Simulation of additive transport from the land surface on the basis of experimental data on heat transfer in the atmospheric surface layer

A method is proposed to study the transport of a passive additive in the atmospheric surface layer with the use of the atmospheric transfer function. This method makes it possible to estimate the spatial distribution of the concentration of a passive additive in the atmospheric surface layer from the additive’s surface source without experimentally determining the vertical profile of the transport coefficient or without resorting to various hypotheses for the character of its behavior. The transfer function, which contains the information on the wind-field structure, can be obtained from simple one-point measurements of surface-and air-temperature fluctuations and from subsequent spectral processing of the data. The effects of the wind-velocity profile and turbulence on the spatial distribution of additive concentration are assessed. This method allows one to simplify experiments during development and verification of the models of atmospheric diffusion. This method may also be useful in emergency situations to predict the propagation of hazardous additives.     

Storms and shoreline retreat in the southern Gulf of St. Lawrence

Storms play a major role in shoreline recession on transgressive coasts. In the southern Gulf of St. Lawrence (GSL), southeastern Canada, long-term relative sea-level rise off the North Shore of Prince Edward Island has averaged 0.3 m/century over the past 6000 years (>0.2 m/century over 2000 years). This has driven long-term coastal retreat at mean rates >0.5 m/a but the variance and details of coastal profile response remain poorly understood. Despite extensive sandy shores, sediment supply is limited and sand is transferred landward into multidecadal to century-scale storage in coastal dunes, barrier washover deposits, and flood-tidal delta sinks. Charlottetown tide-gauge records show mean relative sea-level rise of 3.2 mm/a (0.32 m/century) since 1911. A further rise of 0.7±0.4 m is projected over the next 100 years. When differenced from tidal predictions, the water-level data provide a 90-year record of storm-surge occurrence. Combined with wind, wave hindcast, and sea-ice data, this provides a catalogue of potentially significant coastal storms. We also document coastal impacts from three recent storms of great severity in January and October 2000 and November 2001. Digital photogrammetry (1935–1990) and shore-zone surveys (1989–2001) show large spatial and temporal variance in coastal recession rates, weakly correlated with the storm record, in part because of wave suppression or coastal protection by sea ice. Large storms cause rapid erosion from which recovery depends in part on local sand supply, but barrier volume may be conserved by washover deposition. Barrier shores with dunes show high longshore and interdecadal variance, with extensive multidecadal healing of former inlet and overwash gaps. This reflects recovery from an episode of widespread overwash prior to 1935, possibly initiated by intense storms or groups of storms in the latter half of the 19th century. With evidence from the storms of 2000–2001, this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability, as well as the need for a long-term, large-scale perspective in assessing coastal stability. The expected acceleration in relative sea-level rise, together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern GSL, implies a significant increase in coastal erosion hazards in future.     

Stress and deformation of offshore piles under structural and wave loading

Various offshore structures, especially large structures such as Tension Leg Platforms (TLP), are usually supported by concrete piles as the foundation elements. The stress distribution within such a large structure is a dominant factor in the design procedure of an offshore pile. To provide a more accurate and effective design for offshore foundation systems under axial and lateral wave loads, a finite element model is employed herein to determine the stresses and displacements in a concrete pile under similar loading conditions. A parametric study is also performed to examine the effects of the stress distribution due to the changing loading conditions.     

Phototoxicity of pyrene and benzo[a]pyrene to embryo-larval stages of the Pacific oyster Crassostrea gigas

There is a growing body of evidence to suggest that certain polycyclic aromatic hydrocarbons (PAHs) pose a greater hazard to aquatic organisms than previously demonstrated, due to their potential to cause photo-induced toxicity when exposed to ultraviolet (UV) radiation. The consequences of photo-induced toxicity are reported here for embryo-larval stages of the pacific oyster Crassostrea gigas, following exposure to pyrene and benzo[a]pyrene. During laboratory investigations, significant increases in toxicity were observed in the presence of environmentally attainable levels of UV-radiation, compared with embryos exposed to PAH alone, at levels previously deemed to have little acute biological effect. The phototoxicity of pyrene and benzo[a]pyrene completely inhibited the development to the D-shell larval stage when embryos were simultaneously exposed to 5 microg l(-1) PAH and ultraviolet light (UVB = 6.3 +/- 0.1 microW/cm2 and UVA = 456.2 +/- 55 microW/cm2). A linear relationship was also demonstrated for benzo[a]pyrene phototoxicity with decreasing UV light intensity.     

Reconstruction of sea surface dimethylsulfide in the North Pacific during 1970s to 2000s

We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R² = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year^− 1 in the subpolar region, and 0.01 ± 0.001 nM year^− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m^− 2 year^− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.     

Temperature fluctuations in the atmospheric surface layer over the thermally inhomogeneous underlying surface

The influence of both spatial and temporal temperature inhomogeneities of the underlying surface on the temperature field in an unstably stratified atmospheric surface layer is considered. The methods of correlation and spectral analyses are proposed to estimate statistical characteristics of surface-air temperature fluctuations caused by both turbulent mixing and inhomogeneities in the temperature of the underlying surface. Analysis of experimental data obtained from measurements in the atmospheric surface layer yields estimates for the contribution made by the time-dependent thermal properties of the underlying surface to the total variance of air-temperature fluctuations. It is shown that the additional air-temperature fluctuations generated by surface-temperature inhomogeneities and unrelated to shear flow may reach 70% and 30% of the total variance of measured fluctuations under variable cloudiness and clear skies, respectively. For the height z = 2 m within the wave-number range 2 × 10^?3 rad m^?1 < k < 0.1 rad m^?1, the contribution made by a spatial surface-temperature inhomogeneity to the variance of air-temperature fluctuations does not exceed 10% of the total variance. Correlation and spectral analyses of experimental data make it possible to isolate the spectra of properly turbulent fluctuations from the measured fluctuations and thus to obtain more accurate values of the universal function of similarity theory for temperature in the range of small wave numbers beyond the inertial range.     

GEBCO Centennial Special Issue – Charting the Secret World of the Ocean Floor: The GEBCO Project 1903–2003

This special issue of Marine Geophysical Researches presents five papers dealing with GEBCO, the General Bathymetric Chart of the Oceans, which celebrated its Centennial in April 2003, hosted by the International Hydrographic Bureau and the Principality of Monaco. Over the past 103 years GEBCO has been the sole body dedicated to compiling all available data to produce standardized maps of the oceans and seas covering 71% of planet Earth. Over time GEBCO has undergone a complete transformation as sparse 500 m contours on paper charts were replaced by digital grids with ever-increasing resolution. The 2003 Centennial saw the release on two CDROMS with the first global 1′ grid, produced by methods unheard of in 1984, when GEBCO’s last 6th Edition paper chart set was published. In GEBCO’s second century, the thrust is towards global grids that will capture the resolutions available with evolving deep-water swath mapping technologies, as well as vast improvement in the details of the shallow continental shelves that have traditionally been the preserve of the hydrographic community. As little more than 10% of the oceans have been mapped to the desired level of detail, there is much to be done. However refinements in satellite altimetry appear to offer an interim stop-gap as more multi-beam sonars ply the oceans and as the littoral countries of the world map their adjacent marine areas for submission under Article 76 of UNCLOS (United Nations, 1983, 1999). In addition GEBCO is becoming increasingly proactive, with outreach to the public via the internet and a new GEBCO Map of the World, active data-scrounging, and encouraging development of the first drifting buoys for acquiring data in the inaccessible areas of the Antarctic, SW Pacific, and Arctic Oceans.     

Design of a 3D Chirp Sub-bottom Imaging System

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a pre-amplifier. After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software aboard the acquisition vessel. The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface.