A lipid biomarker investigation of the sources and distribution of organic matter in river-influenced shelf sediments of NE Brazil

• Published in: Organic geochemistry Vol. 151; p. 104162
• Main Authors: Carreira, Renato S., Albergaria-Barbosa, Ana Cecília R. de, Arguelho, Maria de Lara P.M., Garcia, Carlos A.B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2021
• Subjects: Molecular markers; n-Alcohols; Organic matter; Sergipe-Alagoas continental shelf; Sterols; Taraxerol; Molecular markers; Organic matter; Taraxerol; Sterols; n-Alcohols; Sergipe-Alagoas continental shelf
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2020.104162

•Organic matter (OM) in sediments from the NE Brazilian shelf was characterized.•Mud depocenters accumulated OM in a carbonate shelf.•Export of OM by the major local river limited by dam construction.•Smaller rivers contributed mangrove-derived OM to the inner shelf. A better understanding of the sources – continental or marine – and distribution of organic matter (OM) in shelf sediments of areas under distinct natural and anthropogenic forces is essential to obtain a global view of the carbon cycle. In this study, we evaluated the influence of river discharge on the OM accumulation pattern in a portion of the NE Brazilian continental margin (10–15°S) by considering a suite of lipid biomarkers (sterols, n-alcohols, phytol and taraxerol) in surface sediments. A total of 36 samples were collected adjacent to river mouths representing drainage basins of varying size and representing different human intervention levels, namely the São Francisco, Vaza Barris, Sergipe and Piauí-Real rivers. The average concentration of the total quantified lipids was 3.77 ± 1.93 µg g−1, with the lowest values detected at the São Francisco River pro-delta. This result seems to reflect the reductions in the São Francisco river flow during the last decades caused by human interventions (diverse water use and urbanization, among others) and climate change (reduced precipitation) along its drainage basin, which seems to affect other smaller basins to a lesser extent. Our findings highlight that human interventions and climate change are relevant drivers for biogeochemical processes even in shelves receiving the flow from small to medium rivers in Brazil, which agree with other records worldwide. Finally, we hope the data presented herein contribute to the development of a management system based on a watershed-coastal ocean scaling and socio-environmental perspective for the Sergipe and Alagoas shelf.