中世纪温暖期气候变化的花粉化石记录

麦里泥炭剖面高分辨率花粉化石记录表明，东北科尔沁沙地在相当于中世纪温暖期阶段夏季降水量曾显著增加，主要表现为沙丘上的乔木和草本植物均获得了繁茂的生长，花粉沉积速率明显上升。作者推测，在中世纪温暖期中，欧亚大陆作为一个整体夏季温度可能暖于今天，这可能通过增强夏季风环流使中国东北夏季雨量增多，为沙丘植物茂盛生长提供了有利条件。

Climate of the Medieval Warm Period in Maili Region as Inferred from Fossil Pollen Record

In a high-resolution pollen record from Maili Bog, Northeast China, the period from 1000 a BP to 660 a BP stands out as a unique one characterized by the increased pollen concentration and lush growth of plants. It is impossible that the relaxation of human interference stress is the cause for the change, because the population density and intensity of agriculture activities in Liao Dynasty and Jin Dynasty were much larger than the previous periods. The close correspondence of the event with the Medieval Warm Period in the start and end dates, the simultaneous rise in both tree and herb pollen influx in the period, with that of the trees being slightly more obvious,and the modern relationship between sand land plants and climate in the region all call for an explanation involving in a change in precipitation or dryness.Summer rainfall in the Medieval Warm Period had to experience a marked increase for the improved plant growing condition. The documentary records about forest, agricultural harvest and sand dune status, as well as the fossil pollen evidence from the neighboring regions,are generally in favor for the above explanation.A possible mechanics for the rainfall increase is the rise of summer temperature over Eurasia as a whole,which leads to a more vigor summer monsoon circulation in the temperate East Asia.