A Tropical Cocktail of Organic Matter Sources: Variability in Supraglacial and Glacier Outflow Dissolved Organic Matter Composition and Age Across the Ecuadorian Andes

Abstract

The biogeochemistry of rapidly retreating Andean glaciers is poorly understood, and Ecuadorian glacier dissolved organic matter (DOM) composition is unknown. This study examined molecular composition and carbon isotopes of DOM from supraglacial and outflow streams (n = 5 and 14, respectively) across five ice capped volcanoes in Ecuador. Compositional metrics were paired with streamwater isotope analyses (δ 18 O) to assess if outflow DOM composition was associated with regional precipitation gradients and thus an atmospheric origin of glacier DOM. Ecuadorian glacier outflows exported ancient, biolabile dissolved organic carbon (DOC), and DOM contained a high relative abundance (RA) of aliphatic and peptide-like compounds (≥27%RA). Outflows were consistently more depleted in Δ 14 C-DOC (i.e., older) compared to supraglacial streams (mean −195.2 and −61.3‰ respectively), perhaps due to integration of spatially heterogenous and variably aged DOM pools across the supraglacial environment, or incorporation of aged subglacial OM as runoff was routed to the outflow. Across Ecuador, Δ 14 C-DOC enrichment was associated with decreased aromaticity of DOM, due to increased contributions of organic matter (OM) from microbial processes or atmospheric deposition of recently fixed and subsequently degraded OM (e.g., biomass burning byproducts). There was a regional gradient between glacier outflow DOM composition and streamwater δ 18 O, suggesting covariation between regional precipitation gradients and the DOM exported from glacier outflows. Ultimately, this highlights that atmospheric deposition may exert a control on glacier outflow DOM composition, suggesting regional air circulation patterns and precipitation sources in part determine the origins and quality of OM exported from glacier environments.

Update on Our Action Plan for Equity, Inclusion, and Diversity in Publishing at JGR: Biogeosciences

“…To further promote transparency, we now also request a standalone “Statement on Global Collaboration” to expand on these values to be published with the manuscript which needs to include information on any formal agreements, permissions, additional acknowledgments, end users of the research, and ethical considerations, as appropriate for the study (examples of such statements are now published: Holt et al. (2023), Sánchez‐Gutiérrez et al. (2023), and Tully et al.…”

Rock-to-Pharma: Characterization of Shale Oil-Based Nonbiological Complex Drugs along the Production Process by High-Resolution Mass Spectrometry

“…Thus, direct mass spectrometry with atmospheric pressure ionization has become increasingly popular in pharmaceutical research lately . High-field Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been successfully deployed for in-depth molecular speciation of dissolved organic matter, fossil fuels, proteins, as well as other complex organic mixtures . The lowest mass measurement error (root-mean-square error, RMSE, below 40 ppb), highest dynamic range of any mass analyzer, and automatic gain control (AGC) minimizing scan-to-scan variations in ion number enable the identification of species that differ in less of the mass of an electron …”