What controls the isotopic composition of the African monsoon precipitation? Insights from event‐based precipitation collected during the 2006 AMMA field campaign

Abstract

[1] The stable isotopic composition of the tropical precipitation constitutes a useful tool for paleoclimate reconstructions and to better constrain the water cycle. To better understand what controls the isotopic composition of tropical precipitation, we analyze the d 18 O and deuteriumexcess of the precipitation of individual events collected in the Niamey area (Niger) during the monsoon season, as part of the 2006 AMMA field campaign. During the monsoon onset, the abrupt increase of convective activity over the Sahel is associated with an abrupt change in the isotopic composition. Before the onset, when convective activity is scarce, the rain composition records the intensity and the organization of individual convective systems. After the onset, on the contrary, it records a regional-scale intraseasonal variability over the Sahel, by integrating convective activity both spatially and temporally over the previous days.

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

“…1) related to the isotopic composition of precipitation (δD rain ; Sachse et al, 2012). In tropical regions, δD rain is negatively correlated to precipitation amounts (Dansgaard, 1964;Rozanski et al, 1993;Risi et al, 2008), whereas δD wax also incorporates secondary effects of evapotranspiration, plant physiology, and photosynthetic pathway (Sachse et al, 2012). In areas with C 4 grasses, the stable carbon isotopic compositions of the same compounds (δ 13 C wax ) provide additional information about vegetation changes and can be used to differentiate between contributions from grassy (C 4 ) and woody (C 3 ) vegetation (e.g.…”

Interannual variability of isotopic composition in water vapor over western Africa and its relationship to ENSO

“…Risi et al (2008b) and Tremoy et al (2012Tremoy et al ( , 2014 examined the isotopic compositions of precipitation (δ 18 O P ) and vapor (δ 18 O v ), respectively, and both found that δ 18 O records the spatially and temporally integrated convective activity during the monsoon season. Here, δ in per mill units is defined as (R sample /R std -1) × 1000, where R std is VSMOW (Vienna Standard Mean Ocean Water).…”

La composition isotopique de la vapeur d'eau ; apport à l'étude des processus atmosphériques

“…Cette dernière dépend fortement de la variabilité intrasaisonnière de la mousson sud-américaine . En Afrique de l'Ouest, il a été montré que la composition isotopique des précipitations apporte des informations sur la structure, l'organisation et l'intensité de la convection (Risi et al, 2008Risi et Bony, 2011 l'absorption est liée à la concentration selon la loi de Beer-Lambert. Le système utilise une méthode un peu particulière, appelée Cavity Ring-Down Spectroscopy ; en effet, la quantité de vapeur d'eau injectée dans l'instrument n'est pas suffisante pour la sensibilité des capteurs.…”

“…Cette dernière dépend fortement de la variabilité intrasaisonnière de la mousson sud-américaine . En Afrique de l'Ouest, il a été montré que la composition isotopique des précipitations apporte des informations sur la structure, l'organisation et l'intensité de la convection (Risi et al, 2008Risi et Bony, 2011 , respectivement. Ainsi, lors de l'évaporation de la surface de l'océan, la vapeur formée, appauvrie en molécules lourdes, aura une composition isotopique négative.…”