Fate and effects of a heavy fuel oil spill on a Georgia salt marsh

Addition of a heavy oil to a Spartina salt marsh in the autumn resulted in high concentrations of polycyclic aromatic hydrocarbons in sediment and benthic animals. The highest concentrations of phenanthrene, chrysene and fluoranthene in the sediment were 112, 105 and 75 ng/g sediment, respectively. These concentrations rapidly decreased during the 20 week period following the spill. The times for these hydrocarbons to decrease to 50% of their highest values, i.e. half-life, were approximately 100, 70 and 30 days in sediment, mussels and oysters, respectively. Benthic macrofauna species showed three responses to oil addition which included no change, an increase, or a decrease in the population. No changes were noted in populations of fiddler crabs (Uca pugnax), oysters (Crassostrea virginica), and mussels (Modiolus demissus). Mud snails (Nassarius obsoleta) increased in density after the spill due to immigration of adult snails from untreated areas to scavenge on animals killed by the oil. Many of the adult periwinkles (Littorina irrorata) were killed by the oil. In the spring, juvenile periwinkles recolonised to oiled areas as a result of larvae settling.     

Carbon dioxide partial pressures in North Pacific surface waters — Time variations

Observations were made of time variations of the carbon dioxide partial pressures (Pco₂) of the atmosphere and surface sea waters in the Pacific subarctic region. Data were obtained on a cruise of the USC & GSSSURVEYOR in October, 1968 and on the TRANSPAC expedition of the CNAVENDEAVOUR in March–April, 1969. A rise in surface water Pco₂ of 18×10^–6 atm occurred in a period of 30–45 days in March–April due principally to spring warming of surface waters. An average increase of 60×10^–6 atm occurred between October, 1968 and March, 1969 as a result mainly of cessation of summer phytoplankton production and the onset of winter-storm-driven vertical mixing. Because the air-sea Pco₂ gradient not only changed appreciably in magnitude but also changed sign, there are important implications for calculations of air-sea exchange of carbon dioxide on the ocean wide scale.Data contained in this paper comprise part of a dissertation to be submitted by Louis I. Gordon in partial fulfillment of the requirements for the Ph. D. at Oregon State University.     

Effect of agricultural activity on levels of organochlorine pesticides in hard corals, fish and molluscs from the Great Barrier Reef

An organochlorine baseline study of selected corals, fish and molluscs has established that lindane is the only consistently detectable persistent pesticide in Great Barrier Reef organisms sampled. Samples taken during 1976–1977 from twenty reefs between Heron Island and Lizard Island provide evidence from the distribution of lindane that the contamination is related to agricultural usage in the coastal sugar cane growing regions. Consideration is given to the possible mode of transport of lindane to the reef environment. No polychlorinated biphenyls were detected in any of the samples and only scattered samples contained levels of residues other than lindane. Inner marginal shelf reefs of the Great Barrier Reef may be the most pristine environment yet reported for organochlorine pollutants.     

Solubility of hydrous ferric oxide and iron speciation in seawater

Iron solubility equilibria were investigated in seawater at 36.22‰ salinity and 25°C using several filtration and dialysis techniques. In simple filtration experiments with 0.05 μm filters and Millipore ultra-filters, ferric chlorides fluorides, sulfates, and FeOH²⁺ species were found to be insignificant relative to Fe(OH)₂⁺ at p[H⁺] = ?log [H⁺] greater than 6.0. Hydrous ferric oxide freshly precipitated from seawater yielded a solubility product of ${}^1\text{K}{}_{\mathrm{<mtext>so</mtext>}}\text{=}\text{[Fe}{}^{\mathrm{3+}}\text{][H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{?3}}\text{= 4.7 · 10}{}^5$. Solubility studies based on the rates of dialysis of various seawater solutions and on the filtration of acidified seawater solutions indicated the existence of the Fe(OH)₃⁰ species. The formation constant for this species can be calculated as ${}^1\text{β}{}_3\text{=}\text{[Fe(OH)}{}_3{}^0\text{] [H}{}^{\mathrm{+}}\text{]}{}^3\text{/[Fe}{}^{\mathrm{3+}}\text{] = 2.4 · 10}{}^{\mathrm{?14}}$. The Fe(OH)₄^? species is present at concentrations which are negligible compared to Fe(OH)₂⁺ and Fe(OH)₃⁰ in the normal pH range of seawater. However, there is at least one other significant ferric complex in seawater above p[H⁺] = 8.0 (possibly with bicarbonate, carbonate, or borate ions) in addition to the Fe(OH)₂⁺ and Fe(OH)₃⁰ species.     

Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part II—seismic response

Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well-developed in fluvial and deltaic sediments that have been influenced by high-frequency eustatic sea-level fluctuations. The large data base for this study (including 471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information on high-resolution chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and high-resolution seismic responses during three complete sea-level cycles over the entire continental shelf/upper slope of offshore Louisiana. Examination of high-resolution seismic records indicates that well-defined, high-amplitude, laterally continuous reflectors correlate with rising and high stand condensed sedimentary sequences and that the deposits laid down during falling and low-stand periods (expanded sections) are characterized by a wide range of acoustic responses. Discontinuous reflectors with high-amplitude variability, continuous parallel reflectors, and chaotic and amorphous zones are common acoustic responses. The association between a particular lithofacies and a specific acoustic response on 3.5-kHz records was found to be very poor.     

La marge continentale Tunisienne: Résultats d'une étude par sismique réflexion: Sa place dans le cadre tectonique de la Méditerranée Occidentale

Résumé Une série de profils de sismique réflexion effectués au large de la Tunisie et dans le détroit sardano-tunisien aboutissent à l'élaboration d'un schéma géologique interprétatif dans lequel nous replaçons le socle paléozoïque et sa couverture autochtone (Eocène et plio-quaternaire) et allochtone (nappe numidienne). Nous discutons ensuite des manifestations néotectoniques (bassins d'effondrements plio-quaternaires-mouvement de flexure-surrections locales-venues intrusives). Enfin la nature du substratum du détroit sardano-tunisien est discutée en liaison avec les hypothèses dynamiques et statiques relatives à la formation de la Méditerranée occidentale.

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Serial seismic reflection profiles off Tunisia and between Sardinia and Tunisia are presented. Interpretation is given which includes paleozoïc basement and its autochtonous (Eocene and plioquaternary) and allochtonous (Numidian nappe) cover. Recent tectonic activity is discussed, (Plioquaternary foundered basins, flexure, local uplifts, intrusions). Then the nature of the basement of the Sardinia-Tunisia zone is discussed with respect to the various hypotheses on the region of the Western Mediterranean.

     

Geophysical evidence of mud diapirism on the Mediterranean Ridge accretionary complex

Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m^–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m^–1 K^–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified.     

Free vibration of semisubmersibles: A parametric study

Like any other engineering structure, the dynamic aspects of semisubmersible offshore platforms require serious consideration. The free vibrations of the semisubmersible structures have been investigated in the present work, in which the effect of the variation of the length, draft and hull spacings on the natural frequencies and mode shapes has been studied and the nature of the variations and their reasons have been discussed.