Anne Alexandre

Triple oxygen isotopes, and specifically ¹⁷O-excess, provide new opportunities to investigate kinetic fractionation associated with atmospheric moisture sources, continental moisture recycling, and cloud microphysical processes. However, observations of ¹⁷O-excess in precipitation remain extremely scarce in Africa, leaving its potential for tracing atmospheric processes in the West African Monsoon (WAM) largely unexplored. Here we analyze a high-frequency precipitation isotope dataset (δ¹⁸O, δ²H, d-excess, and ¹⁷O-excess) from Benin, comprising a 7-year record at the inland Nalohou station and a complementary 2-year record from a coastal station near Cotonou. Three isotopic clusters are identified inland, corresponding to distinct rainfall regimes. The first is associated with short-lived convective events affected by sub-cloud rain evaporation, while the second reflects more organized convective systems and a weak signature of continental moisture recycling. The third cluster, observed only inland, is characterized by strongly depleted δ¹⁸O together with simultaneous decreases in d-excess and ¹⁷O-excess, and occurs mainly during the mature monsoon stage. Its rainfall characteristics are consistent with larger and more organized convective systems, with a greater contribution from their stratiform component. At the interannual scale, δ¹⁸O variability is more closely related to rainfall characteristics during the mature monsoon phase than to rainfall amount. Overall, these results indicate that, during the WAM mature monsoon phase, precipitation isotopes primarily reflect convective organization and associated cloud microphysical processes, while retaining a weak signature of continental moisture recycling during inland transport. These combined δ¹⁸O, d-excess, and ¹⁷O-excess data provide new observational constraints for isotope-enabled atmospheric and hydrological models.

Triple oxygen isotopes, and specifically ¹⁷O-excess, provide new opportunities to investigate kinetic fractionation associated with atmospheric moisture sources, continental moisture recycling, and cloud microphysical processes. However, observations of ¹⁷O-excess in precipitation remain extremely scarce in Africa, leaving its potential for tracing atmospheric processes in the West African Monsoon (WAM) largely unexplored. Here we analyze a high-frequency precipitation isotope dataset (δ¹⁸O, δ²H, d-excess, and ¹⁷O-excess) from Benin, comprising a 7-year record at the inland Nalohou station and a complementary 2-year record from a coastal station near Cotonou. Three isotopic clusters are identified inland, corresponding to distinct rainfall regimes. The first is associated with short-lived convective events affected by sub-cloud rain evaporation, while the second reflects more organized convective systems and a weak signature of continental moisture recycling. The third cluster, observed only inland, is characterized by strongly depleted δ¹⁸O together with simultaneous decreases in d-excess and ¹⁷O-excess, and occurs mainly during the mature monsoon stage. Its rainfall characteristics are consistent with larger and more organized convective systems, with a greater contribution from their stratiform component. At the interannual scale, δ¹⁸O variability is more closely related to rainfall characteristics during the mature monsoon phase than to rainfall amount. Overall, these results indicate that, during the WAM mature monsoon phase, precipitation isotopes primarily reflect convective organization and associated cloud microphysical processes, while retaining a weak signature of continental moisture recycling during inland transport. These combined δ¹⁸O, d-excess, and ¹⁷O-excess data provide new observational constraints for isotope-enabled atmospheric and hydrological models.

Triple oxygen isotopes, and specifically 17O-excess, provide new opportunities to investigate kinetic fractionation associated with atmospheric moisture sources, continental moisture recycling, and cloud microphysical processes. However, observations of 17O-excess in precipitation remain extremely scarce in Africa, leaving its potential for tracing atmospheric processes in the West African Monsoon (WAM) largely unexplored. Here we analyze a high-frequency precipitation isotope dataset (δ18O, δ2H, d-excess, and 17O-excess) from Benin, comprising a 7-year record at the inland Nalohou station and a complementary 2-year record from a coastal station near Cotonou. Three isotopic clusters are identified inland, corresponding to distinct rainfall regimes. The first is associated with short-lived convective events affected by sub-cloud rain evaporation, while the second reflects more organized convective systems and a weak signature of continental moisture recycling. The third cluster, observed only inland, is characterized by strongly depleted δ18O together with simultaneous decreases in d-excess and 17O-excess, and occurs mainly during the mature monsoon stage. Its rainfall characteristics are consistent with larger and more organized convective systems, with a greater contribution from their stratiform component. At the interannual scale, δ18O variability is more closely related to rainfall characteristics during the mature monsoon phase than to rainfall amount. Overall, these results indicate that, during the WAM mature monsoon phase, precipitation isotopes primarily reflect convective organization and associated cloud microphysical processes, while retaining a weak signature of continental moisture recycling during inland transport. These combined δ18O, d-excess, and 17O-excess data provide new observational constraints for isotope-enabled atmospheric and hydrological models.

Triple oxygen isotopes are powerful tracers of hydrological processes, yet their variability in atmospheric water vapor and the underlying controls remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (δ18OV, d-excessV, 17O-excessV) measured below, within and above a downy oak forest canopy at the AnaEE platform O3HP in the French Mediterranean. This vapor dataset is complemented by isotopic data of precipitation (δ18OP, d-excessP, 17O-excessP) and groundwater, as well as monthly observations of stomatal conductance and transpiration. Seasonal variations in 17O-excessV and d-excessV likely reflect changing evaporative conditions at oceanic moisture sources. d-excessP and 17O-excessP show a similar seasonal pattern, enhanced by summer rain re-evaporation. However, no clear isotopic differences were observed in vapor or precipitation derived from different oceanic source regions and weather regimes, likely due to frequent mixing of multiple moisture sources. Diurnal variations in 17O-excessV and d-excessV reflect a combination of vegetation-related processes, including local evapotranspiration. However, the impact of evapotranspiration was not evident at daily timescales. Although precipitation often deviates from isotopic equilibrium with near-surface atmospheric water vapor at the event scale due to incomplete equilibration and rain re-evaporation, equilibrium water vapor reliably approximates the near-surface isotopic composition of atmospheric water vapor at annual scale. Our results highlight the potential of 17O-excess for understanding water exchange between the land and the atmosphere, regardless of climatic and vegetation conditions. They enhance the mechanistic interpretation of precipitation isotopes, which is essential for reliable paleoclimate reconstructions.

Triple oxygen isotopes are a powerful tracer of hydrological processes, yet their variability in atmospheric water vapor and the processes driving them remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (V) measured at four heights below and above a downy oak forest canopy at the AnaEE platform O₃HP in the French Mediterranean. This vapor dataset is complemented by isotope data from rainfall and groundwater, as well as monthly measurements of stomatal conductance and transpiration. Our results demonstrate that ¹⁷O-excess_V is principally driven by evaporation processes. Seasonal variations in ¹⁷O-excess_V ranging from 33 ± 9 per meg in winter to 25 ± 6 per meg in summer, reflect evaporative conditions in oceanic moisture sources. Diurnal variations, particularly pronounced in summer, with daytime maxima around 33 ± 6 per meg and nighttime minima around 16 ± 7 per meg, are linked to local evapotranspiration and isotope exchange between leaf waters and the atmosphere. On a monthly scale, precipitation is generally close to isotope equilibrium with atmospheric water vapor, except in summer when rain re-evaporation occurs. At event scale, large deviations from isotope equilibrium can occur due to raindrop evaporation and incomplete re-equilibration. Our findings enhance the mechanistic basis for interpreting precipitation isotopes in paleoclimate context, improves the robustness of isotope-based model evaluation, and highlights the potential of ¹⁷O-excess for better understanding of land-atmosphere water exchange across diverse climate and vegetation contexts.

Triple oxygen isotopes are a powerful tracer of hydrological processes, yet their variability in atmospheric water vapor and the processes driving them remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (V) measured at four heights below and above a downy oak forest canopy at the AnaEE platform O₃HP in the French Mediterranean. This vapor dataset is complemented by isotope data from rainfall and groundwater, as well as monthly measurements of stomatal conductance and transpiration. Our results demonstrate that ¹⁷O-excess_V is principally driven by evaporation processes. Seasonal variations in ¹⁷O-excess_V ranging from 33 ± 9 per meg in winter to 25 ± 6 per meg in summer, reflect evaporative conditions in oceanic moisture sources. Diurnal variations, particularly pronounced in summer, with daytime maxima around 33 ± 6 per meg and nighttime minima around 16 ± 7 per meg, are linked to local evapotranspiration and isotope exchange between leaf waters and the atmosphere. On a monthly scale, precipitation is generally close to isotope equilibrium with atmospheric water vapor, except in summer when rain re-evaporation occurs. At event scale, large deviations from isotope equilibrium can occur due to raindrop evaporation and incomplete re-equilibration. Our findings enhance the mechanistic basis for interpreting precipitation isotopes in paleoclimate context, improves the robustness of isotope-based model evaluation, and highlights the potential of ¹⁷O-excess for better understanding of land-atmosphere water exchange across diverse climate and vegetation contexts.

Triple oxygen isotopes are a powerful tracer of hydrological processes, yet their variability in atmospheric water vapor and the processes driving them remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (V) measured at four heights below and above a downy oak forest canopy at the AnaEE platform O₃HP in the French Mediterranean. This vapor dataset is complemented by isotope data from rainfall and groundwater, as well as monthly measurements of stomatal conductance and transpiration. Our results demonstrate that ¹⁷O-excess_V is principally driven by evaporation processes. Seasonal variations in ¹⁷O-excess_V ranging from 33 ± 9 per meg in winter to 25 ± 6 per meg in summer, reflect evaporative conditions in oceanic moisture sources. Diurnal variations, particularly pronounced in summer, with daytime maxima around 33 ± 6 per meg and nighttime minima around 16 ± 7 per meg, are linked to local evapotranspiration and isotope exchange between leaf waters and the atmosphere. On a monthly scale, precipitation is generally close to isotope equilibrium with atmospheric water vapor, except in summer when rain re-evaporation occurs. At event scale, large deviations from isotope equilibrium can occur due to raindrop evaporation and incomplete re-equilibration. Our findings enhance the mechanistic basis for interpreting precipitation isotopes in paleoclimate context, improves the robustness of isotope-based model evaluation, and highlights the potential of ¹⁷O-excess for better understanding of land-atmosphere water exchange across diverse climate and vegetation contexts.

Triple oxygen isotopes are a powerful tracer of hydrological processes, yet their variability in atmospheric water vapor and the processes driving them remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (V) measured at four heights below and above a downy oak forest canopy at the AnaEE platform O₃HP in the French Mediterranean. This vapor dataset is complemented by isotope data from rainfall and groundwater, as well as monthly measurements of stomatal conductance and transpiration. Our results demonstrate that ¹⁷O-excess_V is principally driven by evaporation processes. Seasonal variations in ¹⁷O-excess_V ranging from 33 ± 9 per meg in winter to 25 ± 6 per meg in summer, reflect evaporative conditions in oceanic moisture sources. Diurnal variations, particularly pronounced in summer, with daytime maxima around 33 ± 6 per meg and nighttime minima around 16 ± 7 per meg, are linked to local evapotranspiration and isotope exchange between leaf waters and the atmosphere. On a monthly scale, precipitation is generally close to isotope equilibrium with atmospheric water vapor, except in summer when rain re-evaporation occurs. At event scale, large deviations from isotope equilibrium can occur due to raindrop evaporation and incomplete re-equilibration. Our findings enhance the mechanistic basis for interpreting precipitation isotopes in paleoclimate context, improves the robustness of isotope-based model evaluation, and highlights the potential of ¹⁷O-excess for better understanding of land-atmosphere water exchange across diverse climate and vegetation contexts.

Triple oxygen isotopes are a powerful tracer of hydrological processes, yet their variability in atmospheric water vapor and the processes driving them remain poorly understood. We present a one-year record of triple oxygen and hydrogen isotopes of atmospheric water vapor (V) measured at four heights below and above a downy oak forest canopy at the AnaEE platform O₃HP in the French Mediterranean. This vapor dataset is complemented by isotope data from rainfall and groundwater, as well as monthly measurements of stomatal conductance and transpiration. Our results demonstrate that ¹⁷O-excess_V is principally driven by evaporation processes. Seasonal variations in ¹⁷O-excess_V ranging from 33 ± 9 per meg in winter to 25 ± 6 per meg in summer, reflect evaporative conditions in oceanic moisture sources. Diurnal variations, particularly pronounced in summer, with daytime maxima around 33 ± 6 per meg and nighttime minima around 16 ± 7 per meg, are linked to local evapotranspiration and isotope exchange between leaf waters and the atmosphere. On a monthly scale, precipitation is generally close to isotope equilibrium with atmospheric water vapor, except in summer when rain re-evaporation occurs. At event scale, large deviations from isotope equilibrium can occur due to raindrop evaporation and incomplete re-equilibration. Our findings enhance the mechanistic basis for interpreting precipitation isotopes in paleoclimate context, improves the robustness of isotope-based model evaluation, and highlights the potential of ¹⁷O-excess for better understanding of land-atmosphere water exchange across diverse climate and vegetation contexts.