神农架大九湖四万年以来的植被与气候变化

通过对大九湖6 m长连续沉积岩芯剖面(DJH-1 孔) 7 个样品的AMS¹⁴C年龄测定和151 块孢粉样品的鉴定分析, 揭示了神农架区域4 万以年来植被和气候演变。末次冰期阶段大九湖附近发育森林草地或草地-草甸植被。MIS 3 晚期, ~42-39 cal ka BP之间, 气候相对干冷, 发育森林草地;~39-31 cal ka BP 之间, 气候较为湿润, 草甸扩张并伴随低海拔阔叶树种的发育。MIS 2 阶段, 草甸组分中蒿属显著增加, 高海拔可能分布有荒漠草地, 气候极端干冷;该时期植被带垂直下降达到1000 余m, 按垂直温度递减率推算, 冰盛期阶段该区域温度下降约7℃左右。从冰消期开始, 森林植被开始扩张, 北温带、暖温带和亚热带乔木组分依次增加。约在9.4-4 cal ka BP之间, 演变为亚热带常绿阔叶落叶林, 属全新世适宜期;从约4 cal ka BP以来, 北温带阔叶和针叶树开始增加, 气候趋于凉干。通过对比区域高分辨率的洞穴石笋及高纬冰芯氧同位素记录, 表明神农架区域植被环境变化对气候变化敏感, 并记录了H1, YD气候突变事件;进一步体现出该区域气候环境演变主要与北半球太阳辐射控制的东亚夏季风强度变化有关, 且与北半球高纬气候变化一致。

Pollen-based environmental reconstruction around Dajiuhu Lake, Shennongjia Mountains since 40 ka BP

A 6-m long core (DJH-1) was obtained from Dajiuhu lake, Shennongjia Mountains, Hubei Province. A total of 7 AMS¹⁴C dating data and the identification results of 151 pollen samples revealed the vegetation and climate changes around the study area during the last 40 ka. In the last glaciation, this region was dominated by steppe-meadow vegetation: during the late MIS3 period, it developed from forest steppe in a relatively cold-dry climate (42-39 cal ka BP) into subalpine meadow in wet conditions, associated with the growth of evergreen taxa at lower altitudes. In MIS2 phase, the meadow cover was characterized by the significant increase of Artemisia and possibly accompanied by the development of alpine desert at higher altitudes in extremely cold and dry conditions, due to the high intensification of Asian winter monsoon. Moreover, the shift of vegetation belts during the last glacial maximum indicated that the temperature dropped by about 7℃. Since the deglaciation, forest had expanded, characterized by the increase of cool temperate trees, warm-temperate tree and subtropical trees in sequence. Between 9.4 and 4 cal ka BP, it involved into subtropical evergreen broadleaved and deciduous forest, with the expansion of swamp vegetation, probably corresponding to the Holocene optimum. After ~4 cal ka BP, the increase of cool temperate and coniferous trees suggested that the climate tended to be cool. By comparison with Oxygen Isotope sequences of stalagmites (Hulu and Sanbao caves) in East Asia and ice core (NGRIP) at higher latitude, the results show that the past vegetation changes of Shennongjia area responded sensatatively to the climate changes, and DJH-1 pollen record also recorded H1,YD abrupt events, which further indicate that the past changes in the study area was closely related to the variability of EAM mainly controlled by north hemisphere insolation, and concided with the global changes.