末次冰期亚马逊冲积扇海域千年尺度的水文气候变化
文献类型：学位论文
| 作者 | 王倩1,2
|
| 学位类别 | 硕士 |
| 答辩日期 | 2015-05-23 |
| 授予单位 | 中国科学院大学 |
| 授予地点 | 北京 |
| 导师 | 常凤鸣 |
| 关键词 | 亚马逊冲积扇海域 快速气候变化 降雨模式 热带辐合带 温盐环流 |
| 学位专业 | 海洋地质 |
| 中文摘要 | 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。 |
| 英文摘要 | The Amazon Basin represents the largest land-based atmospheric convection centre on earth and the main source of latent heat in tropical. It plays a fundamental role in supply of heat to the higher latitudes, therefore it has become a hot area of paleoclimate studies. The Amazon Fan is under the influence of western tropical Atlantic water masses, which has a significant impact on ocean dynamics and heat transport. Variations in outflow of Amazon River not only affect the characteristics of the water masses but also control the changes of Atlantic cross-equatorial circulation and the North Brazilian current, thereby regulating the global thermohaline circulation. Site 942 lies adjacent to the mouth of Amazon River and benefits from the massive output of sediment from Amazon Basin, therefore it provides continuous high-resolution palaeoclimate and palaeocean records. In this paper, we reconstruct millennial-scale variations in hydrology and climate on Amazon Fan during the last glacial from the records of oxygen isotopes、Mg/Ca ratio and Ba/Ca ratio on planktonic foraminifera Globigerinoides ruber to discuss the relationship between the environmental change and the shift of ITCZ, as well as the THC. The analysis indicates that the dissolved barium concentrations in this region show an obvious negative correlation to the SSS (R² = 0.95). A lineal equation (SSS =–6.2005*Ba/Caforam + 40.724, R2= 0.98）is established based on the relationship between modern sea surface Ba/Ca and salinity, and a distribution coefficient of Ba reported for planktonic foraminifera. Planktonic foraminiferal Ba/Ca ratios are determined on thirteen samples from Site 942B and 942C to investigate the usability of Ba/Ca in G. ruber (White) and G. sacculifer as an indicator of past sea surface salinity (SSS). Application of this equation to the thirteen ODP 942 samples suggests that for the last 4099 a B.P., SSS estimates based on G. ruber (White)-Ba/Ca show fairly comparable results to the precipitation records indicated by the stalagmite δ18O from South American continent. Ba/Ca in G. ruber (White) is a useful proxy of SSS over the Amazon Fan. During the last glacial, there are a series of millennial-scale variations in δ18O records, respectively Heinrich events and Younger Dryas. During the cooling events, δ18O records are most positive. There is no uniform relation between the Sea Surface Temperature (SST) derived from G.ruber Mg/Ca and millennial-scale variations. But the characteristics of variations in SST are consist with the palaeoclimate trends of Antractic, especially the last deglacial. During the periods of Heinrich and YD cooling events, the Sea Surface Salinity (SSS) increased. Because of the temperature, salinity and global ice volume affect the foraminiferal oxygen isotope together, therefore the rapid changes in δ18O records might be the information of both temperature and salinity. However, the trend of SST shows more similar with Antarctic, so it suggests that the millennial-scale climate change in Amazon Fan mainly reflects the variation in the precipitation pattern. During the H and YD cooling events, a reduction of the Atlantic Meridional Overturning Circulation (AMOC) and related North Atlantic cooling induces a southward movement of the Intertropical Convergence Zone (ITCZ), resulting in a weakened precipitation on Amazon Fan. By comparison, synchronous variations in precipitation patterns on Amazon Fan and deep western tropical Atlantiv conditions show a connection between THC (Thermohaline Circulation) reorganizations and shifts in tropical precipitation patterns by way of variations in North Atlantic SST, changes in the meridional North Atlantic temperature gradient and resulting shifts of the ITCZ. |
| 学科主题 | 海洋地质与环境 |
| 语种 | 中文 |
| 公开日期 | 2015-06-11 |
| 源URL | [http://ir.qdio.ac.cn/handle/337002/22789]  |
| 专题 | 海洋研究所_海洋地质与环境重点实验室 |
| 作者单位 | 1.中国科学院海洋研究所 2.中国科学院大学 |
| 推荐引用方式 GB/T 7714 | 王倩. 末次冰期亚马逊冲积扇海域千年尺度的水文气候变化[D]. 北京. 中国科学院大学. 2015. |
入库方式： OAI收割
来源：海洋研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。