Stable Water Isotope Characteristics of Recent Precipitation from Tiksi and Samoylov Island – Calibration of a Geoscientific Proxy for Northern Siberia

The Siberian Arctic is highly affected by global warming. By reconstructing the past climate evolution, the understanding of ongoing climate changes in Siberia can be improved. For this purpose, stable water isotopes (δ18O, δD) are important geoscientific proxies for climate reconstructions worldwide. In Northern Siberia, stable water isotopes have been applied to ground ice, but they can be only properly used when controls on the stable isotope composition of recent precipitation are understood. In this context, stable water isotopes were analysed for recent precipitation of two sites in Northern Siberia (Lena Delta region), the rather maritime Tiksi at the Laptev Sea coast (71° 38’ N, 128° 52’ E) and the rather fluvial Samoylov Island in the central Lena Delta (72° 22’ N, 126° 29’ E). The aim of this study was the identification of key features and processes controlling the local isotopic composition of precipitation (δ18O, δD, d excess), as a basis for the future interpretation of local geoscientific archives (such as ground ice). The data set comprised the isotopic composition of precipitation from Tiksi and Samoylov Island for a period from June 2004 to May 2017 and September 2013 to August 2017, respectively. Moreover, local meteorological data as well as backward trajectories were used to find the connection between stable water isotopes and meteorology, as well as specific moisture sources affecting the isotopic composition of precipitation. The observation period characterises the isotopic composition of precipitation of a rather warm phase of long-term temperature evolution. The study confirms that δ-values of precipitation in Tiksi and Samoylov Island are mainly affected by air temperature (r = 0.90 and r = 0.84, respectively) and that the d excess of Tiksi is a good reflection of changes in moisture source regions. The highly continental Arctic region is reflected by a clear seasonality in temperatures and δ-values (Δδ18O Tiksi = 19.4 ‰, Δδ18O Samoylov = 19.6 ‰), with a slightly lower seasonality for the maritime setting of Tiksi compared to Samoylov Island. Since other local differences are not obvious in the δ-values of precipitation, δ-values are assumed to be transferable from Tiksi to Samoylov Island. In contrast, the d excess shows a high variability without seasonality patterns. Differences in the d excess (e.g. mean d Tiksi = 3.8 ‰, mean d Samoylov = 5.7 ‰) point to slight differences in moisture source regions. The use of backward trajectories in combination with the seasonal mean d excess of Tiksi has demonstrated to be a good approach for moisture source identification. The Pacific Ocean could be for the first time identified as important moisture source region for Tiksi in winter and spring (e.g. 2004: 62 % and 33 %, respectively). The Atlantic Ocean is confirmed as main moisture source region in summer and autumn. Secondary moisture from open water bodies adds to the water balance in summer. Moreover, the similarity of dδ18O/dT gradients on the event to multi-annual timescale (0.4 – 0.6 ‰/°C) suggests that the current isotope temperature relationship could be suitable for climate reconstructions