福建晋江龙湖中晚全新世沉积的环境意义

Environmental significance of Longhu lake sediments in the Middle and Late Holocene,Jinjiang,Fujian

为研究福建沿海的全新世气候环境变化,对取自晋江龙湖的柱样进行了沉积相、粒度、磁化率、有机碳、有机氮等分析,结合加速器14C测年结果,对龙湖的形成演化以及该地区中晚全新世的气候环境变化进行了研究。认为,龙湖形成于约5580cal.a.B.P.,之前为河流相沉积;约5580～850cal.a.B.P.,该区为深灰色粉沙和砂质粉沙的湖泊相沉积;约850～470cal.a.B.P.,龙湖水位下降,变为沼泽湿地;之后,湖泊水位再次上升,再次形成湖相沉积。各种气候环境指标分析结果显示,自龙湖形成以来,当地的气候呈阶段性相对干、湿变化,并呈变化幅度逐渐减小的趋势。这一方面反映了福建沿海中晚全新世气候的不稳定性,还反映了当地气候环境变化与太阳辐射的长周期变化有关。沼泽湿地的形成,反映当地降水的进一步减少,而湿地的形成年代,可与太阳活动、北大西洋冰筏、亚洲季风等突发事件对比,说明该沼泽层的形成与叠加在气候长期变化趋势下的突发气候事件有关。龙湖沉积记录也表明,气候变冷,福建沿海与台风有关的降水将减少;反之,全球变暖,福建沿海台风降水将增加。

To retrieve the Holocene history of climatic and environmental changes in the coastal area of Fujian Province, we conducted a multi-proxy survey of a lake core （e. g., grain size, magnetic susceptibility, C/N ratio） of the core from the Longhu Lake in Jinjiang with a chronological support of three AMS dates. The chrono-stratigraphic data show that the Longhu Lake was initiated from a floodplain at about 5580 cal. a. B. P. and lasted for about 4370 years （till about 850 cal. a. B. P）. The lake transformed to a marsh at about 850 cal. a. B. P and the marsh then reverted to a lake at about 470 cal. a. B. P. The record of the past about 400 years is absent because the corresponding sediments were removed by a massive dredging in 1958. The proxy data indicate that the climatic wetness fluctuated relatively dramatically since the formation of Longhu Lake in Fujian coastal area. They also show that typhoon-related precipitation intensity has been decreasing for the past 5500 years, suggesting that the declining trend in the intensity of typhoon might have resulted from the declining trend of the solar insolation. The marsh sediment indicates that the precipitation decreased further. According to the AMS ^14C data, the date of marsh environment can be correlated to the events of the Sun activity, the ice raft, Asian monsoon and so on, indicating that the formation of the marsh was related to the global abrupt climate event which was superimposed on the long timescale natural climatic changes. The sediment records from Longhu Lake suggest that during the cold periods the precipitation related to typhoon along the coastal area of Fujian decreased, and vice verse, the global warming will cause the increase of typhoon precipitation there.