Mixed-function oxygenases as biological monitors around petroleum hydrocarbon development sites: Potential for induction by diesel and other drilling mud base oils containing reduced levels of polycyclic aromatic hydrocarbons

The use of oil-based drilling muds has been discouraged in hydrocarbon exploration and production in the marine environment but these muds are presently being used to a considerable degree in the United Kingdom and Norwegian sectors of the North Sea. Field studies in the North Sea have demonstrated only localized impacts around individual drilling sites,^1,2 even including those sites where ‘toxic’ diesel oils were employed as base fluids in drilling muds. Yet the question of disposal of cuttings contaminated with oil from drilling muds remains somewhat controversial. The induction of mixed-function oxygenases (MFO) has been validated on a number of occasions in the field as a sensitive index of low level hydrocarbon exposure (reviewed by Payne),³ including sites in the North Sea where diesel-based muds were used.⁴ The present study demonstrates that any potential for induction by hydrocarbon contaminated cuttings will probably be reduced by substitution of low-aromatic base oils for diesel in drilling mud formulations.     

Wave drift enhancement effects in multi column structures

A theoretical assessment is made of mean wave drift forces on groups of vertical circular cylinders, such as the columns of a floating offshore platform. A complete analytical solution is obtained for two cylinders extending from seabed to free surface, and a long wave approximation is found to provide reliable predictions of the drift force in line with the waves at low frequencies. For moderate separation between the two cylinders, this force is found to tend at low frequencies to a value four times the force on an isolated cylinder.A numerical method is employed to study two surface piercing cylinders truncated below the free surface, and an arrangement of four vertical cylinders characteristic of a floating offshore platform. The mean vertical drift force is found to be reasonably well approximated, over the frequency range of practical interest, by the force on an individual cylinder considered in isolation multiplied by the number of cylinders in the group. Interaction effects, however, have a profound influence on the total horizontal drift force. At low frequencies this force is found to tend to the force on an isolated cylinder multiplied by the squate of the number of cylinders in the group.     

An experimental investigation of plunging breaker boundary layers in the transformation zone

Experimental investigation is made on the boundary layers of the transformation zone (i.e. the region between the last symmetrical wave profile depth and the breaking point) of plunging breakers propagating on a smooth beach with 1/12 uniform slope. Using a laser anemometer, the particle velocities are measured at four verticals along the transformation zone for three different steepnesses of waves within the plunging breaker range. The boundary layer flow in the transformation zone is found mostly of turbulent character and vertical distribution of particle velocities does not seem to conform to the classical law of the wall distribution given for steady-flow boundary layers. The results show that free-stream particle velocities, in the boundary layer of the breaker under the crest phase, increase considerably as the wave progresses towards the breaking point. The boundary layer thickness, defined as the velocity-affected region, remains constant throughout the transformation zone but it decreases with increasing deep-water wave steepness for the particular beach slope tested.     

Upwelling in the Black Sea by the results of numerical experiments and satellite data

The paper analyses results of the numerical simulation of upwelling events in the north-western part of the Black Sea, mostly near the South Crimea. The calculations were performed using a numerical model based on primitive hydrodynamics equations. Emphasis is laid on the case when a salinity front simulating the Black Sea rim current is prescribed in the initial conditions. The interaction of the Black Sea rim current's stream with the coastline and bottom topography leads to the development of an upwelling near the Crimea's coast, even in the absence of wind forcing. The paper discusses the structure of the three-dimensional circulation of waters in the shelf area of the NW Black Sea. Numerical modelling results are matched up with the satellite data obtained by the HRPT receiving station. Translated by Vladimir A. Puchkin.     

The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).     

Sedimentology and morphodynamics of a macrotidal beach, Pendine Sands, SW Wales

The foreshore of Pendine Sands forms the seaward part of an extensive, sandy coastal barrier in a shallow Carmarthen Bay, SW Wales. The sedimentological features of the macrotidal foreshore reflect a tide-induced modification of nearshore wave characteristics. As the tide ebbs, the breaker height may decrease, the surf zone widens and becomes increasingly dissipative, and swash/backwash velocities diminish. A concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient.

A zero net transport model demonstrates that the beach profile is self-stabilising in the short-term, and periodic levelling has shown that the beach is in long-term equilibrium with prevailing conditions, though this does not preclude a significant dynamic response to changing tides and waves.

The flow regimes of wave-generated currents decline as the tide ebbs, and normal beach processes do not usually affect the lower foreshore. Accordingly, there is an overall seaward-fining of the primary framework component of the sands. In more detail, this framework component displays a slight seaward-coarsening across an upper foreshore dominated by high water swash and surf; a rapid seaward-fining across the mid-foreshore in response to the ebb-attenuating swash zone flow velocities; and a slight seaward-fining across the lower foreshore under the action of nearshore shoaling waves. Bedforms vary from a swash/backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore.

The surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions, partly to storms. The upper foreshore is characterised by swash/backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities. The mid-foreshore is composed of coarser-grained shelly traction clogs arranged as landward- and seaward-dipping large-scale cross bedding and/or plane bedding; these are probably storm breaker/surf deposits. The lower foreshore, though partially and sometimes totally bioturbated, shows landward-dipping small-scale cross bedding in very fine sands sorted by nearshore shoaling waves.

Tide- and storm-induced modification of the nearshore flow regimes therefore produces a distinctive shore-normal array of sedimentary facies. Each facies is characterised by diagnostic textural and structural signatures. A prograding sequence of such macrotidal deposits would be similar to, but more extensive than, a comparable microtidal sequence.     

Wave transmission and reflection characteristics of a rigid surface and submerged horizontal plate

The wave transmission and reflection characteristics of a rigidly fixed surface and submerged horizontal plate were investigated experimentally in detail for a wide range of incident wave steepnesses and for different depths of submerge of the plate in deep water conditions in regular water wave fields. The experiments were conducted at the Ocean Engineering Centre, Indian Institute of Technology, Madras, India, in a wave flume 10 m long, 0.3 m wide and in a constant water depth of 0.8 m. The horizontal plate is 0.22 m thick and 1.2 m in length, covering the enrire width of the flume. From the present investigation, it is found that for a rigid surface plate, the coefficient of transmission is a minimum and the coefficient of reflection is a maximum, but the maximum value of the coefficient of energy loss occurs for plates submerged closer to the still-water level (SWL) and not for the surface plate. It is also found that the value of the coefficient of reflection increases with the increase in the value of the Reddy-Neelamani (RN) number, the ratio of horizontal water particle excursion at the bottom of the plate in its absence to the length of the plate. The coefficient of transmission is found to decrease rapidly with increase in the value of RN number up to 0.1. The wave transmission is only 5% for RN from 0.1 to 0.2. It is also found that for RN number greater than 0.04, the minimum energy dissipation is consistently about 60% of the incident wave energy.     

Multipole expansions for wave diffraction and radiation in deep water

A multipole expansion of the velocity potential is described for two- and three-dimensional wave diffraction and radiation problems. The velocity potential is expressed in terms of a series of multipole potentials. The wave terms and the local disturbance terms are represented by separated multipole potentials. Floating bodies and submerged bodies are treated in the same way. This approach differs from that of some other authors, who considered floating bodies and submerged bodies separately and derived entirely different multipoles. Semi-analytical solutions for a circular cylinder in two-dimensional motions are given. It is found that the local disturbance decays rapidly and steadily. The general application of the multipole expansion to arbitrary geometries is also presented, based on a method coupling multipoles to a boundary integral expression. Numerical results for several floating and submerged cylinders are presented.     

Estimates of the characteristics of the horizontal turbulent exchange in the northwestern part of the Pacific Ocean

Estimates of the characteristics of the horizontal turbulent exchange (coefficients of horizontal exchange, scales of deviations of the velocity of geostrophic currents from the background flows, and horizontal scales of perturbations) in the upper ocean layer were obtained on the basis of the data of expeditions held in 1978 and 1980 in the northwestern part of the Pacific Ocean. It is shown that the characteristics of the horizontal turbulent exchange strongly depend on the structure of the background flows, and one of the causes of their variability is related to tropical cyclones. A tendency to a decrease (to different degrees) of the turbulent coefficients in the wake of a tropical cyclone is noted.     

On the use of poorly soluble hygroscopic substances for modification of warm clouds and fogs

From analysis of the relationships between the equilibrium state of condensation nuclei and the relative humidity, a conclusion is made concerning the preferred use of poorly soluble substances for the generation of artificial condensation nuclei (ACN) designed for modification of warm clouds and fogs with the purpose of their dissipation and precipitation formation. The advantage of poorly soluble substances over commonly used soluble salts is that the finely dispersed part of the spectrum of the poorly soluble ACN does not deliquesce and so is not involved in the formation of cloud droplets. For experimental testing of the conclusions, preference was given to cement, whose main soluble substance is calcium oxide with a solubility of about 1 g/l. The spectrum of dispersed cement particles was measured and compared with the spectra of pyrotechnic flares widely used for modification at present. The process of formation of the cloud droplet spectra was simulated in the aerosol chamber of the Institute of Experimental Meteorology by decreasing the preliminarily generated excess pressure. It was found in these experiments that, compared to the spectra of particles formed on background condensation nuclei, the introduction of dispersed cement leads to the broadening of spectra and to a decrease in the concentration of droplets. Even at the early stage of condensation, droplets with radii of ∼20 μm appear. In this case, no “overseeding” phenomenon is observed, which, for soluble substances, manifests itself in an increase in the concentration of cloud droplets with a large ACN concentration. These effects indicate that, according to the existing concepts about the mechanism of warm-cloud modification with hygroscopic substances, the introduction of poorly soluble ACN (in particular, dispersed cement) below the base of cumulus clouds should stimulate coagulation processes and accelerate rain-formation processes. Considerations are given that the introduction of poorly soluble ACN into the already existing cumulus or stratocumulus clouds or fogs should also result in the acceleration of precipitation-formation processes or cloud dispersal. Comparison of cement powder with the well-known means of warm-cloud and fog modification is carried out. Original Russian Text ? N.P. Romanov, A.S. Drofa, N.S. Kim, A.V. Savchenko, G.F. Yaskevich, 2006, published in Izvestiya AN. Fizika Atmosfery i Okeana, 2006, Vol. 42, No. 1, pp. 80–91.