Fatty acid biomarkers of organic matter sources and early diagenetic signatures in sediments from a coastal upwelling area (south-eastern Brazil)

Abstract

Sediment bulk parameters and fatty acid biomarkers were used to investigate the relative contribution of major sources of particulate organic matter during upwelling and non-upwelling conditions, at organic enriched sites on the south-eastern Brazilian coast. The degradation state of the organic material and its implications for benthic food webs were also evaluated. Temperature and salinity values indicate the intrusion of the South Atlantic Central Water in spring with a strong influence at station 4S. C:N ratios and fatty acid biomarkers suggest that sedimentary particulate organic matter is mainly autochthonous and originated from phytoplankton, zooplankton and bacteria, with a minor terrestrial contribution. Short-chain saturated fatty acids predominated, indicating the prevalence of partially degraded detritus. An exception was station 4S, where polyunsaturated fatty acids dominated, indicating the input of labile organic matter linked to upwelling of the South Atlantic Central Water. Fatty acid concentrations and the organic carbon content of the sediments suggest that food quantity is not a limiting factor for benthic fauna. Despite the high organic background of the sediments, the sporadic inputs of labile organic matter associated with South Atlantic Central Water intrusions may produce an important impact on benthic fauna and on the biogeochemistry of the sediments.

Keywords:

• coastal sediments
• particulate organic matter
• fatty acids
• sources
• diagenetic status
• food quality

Acknowledgements

Funding was provided by ‘Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)’, project reference: 02/00022-0. The ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)’ of the Brazilian Government is acknowledged for the fellowship to N. Venturini. PEDECIBA and SNI-ANII are also thanked for financial support. We thank Prof. Dr Michel M. de Mahiques for bulk organic matter characterisation and also the crew of the RV Velliger II for their support during the cruises. We are also grateful to Prof. Dr Philip A. Meyers and two anonymous reviewers for their constructive suggestions and criticisms that helped us to improve a previous version of this manuscript.