Drivers of Organic Molecular Signatures in the Amazon River. Issue 6 (24th June 2021)

• Record Type: Journal Article
• Authors: Kurek, Martin R.; Stubbins, Aron; Drake, Travis W.; Moura, Jose M. S.; Holmes, R. Max; Osterholz, Helena; Dittmar, Thorsten; Peucker‐Ehrenbrink, Bernhard; Mitsuya, Miyuki; Spencer, Robert G. M.
• Is Part Of: Global biogeochemical cycles. Volume 35:Issue 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-24
• Subjects: Amazon river -- carbon cycling -- dissolved organic carbon -- dissolved organic matter -- ENSO -- FT‐ICR MS; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2021GB006938
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: As climate‐driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr −1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra‐high‐resolution mass spectrometry, we detected both intra‐ and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to‐date we showed that compounds were highly correlated to a 6‐month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin‐derived DOM concurrent with lag periods as described here. Plain Language Summary: Increases in atmospheric carbon concentrations originate from many sources and pose a serious threat to global ecosystem health and humanity. The Amazon River delivers one‐fifth of global discharge and represents the largest single flux of dissolved organic carbon (DOC) from land to ocean. As climate change is projected to increase precipitation anomalies throughout the Amazon, flooding and droughts will become more frequent and severe, disrupting the natural seasonal rhythm of the Amazon River. We demonstrate that precipitation anomalies in South America (caused by La Niña) exported an additional amount of DOC from the Amazon River to the Atlantic Ocean than the Mississippi River exports annually. Organic compounds mobilized during the La Niña were more aromatic, presumably from terrestrial sources. These compositions, measured near the mouth of the Amazon River, arrived six months after Pacific sea‐surface temperature and pressure anomalies indicated the onset of La Niña, highlighting the lag time that events in the Pacific take to impact the Atlantic Ocean. Key Points: The Amazon River during a La Niña year exports an additional amount of dissolved organic carbon than the Mississippi exports annually The Amazon River dissolved organic matter composition in a La Niña year was more oxidized and aromatic than during a non‐ENSO year The dissolved organic matter composition in the Amazon River correlates to a 6‐month lag with La Niña indices