ALBERT

Description: Permeability, electrical resistivity, and thermal conductivity measurements were performed on samples from the Bent Hill area of the Middle Valley on the northern Juan de Fuca Ridge. Thermal conductivity measurements were also made on samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal area in the Mid-Atlantic Ridge for direct comparison with previous studies and the Middle Valley results. Electrical resistivity and permeability measurements were made as a function of confining pressure on 15 samples comprising different lithologic compositions found in the Bent Hill area. The effect of pressure on electrical resistivity values is relatively small and the observed frequency dependence is highly controlled by the sulfide content in these rocks. Permeabilities are in the 10**-16 to 10**-20 m**2 (0.1-100 µD) range. Although permeability does not recover in samples that undergo significant permanent deformation, the elastic permeability dependence on confining pressure is relatively small. Permeability correlates with porosity. Permeability anisotropy correlates with the presence of oriented sulfide veins with increased flow parallel to the veins. Thermal conductivity measurements made on 41 samples from Middle Valley and 9 samples from the TAG area show systematic variations due to changes in composition and a weak relationship with porosity for sedimentary samples from Middle Valley. A comparison between the divided-bar and the half-space needle-probe methods of measuring thermal conductivity shows good agreement for the Leg 169 measurements unlike previous results from Legs 139 and 158. The discrepancies observed in earlier studies seem to be related to the long times used in the older measurements for the optimal T vs. ln(t) data interval. The apparatus used during Leg 169 was smaller, sampled a smaller volume of core, and in high conductivity material was not influenced by boundary effects.

Description: The ocean history of reactive phosphorus (P) (i.e., dissolved P available to fuel oceanic primary productivity) is of interest because of the role of P as a biolimiting nutrient, and knowledge of P burial in marine sediments is key to testing hypotheses about temporal changes in P input or output fluxes. Our understanding of the history of the P cycle over the Cenozoic has increased substantially with temporal records of reactive P mass accumulation rates from open-ocean Pacific and Atlantic equatorial sites. However, questions about the relative importance of nutrient burial in ocean-margin sediments relative to burial in open-ocean sediments and about the extent of P remobilization in organic-rich, reducing environments characteristic of margin sediments remain unresolved. Nutrient burial in oceanic boundary current systems has been suggested to have a controlling role in oceanic nutrient budgets in certain time intervals (Vincent and Berger, 1985, doi:10.1029/GM032p0455), with higher sediment accumulation rates balancing the limited spatial extent of these sediments. Some investigators suggest that remobilization of P from reducing sediments in margin settings is a significant positive feedback to primary productivity (e.g., Van Cappellan and Ingall, 1994, doi:10.1029/94PA01455), whereas other results indicate that both P uptake and P release may occur in these settings depending on the balance of organic carbon and iron supply to the sediments and on the oxygenation of bottom waters (McManus et al., 1997, doi:10.1016/S0016-7037(97)00138-5). It is important to quantitatively understand the geochemistry of reactive P in margin sediments, where productivity and delivery of organic-rich material to the sediments in relatively shallow-water settings is often sufficient to promote anoxia in interstitial waters. To address these questions, we determined the P concentrations and geochemistry in sediment samples from eight sites drilled during Ocean Drilling Program (ODP) Leg 167, California margin (Sites 1010-1012, 1014, 1016-1017, and 1021-1022). These results are the first records of reactive P concentrations on long time scales-required for the calculation of P accumulation rates-for sediments from a highly productive eastern boundary current setting. In addition, we determined calcium carbonate contents and biogenic silica concentrations to define the environments of sedimentary production, burial, and diagenesis.