| 北部湾全新世气候与古生态环境演进特征及其驱动因素 |
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| 引用本文：黄向青,崔振昂,林海,夏真,张顺枝.2022.北部湾全新世气候与古生态环境演进特征及其驱动因素[J].地球学报,43(2):129-143. |
| DOI：10.3975/cagsb.2021.042501 |
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| 基金项目:中国地质调查局“海南岛东北部沿海地区综合地质调查”(编号: DD20190308);地质科研项目“南海北部湾全新世环境演变及人类活动影响研究”(编号: 1212010914027) |
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| 中文摘要:北部湾地处南海西北端, 区域广布硅酸盐和石灰岩类, 迄今对其全新世气候、古生态环境演进过程及其背景驱动因素等还有待加强了解。为此, 在北部湾南部海盆钻取了全新统岩芯, 进行了孢粉、粒度、δ18O(氧同位素)等鉴定分析以及14C测年等。分析显示, 孢粉化石主要属种有木本松属、栲属等, 蕨类为水龙骨科、麟盖蕨属, 6.0 ka之后蕨类含量总体较高, 含量均波动变化, 以该界线点粉砂等为上升趋势以及分选变好。常量元素Al2O3等和微量元素总体升高, 而SiO2、CaO、Sr等为降低, 优势矿物为石英等, 风化矿物含量较高。δ18O总体下降了21.20%呈降温趋势, 其分布特征与中国全新世古气温变化可对应, 并以全球和区域气候变化重要节点9.0 ka等划分了气候阶段, 中全新世气候格局转换且西风带南进之后, 北部湾演进成为夏季风和西风带前缘相互作用地带而使得降水增加, 加强了化学风化以及重矿物赤铁矿水成效应。地表受到热胀冷缩以及淋溶风化双重作用, 大暖期鼎盛期亦为风化剧烈阶段, “4.2 ka事件”造成化学风化滞缓, 约自4.0 ka之后CIA等指示的化学风化保持加强。中全新世以来植被多样性指数以基本节点经历了升-降-升三个基本阶段, 总体为提高趋势, 海洋古生产力指标变化与植被多样性指数旋回可对应, 陆源输入增加而使得前者呈增高趋向。研究得出如下认识: 北部湾碎屑物质具有陆源性并对全球和区域气候变化响应敏感, 西风带推进对其先干后湿气候模式建立具有积极的机制效应, 地表风化在太阳迫胁力周期运动和气候调节之下有序旋回进行, 古植被环境趋向总体改善, 由于陆-海之间关系密切, 北部湾亦成为南海北部海洋生态系统的一个重要组成部分。 |
| 中文关键词:北部湾 全新世 古生态 古生产力 |
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| The Driving Factors on Climatic and Palaeo-ecological Evolution of Beibu Gulf since Holocene |
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| Abstract:Located on northwestern South China Sea and the transition zone between continent and marine, less understanding on Beibu Gulf’s background of Holocene palaeo-climatic & ecological evolution needs to further improve. We acquired Holocene sediments drilling cores in its southern basin and made the lab analysis on high resolution samples’ sporopollen fossil, granularity, macro-& micro-geochemical elements, detrital mineral and δ18O and G.ruber 14C aging. Comprehensive analysis and comparison showed that composition of Pinus sp.,Castanopsis sp., Quercus sp., and Microlepia sp., Polypodaceae revealed historic tropical and sub-tropical climatic background, and fern spices’ general growth trend from 6.2 ka and also indicated fluctuations from their distribution. From above time point, silt sand and clay also generally increased and the sorting improved. Indicating continent provenance, Al2O3, Fe2O3, MgO etc increased and SiO2, CaO, MnO, Sr decreased instead, and main minerals were Quartz, Feldspar and weathering mineral. δ18O temporal distritution could primarily corresponded to Chinese Holocece temperature demonstrating a cooling trend from HTO with mean relative difference –21.20% in δ18O, and the basic climatic phrases were classified based on 9.0 ka, 6.2 ka, 4.0 ka, 2.0 ka timing points displayed in regional and also North Atlantic fluctuations. It also showed that Beibu Gulf had become the interaction zone of summer monsoon systems and cold mass frontier after westerly southward shift enhancing the regional precipitation and chemical weathering, which demonstrated in hydro-genesis of heavy mineral Hematite too. Regional litho-surface process included coupled heat expand & extraction and de-silicon & –calcitication to speed up weathering and geochemical elements’s release forming soil horizon further. There were dramatic oscillations of above granularity and other elements during the end part of HTO also called deteriorating period showing a cooling as well as HTO termination trend in China. “4.2 ka Event” exerted significant impacts on sedimentation and since then the chemical weathering continued intensifying. Also the bio-diversity index of sporopollen fossil indicating the palaeo-vegetation’s structure and optimization displayed an overall increase based on above cycling time nodes and thus marine palaeo-produtivity benefited from climatically driving growth of runoff input. The summary could be reached that Beibu Gulf was sensitive to climatic change, westerly southward shift acted a positive effect on precipitation mechanism through climatic mode’s evolution constituting a transiton zone between warm as well as humid and cold air masses, and the litho-surface processes were under the almost orderly regulation of solar radiation forcing and climatic change and there was a close relationship between regional continent and marine forming a complex and had become the fundamental of modern ecosystem and an important marine ecological component of northern SCS. |
| keywords:Beibu Gulf Holocene palaeo-ecology palaeo-productivity |
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