ALBERT

Description: Current measures of microbe‐mediated biogeochemical processes in sediments were examined for their potential use as indicators of heavy metal ecotoxicity in both river sediments and bacterial cultures. Assays were carried out with HgCl2, CuSO4, and 3CdSO4 · 8H2O added to sediment samples and bacterial cell suspensions at concentrations ranging from 0.1 to 10 mM and 0.1 μM to 1 mM, respectively. Chemoautotrophic CO2 fixation by Elbe River sediment microbiota was most sensitive to Hg2+ and Cd2+, but not to Cu2+. Among the estimates of heterotrophic productivity, incorporation of leucine into cellular protein showed clearer dose responses than incorporation of thymidine into bacterial DNA. Thymidine incorporation was highly resistant to and even stimulated by metal ions, particularly in starved and anaerobic cultures of a test strain of Vibrio anguillarum. Similar metal ion induced “overshoot” responses beyond the levels of untreated controls were noted for mineralization of 14C‐glucose by V. anguillarum and, in the case of Cd2+, also in sediment. As a less complex measure of microbial respiratory activity, succinate dehydrogenase (SDH) showed normal dose responses without stimulatory effects, as long as bacterial cell homogenates were assayed. Despite this result, it is concluded that levels of SDH in natural sediment microbiota are inevitably affected by metal‐induced processes of selection and enzyme synthesis, and would thus fail to provide an appropriate measure of metal ecotoxicity. The final conclusion is that current parameters of microbial production and activity often reveal dose responses that do not fulfill basic requirements of ecotoxicity testing in metal‐polluted sediments.

Description: On a transect between 20° and 70°S in the eastern Atlantic Ocean and Weddell Sea, water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon (δ13CΣCO2). These measurements were compared to δ13C values determined on live specimens of the benthic foraminifer Fontbotia wuellerstorfi and closely related genera from the same stations. In addition, at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured. General deepwater and bottom-water mass circulation patterns as inferred from the δ13CΣCO2 are in close agreement with those known from other nonconservative tracers. Very low δ13C values of upper Circumpolar Deep Water (〈0.3‰ Pee Dee belemnite (PDB)) in the Polar Front region and the eastern limb of the Weddell gyre coincide with nutrient maxima. However, a significant decoupling of the dissolved phosphate signal from the δ13CΣCO2 signal is indicated in the abyssal Weddell Sea. We attribute this to temperature-dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom-water formation. Multiple corer water from the sediment/water interface is slightly δ13C depleted relative to deepwater and bottom-water δ13ΣCO2. The surface sediment organic carbon δ13C is 3 to 4‰ lower south of the Polar Front than north of it, and the δ13Corg in freshly accumulated phytodetritus is 3 to 4‰ lower than surface sediment organic carbon δ13C. Comparison of live F. wuellerstorfi δ13C and related genera with bottom-water δ13CΣCO2 exhibits at most stations between the Subtropical Front (≈41°S) and the southern boundary of the Antarctic Circumpolar Current (≈55°S) a significant lowering of foraminiferal δ13C values. Compilation of a mean last glacial/interglacial δ13C amplitude (Δδ13C) from six published southern ocean cores results in a shift of −0.99± 0.13‰ PDB; this shift is greater than that in all other regions. However, all of these cores are from positions close to Recent oceanic fronts. Thus, for these peripheral areas of the southern ocean, we suggest about half of the glacial/interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production.

Description: What limits phytoplankton growth in nature? The answer is elusive because of methodological problems associated with bottle incubations and nutrient addition experiments. We are investigating the possibility that antibodies to proteins repressed by a specific nutrient can be used as probes to indicate which nutrient limits photosynthetic carbon fixation in the ocean. The diatom Phaeodactylum tricornutum Bohlin and the chlorophyte Dunaliella tertiolecta Butcher were grown in batch cultures in artificial seawater and f/2 nutrient lacking either phosphorus, iron, or nitrogen. Chlorosis was induced by nutrient limitation in both species with the exception of phosphorus‐limited D. tertiolecta. The synthesis and appearance of specific proteins were followed by labeling with 14C‐bicarbonate. Nutrient limitation in general leads to a decrease in the quantum efficiency of photosystem II, suggesting that deficiency of any nutrient affects the photosynthetic apparatus to some degree: however, the effect of nitrogen and iron limitation on quantum efficiency is more severe than that of phosphorus. A crude fractionation of the soluble and membrane proteins demonstrated that the large proteins induced under limitation by phosphorus and iron were associated with the membranes. However, small iron‐repressible proteins were located in the soluble fraction. Isolation with anion‐exchange chromatography and N‐terminal sequencing of iron‐repressible, 23‐kDa Proteins from D. tertiolecta, P. tricornutum, and Chaetoceros gracilis revealed that these small soluble proteins have strong homology with the N‐terminal sequence of flavodoxins from Azotobacter and Clostridium. The identity of the flavodoxin from D. tertiolecta was confirmed by immunodetection using antiflavodoxin raised against Chlorella. Flavodoxin was detected only under iron deprivation and was absent from nitrogen‐and phosphorus‐limited algae. Flavodoxin is a prime candidate for a molecular probe of iron limitation in the ocean. The requirements to confirm its utility in nature are discussed.

Description: Etwa ein Drittel des von Menschen freigesetzten Treibhausgases Kohlendioxid (CO2) reichert sich in der Atmosphäre an und verstärkt dort den Treibhauseffekt. Zwei Drittel dieses Eintrags werden der Atmosphäre wieder entzogen und an anderer Stelle deponiert. Doch nur für etwa die Hälfte des wieder gebundenen Kohlendioxids kennen wir bisher die Senken. Wo bleibt der Rest? Um Aussagen über den Verbleib weiterer CO2-Emissionen und damit über die zukünftige Entwicklung des Treibhauseffektes machen zu können, bedarf es der Lösung des Kohlenstoffrätsels.

Description: The effects of nitrate, phosphate, and iron starvation and resupply on photosynthetic pigments, selected photosynthetic proteins, and photosystem II (PSII) photochemistry were examined in the diatom Phaeodactylum tricornutum Bohlin (CCMP 1327). Although cell chlorophyll a (chl a) content decreased in nutrient‐starved cells, the ratios of light‐harvesting accessory pigments (chl c and fucoxanthin) to chl a were unaffected by nutrient starvation. The chl a‐specific light absorpition coefficient (a*) and the functional absorption cross‐section of PSII (σ) increased during nutrient starvation, consistent with reduction of intracellular self‐shading (i.e. a reduction of the “package effect”) as cells became chlorotic. The light‐harvesting complex proteins remained a constant proportion of total cell protein during nutrient starvation, indicating that chlorosis mirrored a general reduction in cell protein content. The ratio of the xanthophylls cycle pigments diatoxanthin and diadinoxanthin to chl a increased during nutrient starvation. These pigments are thought to play a photo‐protective role by increasing dissipation of excitation energy in the pigment bed upstream from the reaction centers. Despite the increase in diatoxanthin and diadinoxanthin, the efficiency of PSII photochemistry, as measured by the ration of variable to maximum fluorescence (Fv/Fm) of dark‐adapted cells, declined markedly under nitrate and iron starvation and moderately under phosphate starvation. Parallel to changes in Fv/Fm were decreases in abundance of the reaction center protein D1 consistent with damage of PSII reaction centers in nutrient‐starved cells. The relative abundance of the carboxylating enzyme, ribulose bisphosphate carboxylase/oxygenase (RUBISCO), decreased in response to nitrate and iron starvation but not phosphate starvation. Most marked was the decline in the abundance of the small subunit of RUBISCO in nitrate‐starved cells. The changes in pigment content and fluorescence characteristics were typically reversed within 24 h of resupply of the limiting nutrient.

Description: According to Sverdrup's (1953) model of the spring bloom, phytoplankton biomass decreases in winter when the mixed layer depth exceeds the critical depth. We have used a one-dimensional mathematical model integrated by the Lagrangian Ensemble method to simulate a population of diatoms during the winter between two growing seasons off the Azores. The model allows us to diagnose the demographic changes in the simulated diatom population from a variety of perspectives. The total population falls to a minimum of 70 million diatoms m-2 at the end of February. The vertical distribution of the population dynamics is first analysed in terms of daily Eulerian averages over 1 m depth intervals. Growth starts in February when the diurnal thermocline becomes shallower than 50 m, but while the mixed layer is still 200 m deep. The natural mortality has a minimum in winter because it is reduced (in the model) with temperature and population density. Eulerian analysis suggests that in winter, diatoms have a life expectancy of more than 3 months, so a significant number will survive the months of December, January and February when there is very little growth. Losses to grazing are negligible in winter. Lagrangian analysis shows how an individual diatom responds to its changing ambient environment caused by variation in depth (due to turbulent mixing) and the diurnal and seasonal changes in the photosynthetically active radiance. The different trajectories followed by the thousands of plankton particles simulated by the model produce diversity in growth rate ranging over several orders of magnitude, so care has to be taken in statistical analysis. The paper ends with a re-assessment of the value of the critical depth and compensation depth as predictors for onset of the spring bloom. The compensation depth was computed by Eulerian averaging over 1 m depth inter-vals each day. For 1 month after the vernal equinox the compensation depth follows the ascent of the mixed layer as it rises from a depth of 100 m to 40 m. Lagrangian analysis reveals that this is due to the photo-adaptation better matching the ambient irradiance experienced by diatoms in the mixed layer compared with those at the same depth in the seasonal thermo-cline. By mid-April the spring bloom has already ad-vanced so far that self shading influences the compensation depth, which then rises into the mixed layer. We conclude that Sverdrup's criterion is not useful for predicting changes in the diatom population simulated by our model.

Description: The demersal fish and cephalopod communities of the continental shelf and upper slope from 17 to 395m deep were studied during five annual cruises between Cape Agulhas and Port Alfred, South Africa. The cruises showed a consistent pattern of an inshore community (〈100m), a shelf community (c. 90–190m) and a shelf‐edge/upper slope fauna (〉200m). These groups were identified by dendrograms and multidimensional scaling cluster analysis, which supported on‐board observations of catch variation with depth. Although the boundaries are not clearly defined, examination of physical features at the clustered stations suggests that depth, temperature and, to a lesser extent, oxygen concentration are important in the grouping. Occasional, apparently anomalous associations of inshore stations suggested that water temperature and oxygen may over‐ride the normal depth distributions of the species groups. This intimates that patterns offish and cephalopod distribution may be dynamic and in part related to the physical parameters of the water body.

Description: 1. Survival, growth and downstream dispersal of trout (especially 0 group) and the relationships of these variables to initial stocking density were studied in north Pennine streams. 2. Two methods were used. First, electrofishing censuses were made in a marked reach of each of four streams over a period of about 20 years. Second, downstream moving trout were trapped in two streams over a 10-year period. Each stream upstream of the trap was experimentally stocked with `swim-up' trout fry, using a different population density each year. 3. Before 1970 the four census reaches showed very large year-upon-year variations in August trout parr densities, with local failures of recruitment in some years. Population densities after completion of Cow Green Reservoir (1970) were generally higher but still showed wide fluctuations. 4. Survival (including the effects of losses by dispersal) from swim-up to early August, for starting population densities of 0-10 fry m-2, was about 10% regardless of initial density. Estimates of survival from August to early October were 30-50% for the census reaches and 55-65% for the areas upstream of the traps. However, for August 0 group densities of 0-0.9 m-2, estimated instantaneous loss rate from August of the first year of life up to age 40-65 months showed a positive curvilinear relationship to population density in the first year of life. Loss rate was, therefore, density-dependent during this period. 5. Estimated instantaneous growth rate day-1 of 0 group fish from swim-up to August and from swim-up to October was inversely related to the natural logarithm of August population density and this was most apparent for August densities of 〈0.15 fish m-2. 6. Although survival from swim-up to August was proportional (about 10%, at starting densities of 10 m-2 or less), the percentages of the total loss attributable to mortality and to downstream dispersal varied considerably with starting density. At starting densities around 4-5 fish m-2 dispersal was negligible. As initial density rose above 4-5 fish m-2 and towards 10 fish m-2 the percentage of loss attributable to dispersal rose towards 30%. As initial densities decreased from 4 to 1.4 fish m-2, the percentage rose to around 20%. Below a starting density of 1.4 fish m-2 the percentage decreased.

Description: Seismically derived depth estimates to the top of the oceanic crust beneath the Hawaiian Islands indicate that the curvature of the deflected lithosphère is much larger than commonly believed. The conservative and model-independent curvature estimates exceed 10−7 m−1 and are comparable in magnitude to curvatures at trenches and outer rise systems. The depth estimates are used to constrain both two-dimensional (2-D) and three-dimensional (3-D) flexural models. The curvature constraints require a 2-D variable elastic thickness that decreases from 35 km in areas away from the volcanic load to 25 km directly beneath the load. In an attempt to understand the nature of the yielding beneath the Hawaiian Islands we introduce two new 3-D models. The first model combines a realistic yield strength based rheology with a new technique for 3-D flexure calculations in which the elastic plate thickness is curvature-dependent. The new variable rigidity model predicts an undeformed (mechanical) plate thickness of 44 km, decreasing to 33 km beneath the big island of Hawaii. The best-fitting mechanical thickness corresponds approximately to the depth to the 600 °C isotherm in 90-m.y.-old lithosphere. The second model uses a broken plate, but here the crack is oriented along the weak Molokai fracture zone rather than along the island chain trend. This unconventional flexure model can explain the observed asymmetry in the depth data across the fracture zone without requiring the excessively large elastic thickness of more conventional broken plate models. Both the proposed models imply that modeling with constant thickness plates may underestimate the true mechanical plate thickness by being unduly influenced by the weak zone beneath the seamounts.