西北冰洋及白令海沉积物颜色旋回与成因  

Sediment color cycles and their causes in the western Arctic Ocean and Bering Sea

作　　者：谢昕[1] 王汝建[1] 肖文申[1] 李悦[1] 

机构地区：[1]同济大学海洋与地球科学学院海洋地质国家重点实验室,上海200092

出　　处：《科学通报》2016年第16期1828-1839,共12页Chinese Science Bulletin

基　　金：国家自然科学基金重点项目(41030859);南北极环境综合考察与评估专项(CHINARE2016-03-02);中国地质调查局地质调查工作项目(水[2016]02-013-012);上海市自然科学基金(15ZR1443400)资助

摘　　要：利用沉积岩芯重建高纬海区古环境变化的瓶颈在于微体生物化石的缺乏限制了有孔虫氧同位素地层学在北冰洋的应用.一些北冰洋岩芯中发现的富Mn褐色旋回沉积似可成为建立冰期尺度年代地层的新手段,但仍存争议.我国多次的北极科考在西北冰洋及白令海的不同海区采获了众多沉积岩芯.对代表性的14根岩芯的测试分析发现,采于西北冰洋陆坡至海盆内的岩芯均有颜色的旋回变化并基本可用颜色反射率参数a*/b*值来指示.a*/b*与Mn,Mn与Mo之间具有较密切的相关变化,沿陆坡向洋盆中央方向,深褐色沉积层中的MnO含量逐渐降低;而采于白令海、北冰洋陆架及近岸深海的岩芯均未出现颜色及Mn含量的旋回变化,且a*/b*与Mn,Mn与Mo之间无任何相关性,同时,MnO含量总体很低.结合部分岩芯的地层年代框架推测,间冰期时,大量风化的陆源Mn元素经陆架被搬运至洋盆,并随洋流分布到氧化环境较强的海区沉积,形成了深褐色沉积层;冰期时,因陆架封冻、海冰覆盖率增高导致还原性沉积环境,造成北冰洋洋盆内形成土黄色或深灰色沉积.在排除成岩作用的影响后,颜色及Mn元素含量的旋回变化应能指示冰期/间冰期旋回变化.A challenge that limits high-latitude paleo-environment investigations is the lack of foraminiferal shell-bearing sediments for stratigraphy constructions. In the Arctic,the Mn-rich brown layers have been proposed as a new approach to establish glacial-interglacial timescale stratigraphy,but their formation mechanisms remain unclear. Until now,only a limited number of sediment cores with Mn-rich brown layers have been studied,and it has been argued that these layers were formed by diagenesis. During past several years,China expeditions have collected many sediment cores from the western Arctic Ocean and Bering Sea offering an opportunity to investigate sediment color cycles in these regions. In this study,we have studied 14 sediment cores from wide geographic and topographic regions including basin,continental slope,continental shelf,and off-shore deep-sea. First,core images were taken by a line scan camera and high-resolution color reflectance was measured by a spectrometer. Second,core sediments were scanned at 1 cm resolution by an XRF core scanner to obtain element content variations. Third,sediment layers with maxima and minima Mn based on XRF data were analyzed by ICP-OES and ICP-MS to crosscheck the reliability of XRF results and provide precise element concentration. Our results show that 9 cores from slope and basin of the western Arctic bear color cycles which can be effectively indicated by a＊/b＊ ratios,as a＊ is chromatic value from green to red while b＊ is chromatic value from blue to yellow. In each of these cores,a＊/b＊ ratios co-vary with contents of Mn and some other redox sensitive trace elements such as Cu,Co,Ni,and especially Mo. Data comparison shows that MnO and Mo concentrations at peak values in the cores gradually decrease,respectively,from 5.22% and 80 ppm on the slope to nearly 1% and 30 ppm in the central basin,whereas minimal MnO and Mo concentrations in these cores always stay around 0.1% and 10 ppm,respectively. By contrast,the 5 sediment cores from Bering Sea,continental

关 键 词：北冰洋 颜色旋回 MN 搬运及沉积过程 氧化-还原环境 

分 类 号：P736.2[天文地球—海洋地质]