Nutrients from the Amazon River’s outflow spread well beyond the continental shelf and drive carbon cycling in the tropical ocean, say scientists who conducted a multi-year study. They will publish their results this week online in the journal Proceedings of the National Academy of Sciences (PNAS).
The researchers discovered a significant and surprising drawdown of carbon dioxide from the atmosphere into the tropical ocean by microorganisms living in the Amazon River’s outflow. The finding reveals the surprisingly large role of tropical oceans and major rivers in the oceans’ total carbon uptake.
“This work has led to an important discovery about the source of nitrogen that fuels the productivity of tropical ocean waters, especially those into which large rivers flow,” said David Garrison, director of the National Science Foundation (NSF)’s biological oceanography program. NSF’s Biocomplexity in the Environment program funded the research.
The Amazon River is the largest river in the world by volume; it also has the largest drainage basin on the planet, accounting for some one fifth of Earth’s total river flow. Because of its vast dimensions, it’s sometimes called “the river sea.”
The Amazon River’s outflow covers an area more than twice the size of the state of Texas for several months each year, said Ajit Subramaniam, a biological oceanographer at Columbia University and lead author of the PNAS paper. (Subramaniam is currently on leave from Columbia, now serving as a rotating program director at NSF.)