The global distribution of natural tritium in precipitation simulated with an Atmospheric General Circulation Model and comparison with observations

Cauquoin, Alexandre; Jean-Baptiste, P.; Risi, Camille; Fourré, Élise; Stenni, Barbara; Landais, A.

doi:10.1016/j.epsl.2015.06.043

Cited by 63 publications

(92 citation statements)

References 47 publications

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“…This is the reason why we restrict our analysis to the comparison of the relative variations of tritium and stable water isotopes in both snow pit profiles and model outputs. The pertinence of such a data‐model comparison is supported by the validation of stable water isotopes and tritium modeled variability (both temporally and spatially) in Antarctica with the LMDZ‐iso model (Risi et al, ; Cauquoin et al, , ). In addition, even if a straightforward comparison is limited by the chronology issue, the mean tritium level is similar in our data (Figure ) and in the modeled outputs (Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…Since 1963 tritium levels in precipitation have been steadily decreasing due to radioactive decay and dilution within the large oceanic reservoir. As a consequence, tritium concentration in precipitation today is very close to the natural level and insignificantly affected by anthropogenic production as shown by a recent modeling of natural tritium concentration in water confronted to present-day measurements in precipitation (Cauquoin et al, 2015). The present-day tritium content of the stratosphere is about 9 × 10 5 tritium unit (TU) (Ehhalt et al, 2002;Fourré et al, 2006) whereas tritium in precipitation is in the range of a few tens of TU (IAEA/GNIP database, International Atomic Energy Agency / HTO concentration in accumulated snow (precipitation and ice crystals settling) can thus be related to stratospheric water input.…”

Section: Introductionmentioning

confidence: 99%

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Tritium Records to Trace Stratospheric Moisture Inputs in Antarctica

et al. 2018

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Better assessing the dynamic of stratosphere‐troposphere exchange is a key point to improve our understanding of the climate dynamic in the East Antarctica Plateau, a region where stratospheric inputs are expected to be important. Although tritium (3H or T), a nuclide naturally produced mainly in the stratosphere and rapidly entering the water cycle as HTO, seems a first‐rate tracer to study these processes, tritium data are very sparse in this region. We present the first high‐resolution measurements of tritium concentration over the last 50 years in three snow pits drilled at the Vostok station. Natural variability of the tritium records reveals two prominent frequencies, one at about 10 years (to be related to the solar Schwabe cycles) and the other one at a shorter periodicity: despite dating uncertainty at this short scale, a good correlation is observed between 3H and Na+ and an anticorrelation between 3H and δ18O measured on an individual pit. The outputs from the LMDZ Atmospheric General Circulation Model including stable water isotopes and tritium show the same 3H‐δ18O anticorrelation and allow further investigation on the associated mechanism. At the interannual scale, the modeled 3H variability matches well with the Southern Annular Mode index. At the seasonal scale, we show that modeled stratospheric tritium inputs in the troposphere are favored in winter cold and dry conditions.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tritium Records to Trace Stratospheric Moisture Inputs in Antarctica

et al. 2018

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“…One of the few studies was by Zhai et al (2013) who compared the performance of four methods including TSAM, TM, latitude effect method, and the DRCM, and found that the reconstructed precipitation tritium contents had an uncertainty range of 133-607 tritium unit (TU), in terms of the standard deviation of the residuals. GCMs can simulate the main characteristics of tritium distributions in the ocean or atmosphere; however, the magnitudes of tritium are not comparable with the observations (Ba & Xu, 2010;Cauquoin et al, 2015;Sarmiento, 1983).…”

Section: Introductionmentioning

confidence: 87%

“…However, long‐term precipitation tritium records are only available at a few sites around the globe (e.g., at International Atomic Energy Agency, IAEA, long‐term sites in Ottawa or Hong Kong); therefore, most groundwater age estimates are made using tritium input values regionalized from the IAEA Global Network of Isotopes in Precipitation (GNIP) station record to the groundwater location of interest. These precipitation tritium regionalization approaches can be classified into three groups, that is, interpolation methods (Celle et al, ; Watson, ), reference curve methods (Doney et al, ; Weiss & Roether, ; Wu, ; Y. Zhang et al, ), and General Circulation Models (GCMs; Ba & Xu, ; Cauquoin et al, ; Koster et al, ; Weiss & Roether, ). These methods can reconstruct atmospheric tritium flux and are very helpful in groundwater recharge estimation and age dating; however, the uncertainties of these methods have rarely been investigated.…”

Section: Introductionmentioning

confidence: 99%

“…These precipitation tritium regionalization approaches can be classified into three groups, that is, interpolation methods (Celle et al, 2001;Watson, 1971), reference curve methods (Doney et al, 1992;Weiss & Roether, 1980;Wu, 1986;Y. Zhang et al, 2011), and General Circulation Models (GCMs; Ba & Xu, 2010;Cauquoin et al, 2015;Koster et al, 1989;Weiss & Roether, 1980). These methods can reconstruct atmospheric tritium flux and are very helpful in groundwater recharge estimation and age dating; however, the uncertainties of these methods have rarely been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Reconstructed Precipitation Tritium Leads to Overestimated Groundwater Recharge

Cheng

2018

JGR Atmospheres

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Time series of precipitation tritium contents are often used for groundwater recharge estimation based on the tritium mass ratio of the (un) saturated zones to precipitation. But records of the precipitation tritium measurements are sparse and often need to be reconstructed. Uncertainties associated with reconstructed records can affect the recharge estimates, but this has received little attention. Here we leverage four >15 m deep, exceptionally well preserved unsaturated zone tritium profiles to quantify the uncertainty in Tritium mass balance from precipitation tritium reconstruction. The tritium profiles have bomb tritium peaks at 7.2–10.5 m below the surface and peaks ranging from 46 to 235 tritium unit. We first estimate the diffuse recharge by the tritium peak method. Since this method is independent of any precipitation tritium reconstruction, the estimated recharge was used as truth to evaluate four precipitation tritium reconstruction methods: two interpolation methods and two reference curve methods. Direct comparison between the observed and simulated precipitation tritium showed that the reference curve methods performed more poorly than the interpolation methods. Indirect evaluation by comparing the recharge rates estimated by the tritium storage method with our truth measurements showed that tritium storage method overestimated recharge by 100% to 200%. Our results suggest that the atmospheric tritium flux was greatly underestimated, especially by the reference curve methods. As such, groundwater recharge at our sites would be overestimated. This has implications for using these standard approaches elsewhere.

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Modeling the global bomb tritium transient signal with the AGCM LMDZ‐iso: A method to evaluate aspects of the hydrological cycle

et al. 2016

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Improving the representation of the hydrological cycle in atmospheric general circulation models (AGCMs) is one of the main challenges in modeling the Earth's climate system. One way to evaluate model performance is to simulate the transport of water isotopes. Among those available, tritium is an extremely valuable tracer, because its content in the different reservoirs involved in the water cycle (stratosphere, troposphere, and ocean) varies by order of magnitude. Previous work incorporated natural tritium into Laboratoire de Météorologie Dynamique Zoom (LMDZ)‐iso, a version of the LMDZ general circulation model enhanced by water isotope diagnostics. Here for the first time, the anthropogenic tritium injected by each of the atmospheric nuclear bomb tests between 1945 and 1980 has been first estimated and further implemented in the model; it creates an opportunity to evaluate certain aspects of LDMZ over several decades by following the bomb tritium transient signal through the hydrological cycle. Simulations of tritium in water vapor and precipitation for the period 1950–2008, with both natural and anthropogenic components, are presented in this study. LMDZ‐iso satisfactorily reproduces the general shape of the temporal evolution of tritium. However, LMDZ‐iso simulates too high a bomb tritium peak followed by too strong a decrease of tritium in precipitation. The too diffusive vertical advection in AGCMs crucially affects the residence time of tritium in the stratosphere. This insight into model performance demonstrates that the implementation of tritium in an AGCM provides a new and valuable test of the modeled atmospheric transport, complementing water stable isotope modeling.

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The global distribution of natural tritium in precipitation simulated with an Atmospheric General Circulation Model and comparison with observations

Cited by 63 publications

References 47 publications

Tritium Records to Trace Stratospheric Moisture Inputs in Antarctica

Tritium Records to Trace Stratospheric Moisture Inputs in Antarctica

Reconstructed Precipitation Tritium Leads to Overestimated Groundwater Recharge

Modeling the global bomb tritium transient signal with the AGCM LMDZ‐iso: A method to evaluate aspects of the hydrological cycle

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