CO<Subscript>2</Subscript> Flux Measurements over the Sea Surface by Eddy Correlation and Aerodynamic Techniques

The measurements of the vertical transport of CO₂ were carried out over the Sea of Japan using the specially designed pier of Kyoto University on September 20 to 22, 2000. CO₂ fluxes were measured by the eddy correlation and aerodynamic techniques. Both techniques showed comparable CO₂ fluxes during sea breeze conditions: −0.001 to −0.08 mg m⁻²s⁻¹ with the mean of −0.05 mg m⁻²s⁻¹. This means that the measuring site satisfies the fetch requirement for meteorological observations under sea breeze conditions. Moreover, the eddy diffusivity coefficient used in the aerodynamic technique is found to be consistent with the coefficient used in the eddy correlation technique. The present result leads us to conclude that the aerodynamic technique may be applicable to underway CO₂ flux measurements over the ocean and may be used in place of the bulk technique. The important point is the need to maintain a measuring accuracy of CO₂ concentration difference of the order of 0.1 ppmv on the research vessels or the buoys.     

Wave run-up and overtopping on smooth and rough slopes of coastal structures

A series of hydraulic model tests has been carried out in a glass wave flume to investigate the influences of wave height, wave period, wave steepness, surf similarity parameter, roughness, layer thickness and porosity on wave run-up and overtopping of 1:2 sloped impermeable and permeable breakwaters fronted by a 1:10 gentle, smooth beach slope. The analysis of results involves the correlation between the overtopping energy transfer with the relative wall height and the relationship between wave run-up and overtopping rate. Further, measured wave run-up and overtopping rates are compared with the results given in the Shore Protection Manual (1984), Automated Coastal Engineering System (1992)and results of other investigators.     

Spatial patterns and environmental risks of ringnet fishing along the Kenyan coast

Ringnet fishing began in the early 20th century and is practised worldwide, mainly to target nearshore pelagic species. The method was introduced to Kenya’s coastal waters by migrant fishers from Tanzania. However, the impacts of this fishing gear remain poorly assessed. We assessed the spatial distribution of ringnet fishing effort and its possible effects on ecosystem components, such as coral reefs, marine megafauna and marine protected areas, on the south coast of Kenya. We tracked 89 ringnet fishing trips made from December 2015 to January 2016 and used spatial multicriteria analysis to determine hotspots of possible environmental risks. The results showed that habitat type and bathymetric profile influenced the spatial distribution of ringnet fishing effort. Mixed seagrass and coral habitats had the highest concentration of the effort. Most of the habitats in the study area were moderately exposed to the impacts of the ringnet fishery. The study identifies high-risk areas that require spatial measures to minimise possible environmental risks of the gear both to habitats and to endangered sea turtles.     

Variations in wave direction estimated using first and second order Fourier coefficients

In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°.     

Towards a more detailed seismic picture of the oceanic crust and mantle

A review is presented of current interpretation techniques in marine refraction seismology with particular emphasis on those features which are most useful in structural studies using ocean bottom seismometers. Travel time analysis techniques are discussed for both refraction and variable angle reflection profiles and are compared with systematic travel time inversion methods. Amplitude and waveform analysis techniques allow a more detailed velocity depth profile to be determined, and are illustrated for both surface and bottom receivers. The study of anisotropy and lateral variations in crustal structure may be usefully combined using delay time function methods but a detailed structural model also requires velocity-depth information. Signal processing techniques which are particularly useful for shear wave and long range propagation studies are also metioned. Structural studies using OBS' should lead to detailed knowledge of the oceanic crust and the P wave velocity distribution in the upper mantle.     

A study of the subarctic boundary region in the Western North Pacific

During autumn 1968 an oceanographic investigation was conducted in the region of the Subarctic boundary between 155°E and 180°. The geostrophic flow of the upper 500 m was remarkably similar in direction; hence the salinity-minimum, Intermediate water must have the same path of flow as water at the surface. A water mass analysis revealed a decrease in the percentage of Subarctic water to the south and east, plus an increase in the homogeneity of water to the east, which supports Reid's conclusions that the salinity minimum results mainly from lateral mixing in the pycnocline in this region. Salinity at the minimum increases toward the south and east, and the density at this level also increases slightly from the western to the central Pacific, perhaps as a result of unequal vertical mixing above and below the minimum.     

Pacific decadal oscillation and European climatic anomalies

By using the NCEP/NCAR reanalysis data sets for 1951–2001, we study the characteristics of Pacific cyclones. It is shown that the northeast-southwest direction is predominant in the displacements of cyclones in the North Pacific. We study the variability of the field of surface atmospheric pressure in different phases of the Pacific decadal oscillation characterizing the temperature anomalies on the surface of the ocean in the region bounded by 20 and 60°N. It is shown that the decadal variations of the North Atlantic Oscillation supported by the large-scale anomalies of the Pacific decadal oscillation is the most important cause of natural decadal oscillations in the European region. We study and evaluate the regional response to the Pacific decadal oscillation by using, as an example, the analysis of variations of the discharge of European rivers. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 13–23, July–August, 2007.     

Nannoplankton of the Atlantic Ocean from sediment trap samples

Calcareous nannoplankton from sediment trap samples collected at six sites in the Atlantic Ocean from 23° S to 73° N (cruise 20 of R/V Vityaz’ and cruise 33 and 34 of R/V Akademik Mstislav Keldysh). Those samples were studied with a scanning electron microscope. In the coastal and open-sea regions of the North and South Atlantic and in the subarctic region of the Norwegian Sea, the conditions are significantly different. In the shelf area of the Benguela upwelling, 11 species were recognized; some of them were agglutinated by diatoms and tintinnides or covered the surface of pellets. The Broken Spur and TAG pelagic areas of the North Atlantic contained up to 43 coccolith species. They included holococcoliths, large pelagic, and delicate easily soluble species distributed over the entire water column. The presence of coccoliths in the high-latitude area of the Norwegian Sea is related to their supply with the warmer North Atlantic waters. These assemblages are distinguished by a low species diversity and an enhancement of the coccolith solubility with the depth increase.     

Seasonal and Spatial Variations of Total Mass Flux around Coral Reefs in the Southern Ryukyus,Japan

Total mass flux, size distribution of sediment particles and some chemical components such as total carbon (TC), total nitrogen (TN) and calcium carbonate (CaCO₃) were monitored monthly using a multi-cup sediment traps at seven coral reef sites (6 reef flat and 1 reef slope) of the Marine Protected Areas around Ishigaki, Kohama, Kuroshima and Iriomote Islands in the southern Ryukyus, Japan from September 2000 to September 2001. The size distribution of trapped sediments revealed mostly uni-modal fine sand to mud in the reef flat and gravelly to coarse sand in the reef slope. The total mass flux ranged between 0.54 to 872 gm⁻²d⁻¹, and showed a pronounced seasonality (high in summer-autumn and low in spring) at each site, which was consistent with the rainfall and typhoon regime. Exceptionally high values were observed on the reef slope (Iriomote) in February–March 2001 (1533 gm⁻²d⁻¹) owing to a large amount of bottom sediment re-suspension. On the reef flat (Todoroki South and North; Ishigaki), values obtained in July–August 2001 (872 gm⁻²d⁻¹) and August–September 2001 (800 gm^{− 2}d⁻¹) indicate the high terrestrial discharge from Todoroki River. Trapped sediment particles consist of CaCO₃ (1.2–27.1%) and a non-carbonate fraction (98.8–72.9%), which contains total carbon (4.9–26%), carbonate carbon (CO₂-C) (0.2–3.1%) and non-carbonate carbon (NC-C) (7.9–25.6%). Total nitrogen content was in the range 0.02–0.48%. TN is contained mainly in the carbonate fraction and NC-C may be contained in the non-carbonate fraction. The low TN/OC ratio of the trapped sediments suggests that they were mostly of terrestrial origin and that both fractions migrated. The high total mass flux derived from Todoroki River exceeded the threshold at which a lethal effect on coral community is caused. The results stress the importance of conducting seasonal studies of sedimentation over more than one year and at more than one location in south Japan coral reef ecosystems to gain an understanding of the processes controlling the total mass fluxes and their nutrients content, also to develop an awareness of how to prevent the damage of coral reef ecosystems and, if it does occur, to allow mitigation measures to be undertaken.     

Effects of polynuclear aromatic hydrocarbons on lysosomal membranes in molluscs

Lysosomal sequestration of polynuclear aromatic hydrocarbons (PNAHs), a major class of environmental contaminant, is a well-established phenomenon;¹ considerably less is known about their pathological effects on lysosomes. Marine molluscs contain a number of lysosome-rich tissues and PNAHs are known to induce deleterious alterations in lysosomal structure and latency of lysosomal enzymes.² The latter are presumed to involve destabilisation of the lysosomal membrane, resulting in increased permeability and reduced enzyme latency. If lysosomal injury involves derangement of membrane-lipid structure due to the interaction of PNAHs then it would be expected that membrane damage would be closely linked to the structural characteristics of the intruding molecule. Our results show that the effects of the isomeric PNAHs phenanthrene and anthracene on digestive cell lysosomal stability were markedly different in the marine mussel (Mytilus edulis) over the same range of tissue concentrations. Lysosomal membrane stability was determined using a cytochemical test for enzyme latency.³