Stable Isotopic Characteristics And Influencing Factors In Precipitation In The Monsoon Region Of Northern China

The ecological environment of the northern monsoon region is fragile of China,and the climate change has a great influence on the ecological environment of the region.The study of the characteristics of the oxygen isotope and the control factors of the rainfall in this area can better understand the hydrological cycle process in this area,and then understand the environmental information of the isotopic records in the geological biological carrier.Based on stable hydrogen and oxygen isotope data(δ¹⁸O,δD)and meteorological observation data for complete hydrological annual precipitation from 2016 to 2017 in the monsoon region of Northern China（Fengxiang,Ningwu and Yiyuan）,the isotopic characteristics of precipitation and the sources of water vapor in these three regions combined were studied.The results showed that δ¹⁸O and δD values in the wet season（June through September）were higher than in the dry season（October to May of the following year）in Fengxiang,Ningwu and Yiyuan.The intercept and slope of the meteoric water line in the three regions were somewhat low,revealing that the water vapor in the rainfall comes mainly from the tropical ocean.On synoptic scale,significantly positive relationships among dry-season precipitation,δ¹⁸Oand temperature manifested remarkable temperature effects,but in the wet season,the temperature effect was not exists.On monthly scale,the relationship was not exists between the change in trend of the average value of monthly weighted δ¹⁸O in precipitation and the average temperature change value in the two regions.However,in the wet season,significantly negative relationships can be found between the average monthly weighted δ¹⁸O in precipitation and rainfall amount,which indicated a remarkable rainout effect.In the dry season,D value is positive,which relate to the source of water vapor from the westerly.But in the wet season,D value in the negative,which relate to the source of water vapor from the eastern sea and the northern continent.Further investigation revealed that continuous precipitation made the values of δ¹⁸O and δD more negative under the same source of water vapor（the rainout effect）.Because the annual rainfall in the monsoon region of Northern China is mainly made up of monsoon rainfall,the oxygen isotope index of geological and biological records,such as stalagmite and tree ring,which inherit meteoric water isotope information,can be used to reconstruct past rainfall changes in northern China.