A simplified model for the transformation of the atmospheric planetary boundary layer overlying a thermal front in the sea

This paper discusses a simplified model for the evolution of the atmospheric planetary boundary layer overlying a thermal front in the sea. The model provides local values of the friction/heat transfer geostrophic coefficients and the direction of surface wind stress, as well as the wind/temperature profiles at any point on the front. With the running over a warm front, the baroclinicity of the internal boundary layer leads to the generation of a near-surface current of air directed down the front. The model can be used to interpret radar imagery of the sea surface with the purpose of determining its mesoscale variability. Translated by Vladimir A. Puchkin.     

About the relationship between acoustic fields and hydrological fields in the area of a mesoscale eddy in the Black Sea

This paper discusses the application of acoustic sounding with the purpose of identifying vortical features in the sea. Analysis of the results of a multidisciplinary acoustic/hydrological experiment conducted in the Black Sea has revealed a stable recurrent correlation between the amplitudinal variance of echo signals, on the one hand, and the peculiarities of water temperature fields, on the other. Given these characteristics, the peripheral and the central areas of a mesoscale eddy essentially differed. This allows us to apply acoustic sounding to identify mesoscale eddies in the sea. Translated by Vladimir A. Puchkin.     

Dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end

This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system.     

A note on significant wave height

In this note conservative bounds for significant crest height and amplitude obtained from the crossing intensity of a sea are presented. For Gaussian models of a sea level, the Rayleigh approximation for the distributions of amplitude and crest height is proved to provide conservative values for the expected significant wave characteristics. The results are illustrated by examples in which both Gaussian and non-Gaussian models for a sea are considered.     

Water flooding of the Oseberg Øst oil field,Norwegian North Sea: Application of formation water chemistry and isotopic composition for production monitoring

This case study demonstrates how natural heterogeneities of formation and injection waters can be applied to a number of production related applications, extending into the mature life of a reservoir. Break-through of injection water, identification and characterisation of production intervals and evaluation of responses to operational events are some of the possible applications during production.The Oseberg Øst oil field in the North Sea represents a complex situation with commingled production from all Brent Group formations. The Sr isotope composition is an excellent parameter for defining the natural baseline of formation water, with a good spatial resolution and vertical stratification. Aquifer water from the Utsira Formation is injected for pressure support, and reinjection of produced water has also been applied since the onset of water production. Utsira Formation water has high Mg, low Ba and low Sr content compared to the reservoir formation waters. Isotopic compositions (δD and ⁸⁷Sr/⁸⁶Sr) are also distinct. A non-reactive behaviour of Ba and Sr is verified from binary cross-plots and geochemical modelling. Break-through of injection water could be identified in five production wells based on Ba/Mg ratios. In one of the reservoir compartments (Beta Saddle), water injection points were changed after approximately three years. The Ba/Mg ratio could also identify the second injection water break-through in one of the wells due to an intermediate period of higher formation water content. Since the Sr content in the Utsira water is low, the ⁸⁷Sr/⁸⁶Sr ratio is a good natural tracer for formation water movements even at high ratios of injected water. In particular, the vertical stratification of ⁸⁷Sr/⁸⁶Sr is useful for quantifying production from different intervals in commingled wells. A methodology for using operational events, such as production allocations or shut-ins, for characterisation of production zones is discussed.     

Education and training for integrated coastal zone management in Europe

This paper provides an overview of the current situation of education and training for ICZM in Europe. This overview results from the analysis of the general characteristics, contents and orientation of a significant number of courses from a representative set of countries and international organizations in Europe. This type of comparatively systematic information provides a framework within which education and training efforts can be meaningfully evaluated from a regional perspective. Based on the survey conclusions, the paper reflects on the level of interconnection between the way in which ICZM is currently taught in Europe and the capacity needs arising from the scenario in which it takes place. In view of such scenario, and in order to advance ICZM practice in Europe, some broad recommendations to enhance education and training efforts are finally provided.     

Terminal velocities of pure and hydrate coated CO2 droplets and CH4 bubbles rising in a simulated oceanic environment

Understanding the upward motion of CO₂ droplets or CH₄ bubbles in oceanic waters is prerequisite to predict the vertical distribution of the two most important greenhouse gases in the water column after these have been released from the seabed. One of the key parameters governing the fate of droplets or bubbles dissolving into the surrounding seawater as they rise, is the terminal velocity, u_T. The latter is strongly influenced by the ability of both compounds to form skins of gas hydrate, if pressure and temperature satisfy thermodynamic framework conditions. Experimental efforts aiming to elucidate the rise properties of CO₂ droplets and CH₄ bubbles and specifically the influence of hydrate skins open the possibility to obtain a parameterization of u_T applicable to both hydrate-coated and pure fluid particles of CH₄ and CO₂. With the present study, we report on experimentally determined terminal velocities of single CH₄ bubbles released to pressurized and temperature-regulated seawater. Hydrate skins were identified by high bubble sphericities and changed motion characteristics. Based on these experiments as well as published data on the rise of hydrate-coated and pure liquid CO₂ droplets and physical principles previously successfully used for clean bubbles near atmospheric pressures, a new parameterization of u_T is proposed. Model predictions show a good agreement with the data base established from the laboratory-based measurements.     

Effect of atmospheric CO2 and solar activity on wind regime and water column stability in the major global upwelling areas

It is not clear whether global warming will favour or reduce global ocean phytoplankton productivity in coastal areas. Moreover, the relative contributions made by natural and/or anthropogenic factors to possible changes in phytoplankton productivity are not clear. As the relationship between primary production and alongshore wind forcing is well established for the Eastern Boundary Current (EBC) ecosystems, our aim is to determine whether the changes experienced over the last five decades (1958–2007) in atmospheric CO₂ and solar activity have been able to affect the wind regime and water column stability in the most biologically productive upwelling areas of California, Canary, Humboldt and Benguela. We approached the work by statistically studying the effect of solar activity and atmospheric CO₂ on surface alongshore wind stress and on water column stability. There was an increasing trend in wind stress and water column stability in all the upwelling areas over the period studied (with the single exception of stability in the California EBC system). The analysis of detrended series evidenced significant relationships between atmospheric CO₂ concentration and wind stress and water column stability in the coastal upwelling areas investigated. In addition, wind stress and stability data were found to be consistent, with negative linear relationships between wind stress and CO₂ in most of the sites in the Benguela, Canary and Humboldt regions associated, as expected, to positive relationships when water column stability is used as regressand. The results of the present study suggest that greenhouse gas forcing, independent of its well known general increasing trend, was able to decrease wind stress intensity and increase water column stability for the period 1958 to present in most of the sites of the four Eastern Boundary Ecosystems studied, with the one exception of the California region. Conversely, the impact of solar activity appeared to be quite low compared to the greenhouse gas forcing.