南海北部MD05-2904站位2万年以来孢粉记录的古环境演变

Paleoenvironmental change base on a pollen record from deep sea core MD05-2904 from the northern South China Sea during the past 20000 years

为了探讨末次冰盛期以来南海北部陆架及周边陆地上的植被演化,选取大陆坡处MD05-2904站位岩芯顶部0～749 cm(80～19189 cal a BP)深海沉积物进行研究,共分析122个孢粉样品,时间分辨率约为157 a.根据孢粉组分的变化,自下至上划分了3个组合带,P1带(749～479 cm,19.2～15.1 cal ka BP)末次冰盛期,大陆架广泛出露,其上覆盖以蒿属为主的草地,同时生长着热带亚热带乔木并偶见莎草科植物茂盛的湿地,北部山地覆盖针叶林且顶部主要生长以铁杉为主的暗针叶林;P2带(479～309 cm,15.1～11.4 cal ka BP)冰消期,草地面积逐渐缩小,同时蕨类植物开始增多,反映气候转暖转湿;P3带(309～1 cm,11.4～0.1 cal ka BP)全新世,植被以常绿落叶阔叶林为主,局部山地上生长着热带山地针叶林,林下广泛分布着喜暖湿的蕨类植物,反应了南亚热带气候环境.值得注意的是,该组合带底部(309～263 cm,11.4～10.1cal ka BP),蒿属、莎草科等草本、部分喜凉的温带乔木及水生植物等花粉迅速增加,揭示了一次冷湿气候事件.对比该站位氧同位素变化,孢粉组合变化所反映的气候变暖,要早于氧同位素变化,可能表明低纬地区冰消期气候转暖超前于高纬地区.

This paper presents the palynological record of deep sea core MD05-2904 （top 749 cm of the sequence, 80-19189 cal a BP） from the South China Sea （SCS）. Base on pollen data from the core, the vegetation type and climate history were reconstructed for the last 20000 years. During the Last Glacial Maximum （zone P1, 749479 cm, 19.2-15.1 cal a BP）, vegetation assemblages were dominated by a large number of herbs, some tropical-subtropical arboreal taxa and some cyperaceous plants, which grew in local wetlands in some exposed areas of the SCS shelf. The northem hills were covered with a large number of conifers. Dark coniferous forests dominated by the hemlock were found on the top of mountains, which indicate that the climate was relatively cold and dry. During the last deglacial period from 15.1-11.4 cal ka BP （zone P2, 479-309 cm）, the sea level rose continuously and the SCS shelf was gradually submerged. In addition, the herbaceous spectrum gradually decreased, suggesting a rise of temperature and humidity. During the Holocene （zone P3, 309-1 cm, 11.4--0.1 cal ka BP）, vegetation assemblages were dominated by broad-leaved evergreen forests. Tropical montane coniferous forests were distributed in the surrounding hills. Under the forest canopy, pteridophytes grew as a response to a southern subtropical climate. However, during of the time when the 309-263 cm interval was deposited （bottom of zone P3, 11.4-10.1 cal ka BP）, the percentage of herbaceous and aquatic plant pollen increased, particularly that of Artemisia and Cyperaceae. This implies that there was a substantial drop in temperature, and an increase in moisture. From comparing deep sea oxygen isotopes data, the deglacial warming seems to have been earlier in low-latitude regions than in high-latitude regions of the Northern Hemisphere.