可将研究区分为近岸低汞区（33 ng/g）、陆架中部汞含量中等区（58 ng/g）和北部深水高汞区（84 ng/g）,整体而言,沉积汞含量的分布由近岸向外海表现出增大的现象。结合沉积物粒度、总有机碳和比表面积等指标,我们发现东西伯利亚陆架沉积物中汞的含量与细粒黏土组分含量呈现出显着的正相关,表明沉积物粒度对汞分布有一定的控制作用。近岸由于受河流输入、海岸侵蚀和环流分选等因素的影响,沉积物粒径较粗导致汞含量较低,而北部陆架深水区的细粒沉积物则吸附了更多的汞。在楚科奇海和拉普捷夫海,沉积汞含量和总有机碳含量有较强的正相关性,而在东西伯利亚海相关性较弱,这可能是因为东西伯利亚海的沉积有机碳来源相对更为复杂。应用²¹⁰Pb和¹³⁷Cs数据建立了北极东西伯利亚陆架4根多管沉积短柱的年代框架,重建了1880年以来沉积汞的变化历史。百年来北极地区气温升高、冻土退化、海冰覆盖面积减小和河流径流增大导致向研究区输运了更多的汞,所以在LV83-15、LV83-22和LV77-35岩芯中检测出沉积汞含量整体增加的变化特征。然而在LV77-44和LV83-15岩芯中的部分时期内却发现了沉积汞含量降低的趋势,主要是因为该岩芯位于季节性海冰边缘,受海冰和径流快速变化的影响较大,该时期内海冰面积快速减退、径流明显增加,导致沉积物平均粒径变粗,进而导致沉积汞含量的降低,表明输入海洋中的汞后期受到海冰、河流等动力因素的影响,会随着沉积物粒度特征的变化而重新分布。北极东西伯利亚陆架沉积汞含量在4至119 ng/g的范围内变化,含量较低。通过对表层沉积物和多管岩芯中沉积汞的富集因子、地质累积指数和汞通量的计算发现,沉积物中汞的富集因子值大部分低于1.5,地质累积指数值大部分小于0,人为汞通量略有增加但含量较低。我们认为百年来北极东西伯利亚陆架沉积汞的含量较低且主要来源于自然过程,受人类活动的影响相对较弱,沉积汞对生态和环境的污染程度较弱。更多还原

【Abstract】 As the most significant global warming region during the last hundred years,the Arctic is warming rapidly at twice the global average rate.The rapid Arctic climate changes and its environmental effects have become a hot spot for polar researches,the East Siberian Arctic shelf is a natural site for researches on sedimentary processes and environmental changes controlled by the integrated sea ice-ocean-river in the continental margin of the Arctic.Rapid Arctic changes such as warming,sea-ice melt,permafrost degradation,increased river runoff,intensifying coastal erosion and increasing productivity have caused a series of changes in the multi-spheric interactions of atmosphere,ocean,ice and land,which have direct impacts on the biogeochemical cycling of mercury in the Arctic.In order to further understand the changing characteristics of sedimentary mercury in the context of rapid Arctic climate changes,we use ²¹⁰Pb and ¹³⁷Cs to establish a chronostratigraphic framework,sediment samples were tested and analyzed for graine size,mercury concentration,major and minor elements,total organic carbon,total nitrogen,δ¹³C and biogenic silica,to preliminarily assess the distribution characteristics,controlling factors and the environmental pollution of mercury in the East Siberian Arctic shelf,to reveal the changes in sedimentary mercury during the last hundred years and its response to rapid climate changes,based on the sample data of surface sediments and multi-tube sediment core samples obtained from three joint Russian-Chinese Arctic scientific researches in 2016,2018 and 2020.The main findings are as follows.We analyzed the mercury content of 87 surface sediments from the East Siberian Arctic Shelf,we found significant spatial variability in mercury concentration,which can be divided into the nearshore low-mercury zone（33 ng/g）,the middle shelf medium-mercury zone（58 ng/g）and the northern deep water high-mercury zone（84ng/g）.In general,the distribution of mercury concentration shows an increase from nearshore to offshore.Combined with sediment grain size,total organic carbon and specific surface area of the sediments,we found that the mercury concentration displays a positive correlation with the clay content in the sediments of the East Siberian Arctic shelf,indicating the controlling effect of sediment grain size on the distribution of mercury.The coarse sediments in the nearshore due to the influence of river input,coastal erosion and hydrodynamic sorting lead to the lower mercury concentration,while the fine-grained sediments in the northern shelf are prone to absorb more mercury.There is a strong positive correlation between mercury and total organic carbon in the Chukchi and Laptev Seas,while the weaker correlation is only found in the East Siberian Sea,probably because the sources of total organic carbon in the East Siberian Sea are more complex.Based on the ²¹⁰Pb and ¹³⁷Cs data,we establish a chronostratigraphic framework for four multi-tube sedimentary columns in the East Siberian Arctic shelf and reconstruct the change of sedimentary mercury since 1880.The increase in temperature,degradation of permafrost,reduction of sea ice cover and increase in river runoff in the Arctic over the past hundred years have led to an increase in mercury transport to the study area,so that an overall increase in sedimentary mercury concentration is detected in the LV83-15,LV83-22 and LV77-35 cores.However,a decreasing trend of sedimentary mercury concentration were detected in LV77-44 and LV83-15 cores for part of the period,mainly because cores are located at the edge of seasonal sea ice and are influenced by the rapid changes of sea ice and runoff.The rapid recession of sea ice area and significant increase of runoff during this period led to the coarsening of average sediment grain size,which in turn led to the decrease of sedimentary mercury concentration.This indicates that the mercury input to the ocean is influenced by sea ice,rivers and other dynamic factors and redistributes with the change of sediment grain size characteristics.The sedimentary mercury concentration of the East Siberian Arctic Shelf varies from 4 to 119 ng/g with low levels.The enrichment factors,geoaccumulation index and flux of sedimentary mercury in surface sediments and multi-tube cores were calculated and found that most of the values of enrichment factors of mercury in sediments were less than 1.5,most of the values of geoaccumulation indexes were less than 0,and slight increase in anthropogenic mercury flux but at low levels.We believe that the sedimentary mercury content of the East Siberian Arctic shelf over the past hundred years is low and mainly originated from natural processes,which is relatively weakly influenced by human activities and the degree of ecological and environmental pollution by sedimentary mercury is weak.更多还原