Determination of phospholipid fatty acid structures and stable carbon isotope compositions of deep-sea sediments of the Northwest Pacific, ODP site 1179

Sediment samples ranging from 0.05 to 278 m below sea floor (mbsf) at a Northwest Pacific deep-water (5564 mbsl) site (ODP Leg 191, Site 1179) were analyzed for phospholipid fatty acids (PLFAs). Total PLFA concentrations decreased by a factor of three over the first meter of sediment and then decreased at a slower rate to approximately 30 mbsf. The sharp decrease over the first meter corresponds to the depth of nitrate and Mn(IV) reduction as indicated by pore water chemistry. PLFA-based cell numbers at site 1179 had a similar depth profile as that for Acridine orange direct cell counts previously made on ODP site 1149 sediments which have a similar water depth and lithology. The mole percentage of straight chain saturated PLFAs increases with depth, with a large shift between the 0.95 and 3.95 mbsf samples. PLFA stable carbon isotope ratios were determined for sediments from 0.05 to 4.53 mbsf and showed a general trend toward more depleted δ¹³C values with depth. Both of these observations may indicate a shift in the bacterial community with depth across the different redox zones inferred from pore water chemistry data. The PLFA 10me16:0, which has been attributed to the bacterial genera Desulfobacter in many marine sediments, showed the greatest isotopic depletion, decreasing from − 20 to − 35‰ over the first meter of sediment. Pore water chemistry suggested that sulfate reduction was absent or minimal over this same sediment interval. However, 10me16:0 has been shown to be produced by recently discovered anaerobic ammonium oxidizing (anammox) bacteria which are known chemoautotrophs. The increasing depletion in δ¹³C of 10me16:0 with the unusually lower concentration of ammonium and linear decrease of nitrate concentration is consistent with a scenario of anammox bacteria mediating the oxidation of ammonium via nitrite, an intermediate of nitrate reduction.     

Thorium isotopes as tracers of particles dynamics and deep water circulation in the Indian sector of the Southern Ocean (ANTARES IV)

Dissolved and particulate samples were collected to study the distribution of thorium isotopes (²³⁴Th, ²³²Th and ²³⁰Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess ²³⁰Th (²³⁰Th_xs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τ_scav). Low τ_scav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the ²³⁰Th_xs scavenging efficiency and explain this difference. An innovative coupling between ²³⁴Th and ²³⁰Th_xs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d^− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d^− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the ²³⁰Th_xs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the ²³⁰Th_xs concentrations. A specific ²³⁰Th_xs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years.     

Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf

In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C₂, homogenous ¹³C₁ values and a large difference (19.7 on average) between ¹³C₁ (–55.2 to –53.6 PDB) and ¹³C₂ (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C₁ at the early thermal cracking stage of labile source materials, after which the C₂ gas is enriched in ¹³C by diffusion or biological alternation at the generation or accumulation site. The homogenous ¹³C₁ values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.     

Contamination of organotin compounds and imposex in molluscs from Vancouver,Canada

Gastropods and bivalves were collected at 15 sites at Vancouver and Victoria, Canada between 24 May and 7 June, 1999, to establish tissue concentrations of butyltin and phenyltin compounds, to record imposex symptoms in gastropods, and to assess the present status of organotin contamination around Vancouver. No neogastropods (such as Nucella lima) were found around Vancouver. Neogastropod populations could have been extirpated by severe TBT contamination in Vancouver, as relatively high concentrations of TBT were detected in tissues of Mytilus trossulus from Vancouver, and the neogastropods distributed in Vancouver might be sensitive to TBT. Recovery from imposex, however, was observed in neogastropod populations from three sites at Victoria and Mission Point. TBT contamination has continued around Vancouver, arising from continuous use of TBT in antifouling paints for vessels larger than 25 m in length; however, TBT has decreased around Victoria and Mission Point. Different patterns of TBT accumulation in tissue were observed among the bivalve species from Vancouver. The highest TBT concentration detected in Tresus capax suggested some possible adverse effects. TBT was the most predominant butyltin component in almost all bivalve specimens surveyed, suggesting a low rate of TBT metabolism. Phenyltin compounds were not detected in any molluscan specimens in this study.     

Occurrence of Nummulitic coralline limestone from offshore Palar Basin,Bay of Bengal,India

Abstract

Palar basin is located between Pennar and Cauvery sedimentary basins of East coast of India in Bay of Bengal, northeast Indian Ocean. Sea floor drill (Wire-line Autonomous Coring System – WACS) with operational capability of up to 3000?m water depth was developed to collect long cores from deep sea floor for geotechnical and ocean resource assessment studies. During the drilling operation it encountered Nummulitic coralline limestone of Lower Eocene age at 18 meters below the seafloor (mbsf) at 850?m water depth indicating carbonated platform presence for the first time at the study region. Bathymetry contour from Naval Hydrography Chart and General Bathymetric Chart of the Oceans (GEBCO) has revealed the presence of shallow mounds from 50 to 200?m depth closure contour near the sampling site at 850?m water depth which might be a submerged carbonated structure. Since, Nummulites are shallow water dwelling fauna (<20?m depth) but its occurrence at 18 mbsf in 850?m water depth is recorded because of the advancement in technology tool for long core sampling by means of sea floor drill.     

Wind-driven interannual variability over the northeast Pacific Ocean

Interannual variability of the sea surface height (SSH) over the northeast Pacific Ocean is hindcast with a reduced-gravity, quasi-geostrophic model that includes linear damping. The model is forced with monthly Ekman pumping fields derived from the NCEP reanalysis wind stresses. The numerical solution is compared with SSH observations derived from satellite altimeter data and gridded at a lateral resolution of 1 degree. Provided that the reduced gravity parameter is chosen appropriately, the results demonstrate that the model has significant hindcast skill over interior regions of the basin, away from continental boundaries. A damping time scale of 2 to 3 years is close to optimal, although the hindcast skill is not strongly dependent on this parameter.A simplification of the quasi-geostrophic model is considered in which Rossby waves are eliminated, yielding a Markov model driven by local Ekman pumping. The results approximately reproduce the hindcast skill of the more complete quasi-geostrophic model and indicate that the interannual SSH variability is dominated by the local response to wind forcing. There is a close correspondence the two leading empirical orthogonal modes of the local model and those of the observed SSH anomalies. The latter account for over half of the variance of the interannual signal over the region.     

Ridge development as revealed by sub-bottom profiles on the central New Jersey shelf

Closely-spaced 3.5 kHz seismic profiles were collected over the north-easterly trending ridge and swale system 50 km east-southeast of Atlantic City, New Jersey. They yield information on the Late Quaternary depositional history of the area, and on the origin of the ridge system. Four of the sub-bottom reflectors identified were sufficiently persistent to warrant investigation and interpretation. These reflectors, which have been cored, lithologically identified, and radiocarbon dated, are stratigraphically higher than the reflectors dealt with by the majority of previous studies. The upper three reflectors are definitely mid- and post-Wisconsin in age and present a record of the most recent glacial cycle. The upper three units associated with the observed reflectors appear to exert a pronounced influence on the bathymetry. The gently corrugated ridge system of Holocene sand is formed over the regionally flat-lying upper unit, an Early Holocene lagoonal silty clay. The characteristically flat, broad depressions of the area are floored by this lagoonal material. Locally, however, marine scour has cut through the silty clay into an underlying unit of unconsolidated fine Pleistocene sand. Several stages of trough development appear to be represented. After penetrating the lagoonal clay, troughs are initially narrow, but when incised through the sand into a lower, Pleistocene, silty-clay unit, the troughs become notably wider. As downcutting is inhibited by the lower clay, the upper clay is undercut as the trough widens in a fashion similar to a desert blowout.

The sub-bottom reflectors indicate that ridge development on the central shelf has involved aggradation as well as erosion. Some ridges seem to have grown by vertical and lateral accretion from small cores. The internal structure of other ridges suggests that they formed by the coalescence of several small ridges. Others appear to have undergone appreciable lateral migration.

The ridges appear to be in a state of continuing adjustment to the hydraulic regime of the deepening post-Pleistocene water column.     

Random dynamic analysis of multi-body offshore structures

A general method for the dynamic analysis of multi-body offshore structures is presented, being based on a constraint matrix approach. A method of deriving the constraint matrix for a general structure is given, and this is then used to derive the equations of motion of a whole system from those of it's component parts. The response of the system to both first and second order random wave forces is found and then used to calculate the forces and moments in the connecting mechanisms. The structure is assumed to have rigid component parts and a linearised frequency domain analysis method is used, although other methods are discussed. To illustrate it's use, the method is applied to both the SBS and Yoke-CALM design of offshore mooring terminal.