湖光岩玛珥湖全新世时期沉积物碳氮同位素组成的环境指示意义

δ~13C and δ~15N in the Sediments of Huguangyan Maar Lake as Proxies for Reconstructing Paleo-productivity and Paleo-environment in the Holocene

通过对湖光岩玛珥湖沉积物的TOC，TN，δ13C，815N和s—ratio的研究，作者重建了全新世期间湖泊初级生产力的变化，从而揭示了湖光岩地区全新世气候演变历史。早全新世时期（10400～6100yrBP），高值的TOC，TN，δ13C和低值的δ15N，s-ratio指示了高水平的湖泊初级生产力，反映温暖湿润的气候条件；8500～7400yr BP期间，815N出现最低值，同时TN出现高值，表明可能受了固氮蓝藻的影响，指示该段时间季风减弱，可能为对应着8．2ka事件；中全新世期间（6100—3600yrBP），TOC，TN和δ13C下降，s-ratio上升，指示湖泊生产力下降，气候逐渐向冷干转变；晚全新世期间（3600yr BP至今），TOC和TN继续下降，δ13C处于最低值，s-ratio达到最大值，代表季风最弱的时期和湖泊生产力持续降低。全新世湖泊生产力的逐渐下降反映了季风的逐步减弱，而驱动因素则是北纬30°太阳辐射的减少。在～1000yrBP以后，δ13C与815N表现出不同于全新世演化趋势的异常，可能指示人类活动的加剧，尤其是烧荒开田对沉积物的影响。

We analyzed the total organic carbon （TOC）, total nitrogen （TN）, bulk organic matter δ13C, and δ15N as well as magnetic index s-ratio in the sediment of Huguangyan Maar Lake in order to reconstruct the lake paleo-productivity and paleo-environmental changes through the Holocene. We divide the I-Iolocene into three stages. The early Holocene （10400~6100 yr BP） is characterized by high TOC, high TN, high δ13Coc and low δ15N as well as low s-ratio, reflecting a high primary productivity and a warm and wet climate; The lowest values of δ15N coupled with high TN during 8500 to 7100 yr BP might be attributed to the expansion of nitrogen-fixation cyanobacteria. During the mid-Holocene （6100~3600 yr BP）, TOC, TN and δ13CToc decreased while δ15N and s-ratio increased, suggesting a decreasing primary productivity and a cooler and drier climate. The late Holocene （3600 yr BP to present） is the coolest and driest period of the Holocene, indicated by the constantly low TOC, TN and saturated s-ratio （-1）. Such trend indicates gradually weakened summer monsoon driven by decreasing summer solar radiation at 30°N through the Holocene. The α13CToc was low and δ15N was high before 1000 yr BP. However, their variations after 1000 yr BP are not consistent with the Holocene climate trend, and are probably a result of anthropogenic activity.