Description of possible causes of the formation of anomalies of the cloud field over the Atlantic-European sector in the spring of 1996

We describe one of possible mechanisms of the formation of anomalies of the cloud field over the North Atlantic and Europe by using, as an example, the processes developed in the Atlantic-European sector during the natural synoptic season in the spring of 1996. It is shown that the anomalies of the cloud field can be classified with the use of the index of the North Atlantic oscillation and the latitude of the center of the Azorean maximum. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Marine mammals from northeast Atlantic: relationship between their trophic status as determined by delta13C and delta15N measurements and their trace metal concentrations

The relationship between trophic position through delta13C and delta15N and trace metal concentrations (Zn, Cd, Cu and Hg) was investigated in the tissues of six marine mammal species from the Northeast Atlantic: striped dolphin Stenella coeruleoalba, common dolphin, Delphinus delphis, Atlantic white-sided dolphin Lagenorhynchus acutus, harbour porpoise Phocoena phocoena, white beaked-dolphin Lagenorhynchus albirostris, grey seal Halichoerus grypus stranded on French Channel and Irish coasts. White-beaked dolphins, harbour porpoises, white-sided dolphins, common and striped dolphins display the same relative and decreasing trophic position, as measured by delta15N values, along both the Irish and French channel coasts, reflecting conservative trophic habits between these two places. Hepatic and renal Cd concentrations were significantly correlated to muscle delta13C and delta15N values while Hg, Zn and Cu did not. These results suggest that Cd accumulation is partly linked to the diet while other factors such as age or body condition might explain Hg, Zn or Cu variability in marine mammals. Combined stable isotope and trace metal analyses appear to be useful tools for the study of marine mammal ecology.     

Comparative tolerance of two estuarine annelids to fluoranthene under normoxic and moderately hypoxic conditions

The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field.     

Inter-annual variability in larval supply to populations of three invertebrate taxa in the northern California Current

We investigated sources of inter-annual variability in larval supply to crab and sea urchin populations at Bodega Head and Point Reyes in northern California. During the spring and summer upwelling seasons of the years 1992 through 1997 we monitored the weekly settlement rates of nine species of crabs and two species of sea urchins. As observed in previous studies, daily values of alongshore windstress, temperature and salinity provided evidence for the poleward flow of relatively warm, low salinity water from south of Point Reyes, an apparent retention zone, during upwelling relaxation events. In years dominated by these events (1992, 1993, 1995 and 1996) we observed that alongshore windstress, temperature and salinity were coherent and temperature was significantly correlated with cancrid crab settlement. During these years the magnitude of cancrid crab settlement and the fraction of cancrid crabs relative to other crab species settling were high. Over four years of concurrent sampling there was consistently greater cancrid crab settlement at the Point Reyes site, within the retention zone, than at Bodega Head. Settlement of non-cancrid crabs (porcellanids, grapsids, pagurids and majids) was not as closely linked to intra-annual patterns of upwelling and relaxation, possibly due to the shorter seasonal availability of larvae allowing for the influence of fewer relaxation events. Settlement of this group among years was positively correlated with environmental indicators of strong seasonal upwelling; high salinity, Bakun upwelling index and low temperature. Sea urchin settlement events were observed in June and July of 1992, 1994 and 1997 during warming periods when salinity and temperature were increasing and alongshore windstress was low. Across the six years of the study, we found that cancrid crab larvae had a more even seasonal availability than larvae of non-cancrid species, which settled in greatest numbers during the early portion of the upwelling season. Sea urchins settled in greatest numbers during the later part of the upwelling season. Together these patterns demonstrate the taxon-specific way that inter-annual variability in larval supply is forced by the coincidence of larval availability with favorable physical transport mechanisms.     

Diet shifts of Caribbean grunts (Haemulidae) and snappers (Lutjanidae) and the relation with nursery-to-coral reef migrations

The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species (Haemulon sciurus and Haemulon flavolineatum) and of two snapper species (Lutjanus apodus and Ocyurus chrysurus) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus, L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodusand O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus, a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.     

Interaction of Surface Waves in a Basin with Floating Broken Ice

The multiscale method is used to obtain asymptotic expansions up to the quantities of the third order for the elevations of the surface of the basin and the velocity potential of motion of liquid particles in the wave disturbances formed in the process of nonlinear interaction of periodic running waves of the first and second harmonics in a homogeneous ideal incompressible liquid of constant finite depth covered with broken ice. The dependences of the amplitude-phase structure of disturbances on the ice thickness, depth of the basin, and the parameters of interacting harmonics are investigated. We estimate the error of evaluation of the characteristics of the formed vertical displacement of the surface of the basin and nonlinear mass transfer introduced by neglecting the curvature of the wave profile in the expression for the velocity potential in deducing the kinematic and dynamic surface boundary conditions for nonlinear approximations.     

Sediment-starved sand ridges on a mixed carbonate/siliciclastic inner shelf off west-central Florida

High-resolution side-scan mosaics, sediment analyses, and physical process data have revealed that the mixed carbonate/siliciclastic, inner shelf of west-central Florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms. The sand ridges, mostly oriented obliquely to the shoreline trend, extend from 2 km to over 25 km offshore. They show many similarities to their well-known counterparts situated along the US Atlantic margin in that both increase in relief with increasing water depth, both are oriented obliquely to the coast, and both respond to modern shelf dynamics. There are significant differences in that the sand ridges on the west-central Florida shelf are smaller in all dimensions, have a relatively high carbonate content, and are separated by exposed rock surfaces. They are also shoreface-detached and are sediment-starved, thus stunting their development. Morphological details are highly distinctive and apparent in side-scan imagery due to the high acoustic contrast. The seafloor is active and not a relict system as indicated by: (1) relatively young AMS ¹⁴C dates (<1600 yr BP) from forams in the shallow subsurface (1.6 meters below seafloor), (2) apparent shifts in sharply distinctive grayscale boundaries seen in time-series side-scan mosaics, (3) maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation, (4) sediment textural asymmetry indicative of selective transport across bedform topography, (5) morphological asymmetry of sand ridges and 2D dunes, and (6) current-meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded. Although larger sand ridges are found along other portions of the west-central Florida inner shelf, these smaller sand ridges are best developed seaward of a major coastal headland, suggesting some genetic relationship. The headland may focus and accelerate the N–S reversing currents. An elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf, allowing them to be more easily influenced by currents and surface gravity waves. Tidal currents, storm-generated flows, and seasonally developed flows are shore-parallel and oriented obliquely to the NW–SE trending ridges, indicating that they have developed as described by the Huthnance model. Although inner shelf sand ridges have been extensively examined elsewhere, this study is the first to describe them in a low-energy, sediment-starved, dominantly mixed siliciclastic/carbonate sedimentary environment situated on a former limestone platform.     

Seismic evidence for pervasive deformation of oceanic sediments in the Eastern Equatorial Atlantic

Seismic reflection profiles from the equatorial Atlantic off Africa between 12°N and 1°N reveal remarkably widespread deformation of oceanic sediments in an area lacking teleseismic activity. Uplift of abyssal plain sequences has occurred along the eastern extensions of large-offset fracture zones on the Mid-Atlantic Ridge. Between the major transforms pervasive deformation is imaged in the sedimentary column. Diapirism and faulting may have been associated with extensive fluid migration and sediment mobilization. The deformation occurred during the late Cenozoic and was probably related to reactivation of Cretaceous transforms.