Tritium as a hydrological tracer in Mediterranean precipitation events

Abstract

Abstract. Climate models are in need of improved constraints for water vapor transport in the atmosphere, and tritium can serve as a powerful tracer in the hydrological cycle. Although the general principles of tritium distribution and transfer processes within and between the various hydrological compartments are known, variation on short timescales and aspects of altitude dependence are still under debate. To address questions regarding tritium sources, sinks, and transfer processes, the sampling of individual precipitation events in Corte on the island of Corsica in the Mediterranean Sea was performed between April 2017 and April 2018. Tritium concentrations of 46 event samples were compared to their moisture origin and corresponding air mass history. Air mass back-trajectories were generated from the novel high-resolution ERA5 dataset from the ECMWF (European Centre for Medium-Range Weather Forecasts). Geographical source regions with similar tritium concentrations were predefined using generally known tritium distribution patterns, such as the “continental effect”, and from data records derived at long-term measurement stations of tritium in precipitation across the working area. Our model-derived source region tritium concentrations agreed well with annual mean station values. Moisture that originated from continental Europe and the Atlantic Ocean was most distinct regarding tritium concentrations with values up to 8.8 TU (tritium units) and near 0 TU, respectively. The seasonality of tritium values ranged from 1.6 TU in January to 10.1 TU in May, and they exhibited well-known elevated concentrations in spring and early summer due to increased stratosphere–troposphere exchange. However, this pattern was interrupted by extreme events. The average altitude of trajectories was correlated with the tritium concentrations in precipitation, especially in spring and early summer and if outlier values of extreme tritium concentrations were excluded. However, in combination with the trajectory information, these outlier values proved to be valuable for improving the comprehension of tritium movement in the atmosphere. Our work shows how event-based tritium research can advance the understanding of its distribution in the atmosphere.

A New Full 3‐D Model of Cosmogenic Tritium 3H Production in the Atmosphere (CRAC:3H)

“…Tritium ( 3 H) is a radioactive isotope of hydrogen with the half-life time of approximately 12.3 years. As an isotope of hydrogen, it is involved in the global water cycle and forms a very useful tracer of atmospheric moisture (e.g., Juhlke et al, 2020;Sykora & Froehlich, 2010) or hydrological cycles (Michel, 2005). In the natural environment, tritium is mostly produced by galactic cosmic rays (GCR) in the atmosphere, as a subproduct of the induced nucleonic cascade and is thus a cosmogenic radionuclide.…”

“…However, as nearly 60 years have passed since the nuclear tests, its global content has reduced to the natural pre-bomb level (Palcsu et al, 2018) and presently is mostly defined by the cosmogenic production. Accordingly, natural variability of the isotope production can be again used in atmospheric tracing, water vapor transport, and dynamics of the stratosphere-troposphere exchanges over Antarctica (Cauquoin et al, 2015;Fourré et al, 2018;Juhlke et al, 2020;László et al, 2020;Palcsu et al, 2018). Moreover, a combination of the 3 H data with other tracers like atmospheric 10 Be, which is also produced by cosmic ray spallation reactions, but whose transport is different, can be a very powerful research tool.…”

Effect of soil thickness on rainfall infiltration and runoff generation from karst hillslopes during rainstorms

“…Isotopic signals can reflect the mixing ratio of pre‐event and event water, and clarify the runoff generation mechanism. The isotope values of runoff generated by the infiltration‐excess mechanism are usually closer to those of rainwater (Juhlke et al, 2020; Zhao et al, 2016). On the contrary, the runoff generated by the saturation‐excess process has mixed pre‐event precipitation that is stored in the soil profile and can be confirmed by isotope hydrograph separation (Klaus & McDonnell, 2013).…”

Isoscape of amount-weighted annual mean precipitation tritium (<sup>3</sup>H) activity from 1976 to 2017 for the Adriatic–Pannonian region – AP<sup>3</sup>H_v1 database

“…Additional stations started operation in the past ∼ 50 years with frequent interruption in data collection (Araguas-Araguas et al, 1996;Krajcar Bronić et al, 1998;Rozanski et al, 1991;Vreča et al, 2008). The demand for long-term precipitation 3 H reference time series in various hydrological and hydrogeological applications across the Adriatic-Pannonian region called forth the use of remote stations (e.g Gessert et al, 2019;Kanduč et al, 2014Kanduč et al, , 2012 and/or motivated the derivation of case-specific "composite" tritium reference curves (e.g., Kern et al, 2009;Krajcar Bronić et al, 1992;Ozyurt et al, 2014;Szucs et al, 2015). Derivation of these ad hoc "composite" 3 H reference curves usually applied different imputation methods to the "gappy" time series and/or employed different interpolation techniques.…”