喀纳斯湖植物残体碳同位素记录的温度波动

Temperature variations over the past 600 years documented by a δ^(13)C record from terrestrial plant remains from Kanas Lake, Altai Mountains, Northwestern China

喀纳斯湖位于阿尔泰山脉南坡,区域森林植被茂盛,气候相对湿润.目前,阿尔泰山脉南坡的古温度记录主要来自于树轮宽度及短时间序列的树轮同位素,从结果来看,最近100多年来似乎没有表现出明显的增温趋势.在全球大部分地区(尤其是北半球中高纬度地区)普遍增温的情况下,是否这一区域因为某些特殊原因对全球气候变暖没有响应,抑或是该区域的树轮对长期趋势表现不明显?本文基于喀纳斯湖湖滨29 m水深处获得的81 cm岩芯,在陆生植物残体AMS ^(14)C定年的基础上,利用陆生C_3植物残体δ^(13)C序列经过大气CO_2浓度校正,探讨过去近600年区域温度对全球气候变化的响应.本文δ^(13)C序列很好地记录了阿尔泰山脉南坡对气候变暖的响应.19世纪前期以来温度在冷暖波动中持续上升;20世纪是近600年来最暖的一个世纪.这种温度变化特征与俄罗斯阿尔泰地区的冰芯、湖泊沉积物和树轮重建的温度记录以及周边地区的温度记录表现出比较一致的趋势,与北半球中高纬度地区多代用指标集成重建温度也表现出很好的一致性.此外,岩芯顶部的δ^(13)C序列表现出降温的趋势,这与近十几年来北半球许多地区出现的增温停滞现象以及喀纳斯湖邻近气象站的器测资料中表现明显的降温趋势相互印证.

Arid central Asia （ACA） is characterized by relatively dry climates and fragile ecosystems, which restrict the survival and development of human beings. A full understanding of the climatic and environmental evolution in the region is not only significant for the thorough understanding of global climate change, but is of importance for the sustainable development of the area as well, especially in the context of ongoing global warming. The Altai Mountains are located in the central part of the ACA and numerous lakes are distributed in the Mountains. Kanas Lake, one of the largest lake in the Altai Mountains of Northwestern China, is surrounded by dense forests. The climate of the area is characterized by relatively abundant precipitation and cold temperatures and the vegetations are very sensitive to climate changes. Recent temperature reconstructions based on the width and short-term series of carbon isotopes of tree-rings from the area did not exhibit an obvious warming trend during the past century. This result is unexpected in the context of ongoing global warming, but it remains uncertain whether the regional climate did not response to global warming due to complex unknown processes, or whether the tree-ring data did not record the signal of long-term warming. A 81-cm-long sediment core （KNS15E） was recovered from a water depth of 29 m near the lakeside of Kanas Lake using a modified piston corer. Here we present the results of stable carbon isotope analysis of a sequence of C3 terrestrial plant remains from core KNS15E. A chronology is constructed from five AMS 14C dates from wood fragments （twigs） and it reveals that the whole core spans the past 570 years. From the context of the sampling site, the soil of the adjacent forest would have been well-supplied with water from rainfall and snowmelt from the mountains which would have been supplied to site as ground water. In addition, based on the previous studies of carbon isotopes of tree-rings and of a-cellulose of sedge plants, the δ13C variations are likely to be mainly related to temperature changes. The raw δ13C values are corrected to pre-industrial values to account for changes in the δ13C value of atmospheric CO2 and for changes in CO2 concentration. The stable carbon isotope record provides a record of temperature changes over the last 570 years which can be clearly divided into the Little Ice Age and the Current Warm Period. The temperature increased continuously since the early 19th century and the 20th century was the warmest period in the sequence. The temperature variations revealed in our study are consistent with temperature reconstructions from ice cores, tree-rings and from Teletskoe Lake in the Russian Altai, as well as with the extratropical NH mean temperature record. In addition, a trend of decreasing temperature is indicated by the decreasing stable carbon isotope ratios of both bulk plant remains and conifer needles in the upper part of the core, which corresponds with the widely-reported phenomenon of a hiatus in global warming in central Asia and with meteorological data from the study region.