广东湖光岩玛珥湖沉积物漫反射光谱数据反映的全新世以来古环境演化

利用漫反射光谱技术得到湖光岩玛珥湖沉积物的叶绿素a浓度.通过与TOC、Sr/Rb比值和磁化率的对比发现,叶绿素a浓度能够忠实地反映湖泊初级生产力的变化,较高的叶绿素a浓度代表季风较强、降雨量较高,反之亦然.湖光岩玛珥湖沉积物多环境代用指标分析结果显示,湛江地区早全新世季风强盛,中全新世季风迅速衰退.这种全新世季风演化模式与北半球季风区的很多地质记录以及北纬30°变化趋势相似,反映了太阳辐射是湛江地区千年尺度季风演化的主要驱动因素,但是湛江地区的季风演化滞后于太阳辐射变化大约2200 a.叶绿素a浓度记录显示6000 a BP左右季风迅速减弱,这与其他记录显示的季风渐变模式不同.一方面,太阳辐射渐变激发了湛江地区植被-大气圈的负反馈作用,这可能是造成6000 a BP左右气候迅速变干的原因之一;另一方面,沉积速率增加导致的稀释作用放大了叶绿素a浓度下降的趋势.3600 a BP以来的沉积环境可能受到了人类活动的影响.

Paleoenvironment evolution since the Holocene reflected by diffuse reflectance spectroscopy from Huguangyan Maar Lake sediments, Guangdong Province

Chlorophyll-a concentration of Huguangyan Maar Lake sediments were determined by diffuse reflectance spectroscopy. Through comparison with TOC, Sr intensity and magnetic susceptibility we concluded that chlorophyll-a can be taken as a reliable proxy of primary production, higher chlorophyll-a absorption reflects stronger monsoon intensity and higher precipitation, and vice versa. Holocene environment evolution at Zhanjiang area reconstructed by chlorophyll-a, TOC, Sr intensity and magnetic susceptibility of Huguangyan Maar Lake sediments demonstrated that the monsoon intensity in Zhanjiang area was strong in the early Holocene and declined dramatically since 6000 a BP. Holocene climate evolutional pattern at Zhanjiang area is similar with many other records from the monsoonal areas of the North hemisphere and summer isolation at 30°N, implying that solar isolation is the driving force of millennial-scale Holocene monsoon evolution at Zhanjiang area. However, monsoonal evolution lags behind solar isolation by about 2200 a. Monsoon strengthen demonstrated by chlorophyll-a declined significantly since 6000 a BP. Nonetheless, all the other records display gradual weakening process. Negative feedback of vegetation-atmosphere induced by solar isolation might have caused quick droughty trend, on the other hand, dilution effect led by increased sedimentary rate may amplify declining trend of chlorophyll-a around 6000 a BP. Sedimentary environment since 3600 a BP could be impacted by human activities.