冰岛北部海域末次冰期以来海冰变化定量重建及其影响机制探讨

Being located in the climatically extremely sensitive Arctic part of the North Atlantic region, the North Icelandic shelf is an area which is highly suitable for conducting studies on regional climate changes. This project attempts to study the relationship between surface sediment diatoms and associated modern sea-ice data in the northern North Atlantic, and to build up a new diatom-based sea-ice cover transfer function. We will also study climate changes and their influence on marine environments in particular sea-ice changes and discuss the relationship between the solar activity and ocean hydrography and their impacts on palaeoclimate based on high-resolution diatom records from two piston cores on the North Icelandic shelf since the Last Glacial Maximum.. In addition, the marine environments during the last 100 years will be reconstructed based on diatom data from two cores on the North Icelandic shelf. The results will be tested by comparison with instrumental records.. The final aim for this project is to reveal the periodically climatic and oceanographic change on the North Icelandic shelf since the Last Glacial Maximum, to test possible correlation of climatic and oceanographic change with changes in solar irradiance, and to discuss the forcing mechanisms behind the palaeoclimatic changes.

冰岛北部海域位于北极－北大西洋地区，了解该海域气候及海冰变化规律及驱动机制，对于预测未来全球气候变化具有十分重要的意义。本项目将在课题组已有的表层沉积硅藻－环境变量数据库的基础上，建立更为全面、系统的适用于冰岛北部海域的表层沉积硅藻－海冰转换函数。并系统分析冰岛北部海域2个高分辨率钻孔末次冰期以来沉积硅藻记录，探讨硅藻组合变化与古海冰变化之间的关系，运用新的转换函数定量重建冰岛北部末次冰期以来的古海冰变化。本项目还将研究该海域2个高分辨率钻孔近100年来硅藻组合所反映的环境指标，并将其与器测资料对比，从而建立由地质学方法得到的古气候、古海洋资料与近代器测数据的对应关系。其最终目标是研究末次冰期以来冰岛北部海冰及气候变化的周期性规律及快速气候变化事件，探讨其与太阳辐射、大洋环流等的关系，试图揭示该海域海冰及气候变化的主要驱动机制。

项目组通过对北大西洋北部海域表层沉积硅藻-环境变量进行统计分析，建立了适用于冰岛北部海域的硅藻-海冰转换函数。首先运用该转换函数定量重建了近70年的海冰变化，通过与近现代器测数据及历史资料的对比，进一步验证了转换函数的可靠性。为全面、系统地认识末次冰消期以来冰岛北部海域海冰及海洋环境变化，项目组对冰岛北部陆架及周边海域的多个沉积钻孔MD99-2271、MD99-2272、MD99-2275及GA306-GC3和GA306-GC4进行了硅藻及海冰生物标志物等的分析，进而定量重建了研究区末次冰消期以来海冰及表层海水温度记录。结果表明，14700-12900 cal. yr BP期间，北大西洋暖流携带的暖水团减弱，冰岛北部陆架主要受东格陵兰寒流携带的极地冷水团的影响，春季海冰覆盖较广。12900-11700 cal. yr BP期间，印明格暖流的增强，使得研究区海冰出现时间不断缩短，偶尔出现季节性海冰的增强。11500 cal. yr BP之后，随着太阳辐射强度的不断增强，冰岛北部陆架区季节性海冰覆盖面积逐渐开始减小直至完全消失。此后，一直到中全新世时期，随着海洋环境逐渐转冷，冰岛北部海域又重新开始出现海冰覆盖。为更好的了解研究区气候及海冰变化的驱动机制，本研究运用气候耦合模型——COSMOS模型模拟了在太阳辐射增强和减弱的边界条件下，海冰覆盖度、海冰输送量及表层海水温度的变化情况，进而从物理海洋学角度分析海冰变化的影响机制。模拟结果表明，太阳辐射变化是当地海冰形成的主要驱动因素。