Impact of deep convective storms on stable isotope in precipitation and climate records, NW-Argentina.

ROHRMANN, ALEXANDER; STRECKER, MANFRED; BOOKHAGEN, BODO; MULCH, ANDREAS; SACHSE, DIRK; PINGEL, HEIKO; MONTERO, CAROLINA

Tubingen

Simposio; GV & Sediment Meeting; 2013

Globally, changes in stable isotope ratios of oxygen and hydrogen (δ18O and δD) in the meteoric water cycle result from distillation and evaporation processes. Isotope fractionation occurs when air masses rise in elevation, cool, and reduce their water-vapor holding capacity with decreasing temperature (Rayleigh distillation). Based on 234 stream-water samples, we demonstrate that areas experiencing deep convective storms in the eastern south-central Andes (22 - 28° S) do not show the expected relationship between δ18O and δD with elevation (isotopic lapse-rate). These convective storms arise in intermontane basins, where diurnal heating forces warm air masses upward resulting in cloud bursts and raindrop evaporation. Because convective storms can reduce or mask isotopic lapse-rates, linking modern or past topography to patterns of stable isotopes can be compromised in mountainous regions, and atmospheric circulation models attempting to predict stable isotope patterns must have sufficiently resolution to capture the fractionation dynamics of convective cells.