Award: OCE-1851494

The ocean and the many rivers that feed into it play a large role in the composition of our atmosphere. The rivers transport organic carbon, which is pulled from the atmosphere by plants, to the oceans where it can either be buried in the sediments and stored for long periods of time or re-released to the atmosphere as CO₂. The composition of the atmosphere over long time scales is partially controlled by how much is stored (buried) and how much is re-released to the atmosphere; more burial means less CO₂ and more O₂ in the atmosphere. This project targeted the Amazon River system's mudbanks, large mobile belts of mud that emanate from the Amazon River and travel up the coast of South America. These mudbanks had been previously thought to re-release lots of CO₂ to the atmosphere. We revisited these mudbanks aboard a U.S.A. oceanographic vessel as wel as onboard a Brazilian river research ship to sample the mudbanks inshore of where they had previously been samples, to coordinate this sampling with samples taken from the Amazon River before it reaches the ocean, and to apply new geochemical methods and approaches to these new samples. Our results show that despite the length of the river (>3,000 km) and the length of the sediment transport through the mudbanks system (~1,500 km), most of the organic carbon transformation happens in 100 km of the river that is affected by tides in the ocean. Outside of this hotspot, and including the mudbanks which were thought to be incinerators of the organic carbon, the organic carbon from the river is largely left alone by natural processes. This breaks from our common knowledge and suggests that mudbanks systems can preserve more carbon than previously thought. These findings require a rebudgeting of the river-to-ocean carbon cycle to accurately reflect this new understanding. This expedition took advantage of the United States of America's academic research fleet of oceanographic vessels and utilized a regional class vessel to conduct research over its longest ever expedition. The use of this vessel was critical due to its abilities to navigate shallower waters than many of the larger oceanographic vessels more accustomed to such long voyages. As such the expedition funded by this project demonstrated the capabilities of our academic research fleet as well as advancing the science of how carbon is transferred between the atmosphere, plants, and the oceans. 

Last Modified: 07/22/2026
Modified by: Brad Erik Rosenheim