The Thermal Reactivity and Molecular Diversity of Particulate Organic Carbon in the Amazon River Mainstem

作者：Sarah Z. Rosengard, José Mauro Sousa de Moura, Robert G. M. Spencer, C. G. Johnson, Ann P. McNichol, Brenna Boehman, Valier Galy · 发表于：Journal of Geophysical Research Biogeosciences · 年份：2025 · DOI：10.1029/2024jg008660 · 被引用次数：3 · 研究领域：Marine and coastal ecosystems、Isotope Analysis in Ecology、Marine Biology and Ecology Research

Abstract The Amazon River mobilizes one of the largest fluxes of particulate organic carbon (POC) from land to coastal ocean sediments, playing an important role in the long‐term sequestration of biospheric organic carbon in the ocean. Ramped oxidation (RPO) analyses of suspended sediments collected from the Amazon River mainstem, Solimões River, Madeira River, and Tapajós River presented an opportunity to parse riverine POC by thermal reactivity, extract the activation energy distributions of specific biomolecular pools in these samples, and characterize the molecular diversity of POC across the floodplain. The thermal reactivity data imply that POC from the Amazon River basin spans a wide but relatively homogenous activation energy range across samples, suggesting that the degradation history of the organic carbon comprising riverine suspended particles is relatively constant across depths within the mainstem and different tributary locations. Coupling activation energy distributions to stable and radiocarbon isotopic analyses shows that ca. 85% of mainstem POC derives from a range of partially degraded terrestrial sources, likely organic matter from mineral soil horizons, and that a similar range of soil sources influences the biomolecular diversity in tributary samples. In agreement with earlier assessments, ca. 10% of the riverine POC flux is fresh vegetation and up to 5% of it is petrogenic organic matter. Expanded RPO analyses of samples across the Amazon river‐to‐ocea...