Comparison of polycyclic aromatic hydrocarbon distributions and sedimentary organic matter characteristics in contaminated, coastal sediments from Pensacola Bay, Florida

In this study, we examined the distribution of polycyclic aromatic hydrocarbons (PAHs) in a contaminated coastal area and the characteristics of the natural organic matter in tandem. We present a detailed study of PAH concentration, distribution, and organic matter characteristics of three core samples from Pensacola Bay, Florida. Solid-state 13C Nuclear Magnetic Resonance (NMR), pyrolysis gas chromatography coupled with mass spectrometry (GC-MS), and tetramethyl ammonium hydroxide (TMAH) thermochemolysis GC-MS were applied to obtain structural details about the sedimentary organic matter. Elemental compositions (carbon and nitrogen) and estimates of black carbon contents are also reported. These coastal sediments were found to contain more PAHs in the upper 15 cm layers than in the bottom 15-25 cm samples. The samples that contained the most PAHs also contained the least amount of aromatic carbon and contained a significant amount of paraffinic carbon. Lignin-derived pyrolysis and TMAH thermochemolysis products were abundant and generally higher in all of the samples in comparison to those reported for modern coastal sediments, indicating a large flux of terrestrial carbon. The black carbon contents were found to range from 4.3% to 6.8%, which are significantly lower than other reports of black carbon in sediments, which represent as much as 65% of the total organic carbon content. The low black carbon content suggests that this type of refractory carbon may not be as responsible for regulating PAH distribution as indicated by other researchers.     

Using ocean ambient noise for array self-localization and self-synchronization

Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of ambient noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.     

Degradation in Cemented Marine Clay Subjected to Cyclic Compressive Loading

The influence of cyclic loading on the strength and deformation behavior of cemented marine clay has been studied. This marine clay is of recent Pleistocene origin and deposited in a shallow water marine environment. Open pits were dug in sheeted enclosures and from these pits, undisturbed samples were taken for strength testing. A series of standard triaxial shear tests and stress controlled one-way cyclic load tests were conducted at consolidation stress ranges below and above the preconsolidation pressure. For the stress levels below the preconsolidation pressure, the cyclic loading has brought about the collapse of the cementation bond through an increase in strains, and at higher pressure ranges, the soil behaves like typical soft clay. This experiment studied the rate of development of strain and pore water pressure and shows that rate is a function of number of cycles, applied stress, and stress history. In addition, soil degradation during cyclic loading is studied in terms of Degradation Index. Attempt has been made to predict stain, pore water pressure, and degradation index through an empirical model.     

Inter-annual variability in larval supply to populations of three invertebrate taxa in the northern California Current

We investigated sources of inter-annual variability in larval supply to crab and sea urchin populations at Bodega Head and Point Reyes in northern California. During the spring and summer upwelling seasons of the years 1992 through 1997 we monitored the weekly settlement rates of nine species of crabs and two species of sea urchins. As observed in previous studies, daily values of alongshore windstress, temperature and salinity provided evidence for the poleward flow of relatively warm, low salinity water from south of Point Reyes, an apparent retention zone, during upwelling relaxation events. In years dominated by these events (1992, 1993, 1995 and 1996) we observed that alongshore windstress, temperature and salinity were coherent and temperature was significantly correlated with cancrid crab settlement. During these years the magnitude of cancrid crab settlement and the fraction of cancrid crabs relative to other crab species settling were high. Over four years of concurrent sampling there was consistently greater cancrid crab settlement at the Point Reyes site, within the retention zone, than at Bodega Head. Settlement of non-cancrid crabs (porcellanids, grapsids, pagurids and majids) was not as closely linked to intra-annual patterns of upwelling and relaxation, possibly due to the shorter seasonal availability of larvae allowing for the influence of fewer relaxation events. Settlement of this group among years was positively correlated with environmental indicators of strong seasonal upwelling; high salinity, Bakun upwelling index and low temperature. Sea urchin settlement events were observed in June and July of 1992, 1994 and 1997 during warming periods when salinity and temperature were increasing and alongshore windstress was low. Across the six years of the study, we found that cancrid crab larvae had a more even seasonal availability than larvae of non-cancrid species, which settled in greatest numbers during the early portion of the upwelling season. Sea urchins settled in greatest numbers during the later part of the upwelling season. Together these patterns demonstrate the taxon-specific way that inter-annual variability in larval supply is forced by the coincidence of larval availability with favorable physical transport mechanisms.     

Interaction of Surface Waves in a Basin with Floating Broken Ice

The multiscale method is used to obtain asymptotic expansions up to the quantities of the third order for the elevations of the surface of the basin and the velocity potential of motion of liquid particles in the wave disturbances formed in the process of nonlinear interaction of periodic running waves of the first and second harmonics in a homogeneous ideal incompressible liquid of constant finite depth covered with broken ice. The dependences of the amplitude-phase structure of disturbances on the ice thickness, depth of the basin, and the parameters of interacting harmonics are investigated. We estimate the error of evaluation of the characteristics of the formed vertical displacement of the surface of the basin and nonlinear mass transfer introduced by neglecting the curvature of the wave profile in the expression for the velocity potential in deducing the kinematic and dynamic surface boundary conditions for nonlinear approximations.     

Mineral assemblages occurring around hydrocarbon vents in the northern Gulf of Mexico

Magnesian calcites are the most abundant authigenic minerals associated with hydrocarbon vents at 25 sites, in water depths ranging from 100 to 600 m in the Green Canyon area and about 2200 m in the Alaminos Canyon area on the Continental Slope of the northern Gulf of Mexico. The most frequently encountered magnesian calcites have 10–15 mol% MgCO₃ and the apparent structural disorder revealed by XRD peak widths increases with Mg substitution. There are no systematic variations in Mg content with respect to water depth or geographic location. The calcite saturation state of the precipitating fluid is primarily determined by the nature of the fluids escaping from the vents, not the ambient seawater.     

The relationship between the amplitudinal characteristics of the high-frequency spectral components of wind-generated waves and the wind velocity over the sea

The relationship between the RMS amplitudes of the wind wave spectral components and the wind speed has been studied at ten frequencies in the band of 0.65–23 Hz. To measure the parameters of the high-frequenci waves, a resistance elevation wave gauge was operated, which was deployed in the Black See on an oceanographic platform near Katsively. The correlation between the wave amplitudes and the wind velocity at high frequencies of 5–23 Hz, corresponding to gravitation-capillary ripples, was found to reach a value of 0.8. At lower frequencies of 0.65–4.3 Hz, corresponding to short gravity waves, it dropped to 0.5–0.7. The response of spectral components to the wind speed variations in the gravity-capillary range is higher than in the range of short gravity waves. The results obtained differ from Phillips' idea about a saturated range for the frequency form of the spectrum of high-frequency gravity waves, since a linear dependence of the spectral amplitudes on the wind speed is established at a wind of force 1–8.Translated by Mikhail M. Trufanov.     

The bottom currents in the area of abyssal hills in the north-east tropical Pacific Ocean

The results of simultaneous measurements of the bottom (6.25 and 35 m above the bottom) currents, deep currents, and surface currents made at three points in the north-east tropical Pacific Ocean are given. The bottom intensification of the current velocity is revealed in a layer of 35–25 m above the bottom. The estimation of the thickness of the bottom boundary layer (BBL) indicates that the velocity intensification is observed over the boundary layer upper border. A 10-day long benthic storm with a maximum measured velocity of 13 cm/s was revealed 6 m above the bottom. As was found, the origin of the benthic storm is associated with the penetration of an anticyclonic eddy down to the bottom.Translated by Mikhail M. Trufanov.