Organic matter, isotopic composition of calcite veins in basement basalt and pore water at DSDP Leg 78A Holes

Sediments of the Barbados Ridge complex, cored on DSDP Leg 78A, contain low concentrations of acid-insoluble carbon (0.05-0.25%) and nitrogen (C/N 1.5-5) and dispersed C1-C6 hydrocarbons (100-800 ppb). The concentrations of organic carbon and 13C in organic carbon decrease with depth, whereas the concentration of dispersed hydrocarbons increases slightly with depth. These trends may reflect the slow oxidation of organic matter, with selective removal of 13C and slow conversion of the residual organic matter to hydrocarbons. Very minor indications of nitrogen gas were observed at about 250 meters sub-bottom at two of the drilling sites. Basement basalts have calcite veins with d13C values in the range of 2.0 to 3.2 per mil and d18O-SMOW values ranging from 28.5 to +30.6 per mil. Interstitial waters have d18O-SMOW of 0.2 to -3.5 per mil and dD-SMOW of -2 to -15 per mil. The oxygen isotopic composition of the calcite veins in the basement basalts gives estimated equilibrium fractionation temperatures in the range of 11 to 24°C, assuming precipitation from water with d18O-SMOW in the range of +0.1 to -1.0 per mil. This suggests that basalt alteration and precipitation of vein calcite occurred in contact either with warmer Campanian seawater or, later, with pore water, after burial to depths of 200- 300 meters. Pore waters from all three sites are depleted in deuterium and 18O, and dissolved sulfate is enriched in 34S at Sites 541 and 542, but not at Site 543.

Sediment descriptions, stage, calcium carbonate, organic carbon, delta 13C and geolipids at DSDP Hole 93-603B

Organic matter contents of black shales from the Cretaceous Hatteras and Blake-Bahama formations have been compared to those from surrounding organic-poor strata using C/N ratios, d13C values, and distributions of extractable and nonsolvent-extractable, long-chain hydrocarbons, acids, and alcohols. The proportion of marine and land-derived organic matter varies considerably among all samples, although terrigenous components generally dominate. Most black shales are hydrocarbon-poor relative to their organic-carbon concentrations. Deposition of the black shales in Hole 603B evidently occurred through turbiditic relocation from shallower landward sites and rapid reburial at this outer continental rise location under generally oxygenated bottom-water conditions.

delta 13C, delta 15N and delta 34S of temperate eelgrass food web in the western Baltic Sea

Simultaneous triple stable isotope analysis of carbon, nitrogen and sulphur was employed to study the temporal variation in the food web of a subtidal eelgrass (Zostera marina) bed in the western Baltic Sea. Samples of three potential food sources: eelgrass, epiphytes and seston, as well as consumer species were collected biweekly from March through September 2011. Temporal variation of stable isotope signatures was observed in primary producers and consumer species. However, variation within a species, particularly omnivores, often exceeded variation over time. The high degree of omnivory among the generalist feeders in this eelgrass community allows for generalist feeders to flexibly switch food sources, thus enhancing food web stability. As coastal systems are subject to seasonal changes, as well as alterations related to human disturbance and climate, these food webs may retain a certain resilience due to their plentiful omnivores.

Calcite composition and stable isotope record of ODP Hole 103-637A peridotites

The peridotite recovered from Ocean Drilling Program Hole 637A, Galicia margin, has suffered extensive low-temperature alteration that includes serpentinization, calcite veining, and calcite replacement. This note presents textural and geochemical data on the serpentine and calcite. Such data indicate that the serpentinization, serpentine veining, and calcite veining of the peridotite occurred in several stages late in the history of the peridotite emplacement, probably after the peridotite was emplaced at crustal levels. It is also apparent that some deformational events (evidenced by faulting and brecciation of both serpentine and calcite veins) continued after the main phase of low-temperature alteration. The geochemistry and petrology, structure, and high-temperature alteration of the peridotite are discussed in separate papers in this volume (Evans and Girardeau, 1988, doi:10.2973/odp.proc.sr.103.138.1988; Girardeau et al., 1988, doi:10.2973/odp.proc.sr.103.135.1988; Kimball and Evans, 1988, doi:10.2973/odp.proc.sr.103.140.1988; Agrinier et al., 1988, doi:10.2973/odp.proc.sr.103.136.1988).