Award: OCE-2333961

This project examined the impact of El Niño Southern Oscillation (ENSO) anomalies on the export of dissolved organic carbon (DOC) and composition of dissolved organic matter (DOM) from the Amazon River to the Atlantic Ocean, as well as the Tapajos River (major tributary of the Amazon). Understanding how ENSO impacts Amazon River carbon flux, and the fate of this material (driven by composition) in the ocean, is important for predicting how future changes in ENSO will impact productivity in the Atlantic Ocean. We observed that during the El Niño period there was equivalent to a reduction of greater than 4 Tg/yr of DOC exported to the Atlantic Ocean. This is equivalent to a decline in DOC export of around two Mississippi River's or that of the Orinoco (the world's third largest river) exported into the Atlantic during El Niño events. Concurrent with this decline in carbon export the composition also changed dramatically shifting toward a more microbial / algal character with ramifications for the fate of this material in the Atlantic Ocean (i.e. less susceptible to photochemical processes in comparison to DOM exported in normal periods from the Amazon). Overall, these findings set a contemporary baseline highlighting the major variability in Amazon to Atlantic carbon export driven by ENSO with major implications for heterotrophy in receiving coastal waters. This is fundamentally important for the oceanographic community when assessing change in particularly coastal systems as it may be driven predominantly by changing land-ocean connectivity.

Last Modified: 12/04/2025
Modified by: Robert G Spencer