【作者】 陆岸青；

【导师】 李珍；

【作者基本信息】 华东师范大学 ， 自然地理学， 2011， 硕士

【摘要】 北部湾是由中国的广西沿海、广东雷州半岛、海南西部,以及越南的东北部所围成的天然半封闭浅水海湾,是受东亚季风与西南季风影响的气候敏感区。由于海南岛的屏障作用,受南海海流作用影响小,适合开展气候变化研究,也有助于理解季风气候变化过程,快速气候变化事件及其驱动机制。当前,对北部湾古气候的研究比较少,且年代控制精度不高。北部湾北部具有较高的沉积速率,可以实现较高分辨率的气候变化恢复研究。本文首先对表层沉积物进行粒度和孢粉分析,获得孢粉分布规律与沉积环境的关系。对Q24孔(岩芯长6.25 m)和Q43孔(岩芯长5.13 m)的柱状样品进行孢粉、粒度、碳屑、C/N、δ13C和XRF全芯扫描等分析,将表层样品中获得的气候代用指标与沉积环境代用指标的关系应该到钻孔数据的综合解译中,在210pb和AMS14C年代框架下,重建了北部湾北部8.50 cal. kyr BP以来的古环境和古气候。主要研究内容及结果如下.(1)表层孢粉分布规律对表层沉积物的粒度和孢粉分析结果表明,孢粉浓度与沉积物的粒径具有一定的正相关；蕨类孢子和松属花粉含量随离岸距离增加而增加,而草本植物花粉含量则随离岸距离的增加而减少。(2.)气候变化过程和模式本研究利用粒度参数作为沉积环境水动力的代用指标,C/N、δ13C和Al/Ti值指示陆源输送变化,孢粉及碳屑为主要气候代用指标,通过校正沉积环境变迁及陆源输送变化对孢粉分布的影响来提取气候变化信息,获得气候变化过程。约8.50 cal. kyr BP琼州海峡的完全开通,现代北部湾基本形成,研究区处于相对稳定的浅海环境,环境对气候代用指标的影响相对较弱。根据沉积相分析及AMS14C年代框架,Q24孔在8.5-4.0 cal. kyr BP期间沉积连续,Q43孔主要为4.0 cal. kyr BP之后的沉积,综合两个钻孔的气候及沉积环境多代用指标的测试结果,恢复8.50 cal. kyr BP以来的气候变化过程：7.84 cal. kyr BP之前,反映比现代温暖湿润的气候特征；7.84～7.36 cal. kyr BP期间,较上一阶段偏凉偏干的气候所致；7.36～6.51 cal. kyr BP期间,变凉变湿的气候特征；6.51～4.09 cal. kyr BP期间,总体上Quercus和湿生草本类型均增加,粒径参数及δ13C值较稳定,反映总体上呈现偏凉湿的气候特征,但结合粒度参数及其它沉积环境指标的变化校正,可以识别出三个亚阶段：6.51～6.00 cal. kyr BP,偏凉湿的气候；6.00-5.80 cal.kyr BP,尚需进一步分离研究气候变化信息；5.80～4.09 cal. kyr BP,反映出气候略偏暖。4.09-1.84 cal. kyr BP期间,由于Q43孔在该阶段取样扰动,记录缺失,仅由一个未扰动样品无法实现高分辨率研究,迄待今后进一步研究；2.20-1.84 cal. kyr BP期间,说明了变凉变干的气候特征；1.84～1.40 cal. kyr BP期间,比上一阶段更加变凉变干；1.40-0.33cal. kyr BP期间,指示了变暖变湿的气候特征。(3)北部湾北部记录的突发性气候冷事件及其驱动机制北部湾北部记录的8.50 cal. kyr BP以来突发性气候冷事件分别为7.8-8.0 cal. kyr BP、8-6.0 cal. kyr BP、1.4-1.8 cal. kyr BP,通过与不同地区和区域记录的冷事件对比,认为这些事件可能太阳辐射和温盐环流有关。更多还原

【Abstract】 The Northern Beibu gulf is a natural semi-closed shallow gulf, which is bounded by Chinese Guangxi coast, peninsula Leizhou of Guangdong, western Hainan, northern Vietnam. It is one of the most significant areas by Asian monsoon, so palaeoclimate research helps to understand climate change process in monsoon area, and rapid climate change events and their driving mechanism.At present, the research about palaeoclimate of Northern Beibu gulf is very few, and the dating precision is also very low. Besides, high sedimentation rate of Beibu gulf during the Holoeene has been shown in previous studies, which makes it possible to exact information from sea sedimenis.,so it has certain theoretical value to study palaeoclimate here.This paper studied particle size, pollen and 210Pb of surface sediment adequately, as a basis for explaining the palaeoclimate characteristic in core. Then we chose two samples of surface sediments from core Q24 (6.25 m) and core Q43 (5.13 m) to 210Pb date, and nine samples to AMS14C date, in order to build the sedimentary-date framework. Then according to the significance of climate proxies pollen, grain size, charcoal, C/N,δ13C, XRF, the history of the environmental changes of Northern Beibu gulf in the past 8.50 cal. kyr BP was reconstructed. The main results of this study include the followings:1.The surface pollen regularities of distribution in Northern Beibu gulfThe sea area,where drilling is located, is affected by monsoon, land stream, tidal, the residual current, so the environmental condition is relatively complicated, and makes pollen distribution rule is very complex. When sediment particle size is small, pollen concentration generally is high; the content of fern spores and pinus become higher and herb lower as farther from the offshore.2.The climate change process and modelThis research use particle size as the proxy of the hydrodynamic of sedimentary environment, and C/N、813C、Al/Ti as the proxies of the land-originchange, and pollen and charcoal as the main proxy of the climate change. We extract information about climate change by correcting the influence of sedimentary environmental and land-originc changes on terrestrial pollen distribution.Qiongzhou Strait was opened fully about 8.50 cal. kyr BP and modern Beibu Bay was formated. Study area was in the stable shallow marine environment, so environmental impacted the climate proxies weakly.According to sedimentary facies and AMS14C age framework, we can found that the deposition of Q24 core during 8.5-4.0 cal. kyr BP was continuous, and Q43 core recorded mainly 4.0 cal. kyr BP deposition, so comprehensive this two cores about the climate and sedimentary environment, we recoveried the climate change process since 8.50 cal. kyr BP:In the study area of core Q24, before 7.84 cal. kyr BP, the climate is humid and warm; during 7.84～7.36 cal. kyr BP, the temperature and humidity are declined; and during 7.36～6.51 cal. kyr BP, the temperature gradually increased, at the same time the humidity is down, but the Sediment grain sizeand other changes inenvironmental indicators,three sub-stages can be identified:6.51-6.00 cal. kyr BP, the climate was a little cooler and wetter,6.00-5.80 cal. kyr BP, it need further information to separate of climate change,5.80-4.09 cal. kyr BP, the climate was warmer; during 4.09-1.84 cal. kyr BP, Because there was only one undisturbed samples in this stage sampling, so we cannot achieve high resolution research. the climate characteristics is cool and dry; during 2.20-1.84 cal. kyr BP the climate was cooler and drier; during 1.84-1.40 cal. kyr BP, the temperature is still low, but humidity gradually increased; during 1.40 -0.33 cal. kyr BP, the climate characteristics is warm and humid.3. The Northern Beibu gulf recorded rapid climate change events and its driving mechanismAccording to partical size, Al/Ti,δ13C, pollen volume concentration, pollen flux, RCC events 7.8-8.0 cal. kyr BP、5.8-6.0 cal. kyr BP、1.4-1.8 cal. kyr BP was recorded in Northern Beibu gulf, Global RCC events of 7.8-8.0 cal. kyr BP、5.8-6.0 cal. kyr BP、1.4-1.8 cal. kyr BP are associated with the solar radiation and Thermohaline Current(THC). Besides,1.4-1.8 cal. kyr BP event may be the main reason that couse continuous wars and regime change frequently in Wei, Chin and the South and North Dynasties.更多还原