Deep-sea suprabenthos assemblages (Crustacea) off the Balearic Islands (western Mediterranean): Mesoscale variability in diversity and production

The composition of suprabenthic crustacean assemblages, their diversity, production (P) and production/biomass (P/B) ratios, were analyzed at species level along two transects situated to the north (N) and south (S) of Mallorca (Balearic Islands, western Mediterranean) at depths between 134 m and 760 m, based on a ca. bi-monthly sampling performed between August 2003 and June 2004. Differences with depth and season in assemblage composition and diversity were analyzed as a function of the contrasting environmental features (e.g. water mass dynamics) of the two areas. We identified 187 species (18 decapods, 5 euphausiids, 16 mysids, 76 gammaridean amphipods, 13 hyperiids, 1 caprellid, 21 isopods and 37 cumaceans). Substantial mesoscale variability in the deep-sea suprabenthic assemblages coupled with diversity trends between the N and S transects were found. Seasonality was the most important gradient influencing the dynamics of suprabenthos over the upper (350 m) and middle (650–750 m) slope in the N area. Conversely, the S area appeared to be more stable temporally with depth as the main gradient inducing assemblage differences. Different depth-related patterns were observed both for diversity and P/B. To the north diversity was very low at the shelf-break, increasing on the upper-slope (H′ > 3.00) and then decreasing again on the middle-slope. To the south diversity increased smoothly downward, reaching the highest values on the middle-slope. Regarding productivity, P/B was highest at intermediate depths to the north (over ca. 450–500 m), while to the south highest P/Bs were found deeper (over ca. 600–650 m). The higher P/B at intermediate depths found along N are likely due to higher % of organic matter (OM) in sediments, a product of oceanographic frontal systems. In particular, P/B was higher along N among omnivores and detritus feeders (e.g. Andaniexis mimonectes, Lepechinella manco and combined cumaceans), coupled to enriched OM in sediments, while along S mesoplanktonic carnivores (Rhachotropis spp.) had higher P/Bs. We conclude that on the north slope the influence of frontal systems and more active flow dynamics of different water masses (WIW and LIW) increases natural disturbance in the area, increasing productivity and diversity of suprabenthic peracarids in the Benthic Boundary Layer. Also, species showed a displacement of their average distributions (their Centres of Gravity, CoG) to shallower depths along N, which is another indicator of more favorable habitat conditions for suprabenthos in the 400–500 m range at N.     

Information-and-measuring drifter system for the monitoring of currents in the coastal zone of the sea

The autonomous drifting buoys equipped with satellite link turn into one of the most important components of the global system of operative observations of the ocean and the surface layer of the atmosphere. However, on the regional level, the problem of analysis of the surface circulation of waters in the coastal zone and sea straits remains quite urgent because the available drifters cannot be used in this case due to their sizes and long intervals between measurements. We present the results of development and testing of a new drifter system aimed at measuring currents. The system is based on the use of buoys operating at depths less than 1 m. To improve the space-and-time resolution of measurements, the buoys are equipped with receivers of the global positioning system (GPS) and GSM modems for the data transfer via cellular communication networks. The drifter system guarantees the possibility of determination of the coordinates of buoys with a resolution of 3 min in time and 14 m in space. We describe the specific features of the design of the proposed information-and-measuring drifter system and present the first results of application of new buoys called “minidrifters” for the pilot monitoring of currents in the Kerch Strait.     

Sonographs of submarine sediment failure caused by the 1980 earthquake off northern California

In 1980, a large earthquake caused extensive sediment failure on the shallow continental shelf off the Klamath River in northern California. Side-scan sonography was used to complement detailed geophysical profiling in identifying specific features and resolving modes of failure. The features include a nearly flat failure terrace mantled with sand boils, collapse craters and sediment flows, and bounded on the seaward side by a meandering continuous toe ridge. Seaward of the terrace lies a compression zone delineated by small pressure ridges. Our findings indicate a temporal progression of failure from lique-faction of shallow subsurface sand to lateral spread of intact blocks to sediment collapse and flow.     

Four-dimensional analysis of the variability of hydrophysical fields in the tropical atlantic and on the shelf of guinea

The problem of monitoring of the mesoscale variability of hydrophysical fields in the shelf zone is considered. The usefulness of the data available in regional information centres is discussed. The possibility of monitoring the dynamics of the oceanic fields in the tropical Atlantic encompassing separate observation sites is demonstrated using the oceanographic databank of the scientific research centre (CERESCOR) in Conakry-Rogbane as an example. The results of assimilation of the hydrophysical survey data derived on the shelf in a telescopic model of the region are given.Translated by Mikhail M. Trufanov.     

Mineral assemblages occurring around hydrocarbon vents in the northern Gulf of Mexico

Magnesian calcites are the most abundant authigenic minerals associated with hydrocarbon vents at 25 sites, in water depths ranging from 100 to 600 m in the Green Canyon area and about 2200 m in the Alaminos Canyon area on the Continental Slope of the northern Gulf of Mexico. The most frequently encountered magnesian calcites have 10–15 mol% MgCO₃ and the apparent structural disorder revealed by XRD peak widths increases with Mg substitution. There are no systematic variations in Mg content with respect to water depth or geographic location. The calcite saturation state of the precipitating fluid is primarily determined by the nature of the fluids escaping from the vents, not the ambient seawater.     

Resource decline and adaptation through time: Fishers in San Miguel Bay, Philippines, 1980–1993

This article examines social conditions in a bay experiencing population growth, gear conflict, overfishing, and general resource decline. Sample surveys of fishing households carried out in 1980 and 1993 in nine villages of San Miguel Bay reveal patterns of continuity and change. The key continuity is sustained overall population growth in fishing villages. Among the key forms of change are those which demonstrate a degree of adaptation to resource decline: decreased participation in fishing; greater reliance of fishing households on nonfishing income; increased dependence on remittances of nonhousehold children; increased participation of women in nonhousehold labor; and dramatic growth in the number of fishing organizations involved in resource management. The findings suggest that resource management policies should be patterned after spontaneous adaptations to resource decline.     

Unevenly compressed flexural-gravitity waves

Free flexural-gravity waves unevenly compressed in an ice-covered basin have been studied using a linear formulation. The conditions were specified allowing determination of the bounds of the angular area of wave disturbances and of the oscillation frequency intervals due to compression. The paper considers the distribution of the wave characteristics over frequency depending on compressive stresses and the direction of wave propagation.Translated by Vladimir A. Puchkin.