Spatial Distribution Of Marine Water Vapor Stable Isotopes And Climatic Significance Of The South Arctic Scientific Research Route

Hydrogen and oxygen stable isotopes are an important part of water molecules.Although they only account for a small proportion in natural water bodies,they are distributed in all links of the water cycle through evaporation,water vapor transport,precipitation and runoff.They are important tracers for studying the process of the water cycle.Great progress has been made in the study of stable isotopes of precipitation,but precipitation is the final product of evaporation,water vapor transport and other links.There are limitations in the analysis of water vapor movement based on stable isotopes of precipitation.Stable isotopes of water vapor can be used to comprehensively analyze the source,transport and supply of water vapor,so as to better understand the water cycle and its feedback mechanism,which has become a research hotspot in the field of geochemistry.Most of the previous studies were limited to fixed-point monitoring on land,and the stable isotopes of water vapor in the ocean have been carried out in succession,but so far,the stable isotopes of water vapor in the Pacific are still blank.Based on the observation results of stable hydrogen and oxygen isotopes of water vapor in the offshore ocean of picarro instrument on the 8th Arctic scientific expedition and the 35th Antarctic scientific expedition,this paper establishes a set of calibration and processing methods suitable for the route measurement.Based on the calibrated data,the spatial distribution laws of stable hydrogen and oxygen isotopes of water vapor and excess deuterium are analyzed,and the indicating significance of stable isotope water cycle of atmospheric water vapor in the offshore ocean is discussed,The main conclusions are as follows:1.Based on the water vapor hydrogen-oxygen stable isotope observation data of the Picarro instrument on the 8th Arctic Scientific Expedition and the 35th Antarctic Scientific Expedition,a set of mass-calibrated hydrogen-oxygen stable isotope databases were formed by memory effect,concentration effect,random error correction and ignored drift effect（because no obvious positive or negative drift was found in the observation data）.2.the North-South polar scientific research route has a large latitude span,mainly passing through the Pacific Ocean,the Arctic Ocean and the Southern Ocean.The meteorological elements are complex,and the hydrological characteristics are variable.The stable hydrogen and oxygen isotopes of water vapor in the near sea atmosphere show a law of variation with latitude.The spatial distribution characteristics of stable hydrogen and oxygen isotopes of water vapor in the northern and southern hemispheres are basically the same,and both decrease with the increase of latitude.However,the dependence of stable hydrogen and oxygen isotopes of water vapor in the southern hemisphere on latitude is much lower than that in the northern hemisphere.The R²of the fitting equation between stable hydrogen and oxygen isotopes of water vapor and latitude in the southern hemisphere is lower than 0.3,while the R²of the fitting equation between stable hydrogen and oxygen isotopes of water vapor and latitude in the northern hemisphere is higher than 0.65,This may be due to the wide distribution of the oceans in the southern hemisphere,resulting in a small change in temperature compared with the northern hemisphere.In the subtropical high pressure zoneδ¹⁸O andδD value is the highest,over the sea ice along the Continental Coast at high latitudesδ¹⁸O andδD is extremely low,which reflects that the mixing of ocean water vapor and water vapor from the mainland and the sublimation of sea ice snow are important factors affecting the changes of water vapor isotopes in the atmospheric boundary layer.3.the spatial distribution of excess deuterium in the atmospheric water vapor near the sea surface is just opposite to that of stable isotopes of hydrogen and oxygen.The excess deuterium increases with the increase of latitude,and a relatively low value appears near the subtropical high pressure zone,while a very high excess deuterium value appears at the edge of the continental ice sheet at high latitudes.In the southern hemisphere,excess deuterium is significantly correlated with relative humidity and sea surface temperature,but not with wind speed.In the Indian Ocean,excess deuterium is only highly correlated with sea surface temperature,but not with relative humidity and wind speed.The tropical waters of the route mainly pass through the Indian Ocean,and the relative humidity of water vapor in almost half of the time exceeds 90%（equivalent to the relative humidity of water vapor samples reaching 100%）,which may affect the correlation between excess deuterium and relative humidity to some extent.4.The HYSPLIT model is used to simulate the backward trajectory of the air mass.It is found that the downdraft in the subtropical high pressure zone can convert the water vapor pressure to the degree of supersaturation,thus forming a relatively high value of stable isotopes of water vapor hydrogen and oxygen near the subtropical high;At the high latitude continental margin,the air mass mainly comes from the polar continent.Due to the dynamic fractionation caused by the strong evaporation on the sea surface,there is a high excess deuterium value.