Continuous water vapor isotope measurements at the Amazon Tall Tower Observatory site during a dry season: Insights into diel atmospheric moisture sources

The recent development and improvement of commercially available laser-based spectrometers have expanded onsite continuous water vapor (H₂O) stable isotope composition (e.g. δ¹⁸O, δ¹⁷O and δ²H) measurements in a variety of sites across the world in the last decade. However, we still lack continuous observations in the Amazon basin region, a region that significantly influences atmospheric and hydrological cycles on local to global scales.

The Amazon Tall Tower Observatory (ATTO) site is located in well-preserved central Amazon upland rainforest. In August 2022, a commercial cavity-ring down (CRDS) analyzer (L2140-i model, Picarro, Inc., USA) was installed 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. Also, deuterium excess (hereinafter called d-excess; d-excess = δ²H–8δ¹⁸O) was assessed to trace processes that contribute to diel variation in atmospheric moisture inside and above canopy.

During the dry season, d-excess generally decreased during the nighttime, reaching minimum values at 6 am to 8 am local time (LT), followed by an increase 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 analyzed and discussed in the presentation.