ALBERT

Description: In the context of the Arctic amplification of climate change affecting the regional atmospheric hydrological cycle, it is crucial to characterize the present-day moisture sources of the Arctic. The isotopic composition is an important tool to enhance our understanding of the drivers of the hydrological cycle due to the different molecular characteristics of water stable isotopes during phase change. This study introduces 2 years of continuous in situ water vapour and precipitation isotopic observations conducted since July 2015 in the eastern Siberian Lena delta at the research station on Samoylov Island. The vapour isotopic signals are dominated by variations at seasonal and synoptic timescales. Diurnal variations of the vapour isotopic signals are masked by synoptic variations, indicating low variations of the amplitude of local sources at the diurnal scale in winter, summer and autumn. Low-amplitude diurnal variations in spring may indicate exchange of moisture between the atmosphere and the snow-covered surface. Moisture source diagnostics based on semi-Lagrangian backward trajectories reveal that different air mass origins have contrasting contributions to the moisture budget of the Lena delta region. At the seasonal scale, the distance from the net moisture sources to the arrival site strongly varies. During the coldest months, no contribution from local secondary evaporation is observed. Variations of the vapour isotopic composition during the cold season on the synoptic timescale are strongly related to moisture source regions and variations in atmospheric transport: warm and isotopically enriched moist air is linked to fast transport from the Atlantic sector, while dry and cold air with isotopically depleted moisture is generally associated with air masses moving slowly over northern Eurasia.

Description: In the context of the Arctic amplification of climate change affecting the regional atmospheric hydrological cycle, it is crucial to characterize the present-day moisture sources of the Arctic. The isotopic composition is an important tool to enhance our understanding of the drivers of the hydrological cycle due to the different molecular characteristics of water stable isotopes during phase change. This study introduces 2 years of continuous in situ water vapour and precipitation isotopic observations conducted since July 2015 in the eastern Siberian Lena delta at the research station on Samoylov Island. The vapour isotopic signals are dominated by variations at seasonal and synoptic timescales. Diurnal variations of the vapour isotopic signals are masked by synoptic variations, indicating low variations of the amplitude of local sources at the diurnal scale in winter, summer and autumn. Low-amplitude diurnal variations in spring may indicate exchange of moisture between the atmosphere and the snow-covered surface. Moisture source diagnostics based on semi-Lagrangian backward trajectories reveal that different air mass origins have contrasting contributions to the moisture budget of the Lena delta region. At the seasonal scale, the distance from the net moisture sources to the arrival site strongly varies. During the coldest months, no contribution from local secondary evaporation is observed. Variations of the vapour isotopic composition during the cold season on the synoptic timescale are strongly related to moisture source regions and variations in atmospheric transport: warm and isotopically enriched moist air is linked to fast transport from the Atlantic sector, while dry and cold air with isotopically depleted moisture is generally associated with air masses moving slowly over northern Eurasia.

Description: Land and atmosphere processes influence the isotopic composition of water vapor during winter. Depending on climatic conditions, stable isotope fractionation occurs during each phase change. Thus, isotopes are valuable proxies for air temperatures and tracers of atmospheric moisture. Hourly data records from 01 July 2015 to 30 June 2016 of meteorological and soil parameters and of water vapor isotopic composition from Samoylov Island, Lena Delta, Siberia at 72°22’ N, 126°29’ E, were investigated to observe local environmental processes during winter and correlations between land, atmosphere, and water vapor isotopes. Winter was defined by the presence of snow (23 September 2015 to 15 May 2016). During winter, water is present in gaseous, liquid, and solid state. The latter was identified in frozen ground, as the active layer froze from 21 October 2015 to 05 June 2016, and on water bodies, as Molo Lake on Samoylov Island had an ice cover from 29 September 2015 to 21 June 2016 and the Lena River had an ice cover from 07 October 2015 to 06 June 2016. Liquid water was though available under the ice cover of Molo and the Lena River. The air was with a mean specific humidity of 1.4 g/kg very dry during winter. Also both δ18O and δD were very low during winter, with means of -41.3‰ for δ18O and -299.6‰ for δD. But large ranges of δ18O and δD were especially observed during four periods of long-term peaks with δ values up to -27.4‰ for δ18O and -201.0‰ for δD on 27 April 2016. This variability is mostly caused by changes of local air temperatures and humidity levels. With 30.4‰, a high mean of deuterium excess during winter provides information about low humidity conditions and strong kinetic fractionation at evaporation and sublimation at the moisture source location. A slope of 7.4 for the δD-δ18O correlation during winter suggests local moisture sources. These results show the possibility to explain water vapor isotopic composition with local land and atmosphere processes with the existing data. Additionally, the exploration of recent water vapor on Samoylov Island and its isotopic composition provides findings which can be used as a reference for the assessment of large-scale variations of climate and the hydrological cycle in the Arctic.