Contrasting chemical and isotopic compositions of organic matter in Changjiang (Yangtze River) estuarine and East China Sea shelf sediments |
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| Authors: | Xu-Chen Wang Ming-Yi Sun An-Chun Li |
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| Institution: | (1) Institute of Oceanography, Chinese Academy of Sciences, Qingdao, 266071, China;(2) Department of Environmental, Earth and Ocean Science, University of Massachusetts at Boston, MA 02120, USA;(3) Department of Marine Sciences, University of Georgia, Athens, GA 30602, USA;(4) College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266003, China |
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| Abstract: | To examine the source and preservation of organic matter in the shelf sediments of the East China Sea (ECS), we measured bulk
C/N and isotopes, organic biomarkers (n-alkanes and fatty acids) and compound-specific (fatty acids) stable carbon isotope ratios in three sediment cores collected
from two sites near the Changjiang Estuary and one in the ECS shelf. Contrasting chemical and isotopic compositions of organic
matter were observed between the estuarine and shelf sediments. The concentrations of total n-alkanes and fatty acids in the shelf surface sediments (0–2 cm) were 5–10 times higher than those in estuarine surface sediments
but they all decreased rapidly to comparable levels below the surface layer. The compositions of n-alkanes in the estuarine sediments were dominated by C26-C33 long-chain n-alkanes with a strong odd-to-even carbon number predominance. In contrast, the composition of n-alkanes in the shelf sediment was dominated by nC15 to nC22 compounds. Long-chain (>C20) fatty acids (terrestrial biomarkers) accounted for a significantly higher fraction in the estuarine sediments compared to
that in the shelf sediment, while short-chain (<C20) saturated and unsaturated fatty acids were more abundant in the shelf surface sediments than in the estuarine sediments.
Stable carbon isotopic ratios of individual fatty acids showed a general positive shift from estuarine to shelf sediments,
consistent with the variations in bulk δ
13CTOCTOC. These contrasts between the estuarine and shelf sediments indicate that terrestrial organic matter was mainly deposited
within the Changjiang Estuary and inner shelf of ECS. Post-depositional diagenetic processes in the surface sediments rapidly
altered the chemical compositions and control the preservation of organic matter in the region. |
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| Keywords: | Organic biomarker stable carbon isotope sediment Changjiang River estuary East China Sea shelf |
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