An extensive series of optical absorption spectra were recorded for waters in the eastern Caribbean Sea, the Gulf of Paria, and the Orinoco River Estuary during the high‐flow period of the Orinoco River in the Fall of 1988. Evidence for high levels of dissolved, colored organic matter (COM) was found throughout the eastern Caribbean, with these levels increasing substantially at stations nearer the Gulf of Paria and the Orinoco River. The dependence of the absorption at 300 nm (a300) on salinity exhibited conservative mixing behavior for transects through the Gulf of Paria. In contrast, transects through the Orinoco Estuary revealed that a300 remained approximately constant or slightly increased with increasing salinity up to 27‰, after which it decreased linearly with increasing salinity. This nonconservative behavior was not produced by COM release from suspended particulate matter at higher salinity, nor did it appear to originate from the sediment. Below 30‰, the slopes of the log‐linearized absorption spectra were independent of salinity (0.0140 nm−1). At higher salinities, the slopes apparently increased, suggesting that the COM is modified. Based on specific absorption coefficients measured for COM isolated from this area, COM input by the Orinoco River is estimated to be ∼ 2.5 × 1012 g C/yr, which represents about 1% of the total global transport of dissolved organic carbon to the ocean. This input is likely to influence substantially the carbon cycle, photochemical properties, and optical characteristics of the waters in this region.

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Nitrogenous nutrients, dissolved silicate, and salinity were measured in surface waters and shallow hydrocasts along similar cruise tracks during the spring (dry season) and fall (wet season) of 1988. Both cruises transected the eastern Caribbean, transited the Gulf of Paria, ran parallel to the Orinoco Delta and into the main channel of the Orinoco River. Trends in primary productivity were also measured by daily carbon 14 incubations. In both seasons, samples covered the range from highly oligotrophic and transparent to highly productive and rich in biogenic and abiogenic particulate matter. Most of the Orinoco outflow appears to turn N to NW and remains in shallow waters off Venezuela and surrounding Trinidad, permitting benthic regeneration of river‐borne nutrients. However, the role of the Orinoco and associated low‐salinity coastal waters in fertilizing large areas of the eastern Caribbean basin, as suggested by satellite imagery, can be approximated crudely from the nutrient composition at Boca de Dragon, which is representative of the nutrient status of these waters as they flow into deeper Caribbean waters. Additional nutrients may be supplied to the area primarily from Amazon‐derived water entering the Caribbean Basin further north, with some coastal upwelling along the continental shelf in the dry season.

Resumen: Algunos aspectos geoquímicos de los sedimentos superficiales del litoral de la costa nororiental del Golfo de Cariaco, estado Sucre, Venezuela, son presentados en esta investigación. La estructura geológica del Golfo es tectónica con presencia de sistema de fallas, en donde los sedimentos del litoral norte pueden ser texturizados como arenosos por ser bastantes permeables en su mayoría y presentar un contenido hídrico promedio de 22,44%. Los contenidos de materia orgánica determinados fueron bajos con promedios de 7,63%, detectándose porcentajes de carbono orgánico de 0,97% y 21,97% de carbonatos de calcio. Se apreciaron concentraciones altas de fósforo (360,03 μg.g -1 ) y de nitrógeno total (396,29 μg.g -1 ), siendo la relación entre estos elementos de 1,09, indicando cierto grado de fertilidad orgánica. Las concentraciones de metales presentaron distribuciones discrepantes, con promedios para hierro de 3348,58 μg.g -1 , manganeso 14,63 μg.g -1 , níquel 13,68μg.g -1 , cinc 11,59μg.g -1 , cromo 10,23μg.g -1 , cobre 2,29μg.g -1 , cadmio 1,04 μg.g -1 y plomo 0,57 μg.g -1 , mostrándose contaminación, especialmente por cadmio. La no linealidad presentada por algunos metales como plomo, cobre, níquel y manganeso con el hierro, sugiere la existencia de entradas de tipo no natural, causadas por fuentes de origen antropogénico. Esta fuente probablemente está influenciada por descargas fluviales, industriales y por el aporte exógeno unidireccional desde la costa sur.Palabras claves. Golfo de Cariaco, estudio geoquímico, sedimentos.Abstract: This research presents some geochemical aspects of the marine surface sediments of the north coast of the Gulf of Cariaco, in the state of Sucre, Venezuela. The gulf has a tectonic structure and a fault system mainly featuring sandy sediments, most of which are quite permeable and have an average hydric content of 22.44%. The content of organic matter detected was low, averaging 7.63%, organic carbon and calcium carbonate commanding 0.97% and 21.97%, respectively. Contrarily, phosphorus and total nitrogen were high, 360.03 mg.g -1 for the former and 396.29 mg.g -1 for the latter, the total nitrogen to phosphorus ratio being 1.09, which indicates a certain degree of organic fertility. The metal concentrations presented different distributions, averaging 3548.58, 14.63, 13.68, 11.59, 10.23, 2.29, 1.04, and 0.57 mg.g -1 for iron, manganese, nickel, zinc, chromium, copper, cadmium, and lead, respectively, indicative of contamination, especially by cadmium. The nonlinearity with the iron presented by some metals such as copper, nickel, and manganese suggests the existence of anthropogenic influxes, probably swayed by river-borne industrial contributions, including the exogenous discharges running seawards from the south coast.

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