The supply and preservation of ancient and modern components of organic carbon in the Canadian Beaufort Shelf of the Arctic Ocean |
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| Institution: | 1. Department of Geological Sciences, Earth & Water Sci. Bldg. 302, 701 Sumter Street, University of South Carolina, Columbia, SC 29208, USA;2. 7137 Wallace Drive, Brentwood Bay, Canada V8M 1G9;3. Department of Fisheries and Oceans, Institute of Ocean Science, PO Box 6000, Sidney, BC, Canada V8L 4B2;4. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;1. Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305, USA;2. Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, Hanover, NH 03755, USA;3. Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA;4. Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;5. Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME 04575, USA;6. Bermuda Institute of Ocean Sciences, Ferry Reach GE01, Bermuda;7. Marine Science Program,and Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC 29208, USA;8. Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;9. Graduate School of Geography, Clark University, Worcester, MA 01610, USA;10. NOAA Pacific Marine Environmental Laboratory, Seattle, WA 98115, USA;11. Université Pierre et Marie Curie, Laboratoire d’Océanographie de Villefranche, Villefranche-sur-Mer 06238, France;12. Takuvik Joint International Laboratory, Département de Biologie and Québec-Océan, Université Laval, Canada;13. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA;14. Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7;1. Department of Geological Sciences, University of Florida, Gainesville, FL, USA;2. Global Aquatic Research LLC, 6276 Ridge Rd., Sodus, NY 14551, USA;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. Geological Institute, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland;3. Third Institute of Oceanography, State Oceanic Administration (SOA), Xiamen 361005, China;4. Laboratory for Ion Beam Physics, Department of Physics, ETH Zürich, 8093 Zürich, Switzerland;5. Institute of Marine Organic Geochemistry, Ocean University of China, Qingdao 266100, China;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 |
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| Abstract: | The provenance of organic matter in sediments from the Mackenzie River and Beaufort Shelf was investigated using the stable carbon and radiocarbon isotopic compositions of bulk organic matter and the stable carbon isotopic compositions of individual organic compounds, including lignin-derived phenols and lipid-derived fatty acids. Most river suspended sediments and shelf surface sediments contained organic carbon characterized by highly depleted Δ14C values that were consistent with average radiocarbon ages exceeding 7000 years. The stable carbon isotopic signatures of lignin phenols were uniformly depleted (?25≥δ13C≥?32‰), indicating the predominant contributions of C3 vascular plant sources. The isotopic compositions of C14 and C16 fatty acids exhibited important contrasts between the river (?36‰ to ?40‰) and shelf (?25‰ to ?29‰) sediments that were consistent with contributions from freshwater algae and/or vascular plants in the former and marine phytoplankton in the latter. Using 14C isotopic mass balance, the abundances of modern and ancient organic matter were quantitatively constrained. The fate of organic matter in the Beaufort Shelf was explored by normalizing these abundances to the specific surface area of sediments. Ancient organic carbon, which may include old pre-aged soil material as well as fossil bitumen or kerogen, accounted for the majority (～70%) of the particulate organic matter exported by the Mackenzie River and deposited in surface sediments of the Beaufort Shelf. Modern organic carbon accounted for ～30% in both river and shelf sediments, with significant contributions from vascular plant-derived materials in both river and shelf samples and from marine algae in the shelf sediments. Respiration (and/or leaching) of particle-bound marine organic matter dominates the carbon metabolism in the Mackenzie Delta/Beaufort Shelf region. However, land-derived pools, including modern carbon derived from vascular plants as well as ancient carbon also appeared to undergo a degree of post-depositional degradation prior to burial in the shelf. These novel source apportionments are reflected in an updated carbon budget for the study area. |
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