低纬西太平洋末次冰期以来海洋孢粉记录对海平面变化的不同响应

摘要

通过对菲律宾南部MD06-3075和婆罗洲东北部MD98-2178两个深海钻孔的孢粉分析,结合氧同位素记录以及西太平洋地区已有的孢粉记录,得到末次冰期研究区域海洋孢粉中的红树林花粉和蕨类孢子含量比间冰期时要低,特别是在末次冰盛期.这可能体现了冰期时海平面较低,湿度较低等环境和气候条件.同时,西太平洋一系列海洋孢粉记录的对比发现,南海南部陆坡地区冰期时的红树林含量仍然较高,巽他陆架等地区冰期时的蕨类孢子含量则表现为明显高值.这些记录的差异可能说明了由于不同地区的地形分布特征不同,在冰期海平面下降时,导致陆架出露的幅度存在明显的差异.如果陆架较宽,则海平面波动会显著改变植被分布范围和孢粉传播距离等,从而对孢粉数据的气候、环境指示意义产生影响.因此,海洋孢粉数据解释时需要结合多种沉积记录指标以及地球物理调查等,提高海平面变化以及相应的沉积环境演化对孢粉搬运沉积的了解程度,增强海洋孢粉中古气候、古环境信息的有效提取.%The climate change in the low latitude area since the last glacial is one of the most hotspot for Quaternary climate research. Meanwhile,the tropical vegetation has a good correspondence with tropical climate change,and it is one of the major factors controlling the climate modeling as well as the environment prediction. But marine pollen record, which was used to reconstruct the history of climate and environment change, reflects not only vegetation state of source area,but also the changes in pollen deposition. The sea-level change would influence the deposition pattern of the marine pollen, especially the mangrove pollen and fern spore, which will make the interpretation of the sedimentation records produce a great deviation with the actual climate and environment condition. It is thus essential to understand the relationship between the sea-level change and the marine pollen record, mainly the mangrove pollen and fern spore record. In this study, the palynological analysis of two marine core, MD06 -3075 (06. 4762°N,125. 8322°E;1878m water depth,30. 76m in length) in the southern Philippines and MD98-2178 (03. 6200°N,118. 7000°E; 1984m water depth, 35.6m in length) in the north East Borneo, the detailed oxygen isotope records, and other marine pollen records in the West Pacific, provide the regional vegetation and climate history since the Last Glacial. Based on AMS C dating and plankton foraminifera oxygen isotope record, the core MD06-3075 covers last 52ka,and the core MD98-2178 covers last 92ka( pollen analysis includes records of the last 77 ka) . The palynological record shows low representation of mangrove pollen and fern spore during the glacial period,indicating lower sea level and drier climate condition during the glacial period than the deglacial period, especially the Last Glacial Maximum. However,through the comparison of marine pollen records in the West Pacific area,there are some different pollen records in the southern South China Sea. It shows significantly high value of mangrove pollen from a marine core in the slope area and fern spore from marine core in the Sunda Shelf. These differences may be caused by the drop of sea level change,which lead to the explosion of the Sunda Shelf and the changes of vegetation distribution and distance between vegetation source and deposition point. Therefore, the interpretation of marine pollen data should be combing with the multiple sedimentary index and the geophysical survey record, which would raise the recognition of the influence of sea level change and the corresponding sedimentary environment evolution on marine pollen transportation and deposition, enhancing the extraction of the paleoclimate and paleoenviroment information from the marine palynology.