278-7 Understanding the spatial and temporal dynamics of the Amazon estuary and the Guianas mudbanks

Session: Understanding Temporal Dynamics in Hydrogeochemistry and Sedimentary Processes in Estuarine Environments

Presenting Author:

Brad Rosenheim

Authors:

Rosenheim, Brad E¹, Galy, Valier², Buck, Kristen³, Colombo, Manuel⁴, Hein, Christopher⁵, Caprara, Salvatore⁶, Ward, Nicholas⁷, Kampel, Milton⁸, Richey, Jeffrey⁹, Crawford, Calyn¹⁰, Moura, José Mauro Sousa¹¹, Valerio, Aline de Matos¹²

(1) College of Marine Science, University of South Florida, Saint Petersburg, FL, USA, (2) Marine Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA, (3) Oregon State University, Corvallis, OR, USA, (4) Virginia Institute of Marine Science, Gloucester Point, VA, USA, (5) Virginia Institute for Marine Science, Gloucester Point, VA, USA, (6) Marine Chemistry, Oregon State University, Corvallis, OR, USA, (7) Pacific Northwest National Laboratory, Richland, WA, USA, (8) Instituçào Nacional de Pesquisas Espaciais, São Paulo, São Paulo, Brazil, (9) University of Washington, Seattle, WA, USA, (10) College of Marine Science, University of South Florida, Saint Petersburg, FL, USA, (11) Universidade Federal de Oueste de Pará, Santarém, Pará, Brazil, (12) Instituão Nacional de Pesquisas Espaciais, São Paulo, São Paulo, Brazil,

Abstract:

The Amazon River, the world’s largest by discharge, displays estuarine processes over a broad range of spatial and time scales. A recent survey of water and surficial sediments from the Amazon’s mouth and its northwestward migrating mudbanks provides new insights into the spatial extent and timing of key processes controlling carbon cycling, nutrient loading, and sediment budgets. Our results indicate that organic carbon loss from river-transported sediments occurs over a surprisingly limited zone (~100 km), especially when contrasted with large drainage basin length (~3000 km, river length of ~7000 km) and the extensive nearshore depositional system along 1500 km of the northern coast of South America. This does not negate the role of coastal sediments, which periodically experience estuarine (mixed freshwater/saltwater) conditions. Our initial results indicate that nutrients stored in sediment porewaters may be more slowly released into the water column than organic carbon over a much larger area. Moreover, our data suggest that nutrients trends have remained consistent, potentially since the Holocene, along this highly dynamic coastal system. Importantly, our results indicate that carbon burial efficiency in this region is substantially higher than previously estimated for this and similar coastal environments.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8224

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