SURFACE SEDIMENT SURVEY OF THE SEABED ON THE NORTHWESTERN SLOPE OF CUBA, SOUTHERN STRAITS OF FLORIDA

The seabed offthe northwestern coast of Cuba was explored to study the sedimentary and biological characteristics of surface sediments in three blocks leased to REPSOLYPF- Cuba S.A., at depths between 1600 and 2000m. Subcoring of surficial sediments was conducted for stable isotopic analysis, total organic carbon and nitrogen contents, and infauna description. Spatial heterogeneity in moderately laminated sediments was detected among blocks. Surface sediments consist of silty and clay materials, mainly composed by calcite, were impoverished in organic matter and rich in hemipelagic components. From the northeastern end of this area (Block III, 1640m) large limestone blocks stained with hydrocarbons were recovered. Rock fragments had a coarse appearance and were impregnated with a strong oil odor. Their external surface had a blackened tar layer and an irregular iron-oxyhydroxide stain. Bulk sediment isotopic analysis (δ[sup]13[/sup]C: -25.7 to -18.5%) revealed a non-methanogenic carbon source, suggesting that oil seepage occurs localized. Source of sedimentary organic carbon was mainly oceanic (δ[sup]13[/sup]C: -18.50 to -19.13 % δ[sup]15[/sup]N: +3.6 to +6.4%; molar C:N ratios of 2.4 to 5). Bottom water conditions were stable (5ml El.[sup]-1[/sup] O[sub]2[/sub], 3-4°C, 35.0psu) and infauna density was low due to reduced organic matter flux to deep sediments. This survey documents one of the deepest oil seeps in the vicinity of the eastern Gulf of Mexico. [PUBLICATION ABSTRACT]