ALBERT

Description: Observations from cruises in the Arabian Sea and data from satellites are interpreted using different realizations of a multi-level primitive equation model and an eddy-permitting reduced-gravity shallow water model of the Indian Ocean. The focus is on the interannual circulation variability of the Arabian Sea, and especially of the meridional location of the Great Whirl (GW). The results suggest that the variability in the western Arabian Sea is not only due to the interannual variability in the wind field, but that a substantial part is caused by the chaotic nature of the ocean dynamics. Decreasing the friction coefficient from 1000 to 500m2s-1 in a 19o numerical reduced-gravity model, the variance of the GW location increases dramatically, and the mean position moves southward by one degree. In the eddy-permitting experiments analyzed, both mechanisms appear to determine the GW location at the onset of the GW dynamics in late summer.

Description: Sea-surface height data acquired by the TOPEX/POSEIDON satellite over the Arabian Sea from October 1992 to October 1998 are analyzed. Strong seasonal fluctuations are found between 61 and 101N, which are mainly associated with westward propagating annual Rossby waves radiated from the western side of the Indian subcontinent and that are continuously forced by the action of the wind-stress curl over the central Arabian Sea. An analysis of hydrographic data acquired during August 1993 and during January 1998 at 81N in the Arabian Sea reveals the existence of first- and second-mode annual Rossby waves. These waves, which can be traced as perturbations in the density fields, have wavelengths of 12�103 and 4.4�103km as well as phase velocities of 0.38 and 0.14 m/s, respectively. The waves are associated with a time-dependent meridional overturning cell that sloshes water northward and southward. Between 581 and 681E in the central Arabian Sea, we found a Rossby-wave induced transport in the upper 500m of about 10 Sv southward in August 1993 and northward in January 1998. Below 2000 m, there was still a northward transport of 3.2 Sv in August 1993 and a southward transport of 4.8 Sv in January 1998. A comparison of steric height differences between August 1993 and January 1998 calculated from the observed density fields as well as calculated from the reconstructed density fields using first- and second-mode annual Rossby waves agree quite well with the corresponding sea-surface height differences. Implications resulting from the reflection of annual Rossby waves, like fluctuations of the western boundary currents, are discussed.

Description: Phytoplankton (〉100 µm) abundance was studied in the open waters of the Gulf of Aqaba during the summer stratification period of 1996. A succession took place among the major phytoplankton groups, with diatom numbers decreasing throughout the summer. The diazotrophic cyanobacteria Trichodesmium spp. became more prominent as the stratification period progressed; 5 Trichodesmium species were identified: T. thiebautii, T. erythraeum with tuft-shaped colonies and Trichodesmium sp. with puff-shaped colonies were common at ~102 colonies m-3 throughout the stratification period, whereas T. tenue and T. hildebrandtii were more rare. A bloom of T. thiebautii and T. erythraeum with 〉106 tuft colonies m-3 was observed in coastal waters of the Gulf during fall 1997. Tuft-shaped colonies were dominant near the surface, while puff-shaped colonies of Trichodesmium sp. were mainly found in the bottom half of the photic zone. These depth distributions were maintained for more than 2 mo, suggesting that the 2 colony types occupied distinct niches. Puff-shaped colonies were found to have higher chlorophyll a contents than tufts, but their photosynthetic activities were not significantly different. Fatty acid analysis of dominant plankton species yielded new trophic relationships for Trichodesmium spp. The Trichodesmium spp.-specific fatty acid C22:2 ω6 was found in Macrosetella gracilis (the sole copepod to graze on Trichodesmium spp.) and in chaetognaths, suggesting that these carnivorous zooplankton fed on M. gracilis. Furthermore, this fatty acid was observed in the filter-feeding Salpa maxima, which was abundantly present in the Gulf of Aqaba during June 1997.

Description: The combined and interactive effects of climatic and ecological factors are rarely considered in marine communities. We designed a factorial field experiment to analyze (1) the interactive effects of ambient UV radiation and consumers; and (2) the effects of photosynthetically active radiation (PAR 400 to 700 nm), UVA (320 to 400 nm) and UVB (280 to 320 nm) radiation on a marine hard-bottom community in Nova Scotia, NW Atlantic. Species recruitment and succession on ceramic tiles were followed for 5 mo. We found strong negative UV effects on biomass and cover of the early colonizing macroalga Pilayella littoralis, whereas UVB was more harmful than UVA radiation. Consumers, mainly gammarid amphipods, increased P. littoralis biomass when UV was excluded, probably through fertilization. These initially strong and interacting UV and consumer effects on total biomass and cover diminished as species succession progressed. Species diversity was not affected by experimental treatments, but significant shifts in species composition occurred, especially at the recruitment stage. Red algae were most inhibited by UV, whereas sedentary invertebrates and some brown algae tended to increase under UV exposure. Consumers suppressed green and filamentous brown algae, but favored the other groups. Again, these effects diminished during the later stages of succession. We conclude that UV radiation can be a significant structuring force in early successional benthic communities, and that consumers can mediate its effects.

Description: Between 1991 and 1999, carbon measurements were made on twenty-five WOCE/JGOFS/OACES cruises in the Pacific Ocean. Investigators from 15 different laboratories and four countries analyzed at least two of the four measurable ocean carbon parameters (DIC, TAlk, fCO2, and pH) on almost all cruises. The goal of this work is to assess the quality of the Pacific carbon survey data and to make recommendations for generating a unified data set that is consistent between cruises. Several different lines of evidence were used to examine the consistency, including comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements. With the adjustments proposed here, the data can be combined to generate a Pacific Ocean data set, with over 36,000 unique sample locations analyzed for at least two carbon parameters in most cases. The best data coverage was for DIC, which has an estimated overall accuracy of ∼3 μmol kg−1. TAlk, the second most common carbon parameter analyzed, had an estimated overall accuracy of ∼5 μmol kg−1. To obtain additional details on this study, including detailed crossover plots and information on the availability of the compiled, adjusted data set, visit the Global Data Analysis Project web site at: http://cdiac.esd.ornl.gov/oceans/glodap.

Description: The effect of methane released from decomposing surficial gas hydrates (SGH) on standing stocks and activities of the small-sized benthic biota (SSBB; i.e. bacteria, fungi, protozoa, and meiobenthic organisms) was studied at about 790 m water depth, at the Hydrate Ridge, Cascadia subduction zone. Presence of SGH and elevated sulfide concentrations in the sediment were indicated by extensive bacterial mats of Beggiatoa sp. and clam fields of the bivalve mollusc Calyptogena sp. Vertical and horizontal distribution patterns of the SSBB biomass were derived from DNA and total adenylate (TA) sediment assays. Potential bacterial exoenzymatic hydrolytic activity was measured using fluorescein-di-acetate (FDA) as substrate. Estimates of chemoautotrophic production of particulate organic carbon (POC.) were determined by 14CO2 uptake incubations. Inventories of chl a and pheopigments were determined as parameters of surface water primary produced POC input. Average SSBB biomass in clam field sediments integrated over the upper 10 cm (765.2 gC m-2, SD 190.1) was 3.6 times higher than in the adjacent control sites (213 gC m-2, SD 125). Average SSBB biomass in bacterial mat sediments, which were almost devoid of eukaryotic organisms 〉 31 µm, was 209 gC m-2 (SD 65). Significant correlations between FDA, DNA and plant pigments imply that productivity of the SSBB at SGH sites is only partially uncoupled from the primary production of the surface water. Areal estimates of autotrophic Corg production at control sites, bacterial mat sites and in clam field sites were 5.7, 59.7 and 190.0 mgC m-2 d-1, respectively. Based on different models predicting vertical POC fluxes from surface water primary production and water depth, these autotrophic POC productions account for 5 to 17% (controls), 35 to 68% (bacterial mats), and 63 to 87% (clam fields) of the bulk POC (sum of allochthonous POC input through the water column and sedimentary autochthonous autotrophic POC production) provided at the various sites. At SGH sites inventories of chl a and pheopigments, integrated over the upper 10 cm of the sediment, were half of that found at the control sites. This might be due to enhanced degradation of phytodetritally associated organic matter. The resulting low molecular weight organic carbon compounds might stimulate and fuel sulfate reduction, which is conducted in a microbial consortium with anaerobic methane consuming archaea. This syntrophic consortium might represent a prominent interface between gas hydrate derived carbon and allochthonous Corg flow. We infer that degradation kinetics of SGH is affected by, e.g., seasonally varying input of allochthonous organic matter.

Description: The bottom and deep circulation in the Somali Basin are investigated on the basis of hydrographic and direct velocity profiles from three shipboard surveys carried out during the southwest monsoon in 1995 and of velocity time series from the WOCE mooring array ICM7. The inflow of bottom water into the Somali Basin through the Amirante Passage drives a thermohaline circulation, which may be modulated by the monsoon wind forcing. Details of the abyssal circulation have been discussed controversially. Deep velocity records from the mooring array in the northern Somali Basin are dominated by fluctuations with periods of 30–50 days and amplitudes above Full-size image (〈1 K). Despite this strong variability annual record averages indicate the existence of a deep western boundary current (DWBC) below Full-size image (〈1 K) at the base of the continental slope south of Socotra Island as part of a cyclonic bottom circulation. The southwestward DWBC transport off Socotra Island is estimated to Full-size image (〈1 K). The bottom and deep water exchange between the Somali and Arabian Basin north of 7°N is estimated from two cross-basin geostrophic velocity sections referenced by vertically averaged LADCP currents. For the bottom water, an eastward transport into the Arabian Basin of Full-size image (〈1 K) and Full-size image (〈1 K) was determined in June and August, respectively, while for the deep-water layer above Full-size image (〈1 K) eastward transports of Full-size image (〈1 K) in June and Full-size image (〈1 K) in August were obtained.

Description: The sediment beneath and at various distances from the fish farm cages in Cephalonia bay (Eastern Mediterranean) was investigated seasonally through sediment profiling imagery (SPI) as well as through monitoring of geochemical variables and macrofaunal assemblages. The SPI images (SPI) repeatedly showed the same qualitative pattern along the benthic enrichment gradient with readily identifiable attributes such as depth of dark sediment, signs of outgassing and bioturbation marks. Quantitative comparisons showed that a large number of SPI attributes showed significant positive or negative correlation with geochemical and biological attributes describing the effect of fish farming on the seabed. All multivariate patterns obtained through the analysis of SPI attributes were highly correlated to those obtained from standard multivariate analysis of macrofauna during the respective seasons. It is argued that SPI provides an integrated assessment of the sedimentary conditions and therefore may be used as a complement of or even a substitute for standard sampling methods when mapping the effects of aquaculture on silty substrates

Description: Sediment incubation microcosms, multitrap apparatus and water column variables have been employed to describe the dynamic changes in benthic-pelagic coupling between nutrient pools in the Pontevedra ria, NW Spain, during spring and summer 1998. A comparison of the chemical characteristics of suspended and bed sediment together with sediment nutrient effluxes revealed that particulate organic nitrogen and carbon were progressively depleted upon transit through the nutrient pools. The main fate of particulate organic nitrogen reaching the bed sediment is denitrification, although resuspension is also important. An estimate of net denitrification (Dnet) was made at 2 muddy sites in the ria with a mass balance at the benthic boundary layer. First-order approximations calculate Dnet to be 178 and 182 µmolN m-2 h-1 at the 2 stations, and agree well with previous modelling estimates. Denitrification is highest when upwelling relaxes and the flux of organic matter to the sediment increases. Regular inputs of offshore water ensure water renewal and re-oxygenation of bottom waters, thus preventing anoxia, particularly in the summer. With upwelling, large quantities of ammonium are effluxed to the water column (250 µmolNH4+ m-2 h-1), probably as a result of the bed sediment resuspension engendered by upwelling and stirring of phytodetrital fluff held in suspension as neutrally buoyant material above the sediment surface. We hypothesise that hydrodynamical processes play an important role in determining the quantity of nutrients remineralised in the Pontevedra ria and, in the case of nitrogen, the rate of denitrification at the benthic boundary layer.

Description: Gas hydrates occur at the sediment surface on the southern summit of Hydrate Ridge, Cascadia convergent margin. The hydrates are found in mounds several meters in diameter and up to 2 m high, and are covered by sediment and mats of the filamentous sulfur-oxidizing bacteria Beggiatoa. The mounds are surrounded by vesicomyid clams (Calyptogena pacifica, C. kilmeri), which in turn are encircled by solemyid bivalves (Acharax sp.). The zonation pattern of 3 species (Calyptogena spp. and Acharax sp., which harbor chemoautotrophic bacteria in their gills, and the chemoautotrophic Beggiatoa), is also reflected in a change in the entire community structure. Beggiatoa, Calyptogena spp. and Acharax sp. are shown to be characteristic species for the different communities. The Beggiatoa community directly overlaying the gas hydrates consists of seep endemic species in high densities: gastropods (Provanna laevis, P. lomana, Pyropelta corymba, Hyalogyrina sp. nov.), bivalves (Nuculana sp. nov.) and polychaetes (Ampharetidae, Polynoidae, Dorvilleidae). Based on pooled samples, the rarefaction curves show a decrease in species diversity in the Beggiatoa and Calyptogena communities. The hydrogen sulfide gradients in the porewater of sediments below the different communities dominated by either Beggiatoa, Calyptogena spp. or Acharax sp. vary by 3 orders of magnitude. The diffusive sulfide flux based on the measured sulfide concentration gradients is highest in Beggiatoa sp. communities (23 ± 13 mol m-2 yr-1), slightly less in Calyptogena communities (6.6 ± 2.4 mol m-2 yr-1), and low in Acharax communities (0.05 ± 0.05 mol m-2 yr-1). The difference in the sulfide environment is a factor influencing the distribution patterns of the chemoautotrophy-dependant and heterotrophic species at the deep-sea sediments containing gas hydrate.

Description: A colony of Humboldt penguins Spheniscus humboldti in central Chile was monitored from August 1995 to July 2000 to determine patterns of breeding and colony attendance and how these were affected by climatic (rainfall) and oceanographic (El Niño) factors. Nests were periodically checked for contents and roosting birds were counted from vantage points. Two main breeding events were observed: between August and January (spring event) and between April and June (autumn event). Whereas the spring event regularly produced offspring, the autumn event was systematically affected by rains, causing considerable nest desertion. Adults were present in the colony from August to May, abandoning the colony during winter after the nests were flooded. Juveniles occurred only between November and March. Adults moulted mainly in February, while juveniles moulted in January. During the 1997/98 El Niño episode, the number of breeding pairs was 55 to 85% lower than the mean, the onset of nesting was delayed, and abnormally heavy rainfall flooded nests. While the number of breeding pairs was significantly related to sea surface temperature anomalies (SSTA), breeding success was not. The attendance of adults and juveniles at the colony during El Niño was 25 and 73% lower, respectively, than the mean attendance. This 2-peak breeding strategy of Humboldt penguins appears to have evolved in response to the more favourable oceanographic and climatic conditions of Perú, where breeding is continuous and not interrupted by rains. Although less productive, the species probably maintains its autumnal breeding in central Chile because this provides additional offspring to supplement those regularly produced during the spring event.

Description: Zooplankton grazing on bacterio- and phytoplankton was studied in the Gulf of Aqaba and the Northern Red Sea during Meteor Cruise Me 44-2 in February-March 1999. Protozoan grazing on bacterioplankton and autotrophic ultraplankton was studied by the Landry dilution method. Microzooplankton grazing on phytoplankton 〉6 µm was studied by incubation experiments in the presence and absence of microzooplankton. Mesozooplankton grazing was studied by measuring per capita clearance rates of individual zooplankton with radioactively labelled food organisms and estimating in situ rates from abundance values. Protozoan grazing rates on heterotrophic bacteria and on algae 〈6 µm were high (bacteria: 0.7 to 1.1 d-1, ultraphytoplankton: 0.7 to 1.3 d-1), while grazing rates on Synechococcus spp. were surprisingly low and undetectable in some experiments. Mesozooplankton grazing was weak, cumulative grazing rates being ca. 2 orders of magnitude smaller than the grazing rates by protozoans. Among mesozooplankton, appendicularians specialised on smaller food items and calanoid copepods on larger ones.

Description: Two new isomalabaricane triterpenes, stellettin H (1) and stellettin I (2), have been isolated from the marine sponge Rhabdastrella globostellata, collected from the Philippines. Stellettins A−D (3−6), (−)-stellettin E (7), and rhabdastrellic acid-A (8) were also isolated and characterized. Stellettin B (4) and (−)-stellettin E (7) showed selective cytotoxicity toward p21WAF1/Cip1-deficient human colon tumor (HCT-116) cells with IC50 values of 0.043 and 0.039 μM, respectively.

Description: Raf/MEK-1/MAPK cascade inhibitor activity-directed fractionation of the sponge Stylissa massa afforded eight known alkaloids:  aldisine (1), 2-bromoaldisine (2), 10Z-debromohymenialdisine (3), 10E-hymenialdisine (4), 10Z-hymenialdisine (5), hymenin (6), oroidin (7), and 4,5-dibromopyrrole-2-carbonamide (8). Both 4 and 5 showed significant enzyme inhibitory activity (IC50 3 and 6 nM, respectively). Secondary assays identified these compounds as potent MEK-1 inhibitors. Compounds 4 and 5 also inhibited the growth of human tumor LoVo cells.

Description: The increasing environmental pressures on estuarine and coastal waters call for improved monitoring techniques of chemical constituents to aid management decisions. Automated stripping voltammetry is a suitable technique for continuous, near real-time monitoring of trace metals in marine systems. This contribution describes the application of voltammetric monitoring techniques in estuarine and coastal waters of the UK and Spain. The high spatial and temporal resolution of the data obtained, allows a thorough interpretation of the trace metal sources and behaviour. Future trends in this field research include submersible sensors which can be remotely deployed for a period of several weeks.

Description: Factors responsible for aggregations of jumbo flying squid Dosidicus gigas, an important component of the marine food web and target of commercial fisheries off the Costa Rica Dome in the Eastern Tropical Pacific Ocean (ETP), were examined during 2 years of different extreme oceanographic conditions: fall 1997 El Niño and fall 1999 La Niña. A high abundance of squid occurred in association with the well-developed countercurrent ridge (upwelling) off the Costa Rica Dome during fall 1997, but not during fall 1999, when the countercurrent ridge was less developed. Two features of the well-developed countercurrent ridge were considered important for the occurrence of high jumbo flying squid concentrations. Firstly, subsurface chlorophyll a (chl a) maxima were formed along the countercurrent ridge, resulting in integrated chl a concentrations in the upper 100 m being relatively high considering the generally low productivity of the ETP during an El Niño event. Secondly, a strong salinity front formed along the North Equatorial Countercurrent, which is possibly responsible for retention of jumbo flying squid in the ridge. Large yellowfin tuna Thunnus albacares, which mainly feed on micronekton (small fishes, cephalopods and swimming crabs), as do jumbo flying squid, were also more highly concentrated along the countercurrent ridge during 1997 than during 1999. It was noted that skipjack tuna Katsuwonus pelamis and small yellowfin tuna, which mainly feed on zooplankton, were associated with the equatorial ridge in the ETP, indicating that prey faunal components may also play an important part in the close association of jumbo flying squid with the countercurrent ridge.

Description: The differences in the water mass distributions and transports in the Arabian Sea between the summer monsoon of August 1993 and the winter monsoon of January 1998 are investigated, based on two hydrographic sections along approximately 8°N. At the western end the sections were closed by a northward leg towards the African continent at about 55°E. In the central basin along 8°N the monsoon anomalies of the temperature and density below the surface-mixed layer were dominated by annual Rossby waves propagating westward across the Arabian Sea. In the northwestern part of the basin the annual Rossby waves have much smaller impact, and the density anomalies observed there were mostly associated with the Socotra Gyre. Salinity and oxygen differences along the section reflect local processes such as the spreading of water masses originating in the Bay of Bengal, northward transport of Indian Central Water, or slightly stronger southward spreading of Red Sea Water in August than in January. The anomalous wind conditions of 1997/98 influenced only the upper 50–100 m with warmer surface waters in January 1998, and Bay of Bengal Water covered the surface layer of the section in the eastern Arabian Sea. Estimates of the overturning circulation of the Arabian Sea were carried out despite the fact that many uncertainties are involved. For both cruises a vertical overturning cell of about 4–6 Sv was determined, with inflow below 2500 m and outflow between about 300 and 2500 m. In the upper 300–450 m a seasonally reversing shallow meridional overturning cell appears to exist in which the Ekman transport is balanced by a geostrophic transport. The heat flux across 8°N is dominated by the Ekman transport, yielding about –0.6 PW for August 1993, and 0.24 PW for January 1998. These values are comparable to climatological and model derived heat flux estimates. Freshwater fluxes across 8°N also were computed, yielding northward freshwater fluxes of 0.07 Sv in January 1998 and 0.43 Sv in August 1993. From climatological salinities the stronger freshwater flux in August was found to be caused by the seasonal change of salinity storage in the Arabian Sea north of 8°N. The near-surface circulation follows complex pathways, with generally cyclonic-circulation in January 1998 affected at the eastern side by the Laccadive High, and anticyclonic circulation in August 1993.

Description: Three View the MathML sourceacoustic transceivers were deployed on either side of the eastern entrance of the Strait of Gibraltar during April–May 1996 to determine the feasibility of using acoustic methods to make routine, rapidly repeated, horizontally integrated measurements of flow and temperature in straits. Reciprocal transmissions between the transceivers were used to test the feasibility of using traditional ray differential travel times to monitor the component of flow along the acoustic paths. Transmissions directly across the Strait were used to test the feasibility of using horizontal arrival angle fluctuations and acoustic intensity scintillations to monitor the flow perpendicular to the acoustic path. The geometry was selected to provide ray paths that only sample the lower-layer Mediterranean water, so that the feasibility of monitoring the Mediterranean outflow using the various methods could be evaluated. The acoustic scintillation method did not yield useful current estimates, but the experimental parameters were not optimized for this approach. Since the low-frequency variability in log-amplitude was found to be highly correlated at receivers View the MathML source apart, it is possible that acoustic scintillation measurements using different receiver spacings and more rapid sampling might yield better results. The horizontal deflection method gave encouraging results at the time of neap tides, but less so during spring tides. For this approach, both theoretical estimates and measured phase differences between the horizontally separated receivers suggest that internal-wave-induced horizontal arrival angle fluctuations may fundamentally limit the precision with which arrival angles can be measured. Further work is needed to determine if a smaller horizontal spacing and higher signal-to-noise ratios would yield better results. Reciprocal travel time measurements diagonally across the Strait performed the best of the three methods, giving absolute flow estimates consistent with those derived from current-meter data. The fractional uncertainty variance for the lower layer tidal transport from a single tomographic path was estimated to be 0.017 (i.e. 98% of the a priori tidal transport variance was resolved). The spatial scales of the sub-tidal flow are thought to be significantly shorter than those of the tidal flow, however, which means that a more elaborate monitoring network is required to achieve the same performance for sub-tidal variability. Finally, sum travel times from the reciprocal transmissions were found to provide good measurements of the temperature and heatcontent in the lower layer.

Description: The late Tertiary tectonic and geological evolution of the Southern Andes at 33–34°S has been strongly controlled by the Challenger–Juan Fernández–Maipo (CH–JF–M) structural system. The present configuration of a flat slab between 28–33°S may be explained by a series of favorable conditions evolving with time since the breakup of the Farallon Plate at 25 Ma. The dramatic shift of the pole of rotation and the rapid eastward propagating rift along the Challenger Fracture Zone induced an unbalanced slab pull force, south of the CH–JF–M, that may have triggered the detachment of the subducting slab. The upwelling of a warmer asthenospheric material and the partial melts of the slab are likely consequences that are consistent with the anhydrous tholeiitic late Oligocene volcanism and the anomalous adakite-type magmatism of the early Miocene, respectively. The present seismogenic zone across the CH–JF–M tectonic boundary shows a continuity for more than 600 km along the flat slab segment, in contrast with the much shorter slab southward. Such a tectonic configuration is probably a quasi-steady condition since 25 Ma. Gravity modeling along the JF chain and the broadly located focal mechanisms at the locus of the already subducted JF chain indicate a thick (〉25 km), wide (100 km), and continuous belt of lighter oceanic crust, which is the major contribution to the positive buoyancy of the slab. The decoupling of the subducted slab at intermediate depths further contributes to the flattening of the slab, focusing the buoyancy forces associated with the thickened oceanic crust along the already subducted JF chain. The absolute plate reconstruction during the Miocene shows that the JF collision against the margin migrates southward, in agreement with geological and tectonic observations that further support the causative relationship between the flattening of the slab and the subduction of the JF chain. Preliminary deformation models for the indentation of the JF ridge against the continental lithosphere is consistent with the particular east–west trend of the Maipo deformation zone, connecting in this way the CH–JF–M major tectonic boundary in the ocean-continent lithosphere system.

Description: In this paper, different types of new data sets (hydrography, Lagrangian and Eulerian current measurements) and Quasi-Geostrophic model results, obtained after altimetric data assimilation, are used to study the structure and variability of the Azores Current and Frontal system. The Azores Current was observed to transport between 11.0 and 18.0 Sv eastwards and the associated Counter Current some 2.0–10.0 Sv to the west, resulting in a net value of about 8–9 Sv. Furthermore, both data and model results revealed a meandering Azores Current, where some freely rotating eddies were also identified. These hydrographic and Lagrangian results exhibit space and time scales that agree fairly well with the dynamics shaped by baroclinic instability. Current meters moored across the Azores Current system delineated a mean Counter Current flowing westwards with a maximum subsurface core of about 2.0 cm/s at a mean depth of 800 dbar. This is in excellent agreement with previous studies, which explains this Azores Counter Current as the rectification process of the geostrophic turbulence occurring north of the main Azores Current stream. A new scheme is proposed for the formation mechanism of the freely rotating cyclonic eddies observed south of the Azores. It is shown that the north–south contrast thickness of the 17–19°C water layer across the Azores Front decreases downstream. This will create, in turn, a downstream increase of the most unstable wavelength, in a non-linear baroclinic instability context. As a consequence, both large cyclonic and anticyclonic features are able to form at the eastern side of the Azores Current (around 19°W), while at the western side (around 35°W) only large anticyclones will survive (western-generated cyclones will be small enough to be quickly dissipated). This means that the eastern cyclones of the Azores Current may live longer than the shorter western ones. However, because longer-lived cyclonic eddies propagate westwards with a mean speed of 2.5 km/day, they may be observed south of Azores and of the main stream several months later, although they were not formed there.

Description: We examined how seabirds might be used to study marine environmental variables, which necessitates knowing location and the value of the variable to be studied. Five systems can potentially be used for determination of location: VHF (Very High Frequency) telemetry, PTT (Platform Terminal Transmitters) telemetry, GLS (Global Location Service) geolocation methods, dead reckoning and GPS (Global Positioning System), each with its own advantages with respect to accuracy, potential number of fixes and size. Temperature and light were used to illustrate potential difficulties in recording environmental variables. Systems currently used on seabirds for measurement of temperature respond slowly to environmental changes; thus, they may not measure sea surface temperature adequately when contact periods with water bodies are too short. Light can be easily measured for light extinction studies, but sensor orientation plays a large role in determining recorded values. Both problems can be corrected. The foraging behaviour of seabirds was also examined in order to identify those features which would be useful for determination of marine environmental variables at a variety of spatial and temporal scales. Area coverage by birds is highly dependent on breeding phase and tends to be concentrated in areas where prey acquisition is particularly enhanced. The identification of these sites may be of particular interest to marine biologists. 'Plungers' and 'divers' are potentially most useful for assessment of variables deeper within the water column, with some divers spending up to 90% of their time sub-surface. Few seabirds exploit the water column deeper than 20 m, although some divers regularly exceed 50 m (primarily penguins and auks), while 2 species dive in excess of 300 m. The wide-ranging behaviour of seabirds coupled, in many instances, with their substantial body size makes them potentially excellent carriers of sophisticated environmental measuring technology; however, the ethical question of how much the well-being of birds can, and should, be compromised by such an approach needs to be carefully considered.

Description: To study the EasternBoundaryCurrentsystem off Northwest Africa in detail several CTD/ADCP-sections and long-term mooring work were carried out in the channel between Lanzarote and Africa. The observations are compared with a fine-resolution model, which was developed in the framework of the CANIGO project. The water masses, which are observed in this area, are characterised and classified in density ranges. The current field shows a high spatial and temporal variability with maximum velocities of about 35 cm/s. Seasonal means as well as currents averaged across the channel are only a few cm/s. In the surface water a steady southward flow in the middle of the channel indicates the CanaryCurrent in this area. During fall a strong northward current is observed close to the African shelf. Though the CanaryCurrent strengthens during summer and fall due to an increase of the trade winds, the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side. A northward undercurrent with a mean velocity of +2.3 cm/s is observed at the African slope in 950 m depth. The poleward transport of AAIW increases during fall and a strong influence of relatively fresh AAIW is observed during that time. Most of the observations fit well to the results of the CANIGO model, but the occurrence of MW at the bottom of the channel and the corresponding southward flow cannot be resolved by the model.

Description: Light abundance is a major prerequisite for primary production in pelagic ecosystems, influencing the evolution of the marine environment. Realistic simulations of planktonic ecosystems therefore require an appropriate representation of the underwater light field. Taking a look at the different biogeochemical models discussed in literature, one finds a variety of descriptions for the distribution of light, or more specific, photosynthetically available radiation (PAR) in the water column. This paper compares the effect of different parameterizations of PAR on the primary production and phytoplankton evolution at the European Station for Time-Series in the Ocean Canary Islands (ESTOC) station (29°10′N, 15°30′W) north of Gran Canaria, Canary Islands. Observations from two cruises in 1997 are used to illustrate the winter and spring situation at the time-series site. Four alternative PAR descriptions are used in a one-dimensional coupled biological–physical model of the upper ocean driven by daily forcing fields over a 5-year period. The biological model is a simple nitrate-phytoplankton–zooplankton-detritus model. Although the different descriptions are found to have only a small effect (±3%) on the annual primary production, we observe significant changes in the vertical distribution of simulated phytoplankton. The large variation (±32%) in the near-surface chlorophyll contents will be of particularly crucial importance when using satellite ocean-color sensors for model validation and parameter estimation. For future three-dimensional biogeochemical models, a computationally efficient and accurate parameterization of the light field will be particularly relevant.

Description: We report how different zooplankton groups (doliolids, cladocerans and copepods) are able to influence the coastal pelagic food web, including the microbial food web, in waters of the NW Mediterranean. We studied the effect of grazing and of grazing-induced nutrient recycling mediated by different types of zooplankton grazing on a natural phytoplankton community. Experiments were conducted in semicontinuous 2-stage chemostats. The 1st stage vessels contained seawater from Blanes Bay, Spain (NW Mediterranean) including its natural phytoplankton community; the 2nd stage vessels contained the same seawater and copepods, cladocerans or doliolids. At daily intervals we transferred part of the medium from the 2nd to the 1st stage flasks, which contained ungrazed algae and excreted nutrients. In this way, the zooplankton could influence phytoplankton dynamics both by selective grazing and by differential excretion of limiting nutrients. In the 2nd stage flasks grazing changed the algal community composition. Doliolids and cladocerans promoted the growth of large algae and copepods shifted the size spectrum towards small sizes. This effect was transferred to the 1st stage flasks. Doliolids, cladocerans and copepods also affected the microbial food web in different ways. Size-selective grazing led to differences in the nanoplankton concentrations. These in turn affected bacterial concentrations in a trophic cascade. The potential to modify a given algal population increased with increasing selectivity of the grazer.

Description: Both surface texture and littorinid grazing are known to influence the establishment of many shallow-water benthic hard-bottom communities. However, the effects of these factors and their interactions have not yet been investigated in a quantifiable manner. This investigation aims to assess the interactive effect of both factors in a strictly standardized manner. Natural recruitment by diatoms, the barnacle Balanus improvisus and the tube-building polychaete Polydora sp. was monitored under a 2-factorial treatment: grazing by the periwinkle Littorina littorea (Factor 1; 2 levels: I or no snails per plate) on artificial recruitment plates of different initial surface rugosities (Factor 2; 5 levels: smooth, 0.1, 0.5, 1 and 5 mm rugosity elements), In the absence of grazers, barnacle recruitment decreased with increasing initial rugosity, polychaete recruitment peaked at intermediate rugosities, and diatoms exhibited contrasting recruitment patterns in an in vitro and an in situ experiment. When preferred recruitment sites coincided for Polydora and B. improvisus, a competition for space could be inferred from a negative correlation between the 2 species. However, when the overlap of requirements weakened on the 5 rugosities, the relationship was positive, but was not statistically significant. Grazing efficiency by L. littorea depended on initial rugosity, generally showing minimum values on intermediate rugosities which is attributable to a mismatch between radula dimensions and surface structures in these rugosity classes. Additionally, grazing effects tended to increase with higher prey densities. As all factors-initial rugosity, grazing, colonizer species-interact with each other, the outcome of recruitment under combined factors is difficult to predict from single factor effects.