北部湾海槽中全新世以来气候变化与重金属积累关系

【目的】为了探寻北部湾湾口重金属沉积规律,研究中全新世以来该地区海槽重金属分布、累积及联系。【方法】在北部湾南部海槽处钻取200cm长度岩芯进行垂直分样,并对典型重金属Pb、Cr、Zn,微量元素,粒度,矿物,14 C定年等指标进行综合测试及分析。【结果】岩芯沉积物的化学蚀变指标CIA显示,气候波动变化,总体上气候趋向暖湿,陆源供给加大,可分为两个基本气候阶段;重金属具有陆源性,且细粒级与重金属对气候波动响应明显,含量随深度变浅,即随气候演进而呈增加趋势;岩芯沉积物组分以悬移质为主,与海水悬移质粒级有对应性,其中重金属来自吸附与再沉积,6~9φ为吸附粒级;重金属积累系数fa变化曲线显示,重金属自25cm以来积累加快,Pb的相对斜率增加且分化明显。【结论】重金属含量变化是对气候波动的响应,晚全新世后期重金属(尤其是Pb)积累有加快趋势,可能与人类活动有关。

Climatic Change and Accumulative Characteristics of Heavy Metals in Beibu Gulf Trough Since Middle Holocene

Objective]Because of less understanding to heavy metal accumulation in sedimentary center in Beibu Gulf trough in coastal bays and estuaries,it is necessary to study the distribu-tion,accumulation and relationship of heavy metals along with sedimentary environment change since Holocene.Methods]Based on 14 C dating,laboratory test of granularity and geochemis-try was conducted in 30 samples from 200 cm-length sediment core in Beibu Gulf trough.The distribution of heavy metals Pb,Cr and Zn and their relation with environment factors were an-alyzed.Results]Chemical erosion indicator CIA and other indicator basically oscillated in two stages,showing a climatic trend to warmer and wetter.Heavy metals had continent provenance and an increasing trend with positive respond to climatic change.Sediment core was mainly composed of suspended sediment compositions, revealing that heavy metals accumulated by the way of suspended matters ’adsorption and re-settlement with adhesive grain sizes 6 ~9 φ. Through the method of 150 cm-length progres-sive and dynamic background value calculation, the vertical accumulation index fa from 50 cm was obtained firstly,showing that heavy metals came into the accumulation state from 25 cm and their accumulation rate especially Pb distinguished with other two heavy metals.Conclu-sion]The vertical distribution and behavior characteristics of heavy metals are basically the re-sponse to climatic variation and trend,and a growing trend of abovementioned heavy metals es-pecially Pb since latest Holocene reveals anthropogenic impacts.