Study On The Peat Sediment Record In Fujian Mountains Since Late Holocene

The last 2000 years are an important bridge to connect the past geological time and the modern rich observation data period, so choosing the suitable area and index to study the recent climate change process in the last 2000 years is of great significance for predicting the future climate change. Fujian province is a typical region of East Asian monsoon, its topography is mainly mountainous and hilly terrain, what's more, the mountain basins are flat and parts of them have the typical peat deposits, so it's a good carrier to record the information of climate change. This paper chooses peat sections of Xianshan in Pingnan and Tianbaoyan in Yongan as the research objects. Through analysis of peat cellulose carbon isotope (?13C)?chroma?moisture content and magnetism and other environmental proxies, the past lka environmental evolution process of the study areas was reconstructed, and the possible mechanism of the regional climate environment evolution process was discussed. Draw the conclusion as follows:(1) Xianshan basin drilling 358cm, according to AMS14C data, its bottom boundary is in AD 600a. According to the analysis of the ?13C, the following three stages were divided:AD 600-910a, the ?13C is lighter, indicating that Xianshan basin is in the peat swamp sedimentary environment during this period; AD 910-1640a, the ?13C is heavier, and two partial lighter phases existed, but the overall value is relative heavier, indicating the growth of more submerged vegetation; from AD 1640a to now, the ?13C is lighter in this stage, and have small amplitude fluctuations, indicating the herbaceous peat swamp depositional environment.(2) Tianbaoyan basin drilling 97cm, according to AMS14C data, its bottom boundary is in AD 800a. According to the analysis of the ?13C, the following three stages were divided:AD 800-1300a, the ?13C is heavier, indicating that the growth of submerged vegetation; AD 1300-1600a, the ?13C is lighter, showed that the C3 vegetation was lush, indicating that swamp sedimentary environment in this stage. From AD 1600a to now, the ?13C is heavier than that in the first stage but lighter than that in the second stage, indicating that part of submerged vegetation residues floated in this stage.(3) According to the survey of region, the mountain basin is located in a high altitude, no rivers flow into the basin, the basin mainly rely on precipitation recharge, so the development of the peat and its sedimentary environment changes are mainly controlled by regional precipitation. Based on this, the precipitation change in past lka of the study area is mainly divided into the following 3 stages:Xianshan:AD 600-910a, the peat cellulose ?13C of the overall performance is lighter, the value TOC% also is high, as the typical peat swamp sedimentary environment, indicating less precipitation; AD 910-1640a,?13C of the overall performance is heavier, showing that the increase of aquatic plants in the basin, indicating more precipitation in this stage; and magnetic susceptibility is also high, indicating severe erosion and the transporting of magnetic minerals from the surrounding to the basin, meanwhile, it also shows the overall precipitation was abundant; From AD 1640a to now,?13C is lighter, the value TOC% also is high,the magnetic susceptibility value is low, proved this stage less precipitation, less debris erosion. Tianbaoyan:AD 800-1300a,?13C is heavier, indicating the growth of submerged vegetation and the abundant rainfall; AD 1300-1600a,?13C is lighter, showed that the C3 vegetation was lush and less precipitation; From AD 1600a to now, the ?13C is slightly heavier than that of the second stage, indicating that small precipitation increasing.(4) Through the analysis of carbon isotope comparison, founding that the sequence of climatic variation reflected by peat profiles of Xianshan and Tianbaoyan has a good corresponding relationship in a decade to century scale:AD 900-1300a (MWP), the two regional indexes prove the abundant rainfall; AD 1300-1800a (LIA), prove the less rainfall, Xianshan profiles humid fluctuations is severe and Tianbao rock profile almost no fluctuations; From AD 1800a to now, the precipitation in the Xianshan region was still relatively small, and that in Tianbaoyan region precipitation increased. Through the comparative analysis of precipitation change and solar activities, founding that in the ten years-hundred years time scale they have positive correlation, When the solar activity decreased, the precipitation in the study area decreased, reflecting the climate change of the mid low latitude subtropical monsoon region has a good response to the solar activity, which provides a basis for predicting the future trend of precipitation in the region.