Hydroclimatic seasonality recorded by tree ring δ18O signature across a Himalayan altitudinal transect

• Published in: Earth and planetary science letters Vol. 518; pp. 148 - 159
• Main Authors: Brunello, Camilla Francesca, Andermann, Christoff, Helle, Gerhard, Comiti, Francesco, Tonon, Giustino, Tiwari, Achyut, Hovius, Niels
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2019
• Subjects: dendroclimatology; Himalayan hydroclimate; monsoon onset; oxygen fractionation model; pre-monsoon; seasonal precipitation; monsoon onset; pre-monsoon; Himalayan hydroclimate; oxygen fractionation model; dendroclimatology; seasonal precipitation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2019.04.030

Water stable isotope ratios of tropical precipitation predominantly reflect moisture source and precipitation intensity. Trees can incorporate the isotopic signals into annual tree-ring cellulose records, permitting reconstruction of the temporal changes of hydroclimate over decades to millennia. This is especially valuable in the Himalayas where the understanding of monsoon dynamics is limited by the lack of a dense and representative observational network. We have analyzed tree ring δ18O records from two distinct physiographic sites along the upper Kali Gandaki valley in the central Nepal Himalayas, representing the wet High-Himalayas and the Trans-Himalayan dryland to the north. Empirical correlations and regression analyses were compared to an in-situ calibrated oxygen isotope fractionation model, exploring the relationships between tree ring δ18O and seasonal-mean variability of hydroclimatic forcing at the different locations. For this purpose, gridded precipitation data from the Asian rain gauge dataset APHRODITE, as well as high resolution onsite observations (relative humidity, air temperature, δ18O of precipitation and radial tree growth) were used. We found that two distinct sets of meteorological values, reflecting pre-monsoon and monsoon conditions, are needed to reproduce the measured tree ring δ18O values from the High-Himalayan site, but that a single set of monsoonal values performs best for the Trans-Himalayan site. We conclude that Trans-Himalayan trees capture long-term changes in strength of the Indian summer monsoon. In contrast, High-Himalayan tree ring δ18O records a more complex hydro-climatic signal reflecting both pre-monsoon and monsoon seasons with very contrasting isotopic signatures of precipitation. This difference in the two hydroclimatic proxy records offers an opportunity to reconstruct first-order hydroclimate conditions, such as local precipitation rates, and to gain new insights into monsoon timing and seasonal water source determination across the Himalayan orographic region. •Hydroclimate seasonality is preserved in tree ring δ18O from the Central Himalayas.•A fractionation model confirms relationships from empirical correlation analyses.•High-Himalayan tree ring δ18O compounds pre- and monsoon signals•Trans-Himalayan tree ring δ18O only contains monsoon signal.•At different locations across the Himalayas, different climate features are recorded.