末次冰期以来巽他陆架东北部陆坡区正构烷烃分布特征及其古植被意义  

Composition Distribution of n⁃Alkanes in Slope Sediments of the Northeast Sunda Shelf since the Last Glacial Period and Its Palaeo⁃Vegetation Significance

作　　者：崔子恒 贺娟[1] 贾国东[1] Cui Ziheng;He Juan;Jia Guodong(State Key Laboratory of Marine Geology Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《地球科学》2021年第1期331-340,共10页Earth Science

基　　金：国家重点研发计划“末次冰消期以来碳氮硫循环与全球变化的关系”项目(No.2016YFA0601104).

摘　　要：为了讨论末次冰期以来巽他陆架东北部植被情况及巽他陆架在冰期时的碳循环意义.对位于南海西南部陆坡的18252⁃3站位岩心柱沉积物中长链正构烷烃组分的平均链长(ACL27⁃33)、碳优势指数(CPI27⁃33)、烷烃含量(ΣoddC27⁃C33)、及烷烃比值等指标进行了分析.结果显示:末次冰期以来CPI27⁃33表现出与海平面变化具有很好的相关性.冰期时,CPI27⁃33值表现出明显的奇偶优势,指示了叶蜡烷烃新鲜程度很高,应该主要来自附近出露陆架区的近源供应.冰期低海平面时ΣoddC27⁃C33(ng/g)总体高于全新世,也与陆源供应靠近陆坡区有关.ACL27⁃33自40 ka B.P.以来呈上升趋势,指示草本植被发育增多和/或气候略为变干.从烷烃记录来看,冰期陆架出露时,n⁃C29及n⁃C31烷烃相对含量相差不大且均远高于n⁃C33,至全新世n⁃C29显著降低,而n⁃C33则显著增高.结合ACL27⁃33及烷烃比值数据,可以大致推测冰期出露的研究站位附近陆架地区很可能以热带雨林分布为主.将本文数据与巽他陆架东南部陆坡区数据进行综合分析,推测面向南海的巽他陆架东部地区在冰期时呈现热带雨林景观的可能性很大.由于雨林植被具有巨大的碳蓄积量,因此巽他陆架在冰期时很可能会是一个巨大的陆地碳储库.To better understand vegetation change in the northeastern Sunda shelf since the last glacial period and its significance for carbon cycle,we analyzed long⁃chain n⁃alkanes in a sediment core(18252⁃3)on the southwest slope of the South China Sea covering the last 40000 years.Our data show that carbon preference index(CPI27⁃33)was correlated well with sea level changes since the last glacial period.During the glacial time,greater odd⁃to⁃even predominance and higher concentration of long⁃chain n⁃alkanes(C27⁃C33)than thereafter reflect higher freshness of these leaf wax n⁃alkanes,indicating a main vegetation source from the nearby exposed shelf.This could be also the cause for the higher contents of total leaf wax n⁃alkanes(ΣoddC27⁃C33)during the glacial low sea⁃level time.The average chain length(ACL27⁃33)increased since 40 ka B.P.,reflecting more herbaceous contribution and/or slight drying of climate.Our data also show that the relative content of n⁃C29 and n⁃C31 alkanes was not significantly different and much higher than that of n⁃C33 on the exposed Sunda shelf during the glacial period.However,the relative content decreased for n⁃C29 significantly,but increased for n⁃C33 in Holocene.Along with previous studies in the southeastern Sunda shelf,the data indicate that the exposed shelf was dominated by tropical rainforest during the glacial period.Because the tropical rainforests may reserve substantial organic carbon,the Sunda shelf was likely to be a huge carbon sink during the glacial period.

关 键 词：巽他陆架 正构烷烃 植被类型 末次冰期 地球化学 

分 类 号：P736.1[天文地球—海洋地质]