Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: Possible contribution of organic carbon from savannas

Ernesto Medina, Marta Francisco, Leonel Sternberg, William T. Anderson

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

The 87Sr, 13C, and 15N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The 87Sr/86Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ13C values were relatively high averaging -21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ13C values did not differ significantly among transects. High δ13C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ15N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ15N values differed significantly among transects (4.9-5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position.

Original languageEnglish (US)
Pages (from-to)527-536
Number of pages10
JournalEstuarine, Coastal and Shelf Science
Volume63
Issue number4
DOIs
StatePublished - Jun 1 2005

Keywords

  • Amazon River
  • Continental shelf
  • Organic matter
  • Orinoco Delta
  • Sediments
  • Stable isotopes

ASJC Scopus subject areas

  • Aquatic Science
  • Oceanography

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