[A-CG39] 陸域生態系の物質循環

[ACG39-P02] Diel moisture variations in a central Amazon rainforest during a dry season evaluated by continuous water vapor isotope tower measurements

*Shujiro Komiya¹、Sam Jones¹、Hella van Asperen¹、Jost Lavric²、Getachew Adnew³、Robbert Moonen³、Santiago Botía⁴、Cléo Quaresma Dias-Júnior⁵、Ricardo Acosta Gotuzzo⁶、Rosaria Rodrigues Ferreira⁶、Fumiyoshi Kondo⁷、Susan Trumbore¹ (1.Biogeochemical Processes Department, Max Planck Institute for Biogeochemistry、2.Acoem Australasia、3.Institute for Marine and Atmospheric Research Utrecht, Utrecht University、4.Biogeochemical Signals Department, Max Planck Institute for Biogeochemistry、5.Department of Physics, Federal Institute of Para (IFPA)、6.Amazon Tall Tower Observatory (ATTO), Large Scale Biosphere-Atmosphere in the Amazon (LBA) Program, INPA、7.Japan Coast Guard Academy)

キーワード：Water vapor stable isotopes, d-excess, Amazon rainforest, diel variation, ATTO

The recent development and improvement of commercially available laser-based spectrometers have enabled onsite continuous water vapor (H₂O) stable isotope composition (e.g. δ¹⁸O, δ¹⁷O and δ²H) observation in a various sites across the world. However, the continuous observation is still rare in Amazon basin region, that contains the largest continuous tropical forest and significantly influences atmospheric and hydrological cycles on local to global scales. The continuous water vapor isotope observation with a flux and meteorological tower measurements in the Amazon rainforest is essential for improving our understanding of the Amazon rainforest water cycling.

In August 2022, we installed a commercial cavity-ring down (CRDS) analyzer (L2140-i model, Picarro, Inc., USA) to continuously measure water vapor isotope compositions at four levels (79, 38, 24, and 4 m above ground) of the 80 m walk-up tower in the Amazon Tall Tower Observatory (ATTO) site, located in well-preserved central Amazon upland rainforest. We assessed deuterium excess (hereinafter called d-excess; d-excess = δ²H –8 δ¹⁸O) to trace processes that contribute to diel variation in atmospheric moisture inside and above canopy during the dry season.

D-excess generally decreased over the nighttime to minimum values at 6 am to 8 am local time (LT), and subsequently increased to maximum values at 12 pm to 4 pm. The diel d-excess variation indicates that atmospheric entrainment occurred in the early morning and evapotranspiration was a dominant moisture source in the afternoon. Further results will be presented and discussed in the presentation.