Incidence de la cinetique de decroissance de la temperature apres le choc thermique sur les modifications d'activite des esterases et les possibilites de survie de Scolelepis (malacoceros) fuliginosa (annelide polychete)

Scolelepis fuliginosa reared in the laboratory at 13°C were put through 10-min thermal shocks at 16°C and 18°C and were then submitted to either a slow or a rapid temperature reduction. After the thermal shock, a posterior fragment of each specimen was cut off at intervals, until six days. Samples were submitted to electrophoresis on polyacrylamide gel, esterase activity being determined with α-naphthyl acetate.Enzymograms show that thermal shocks act on esterases in decreasing the activity of the main fractions. Immediate effects result in a very precocious enzymic response; more long-term effects depend on the maximum temperature, the animal's sex and the kinetics of the post-shock thermal reduction.Females are more sensitive than males. For a given Δt, esterase changes are greater and more long-lasting. After a 16°C Δt, a rapid decrease in temperature prevents the loss of activity of the middle and fast fractions in males and delays, by about 10 h, the alteration of female esterases. After 18°C ΔT, loss of activity of the middle and fast fractions occurs in less than 1 h, independently of the thermal kinetics, but survival is only possible—solely for males—with a rapid decrease in temperature which also delays females' deaths by between 24 and 48 h.In conclusion, a rapid decrease in temperature gives organisms a better resistance to thermal shock, as determined by esterase activity and controls the lethality of a high Δt.     

Evolution à Long terme (1978–1986) des populations d'Amphipodes des sables fins de la pierre noire (baie de morlaix, manche occidentale) aprs̀s la catastrophe de l'Amoco Cadiz

Greatly reduced in 1978 by the Amoco Cadiz oil spill, the amiphipod populations of the fine sand community of Pierre Noire in the Bay of Morlaix have not yet fully recovered 8 years after the pollution. The sublittoral sandi-mud benthic communities in the western part of the English Channel show a discontinuous distribution, occurring in isolated zones which are localized in estuaries and bays. The amphipods, which are characteristic of these communities and lack a pelagic larva, form insular populations. This insular distribution delays their re-introduction to the fine sand community of Pierre Noire. Moreover, the biological and demographic characteristics of the species entail limited periods of recolonisation and increase in population.     

Chromium(III) — chromium(VI) interconversions in seawater

The stable form of dissolved chromium in oxygenated seawater is Cr(VI). But Cr(III)-species are also present at an analytically significant level. It is shown that Cr(III) is oxidized only slowly by dissolved oxygen, and that manganese oxide is a strong catalyst for such oxidation. However, the low oceanic concentration of suspended MnO₂ impedes the conclusion that the former process is quantitatively less important than the latter one. The distribution of dissolved chromium among Cr(VI)- and Cr(III)-species is probably kinetically controlled.     

Evolution des hydrocarbures et des populations bactériennes et microphytiques dans les sédiments des marais maritimes de l'ile grande pollués par l'Amoco cadiz: 2—Evolution des peuplements microphytiques

In this work we attempt to estimate the short- and long-term effects of the Amoco Cadiz oil spill on benthic microalgal populations (cyanophytes and diatoms) which, under natural conditions, live on upper layers of ‘schorres’ soils or of ‘slikke’ muds in the Ile Grande salt marsh system (Côtes du Nord, France). These populations were completely destroyed in 1978 in the oil-affected sites. Ubiquitous species settled fairly rapidly on intertidal polluted muds (tidal flat). The chlorophyll a content values reached 100 μg g⁻¹ dry sediment, i.e. 1000 mg m⁻² in 1980. Conversely, the salt marsh soils are still much less densely repopulated 3 years after the Amoco Cadiz grounding—especially when they are infrequently flooded (3 to 40 μg Chl.a g⁻¹, i.e. 40 to 270 mg m⁻²). Some of these soils remain ten times less populated than reference stations.     

Distribution of whitemouth croaker (Micropogonias furnieri, Desmarest 1823) larvae in the Río de la Plata estuarine front

Whitemouth croaker (Micropogonias furnieri) larvae obtained and hydrographic data collected in the Rio de la Plata estuary (35°S–56°W) between 1987 and 2000 were used to explore the early life stages spatial and temporal distribution patterns and their relation to oceanographic features. The spatial distribution, restricted to a band in the inner part of the estuary, coincided with the bottom salinity front and the maximum turbidity zone (MTZ, turbidity front). Larvae were present during the warmest months (October through May) within a range of 14–24.5 °C temperature and 0.9–33 salinity. A vertically stratified sampling performed in the region where the largest abundance was found (December 2005 and March 2006) was used to test the hypothesis that larvae retention occurs in the bottom salinity front.The vertically stratified sampling showed larvae throughout the water column with high predominance in the river–estuary transition zone. A positive correlation between abundance and the bottom salinity horizontal gradient was found. The size analysis showed that the largest individuals (>10 mm SL), probably undergoing the settlement process, inhabited near the bottom and that the smallest (<10 mm SL) were present in the whole water column. Length distribution along the front showed no trend.Results support the estuarine retention hypothesis of previous studies on whitemouth croaker gravid females, eggs distribution and outcomes from a numerical simulation model. Retention in the salinity front/MTZ would allow larvae to benefit from food accumulation in the region, the high turbidity level provide shelter against predators and retention in the estuary secure closeness to the main nursery ground.     

Near-surface current measurement from a surface following data buoy (DB1)—II. An harmonic and residual analysis of current meter records

This part of the paper examines near-surface current data from different periods during the test mooring of the data buoy, DB1.Harmonic analyses show that variations in the major tidal constituents between each period are not significantly greater than the standard error of the measurement: the differences observed in the principal lunar semi-diurnal tide are explained partly in terms of a modulation by adjacent constituents. Unexpected forms for the quarter diurnal tidal ellipses derived from the DB1 data have been found also in independent measurements, in which a different mooring technique had been used. These are therefore unlikely to be of instrumental origin.Non-tidal energy at periods exceeding three days is shown to correlate with changes in wind and surface elevation, the correspondence between wind and current being greatest during a period of strong winds, when current at 3 m depth was 0.9% of wind speed at 8 m. The data are interpreted in favour of an Eulerian current rather than Lagrangian Stokes transport due to waves. Rectification of wave orbital velocities due to buoy motion is not detectable.In view of the overall quality of the data it is concluded that this combination of surface following buoy and long-path acoustic current meter can contribute usefully to the determination of mean near-surface currents in the open sea.     

Nearshore retention of upwelled waters north and south of Point Reyes (northern California)—Patterns of surface temperature and chlorophyll observed in CoOP WEST

Retentive embayments can be found near capes in upwelling regions, where they stand out as relatively warm features with higher chlorophyll a concentrations than surrounding waters. Within the area of the “Wind Events and Shelf Transport” study site (WEST) from the Gulf of the Farallones to Point Arena (37.5–39°N and 122.5–124°W), we describe two retentive embayments, extending approximately 20 km north of Point Reyes, and 30 km south of Point Reyes in the northern Gulf of the Farallones. These areas are identifiable from chlorophyll a (SeaWiFS) and sea-surface temperature (MODIS) satellite radiometry. Additional data from moorings and drifters were used to further characterize these retentive features. The persistence of these features is on time scales between 2 and 10 days, determined from time-series analysis of mooring data for chlorophyll and temperature. The alongshore wind stress is negatively correlated with chlorophyll and temperature mooring values. The time scale of persistence of these retentive features was similar to both the upwelling-relaxation timescale and the timescale of phytoplankton bloom development. The WEST region is notable in that the spring and summer is subject to the strongest wind stress along the US west coast, yet the coastal waters are highly productive. Based on our observations, we suggest that the apparent persistence of high biomass coastal waters in this strongly advective and wind-dominated system may be partially explained by the presence of retentive features identified in this study.     

Using the Mellor–Yamada mixing scheme in seasonally ice-covered seas—Corrigendum to: Parameterization of vertical mixing in the Weddell Sea [Ocean Modelling 6 (2004) 83–100]

A coding error in the s-Coordinate Primitive Equation Model (SPEM) has led to misleading statements about the behaviour of the Mellor–Yamada level 2 parameterization of vertical mixing. It has been claimed that the scheme removes static instability only very slowly and preserves statically unstable stratifications for an unrealistic long time. This note corrects this statement by demonstrating that the Mellor–Yamada mixing scheme, if implemented correctly, tends to overestimate rather than underestimate vertical mixing in seasonally ice-covered seas. Similar to other mixing schemes with the same behaviour, this leads to spurious open ocean deep convection, an unrealistic homogenization of the water column, and a significant reduction of sea ice volume.     

Near-surface current measurement from a surface following data buoy (DB1)—I : An intercomparison of records from data buoy current meters and near-surface drifting float displacements

The measurement of near-surface current in the open sea presents difficult problems, of both sensor design and mooring in the surface wave field. However, knowledge of such currents is of considerable importance in research and offshore engineering. Consequently the development of an acoustic surface current meter has received particular attention within an experimental data buoy project which has been undertaken in the United Kingdom (DB1 Project). The development of any new sensor is necessarily followed by a thorough analysis of its performance, and it is this aspect to which this paper is devoted. The first part describes an experiment in which the displacements of drifting floats, tracked acoustically, were compared with the integrated output from the acoustic current meter: also a comparison with a buoy-mounted electromagnetic sensor. The extent of agreement between these different techniques is examined.A subsequent part discusses some longer term aspects of the performance of the current meter, which has operated almost continuously for 18 months at a test site close to the east coast of England.