Recent and fossil benthic foraminifera in the Adriatic Sea : distribution patterns in relation to organic carbon flux and oxygen concentration at the seabed

The results of the present study indicate that benthic foraminiferal abundance in Recent and fossil sediments. provides a basis for estimation of present and past organic carbon flux at the seabed. Whereas the production of infaunal foraminifera may be enhanced by lateral supply of organic carbon, the abundance of epifaunal foraminifera may be a more reliable measure of the vertical supply of organic carbon. Oxygen deficiency in the bottom water may result in replacement of the normal epifaunal community by a community dominated by low-oxygen tolerant infaunal foraminifera. Under such conditions reliable estimation of the vertical organic flux seems not possible

Enhanced short-term sediment deposition within the Nazaré Canyon, North-East Atlantic

International audienc

Near-bed perticle deposition and resuspention in a cold-water coral moundd area at the Southwest Rockall trough margin, NE Atlantic

Cold-water coral reefs and mounds are observed mainly on slopes and topographic highs, in areas with high current speeds. Previous investigations of the near-bed hydrodynamic regime around cold-water coral mounds at the Southwest Rockall Trough margin have revealed the presence of internal waves with a diurnal tidal frequency. Hitherto only short-term measurements existed on the particle supply to the corals and data are lacking on the seasonal variability. Bottom landers equipped with sensors recording near-bottom current dynamics were deployed at two sites in a mound area on the Southwest Rockall Trough margin, one with a dense coral cover and one without coral cover. At both sites a similar seasonal variation in internal-wave activity was recorded with high activity during winter and summer months and less dynamic conditions in spring and autumn. Increased intensity of internal-wave activity, reflected in higher average near-bottom current speed and amplitude of daily temperature fluctuations, results in higher mass fluxes as recorded in the sediment traps. On the site without coral cover, mass fluxes are two times higher, compared to the site with dense coral cover. During periods of high mass fluxes a predominance of resuspended material was observed at both sites, as indicated by reduce

Modeling the long-term population dynamics of benthic foraminiferal communities using field and experimental data

A mathematically simple model is used to simulate the long-term impact of variable food flux and oxygenation over decades. [nput characteristics were offspring and generation length, the values of which are derived from laboratory experiments. Other input consisted of a parameter describing the sensitivity of taxa to variation in oxygenation; values for this constant were derived from field data. A fourth parameter describing sensitivity to competition was obtained by inverse modeling. We simulated a 30 years time series with initially high eutrophication and low oxygen values. The model showed that opportunistic taxa, characterized by a high reproductive success, could successfully compete in environments marked by periodically occurring severe oxygen stress. Under permanent low oxygen conditions they were replaced by deep infauna. Under improved environmental conditions, the assemblage was dominated by taxa that are adapted to food-limited conditions. Oxygen appeared to be a more important parameter than food in the recovery of the ecosystem after an initial eutrophic state. The simulated sequences were compared with the historic development of the Adriatic Sea over the past 160 years, which also documents a change between trophic extremes

Modeling the long-term population dynamics of benthic foraminiferal communities using field and experimental data

A mathematically simple model is used to simulate the long-term impact of variable food flux and oxygenation over decades. [nput characteristics were offspring and generation length, the values of which are derived from laboratory experiments. Other input consisted of a parameter describing the sensitivity of taxa to variation in oxygenation; values for this constant were derived from field data. A fourth parameter describing sensitivity to competition was obtained by inverse modeling. We simulated a 30 years time series with initially high eutrophication and low oxygen values. The model showed that opportunistic taxa, characterized by a high reproductive success, could successfully compete in environments marked by periodically occurring severe oxygen stress. Under permanent low oxygen conditions they were replaced by deep infauna. Under improved environmental conditions, the assemblage was dominated by taxa that are adapted to food-limited conditions. Oxygen appeared to be a more important parameter than food in the recovery of the ecosystem after an initial eutrophic state. The simulated sequences were compared with the historic development of the Adriatic Sea over the past 160 years, which also documents a change between trophic extremes

水資源の分配に関する法制度 : その歴史と現状

特集・都市と水資源の確

Sedimentary processes in the middle Nazaré Canyon

Nazaré Canyon extends from a water depth of 50 m near the Portuguese coast to 5000 m at the edge of the Iberian Abyssal Plain. The system is not connected to a modern river and instead obtains its present day sediment input by capture of along-shelf sediment transport. Much of this sediment is deposited in the middle canyon between about 2700 and 3800 m. However, the middle canyon is a highly heterogeneous environment, with areas of both high and low sedimentation rates, exposed rock outcrop, erosion and stable and unstable slopes in close juxtaposition. This paper explores how the various sedimentary processes interact to create the observed heterogeneous canyon environment, which will influence benthic biodiversity in the canyon. Seafloor heterogeneity is investigated using a nested approach to data interpretation, using local high-resolution data to calibrate regional lower resolution data. Six different data types, ship and ROV-mounted swath bathymetry, 30 kHz sidescan sonar images, sediment cores, seafloor video/photographs and current metre/acoustic backscatter data, were incorporated into the analysis. The main morphological characteristic of the middle canyon is a narrow, steep-sided, axial channel flanked by gently sloping terraces. Small-scale landsliding, active at the present day, is the main process that exposes a variety of substrates, ranging from semi-consolidated Holocene sediments to rock of probable Mesozoic age, on the steep axial channel walls. The axial channel floor is characterised in part by large-scale sediment bedforms and in part by landslide debris, suggesting some reworking of landslide debris by currents within the channel. The terraces are interpreted as inner levees with high sedimentation rates. Cores show a dominantly muddy sequence interrupted by thin turbidite sands emplaced on decadal to centennial timescales. The fine-grained sedimentation is the product of continuous settling from fine-grained flows that range from gravity currents to lateral advection of nepheloid layers. The close proximity of areas of high sedimentation and erosion creates a highly heterogeneous seafloor, with the highest heterogeneity on the steepest slopes

Hydrodynamic controls on cold water coral growth and carbonate mound development at the SW and SE Rockall Trough Margin, NE Atlantic Ocean.

Long-term (≤1-year) records obtained by seabed observatories (BOBO) and repeated (24-h) CTD casts show the presence of a highly energetic environment in and around two cold-water carbonate-mound provinces, on the Southwest and Southeast Rockall Trough (SW and SE RT) margin. Carbonate mounds, covered with a thriving coral cover, are embedded mainly in the Eastern North Atlantic Water (ENAW) and are observed in a confined bathymetric zone between 600 and 1000 m water depth. Cold-water corals seem to be restricted in their growth by temperature and food availability. The presence of living corals on top of the carbonate mounds appears linked to the presence of internal waves and tidal currents in the water column, and consequently carbonate mound structures are shaped by the local hydrodynamic regime. Mound clusters have an elongated shape perpendicular to the regional contours and corresponding to the direction of the highest current speeds. On the SW RT margin temperature, salinity and current speed reflect a diurnal tidal pattern, causing maximum temperature variations at 900 m depth of more than 3 °C. Current speeds up to 45 cm

Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications

International audienc