Grain-size of Organic Debris in Sediments from Wudalianchi Crater Lake in Heilongjiang Province Record the Evolution of Summer Monsoon Precipitation at Millennial-to Centennial-Scale in the Early Holocene
目前已在我国大量地质记录中发现全新世早期的千百年尺度气候事件,但较高纬度地区相应的记录仍较少。因此,有必要在我国较高纬度地区进行千百年尺度气候事件的重建。本文对五大连池火山口湖沉积物进行研究,以精确的14C年代框架为基础,对沉积物(未去除有机残体)粒度数据进行粒级-标准偏差分析,提取了 >83 mum敏感粒级,发现该粒级主要成分为有机残体,其粒度和含量可作为夏季风降水代用指标,进而利用该组分重建了我国东北地区早全新世夏季风降水演化历史。结果表明,我国东北地区早全新世季风降水频繁波动,存在 ~ 8.6 ka, 9.2 ka, 10.2 ka和11.6 ka四次千百年尺度显著弱夏季风事件。在年代误差范围内,四次弱夏季风事件与我国季风区其他气候记录、北大西洋冰筏沉积及太阳活动记录在时间上均有较好的一致性,指示早全新世千百年尺度干旱事件在我国季风区普遍存在,且与北大西洋浮冰事件及太阳活动密切相关。但五大连池火山口湖有机残体粒度记录的四次千百年尺度弱夏季风事件持续时间明显短于其他气候记录中的相应事件,初步推测为北大西洋浮冰事件通过影响热带季风进而影响较高纬度地区,季风信号从低纬传输至高纬变弱,致使事件持续时间明显缩短。
英文摘要:
Millennial- to centennial-scale climate events in the early Holocene have been detected from numerous geological records in China,but records in high latitudes are still limited. Therefore,it could contribute to this research if such records are reconstructed in higher latitude regions of China. In the present study,grain sizes of a sediment core retrieved from a crater lake in Northeast China were analyzed. Sensitive grain size component of >83 mum was extracted by analyzing the grain size versus standard deviation curve of sediment,organic debris was not excluded. This component was mainly organic debris and can be used as a proxy of summer monsoon precipitation. Based on chronology from precise 14C dates and the results of grain size analysis,a sequence of early Holocene summer monsoon precipitation in Northeast China was reconstructed. The results indicate that early Holocene monsoon precipitation in Northeast China fluctuated frequently with four millennial to centennial weak events of summer monsoon at ~ 8.6,9.2,10.2 and 11.6 ka BP. All of these weak monsoon intervals corresponded well with those in other climate records within chronological errors,e. g. records from the monsoon regions of China, North Atlantic ice-raft events and the solar activity records. The synchronicity of these records suggests widely spread drought events at millennial-to centennial-scale in the monsoon regions of China,and might link closely to the North Atlantic ice-raft events and solar activity. However,the durations of the four weak summer monsoon precipitation events recorded by grain sizes in the Wudalianchi lake sediments were significantly shorter than those in other climate records. One possible explanation is that the North Atlantic ice-raft events impacted high latitude regions via summer monsoon,while monsoon signal weakened gradually from low latitudes to high latitudes, resulting in the shorter duration of the events in our record.