摘要
青藏高原现代季风边缘区中晚全新世气候重建存在较大的差异，对位于青藏高原东北部共和盆地更尕海的GGHA孔岩芯进行了孢粉分析（平均分辨率为80年，最高分辨率约10年），重建了过去6．3ka以来区域植被和气候的演化历史。6．3cal．kaB．P．以来盆区广泛发育以蒿属、藜科和禾本科为主的荒漠植被，以及一定面积的以禾本科和蒿属为主的草原植被，其中：1）6．3—5．6cal．kaB．P．，盆区周围山地发育有少量以松属为主的针叶林，此时夏季风较强，低A／C值指示湖区相对湿度偏低，但湖区周围仍有小面积沼泽草甸发育；2）5．6—4．1cal．kaB．P．，乔木花粉含量显著降低表明周围山地森林面积逐渐减小，至4．1cal．kaB．P．山地森林已衰退消失，盆区草原和荒漠面积有所扩大，莎草科花粉含量低指示湖泊周围沼泽草甸面积缩小，A／C值指示总体湿度有增加趋势；3）4．1～3．1cal．kaB．P．，周围山地森林不再发育，湖区湿度剧烈波动，湖泊周围沼泽草甸发育停滞；4）3．1cal．kaB．P．以来，蒿属和莎草科含量呈下降趋势，A／C值逐渐降低指示干旱化程度加深，以藜科为主荒漠草原面积增加并伴随以禾本科和蒿属为主的草原面积减小，麻黄和白刺含量有所增加，说明研究区气候较前一阶段更加干旱。中晚全新世以来盆区气候和盆区周围山地森林的衰退可能与夏季太阳辐射的降低以及与之相关的亚洲夏季风减弱有关。
Paleoenvironmental studies are essential for understanding the future climate changes and their impacts on our environment. A key area for investigating long-term environment changes is the Tibetan Plateau （TP） because the environmental changes of TP are highly sensitive and strong effect to climate changes. The Gonghe basin is an intermontane basin on the northeastern TP, which is influenced by Asian monsoon and westerly. Due to its unique topography, the past palaeoclimate studies in this region show a complicate humidity pattern during the Mid-Late Holocene. Genggahai Lake （ 36° 10′50″N- 36°11′57″N, 100°05′33″- 100°07′33″E ; 2858m a. s. l.） , a shallow grass- type lake in the Gonghe basin, includes Upper Genggahai Lake and Lower Genggahai Lake. The Lower Genggahai Lake is nearly desiccated, connecting with Lower Genggahai Lake through groundwater. The Upper Genggahai Lake has a surface area of about 2km2. A 782-cm-long drilling core （GGHA） and a 750-cm-long drilling core （GGHB） were obtained from the center of Genggahai Lake （36°11′2″N, 100°06′15″E）. By comparing their grain-size and magnetic susceptibility profiles, the missing sediments from core GGHA were supplement by corresponding sediments in core GGHB. The 12 samples of aquatic plant macrofossil were selected for Accelerated Mass Spectrometry （AMS） 14C dating. In this study, we select a total of 85 samples from the upper part of the core GGHA range from 0 to 581m, which were performed for pollen analysis to detect vegetation compositions and climate changes on Gonghe basin since 6.3cal. ka B.P. The pollen data from Genggahai Lake suggested that the study area was mainly covered by desert steppe/steppe vegetation dominated by Artemisia, Amaranthaceae （Chenopodiaceae） and Poaceae over the last 6.3cal.ka. （1）From 6.3cal.ka B.P. to 5.6cal. ka B.P., the montane forest, surrounded the Gonghe basin, was composed by conifer （Pinus）. Slightly high percentage of Cyperaceae pollen possibly reflects a small area of wetland around the lake. In addition, a low A/C ratio indicated a low relative humidity during this period. （2） The montane forest decline started at 5.6cal. ka B.P. and disappeared at 4.1cal.ka B.P., accompanied by expanding Artemisia-dominated steppe/desert steppe and shrinking Cyperaceae- dominated swamp meadow. The increasing value of A/C ratio indicated that the climate inside the Gonghe basin became relatively humid during this period. （3）During the 4.1 -3.lcal.ka B.P., the variable A/C ratio indicated highly fluctuated humidity in study region. Local vegetation was still covered by steppe and desert steppe, and the swamp meadow degraded because of limited moisture. （4）After about 3. l cal.ka B.P., the deceasing percentages of Cyperaceae and Artemisia and the increasing percentage of Ephedra and Nitraria （typical arid plants） illustrated that the climate was more arid than former stage. The vegetation surrounding Genggahai Lake was mainly desert steppe, and the area of steppe, dominated by Artemisia and Poaceae, was decreasing. Generally, our research has an important implication for understanding the long-term vegetation history responses to climate forcing on the northeastern TP. The pattern of vegetation changes indicates a drying climate trend, consistent with other independent climate records in relation to a weakening summer monsoon and decreasing summer insolation during the Mid-late Holocene. And, the regional humidity is responsible for forest decline during this period.
出处
《第四纪研究》
CAS
CSCD
北大核心
2016年第2期247-256,共10页
Quaternary Sciences
基金
国家重点基础研究发展规划项目（973项目）（批准号：2012CB956102）和国家自然科学基金项目（批准号：41171168和41271219）共同资助
致谢宋磊等参与野外岩芯取样工作,特此感谢.
关键词
共和盆地
更尕海
孢粉
植被
气候变化
中晚全新世
Gonghe basin, Genggahai Lake, pollen, vegetation, climate change, Mid-Late Holocene
