Carbon remineralization in the Amazon–Guianas tropical mobile mudbelt: A sedimentary incinerator |
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| Institution: | 1. Marine Sciences Research Center, Stony Brook University, Stony Brook, NY 11794-5000, USA;2. Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA;1. School of Oceanography, University of Washington, Box 357940, Seattle, WA 98195-7940 USA;2. Dept. of Geology and Geophysics, Boston College, Chestnut Hill, MA 02467 USA;3. U.S. Geological Survey, Coastal and Marine Geology, 384 Woods Hole Road, Woods Hole, MA 02543-1598 USA;1. Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden;2. Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden;3. CNR-National Research Council of Italy, ISMAR-Marine Sciences Institute, Bologna, Italy;4. Geological Institute, ETH Zürich, Zürich, Switzerland;5. International Arctic Research Center, University Alaska Fairbanks, Fairbanks, USA;6. Pacific Oceanological Institute, Russian Academy of Sciences, Vladivostok, Russia;7. Tomsk National Research Politechnical University, Tomsk, Russia;8. DTU-Nutech, Technical University of Denmark, Roskilde, Denmark;1. Department of Applied Environmental Science, Stockholm University, Sweden;2. Bolin Centre for Climate Research, Stockholm University, Sweden;3. International Arctic Research Center, University Alaska Fairbanks, Fairbanks, AK, USA;4. Pacific Oceanological Institute, Russian Academy of Sciences, Vladivostok, Russia;5. Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden;1. Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education/Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China;2. Institute of Marine Organic Geochemistry, Ocean University of China, Qingdao 266100, China;3. Qingdao Institute of Marine Geology, Qingdao 266071, China;4. Key Laboratory of Marine Sedimentology and Environmental Geology, State Oceanic Administration, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai, China;2. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany;3. Department of Geosciences, University of Bremen, Bremen, Germany;4. MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany;1. Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education/Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China;2. Key Laboratory of Global Change and Marine-Atmospheric Chemistry of State Oceanographic Administration, Third Institute of Oceanography, SOA, Xiamen 361005, China;3. Geological Institute, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland;4. Laboratory for Ion Beam Physics, Department of Physics, ETH Zürich, 8093 Zürich, Switzerland;5. Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. Geological Institute, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland;3. Department of Geological Oceanography and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, China;4. Laboratory of Ion Beam Physics, ETH Zürich, Otto-Stern-Weg 5, 8093 Zürich, Switzerland;5. Department of Earth Science-Geochemistry, Geosciences, Utrecht University, 3584 CD Utrecht, the Netherlands |
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| Abstract: | The Amazon River spawns a vast mobile mudbelt extending ～1600 km from the equator to the Orinoco delta. Deposits along the Amazon–Guianas coastline are characterized by some of the highest Corg remineralization rates reported for estuarine, deltaic, or shelf deposits, however, paradoxically, except where stabilized by mangroves or intertidal algal mats, they are usually suboxic and nonsulfidic. A combination of tides, wind-driven waves, and coastal currents forms massive fluid muds and mobile surface sediment layers ～0.5–2 m thick which are dynamically refluxed and frequently reoxidized. Overall, the seabed functions as a periodically mixed batch reactor, efficiently remineralizing organic matter in a gigantic sedimentary incinerator of global importance. Amazon River material entering the head of this dynamic dispersal system carries an initial terrestrial sedimentary Corg loading of ～ 0.7 mg C m?2 particle surface area. Total Corg loading is lowered to ～ 0.2 mg C m?2 in the proximal delta topset, ～60–70% of which remains of terrestrial origin. Loading decreases further to 0.12–0.14 mg C m?2 (～60% terrestrial) in mudbanks ～600 km downdrift along French Guiana, values comparable to those found in the oligotrophic deepsea. DOC/ΣCO2 ratios in pore waters of French Guiana mudbanks indicate that >90% of metabolized organic substrates are completely oxidized. Within the Amazon delta topset at the head of the dispersal system, both terrestrial and marine organic matter contribute substantially to early diagenetic remineralization, although reactive marine substrate dominates (～60–70%). The conditional rate constant for terrestrial Corg in the delta topset is ～0.2 a?1. As sedimentary Corg is depleted during transit, marine sources become virtually the exclusive substrate for remineralization except very near the mangrove shoreline. The δ13C and Δ14C values of pore water ΣCO2 in mudbanks demonstrate that the primary source of remineralized organic matter within ～1 km of shore is a small quantity of bomb signature marine plankton (+80‰). Thus, fresh marine organic material is constantly entrained into mobile deposits and increasingly drives early diagenetic reactions along the transit path. Relatively refractory terrestrial Corg is lost more slowly but steadily during sedimentary refluxing and suboxic diagenesis. Amazon Fan deposits formed during low sea level stand largely bypassed this suboxic sedimentary incinerator and stored material with up to ～3X the modern high stand inner shelf Corg load (Keil et al., 1997b. Proceedings of the Ocean Drilling Program, Scientific Results. Vol. 155. pp. 531–537). Sedimentary dynamics, including frequency and magnitude of remobilization, and the nature of dispersal systems are clearly key controls on diagenetic processes, biogeochemical cycling, and global C storage along the continental margins. |
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