Expressing leaf water and cellulose oxygen isotope ratios as enrichment above source water reveals evidence of a Péclet effect

Abstract There is an increasing ecological interest in understanding the gradients in H₂ ¹⁸O enrichment in leaf water (i.e. a Péclet effect), because an appreciation of the significance of the Péclet effect is important for improving our understanding of the mechanistic processes affecting the ¹⁸O composition of leaf water and plant organic material. In data sets where both source water and leaf water ¹⁸O data are available, we can evaluate the potential contribution of a Péclet effect. As an example, we recalculate data published earlier by Roden and Ehleringer (1999, Oecologia 121:467–477) as enrichments in leaf water (_L) and cellulose (_cell) above source water. Based on these recalculations, we present support for the relevance of a Péclet effect in leaves. Further, we demonstrate that the subtle variations in _L and _cell caused by a Péclet effect may be masked in experimental systems in which variation in the source water oxygen isotope ratio is considerable.     

“Too low” δO of paleo-meteoric, low latitude, water; do paleo-tropical cyclones explain it?

Isotopic analysis of rock samples showed anomalously ¹⁸O-depleted reconstructed isotopic composition of paleo-meteoric water over southern Israel between the Late Cretaceous and the Early Miocene, with δ¹⁸O_W as low as −14‰ [SMOW]. This range is significantly “lighter” than the expected values for rain at the relevant paleo-latitudes (~ 8^°N to 25^°N). It is similar or lighter than areas with meteoric water at the present climate, in which rainfall contribution from tropical cyclone (TC) is significant. Rainfall from TCs is ¹⁸O-depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles. A paleo-geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area. Thus, TCs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east. The reconstructed composition of the rainwater implies dominance of TCs at these times. Furthermore, the combination of warmer seas and lighter rainwater than at present suggests that the TCs were more dominant than in the most TC-prone coastal areas at the present climate. The results of the present study suggest that climate during the relevant time periods was very different from the present, with TC activity similar or exceeding the most TC prone locations in the world at the present climate. This might also hint that warmer sea waters in the geological past were conducive to greater TC activity than in the present climate. Answering this question requires additional research.