Soumaya Belmecheri is a dendrochronologist who uses stable isotope ratios in tree rings to better understand the role of trees and forest ecosystems in the carbon cycle, how trees respond to climate-related stress, and how tropical trees can be used to track important atmospheric circulation features.
Soumaya’s work takes advantage of new technology for sampling and analyzing carbon and oxygen isotopes. Traditional laboratory methods for isotope sampling and measurement have been extremely time consuming, requiring dedicated samples, with a resolution mostly limited to annual rings. Soumaya has devoted the past year to setting up, calibrating, and developing protocols for Laser Ablation-Isotope Ratio Mass Spectrometry (LA-IRMS), which has the capacity to sample isotopes at the cellular level through laser ablation, then measure both carbon and oxygen ratios using mass spectrometry. This high-resolution, precise sampling enables the generation of isotope measurement time series at the seasonal level. This is especially important for tropical trees, which do not have reliably annual rings, which precludes their sensitivity to climate from being fully explored and utilized.
One of Soumaya’s main research areas concerns the carbon cycle, and specifically, in tropical forests. Tropical forests are significant carbon sinks, but their capacity is reduced during times of climatic stress, and especially during the droughts that are characteristic of El Niño events. However, little is known about the drought stress response documented in recent years, relative to the past. Is the response changing? Are trees responding to droughts that have become more prolonged and severe? How does drought stress influence the capacity of tropics trees to sequester carbon in the past compared to today? Soumaya and Brazilian colleagues (including Ana Claudia Batista, a postdoctoral researcher who was a visitor to the LTRR) are collaborating to address these questions. Samples from Brazilian tropics are in the queue to be analyzed later this year, when the LA-IRMS is fully operational.
A second area of Soumaya’s research utilizes oxygen isotopes to reconstruct the path of the Intertropical Convergence Zone (ITCZ), the most important circulation feature in the tropics for the delivery of seasonal precipitation. This project will develop a longitudinal transect of sampling sites from the Amazon through Central America to reconstruct spatial patterns of the ITCZ, and to learn more about changes in ITCZ seasonality and related climate dynamics. Several graduate students are involved in this project, including LTRR graduate student Isabel Gonzalez Mendez and Brazilian graduate student, Bruna Hornin, a Haury Fellowship visitor. Soumaya envisions this project, and the LA-IRMS lab in general, to be a training hub for isotope dendrochronology, especially for graduate students and international researchers. The LTRR LA-IRMS is the only system in the US set up specifically for dendrochronology (world-wide, there are only 3-4 of these dendro-focused labs).
Soumaya has worked tirelessly to establish the LA-IRMS lab, a part of the new TIME lab, acquiring the instrumentation, then installing the equipment, teaching herself how to run the system, calibrating measurements, and troubleshooting at each step. She has recruited and employed a team of undergraduate students (see the newsletter article on the CURE course) to assist in establishing lab protocols to ensure robust, quality data. In the process, the students have received training and have become valuable technicians. The lab is also part of Vertically Integrated Projects (VIP), a UA program designed to engage undergraduate and graduate students in team-based multidisciplinary research. The Isotropics VIP (teams.https://uavip.arizona.edu/isotropics), led by Soumaya, LTRR Director Kevin Anchukaitis, and graduate student Isabel Gonzalez Mendez, is currently recruiting students to participate in tropical dendrochronology projects this spring.
