The Distinct Composition and Transformation of Terrestrial Organic Carbon in the Yukon River Delta and Plume During the Mighty Spring Freshet

• Published in: Journal of geophysical research. Biogeosciences 2024-06, Vol.129 (6), p.n/a
• Main Authors: Burns, A. J., Spencer, R. G. M., Kellerman, A. M., Yan, G., Leonard, L., Kaiser, K., Mannino, A., Tzortziou, M., Hernes, P. J.
• Format: Article
• Language: English
• Subjects: Amplification; Arctic zone; Aromatic compounds; Biogeochemistry; Biomarkers; Carbon; Carbon cycle; Carbon sources; Coastal processes; Coastal zone; Coastal zones; Complexity; Continuums; Deltas; Diagenesis; Dissolved organic carbon; Freshwater; Genetic transformation; Ice environments; Information processing; Inland water environment; Landscape; Lignin; Phenols; Plants; Rivers; Salinity; Salinity effects; Salinity gradients; Seasonal variation; Seasonal variations; Summer; Surface water; Terrestrial environments; Water analysis; Water sampling
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007812

Arctic amplification is leading to increased terrestrial organic carbon (terrOC) mobilization with downstream impacts on riverine and marine biogeochemistry. To improve quantification and characterization of terrOC discharged to the Arctic Ocean, Yukon River delta samples were collected during three stages of the annual hydrograph (ascending limb/peak freshet, descending limb, late summer) and across a land‐to‐ocean salinity gradient (0.08–29.06 ppt). All samples were analyzed for dissolved organic carbon (DOC) concentration and lignin phenols to determine seasonal variability in riverine terrOC and salinity‐induced transformation of highly aromatic terrestrial compounds. Additionally, the relationship between lignin and absorbance at 350 and 412 nm was assessed to determine the feasibility of using optical proxies for accurate quantification, both seasonally and across expansive salinity gradients. Lignin phenols were highest during the ascending limb/peak freshet (0.58–0.97 mg/100 mg OC) when riverine DOC was dominated by young vascular plant sources, whereas lignin phenols were lower (0.15–0.89 mg/100 mg OC) and riverine DOC more variable in terrestrial source and diagenetic state during the descending limb and late summer. Across the sampled salinity gradient, there was disproportionate depletion of lignin (up to 73%) compared to DOC (up to 22%). Finally, while optical proxies can be used to quantify lignin within seasonal or spatial contexts, increased uncertainty is likely when expanding linear correlations across Arctic land‐ocean continuums. Overall, results indicate seasonal, spatial, interannual, and climatic controls that are amplified during high‐flow conditions and important to constrain when investigating Arctic terrOC cycling and land‐ocean DOC flux. Plain Language Summary The Arctic is experiencing an amplified warming phenomenon that is driving a variety of landscape changes. Through these landscape transformations, large amounts of organic carbon can be transported to nearby rivers. However, the fate and transport of organic carbon along Arctic land‐ocean continuums is largely unknown, primarily due to simultaneous complex processes that occur in deltas and coastal zones. To improve the quantification of landscape‐derived dissolved organic carbon (DOC) transported from the land to the Arctic Ocean, surface water samples were collected throughout the Yukon River delta (Alaska, USA) during three distinct seasons and across a land‐ocean sali