亚洲内陆干旱区巴里坤湖记录的H1突变事件

对亚洲内陆干旱区Heinrich (H)事件发生时的气候状况和植被响应过程的研究有利于加深对内陆干旱生态系统与气候突变事件关系的理解.本研究以新疆巴里坤湖BLK11A岩芯450~610 cm段的沉积物为研究载体,基于AMS 14C年代控制,通过岩性、粒度、 X射线荧光光谱元素钛含量( XRF-Ti)和孢粉变化特征等对H1突变事件(17~15 cal. ka B. P.)发生时流域的气候特征和植被分布状况进行了重建.研究结果表明: 1)H1时期湖泊岩性以砂质或者粉砂质的浅湖相为主,湖泊水位较低.沉积物粒度分布频率曲线表现出与流域现代扬尘一致的双峰分布特征,同时XRF-Ti含量增加,两者共同指示了流域局地扬尘发生频率增加,且对湖泊物质输入起主导作用;2)该时期耐旱的荒漠植被比例显著增加,植被覆盖度降低,流域生物量也相应降低,代表了流域植被显著退化;3)结合中纬度欧亚内陆干旱区其他地质记录,发现这一区域H1时期整体以冷干气候为主,风沙活动加强,湖泊萎缩,植被退化.主要原因为西风携带水汽的减少,使得能够到达该内陆区域的降水减少,另一方面温度降低导致了冰雪融水补给的减少,两者共同导致了内陆干旱区植被和环境的退化.

Vegetation and climate history in the arid inland area during the H1: Multi-proxy data of the Balikun Lake

Reconstructing the vegetation and climate in the arid inland areas during the Heinrich 1 (H1) event is beneficial for us understanding the relationship between arid ecosystem and abrupt climate change. We use multi-proxy analyses (e.g., lithology, gain size, LOI, XRF-Ti, pollen) of a sediment core BLK11A obtained from Balikun Lake, eastern Tienshan Mts. in Xinjiang, China, to elucidate variations in sedimentation, vegetation and climate during the postglacial, with emphasis on the H1 event. Balikun Lake (43°36'~43°45'N, 92°42'~92°54'E;1575 m a.s.l.) is located in the west of the Balikun basin. The Balikun basin is a faulted plateau basin situated in the eastern part of Xinjiang. It lies between the Balikun Mountains to the south and the Moqinwula Mountains to the north Balikun Lake is a hydrologically closed inland lake with a peculiar wetland-arid ecosystem. A number of alluvial fans are distributed in the western basin, and the Dahe River originates on the northern slopes of the Balikun Mountains, runs along the Balikun steppe to the west and finally discharges into Balikun Lake. The BLK11A core (62.5 m;43°39'51"N, 92°48'10"E) was taken from the centre of Balikun Lake in June 2011. In this study, we focus on a segment of the core between 450 cm and 610 cm to study climate change during H1 (17~15 cal.ka B. P.). The core was subsampled at 1-cm intervals in the laboratory and then freeze-dried. The chronology framework of the core was established by six accelerator mass spectrometry (AMS) 14C dates measured by Beta Analytic Inc., USA on various fractions. The results show that:(1) the H1 deposition was dominated by sandy silt or silty sand, along with the high value of XRF-Ti, both indicated a high frequency of dust storm around the Balikun Lake, which in turn brought more coarse material to the lake. Grain-size distribution of the H1 samples showed a similar mode to the modern aeolian dust collected from Balikun region.(2) Regional vegetation around Balikun Lake during the H1 was mainly dominated by desert and/or desert-steppe, with low vegetation cover reflected by the low pollen concentration, suggested a degraded environment, also the watershed bio-productivity showed a relatively low value.(3) A synchronous cold-dry climate prevailed over the mid-latitude inland areas of the Eurasia during the H1, and it caused a catastrophic drought condition along these areas with an increase in aeolian input, shrink in lake area, and degradation of vegetation. The general pattern of widespread aridity in the arid inland areas during the H1 was generally caused by decreased evaporated water vapor along the westerlies linked to the low temperature, together with limited meltwater contributions of the mountain glaciers.