Organic carbon, phosphorus and nitrogen in surface sediments of the marine-coastal region north and south of the Paria Peninsula, Venezuela

The organic carbon, phosphorus and nitrogen content of silt and clay fractions of surface sediments from the marine-coastal region north and south of the Paria Peninsula (PP) were quantified. Organic carbon concentrations (Corg) were determined by dry combustion after decarbonation with 10% hydrochloric acid, and total phosphorus (TP) and total nitrogen (TN). This information was then used to produce maps of the iso-concentrations of the distribution of these elements in the sub-marine continental shelf north of the PP and in the Gulf of Paria (GP). In the silt fraction, the Corg concentration, TP and TN showed average values of 1.53, 0.04 and 0.03%, respectively. The highest Corg, PT and NT values were recorded from silts from the PP with a gradual increase towards the west and the lowest figures were found in the GP. In the clay fraction, Corg, TN and TP had mean values of 1.64, 0.13 and 0.04%, respectively, and showed a spatial distribution very similar to the silt fraction, indicating the influence of ocean currents and coastal upwelling patterns. The C/N ratio had an average of 23.67 and showed that the Corg present in the PP sediments is of marine origin, resulting from primary productivity, especially towards the west. This zone has been identified as the most productive in this region due to coastal upwelling and the influence of the Orinoco and Amazon rivers (Gomez 1996 ; Monente 1997 ). In contrast, a greater variability in the parameters measured was found in the GP sediments, probably due to the mixing of marine and continental Corg, confirming the influence of the Orinoco and Amazon waters brought by the Guyana Current.