The effect of sea level change on nutrient supply to the anoxic Cariaco demonstrates the fundamental importance of nitrogen (N2) fixation and phosphate to oceanic production. As N2 fixation produces biomass of low delta15N and has been reported to be an important component of the nitrogen cycle in the modern Cariaco Basin, we propose that it contributes to the light interglacial delta15N (~2-3) values observed in the Ocean Drilling Program (ODP) site 1002 sediment record. During the glacials the sediments are bioturbated (oxic conditions) with low total organic carbon (TOC) contents and sedimentary delta15N values of ~5, suggesting that nitrogen (N2) fixation contributed little to the N nutrition of Cariaco surface waters. The most plausible explanation for the inferred glacial/interglacial changes in N2 fixation in the Cariaco is that they have occurred in response to variations in the N/P ratio of the nutrient supply, driven by changes in denitrification.
Reprinted by permission of the American Geophysical Union.
Lind, I. 1997. A modified Wyllie equation for the relationship between porosity and sonic velocity of mixed sediments and carbonates from the Caribbean Sea. In Middleton, M. (Ed.), Nordic Petroleum Series III, Research in Petroleum Technology: Aas (Nordisk Energi Forskningsprogram), 123-137.
Continuous drill cores from the Caribbean Sea of up to 1 km thick mixed sediments and carbonates were recovered by Ocean Drilling Program Leg 165. The sediments range in porosity from 10% to 80% and in carbonate content from 20% to 95%. Unconfined P-wave velocities from this material were measured by ODP on freshly retrieved water saturated material, and are here compared to similar data from ODP Leg 130 (Ontong Java Plateau) where more than 95% pure carbonates were recovered. To fit low porosity as well as high porosity data, Wyllie's equation can be modified by replacing the porosity by the ratio between porosity and critical porosity. Irrespective of clay content the same modified Wyllie type linear relationship was found between the P-wave travel time and porosity. For samples from the Caribbean a critical porosity of 73% was found. A critical porosity of 68% was found for samples from the Ontong Java Plateau.