末次冰期亚马逊冲积扇海域千年尺度的水文气候变化

发布时间：2018-05-18 00:44

本文选题：亚马逊冲积扇海域 + 快速气候变化　；参考：《中国科学院研究生院(海洋研究所)》2015年硕士论文

【摘要】：亚马逊盆地是世界最大的陆地大气对流中心,以及热带地区热量来源的主要区域,亚马逊盆地对流降雨在向高纬地区输送热量过程中起了关键作用,调控着全球环境气候变化,成为古气候与古环境研究的热点地区。亚马逊冲积扇海域处于西热带大西洋水团影响之下,该水团对大洋动力过程和洋内热量转移相当重要,亚马逊流域淡水输入的变化不仅对该水团的特征有重要影响,更控制着大西洋跨赤道环流-北巴西沿岸流的变异,从而调节着全球温盐环流。ODP942站毗邻亚马逊河口,得益于亚马逊河大量沉积物的输入,其岩芯样品是区域气候和海洋环境高分辨率重建的良好材料。本文利用亚马逊冲积扇海域ODP942站位海洋沉积岩芯中浮游有孔虫Globigerinoides ruber壳体氧同位素(δ18O)、Mg/Ca比值以及Ba/Ca比值记录重建了4万年以来亚马逊盆地千年尺度的水文气候变化,讨论了其环境变迁与ITCZ位置迁移和大洋温盐环流之间的关系。研究表明表层海水溶解Ba浓度与表层海水盐度(SSS)之间存在显著的负相关关系(R2=0.95),依据亚马逊河口区域现代海水Ba与SSS的相关关系以及Ba在海水和有孔虫壳体之间的分配比例建立了一个区域浮游有孔虫Ba/Ca比值与SSS的回归公式:SSS=-6.2005*Ba/Ca foram+40.724(R2=0.98)。根据942站位G.ruber(White)和G.sacculifer壳体Ba/Ca测试值计算的近4100 a B.P.来的SSS变化显示:与G.sacculifer相比,利用G.ruber(White)Ba/Ca比值估计的SSS变化与热带南美石笋δ18O指示的降水记录有良好的可比性,G.ruber(White)Ba/Ca比值是亚马逊冲积扇海域SSS良好的替代指标,为进一步通过G.ruber(White)壳体Ba/Ca比值恢复区域淡水输入及降水变化奠定了基础。亚马逊冲积扇海域有孔虫壳体氧同位素记录了4万年以来北半球高纬地区的快速气候变化事件,分别为Heinrich事件的H1-H4、Dansgaard-Oeschger(D-O)旋回1-8及Younger Dryas(YD)事件,Heinrich及YD冷事件期间,G.ruber壳体δ18O值变大;D-O暖期,δ18O值变小。通过有孔虫壳体Mg/Ca比值重建的表层海水温度(SST)对北半球高纬地区快速气候变化响应较弱,但是与南极冰芯记录的古气候变化趋势较为一致,尤其是显示出末次冰消期以来表层海水温度的持续增加。通过海水氧同位素值(δ18Osw)记录的表层海水盐度显示在Heinrich事件H1-H3及YD事件期间SSS较高。SST变化趋势显示亚马逊冲积扇海域表层海水温度变化与南极气候变化更为密切,说明了亚马逊冲积扇海域记录的千年尺度的快速气候变化事件主要反映在降雨模式的变化。Heinrich、YD事件期间,大西洋经向翻转环流(AMOC)减弱,气候变冷,ITCZ向南移动,使亚马逊冲积扇海域降雨减少。通过对比,亚马逊冲积扇海域降雨模式变化与深部热带大西洋变化同步,说明了热带地区降雨模式变化与大洋温盐环流的改组之间的联系,北大西洋表层海水温度变化、北大西洋经向温度梯度变化及ITCZ的南北迁移,使得该区域降雨模式发生改变。
[Abstract]:Amazon basin is the largest terrestrial convection center in the world and the main area of heat sources in the tropical region. The Amazon basin has played a key role in transporting heat from the high latitude area in the Amazon basin. It regulates the global environmental climate change and becomes a hot spot in the study of paleoclimate and paleoenvironment. Under the influence of the the Atlantic water mass in the Western tropics, the water mass is very important to the ocean dynamic process and the intra ocean heat transfer. The change of the freshwater input in the Amazon basin not only has an important influence on the characteristics of the water mass, but also controls the variation of the cross equatorial circulation in the north of the Atlantic and the northern Brazil coastal flow, thus regulating the adjacent.ODP942 station adjacent to the global temperature and salt circulation. The Amazon estuary, benefited from the input of a large amount of sediment in the Amazon River, is a good material for high resolution reconstruction of regional climate and marine environment. This paper uses the oxygen isotope of planktonic foraminifera Globigerinoides ruber (delta), Mg/Ca ratio and Ba/Ca ratio in the marine sedimentary core of the Amazon alluvial fan ODP942. The value records rebuilt the hydrological climate changes of the Millennium scale in the Amazon basin for 40 thousand years, and discussed the relationship between the environmental changes and the ITCZ position migration and the ocean temperature and salt circulation. The study shows that there is a significant negative correlation between the dissolved Ba concentration in the surface sea water and the salinity of the surface sea water (SSS), which is based on the Amazon estuary area. The correlation between Ba and SSS in modern sea water and the distribution ratio of Ba between sea water and foraminifera shell set up a regression formula for the Ba/Ca ratio of planktonic foraminifera and SSS: SSS=-6.2005*Ba/Ca foram+40.724 (R2=0.98). According to the 942 stations G.ruber (White) and G.sacculifer shell Ba/Ca test values Compared with G.sacculifer, the SSS changes estimated by the G.ruber (White) Ba/Ca ratio have a good comparability with the precipitation records indicated by tropical South American stalagmite Delta 18O. The G.ruber (White) Ba/Ca ratio is a good substitute for SSS in the Amazon alluvial fan sea area, and is to further restore the region fresh water transport through the G.ruber (White) shell ratio. The oxygen isotope of the foraminifera shell in the Amazon alluvial fan area has recorded the rapid climate change events in the high latitude region of the northern hemisphere for 40 thousand years, respectively, for the H1-H4, Dansgaard-Oeschger (D-O) cycle 1-8 and Younger Dryas (YD) events of the Heinrich event, the 18O value of the G.ruber shell Delta during the Heinrich and YD cold events. In the warm period of D-O, the value of delta 18O becomes smaller. The surface seawater temperature (SST) rebuilt by the Mg/Ca ratio of the foraminifera shell is weak in response to the rapid climate change in the high latitude region of the northern hemisphere, but the trend of palaeoclimate change recorded in the Antarctic ice core is more consistent, especially in the surface sea surface temperature increasing since the last glacial period. The salinity of the surface sea water recorded by the oxygen isotope value (delta 18Osw) shows that the higher.SST trend of SSS during the events of the Heinrich event H1-H3 and YD shows that the temperature changes in the surface water temperature of the Amazon alluvial fan are more closely related to the changes in the Antarctic climate, which indicates that the rapid climate change events of the Millennium scale recorded in the Amazon alluvial fan are the main events. It is reflected in the variation of the rainfall pattern.Heinrich, the YD event, the the Atlantic meridional circulation (AMOC) weakened, the climate became cold, and the ITCZ moved southward to reduce the rainfall in the Amazon alluvial fan. By contrast, the rainfall patterns in the Amazon alluvial fan were synchronized with the changes in the deep tropical the Atlantic, indicating the variation of rainfall patterns in the tropics and the changes in the rainfall patterns in the tropical regions. The relationship between the change of the ocean temperature and salt circulation, the change of surface sea temperature in the North Atlantic, the change of the North Atlantic meridional temperature gradient and the migration of the north and south of ITCZ make the rainfall pattern change in this region.
【学位授予单位】：中国科学院研究生院(海洋研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P532

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