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The kelp Laminaria hyperborea is a dominant component of the subtidal nearshore ecosystem and is subjected to a heterogeneous wave and current climate. Water motion is known to influence physiological processes in macroalgae such as photosynthesis and nutrient uptake attributed to mass-transfer limitation. The study attempts to establish the effect of water motion on the growth rates of blades and elongation rates of the stipes of L. hyperborea at adjacent wave-exposed and wave-sheltered locations over a 12 month period from field observations. The observations were supported by detailed physical and chemical measurements (light, temperature, seawater nutrient concentrations and hydrodynamics) and of tissue carbon and nitrogen concentrations together with δ 13 carbon. Despite a 30% difference in the root mean square of the velocity ( Vel rms ) between the two survey locations, there was no evidence to suggest that water motion had any direct influence on the growth rates of either the blades or elongation of stipes of L. hyperborea . No significant differences were observed between either environmental or plant physiological variables between the sheltered and exposed locations. Using an integral velocity parameter ( Vel rms ) the present study also highlighted the importance of the tidally induced current component of water flow in the subtidal zone.

The effect of modified flow on epifaunal boulder reef communities adjacent to the SeaGen, the world's first grid-compliant tidal stream turbine, were assessed. The wake of the SeaGen was modelled and the outputs were used in conjunction with positional and substrate descriptor variables, to relate variation in epifaunal community structure to the modified physical environment. An Artificial Neural Network (ANN) and Generalised Linear Model (GLM) were used to make predictions on the distribution of Ecological Status (ES) of epifaunal communities in relation to the turbulent wake of the SeaGen. ES was assigned using the High Energy Hard Substrate (HEHS) index. ES was largely High throughout the survey area and it was not possible to make predictions on the spatial distribution of ES using an ANN or GLM. Spatial pattern in epifaunal community structure was detected when the study area was partitioned into three treatment areas: area D1; within one rotor diameter (16 m) of the centre of SeaGen, area D2; between one and three rotor diameters, and area D3; outside of three rotor diameters. Area D1 was found to be significantly more variable in terms of epifaunal community structure, bare rock distributions and ES than areas D2 and D3.

Nitrogen metabolism was examined in the intertidal seaweeds Fucus vesiculosus, Fucus serratus, Fucus spiralis and Laminaria digitata in a temperate Irish sea lough. Internal NO(3) (-) storage, total N content and nitrate reductase activity (NRA) were most affected by ambient NO(3) (-), with highest values in winter, when ambient NO(3) (-) was maximum, and declined with NO(3) (-) during summer. In all species, NRA was six times higher in winter than in summer, and was markedly higher in Fucus species (e.g. 256 +/- 33 nmol NO(3) (-) min(-1) g(-1) in F. vesiculosus versus 55 +/- 17 nmol NO(3) (-) min(-1) g(-1) in L. digitata). Temperature and light were less important factors for N metabolism, but influenced in situ photosynthesis and respiration rates. NO(3) (-) assimilating capacity (calculated from NRA) exceeded N demand (calculated from net photosynthesis rates and C : N ratios) by a factor of 0.7-50.0, yet seaweeds stored significant NO(3) (-) (up to 40-86 micromol g(-1)). C : N ratio also increased with height in the intertidal zone (lowest in L. digitata and highest in F. spiralis), indicating that tidal emersion also significantly constrained N metabolism. These results suggest that, in contrast to the tight relationship between N and C metabolism in many microalgae, N and C metabolism could be uncoupled in marine macroalgae, which might be an important adaptation to the intertidal environment.

The influence of oscillatory versus unidirectional flow on the growth and nitrate-uptake rates of juvenile kelp, Laminaria digitata, was determined seasonally in experimental treatments that simulated as closely as possible natural environmental conditions. In winter, regardless of flow condition (oscillatory and unidirectional) or water velocity, no influence of water motion was observed on the growth rate of L. digitata. In summer, when ambient nitrate concentrations were low, increased water motion enhanced macroalgal growth, which is assumed to be related to an increase in the rate of supply of nutrients to the blade surface. Nitrate-uptake rates were significantly influenced by water motion and season. Lowest nitrate-uptake rates were observed for velocities

The standing stocks and production rates of particulate organic carbon (POC) and biogenic silica (bSiO2) were measured in the upper water column at 10 stations in the North East Atlantic during the spring 2001 diatom bloom. The elemental composition of the particulate pool was rather homogeneous with depth, suggesting that any material being exported from the photic zone was generally similar in composition to the ambient pool. Pronounced vertical structure was observed in uptake ratios resulting from the strong light dependence of the carbon fixation and the weak light dependence of biogenic silica production. The integrated C/Si molar ratios of particulate material were found to be generally larger than the corresponding assimilation ratios. We interpret this discrepancy as implying a preferential mineralization of Si relative to C from particulate matter during the earliest stages of processing in the upper water column. The preferential mineralisation of Si relative to C in the early stages of particle processing contrasts with processes occurring deeper in the water column, where C is typically mineralised preferentially to Si, and particulate matter becomes enriched in bSiO2. In the northern North Atlantic, the balance of mineralisation of Si relative to C from sinking organic matter with depth is likely to strongly influence the role of diatoms in export production.

41 páginas, 14 figuras, 4 tablas, Time series of wind-stress data, AVHRR and SeaWiFS satellite images, and in situ data from seven cruises are used to assemble a coherent picture of the hydrographic variability of the seas off the Northwest Iberian Peninsula from the onset (September–October) to the cessation (February–May) of the Portugal coastal counter current (PCCC). During this period the chemistry and the biology of the shelf, slope and ocean waters between 40° and 43°N have previously been undersampled. Novel information extracted from these observations relate to: 1. The most frequent modes of variability of the alongshore coastal winds, covering event, seasonal and long-term scales; 2. The conspicuous cycling between stratification and homogenisation observed in PCCC waters, which has key implications for the chemistry and biology of these waters; 3. The seasonal evolution of nitrite profiles in PCCC waters in relation to the stratification cycle; 4. The Redfield stoichiometry of the remineralisation of organic matter in Eastern North Atlantic Central Water (ENACW)—the water mass being transported by the PCCC; 5. The separation of coastal (mesotrophic) from PCCC (oligotrophic) planktonic populations by a downwelling front along the shelf, which oscillates to and fro across the shelf as a function of coastal wind intensity and continental runoff; and 6. The photosynthetic responses of the PCCC and coastal plankton populations to the changing stratification and light conditions from the onset to the cessation of the PCCC., These cruises were performed with the financial support of the CICYT grant No. MAR97-2068-CE and the EU contract numbers MAS1-CT90-0017 (The Control of Phytoplankton Dominance) MAS2-CT93-0065 (MORENA) and MAS3-CT97-0076 (OMEX II-II).

Primary production was measured at a series of stations in austral summer 1996 in the vicin- ity of South Georgia. Five stations were occupied along a 700 km transect southeastwards towards the western tip of South Georgia. Three stations were located north of the Antarctic Polar Front (PF) with mean primary production of 0.41 g C m -2 d -1 compared to 0.54 g C m -2 d -1 for the stations south of the front. Three stations were in the shelf break and off-shelf region to the east of South Georgia where the lowest rates of primary production were recorded (mean 0.34 g C m -2 d -1 ). At a further 4 stations north- west of the island, primary production was significantly greater: 0.8 to 2.5 g C m -2 d -1 (mean 1.5 g C m -2 d -1 ). Photoinhibition was a marked feature of the production profiles, resulting in the underestimation of column production by 4 to 16%. An assessment is made of the primary production required to main- tain a representative assemblage of metazooplankton around South Georgia composed of 30 g fresh mass (FM) m -2 krill and 20 g FM m -2 copepods. The total C requirement of both groups at maximum growth rate is estimated as 0.93 g C m -2 d -1 , with 0.54 g C m -2 d -1 required to maintain basal metabolism (i.e. for zero growth). Local primary production rates are well in excess of the C demands for basal metabolism by the metazooplankton, and likewise the highest regional values exceed those for maxi- mum metazooplankton growth. It is also estimated that the krill biomass required to sustain higher predators during their breeding season could be supported by local production at plausible maximum krill growth rate. In particular, high primary production found in this study to the northwest of South Georgia appears to be adequate to sustain maximum growth rate by krill when their biomass is 30 g FM m -2 , when krill production will exceed predator removal. It is already well known that advection from higher latitudes is important in supplying energy to the South Georgia system. This study adds to the evidence that locally enhanced primary production is also important in supporting the local food web.

Nitrate and phosphate uptake mechanisms have been characterised under conditions of 100 and 50% seawater in 3 common brown algae of NW Europe: Fucus vesiculosus, F. serratus and Laminaria digitata. Under low salinity, the growth rate and internal nitrate accumulation of F. serra- tus significantly increased (20 and 48%, respectively), but no significant changes were observed for F. vesiculosus and L. digitata. However, nitrate uptake rates were reduced in L. digitata, so that this species was less adaptable to low salinity than the Fucus species. Both F. vesiculosus and F. serratus reached a steady-state uptake rate after acclimation regardless of the salinity treatment. All 3 species had a high capacity for storing inorganic N and P intracellularly. The results for F. serratus pointed to a dual mechanism of adaptation to the special characteristics of the intertidal environment where it grows. Non-saturating (low affinity) nitrate uptake and biphasic (double Michaelis-Menten curve) phosphate uptake are adaptations to high nutrient concentrations. Temporal partition of cellular energy for carbon metabolism and nutrient uptake is also suggested as an adaptation to the transient nutrient inputs occurring in these environments.

A Lagrangian experiment was set up at 47°N 20°W in the northeast Atlantic as part of the Joint Global Ocean Flux Study (JGOFS) programme. As an integral part of the programme, this study investigated the uptake of carbon and nitrogen into different algal size classes, and quantified the export of carbon using 15 N stable isotope and 14 C radioisotope studies. Good quality f -ratio field data is of fundamental importance to multi-compartment nitrogen-based upper ocean ecosystem modelling of carbon fluxes: this study provides an appraisal of current north Atlantic field measurements making comparisons with our findings. A phytoplankton bloom was tracked for 18 d from 1 May 1990. Waters were initially well-mixed with surface nutrients of 4–6 mmol NO 3 m −3 and 1.5–2.5 mmol SiO 4 m −3 and surface biomass of 1–1.5 mg chl a m −3 , indicating the likely onset of a bloom. Increased insolation and vertical stability produced a diatom-dominated bloom with a surface biomass peak of 3.5 mg chl a m −3 , decreased nutrient values (0.5 mmol NO 3 m −3 , 0.35 mmol SiO 4 m −3 ), and maximum integrated carbon uptake values of 1970 mg C m −2 d −1 on 17 May. Maximum nitrogen uptake values of 251 mg NO 3 m −2 d −1 were measured on 14 May during the greatest flagellate growth phase. Integrated production rates over the experiment ranged from 0.5 to 1.0 g C m −2 d −1 , and carbon export was estimated at 480 (using NO 3 uptake and Redfield ratios) or 570 (using integrated C assimilation values and the mean weighted f -ratio) mg C m −2 d −1 . The decoupling of maximum carbon and nitrogen uptake rates over a three-day period indicates that it may not be appropriate to use Redfield ratios to convert nitrate-estimated new production to carbon export values, even over time scales of a month. Primary production values are comparable to 1989 North Atlantic Bloom Experiment (NABE) data, despite the fact that phytoplanktonic taxonomic data for the 1990 bloom were very different from the more typical bloom conditions of 1989. Throughout the experiment the greatest biomass occurred in the 1–5 μm size range, which accounted for an average of 50% of the total production and >50% of nitrate uptake and ammonium uptake. In addition, both the net- and nanoplankton communities preferentially assimilated nitrate, which challenges the assumption that new production can be directly equated to export production on the time-scale of weeks.

Phytoplankton biomass and rate of production were measured along a transect from 57.54°N to 37.01°N in the northeast Atlantic during July 1996 and at a series of stations over a 7-day period at 37°N 20°W. Surface nutrient concentrations ranged from 4 μmol l −1 NO 3 − , and 0.35 μmol l −1 PO 4 3− at 57.54°N to −1 NO 3 − and ∼10 nmol l −1 PO 4 3− at 37.01°N. The greatest phytoplankton biomass and production were measured in the vicinity of a frontal system at 50°N, and there was a general decline in total phytoplankton biomass and production to the south of the transect. Production was measured in three size fractions. At the station with the highest chlorophyll concentrations (50.34°N), phytoplankton cells larger than 5 μm dominated the assemblage, accounting for 72% of the chlorophyll concentration (22.9 mg m −2 ) and 51% of primary production (54.1 mmol Cm −2 d −1 ), but picophytoplankton production was also high (43%). At 57°N, carbon fixation by the >5 μm fraction accounted for 75% of the daily production of 60.75 mmol Cm −2 d −1 . At 37°N, picophytoplankton was the dominant group, accounting for ∼58% (10 mg m −2 ) of chlorophyll and ∼64% (46 mmol Cm −2 d −1 ), of primary production. Nitrate, ammonium and phosphate uptake rates also were determined. Although high nitrate uptake rates were measured in the surface water at ∼50°N, the greatest uptake rates of both depth-integrated nitrate and ammonium were at the south of the transect. At 37°N, a deep euphotic zone was present and light penetrated through the nitracline; total nitrate uptake was enhanced because of assimilation at the base of the euphotic zone. As a consequence, high values of depth-integrated f -ratio were measured in the oligotrophic waters at the south of the transect. Phosphate was predominantly incorporated into the picoplankton fraction, which included heterotrophic and autotrophic components, at all stations and a significant proportion of phosphate uptake occurred in the dark. The C : N : P assimilation ratios were variable throughout the region; phosphate uptake was generally greater than would be expected if nutrient assimilation were in proportion to the Redfield ratio.

Data are summarised for two Lagrangian experiments in the North Atlantic in early summer 1996. At 59°N 20°W, plankton dynamics was studied in an SF6 tracer release experiment within a mesoscale eddy over a 9-day period. At 37°N 20°W, a second experiment followed a drifting buoy for 7 days. The data obtained in these two experiments have been averaged for 3 depth strata; the euphotic zone, the surface mixed layer (SML), and the seasonal thermocline immediately beneath the surface mixed layer. At 59°N, the euphotic zone was only marginally deeper than the SML, but at 37°N the SML was ca 30 m and the euphotic depth was ca 110 m. At 37°N, nutrient concentrations in the SML were low but significant new production occurred in the thermocline because of light penetration into the nutricline. The particulate organic carbon (POC) concentration of the SML at 59°N was 13–15 μmol C kg−1, but at 37°N POC concentrations were 4 μmol C kg−1. These POC measurements include biota and detritus. As a way of investigating latitudinal differences in the plankton communities, estimates have been made of the carbon and nitrogen content of phytoplankton, bacterioplankton, microzooplankton and mesozooplankton. At both 59°N and 37°N, phytoplankton was the largest component, accounting for ca 50% of the planktonic biomass in the SML. At 59°N, microzooplankton was 16% of the planktonic carbon, but at 37°N this reduced to 8% of the total. Mesozooplankton was a relatively constant proportion (ca 20%) of the planktonic carbon in the SML at both 59°N and 37°N. Bacterioplankton was 14% of the biomass at 59°N, increasing to 24% in the microbial loop-dominated system at 37°N. Mean carbon fixation rate in the oligotrophic southern station was 24% of that at the north, with more carbon fixation below the SML at 37°N than at 59°N. Respiration rates showed little variation with latitude, and the rates at 37°N were 80% of those at 59°N. Nitrate and ammonium uptake rates were very low in the oligotrophic conditions in the SML at 37°N, but nitrate uptake in the euphotic zone was comparable to that at 59°N. Ammonium uptake by phytoplankton was also significantly greater at 37°N, in both the euphotic zone and thermocline, but uptake in the SML was only 20% of that in the SML at 59°N.

The UK PRIME cruise, June–July 1996 in the NE Atlantic, consisted of two legs. During the first, detailed chemical and biological observations were made in time-series mode adjacent to the centre of a cold-core eddy in the vicinity of 59°N 20°W using SF6 tracer techniques as the basis for the Lagrangian study. The eddy, which appeared to have been formed the previous winter, remained coherent over the 9 days of the survey and advected only slowly. The phytoplankton community in the eddy was dominated by the coccolithophorid Coccolithus huxleyi. High microzooplankton grazing rates indicated minimal export losses from the surface layer. Significant shifts in many, but not all, of the chemical and biological properties measured were observed over the course of the experiment, especially after the passage of a storm event, which resulted in considerable deepening of the mixed layer followed by a return to fully stratified conditions. The second leg consisted of a transect from 59°N 20°W to 37°N 19°W, with a further Lagrangian time-series study based on a drogue marker initiated at the southern end of the transect. Maximal biological activity was generally encountered in the region between two fronts located at 52.5°N and 48°N, while to the south of 48°N oligotrophic conditions prevailed. At the southern Lagrangian site, a deep chlorophyll maximum was present and high column new production was recorded as a result of the euphotic zone extending below the depth of the nutricline. Microzooplankton grazing rates were lower at this location than at the northern eddy site. The influx of a warm, saline water body into the upper layers during the southern survey led to a major shift in many of the biological and chemical properties being measured. At both the northern and southern Lagrangian sites, the biomass of the mesozooplankton exceeded that of the microzooplankton.

Chlorophyll a (chl a) concentrations and primary production by the 0.2–2, 2–18 and >18 μm phytoplankton size-fractions were estimated along a transect in the NW Indian Ocean extending from the coast of Oman to 8°N 68°E during the late SW monsoon and autumn intermonsoonal seasons in 1994. Primary production was estimated using the 14C technique with either in situ or simulated in situ incubations. During the late monsoon season, maximal chl a and production values were recorded in the coastal upwelling zone with values of 69 mg m-2 and 3800 mg C m-2 d-1, respectively. The maxima, which were distributed patchily in this region, were dominated by the >18 μm size-fraction. Over the remainder of the transect chl a concentrations and production averaged 30 mg m-2 and 1500 mg C m-2 d-1, respectively, with approximately equal contributions by the three size-fractions in the case of chl a at the majority of stations, but in general, with a maximum in production in the 0.2–2 μm fraction. Immediately following cessation of the SW monsoon wind, chl a and production values over the northern part of the transect decreased to values similar to those over the southern part of the transect at the time of the SW monsoon, with the contributions by the three size-fractions being approximately equal. During the following intermonsoonal season, both chl a concentrations and production across the section were dominated by the 0.2–2 μm size-fraction, with average chl a and production values of the order of 20 mg m-2 and 750 mg C m-2 d-1, respectively. Considerable variation in production values, however, was exhibited across the transect. A clearly defined subsurface chl a maximum was only recorded at the southernmost stations of the transect in oligotrophic waters: the feature did not develop universally across the transect during the intermonsoon.

Data collected during three expeditions to the Arabian Sea are examined to characterise the changes in phytoplankton properties between the intermonsoon and monsoon seasons. The results are used to elucidate the key changes that lead to the occurrence of phytoplankton blooms following the onset of the monsoon winds. Contrary to expectations, changes in the assimilation number and the initial slope of the photosynthesis-light curve decreased in the SW monsoon season, apparently in the wrong sense for them to account for the incidence of blooms in the Arabian Sea during this season. On the other hand, there were strong differences between the intermonsoon and monsoon values of the chlorophyll-specific absorption coefficient for the phytoplankton, probably arising from seasonal changes in cell size and community composition. The sense of these changes was such as to increase substantially the maximum quantum yield for photosynthesis during the monsoon season compared with the intermonsoon. When these results are applied in a simple expression for the daily, primary production of the water column, they can explain the rapid accumulation of phytoplankton observed in the Arabian Sea following the start of the monsoon season. Thus, the occurrence of seasonal blooms in the Arabian Sea depends on combined variations in both the optical and photosynthetic characteristics of phytoplankton in the region.

A size-structured ecosystem model was developed and fitted to an extensive set of observations of size-fractionated biomass, primary and heterotrophic bacterial production, respiration, particle flux, and zooplankton herbivory obtained on a cruise in the NE Atlantic during 20 days of the spring bloom. Rates of water-column-integrated primary production and heterotrophic bacterial production were used to force the model, and the model parameters were determined by optimizing the model to the remaining observations. A unique model solution was not possible in the absence of dissolved organic carbon (DOC) measurements. By setting a weak constraint on the DOC concentrations (that they should remain broadly constant), a solution was obtained that predicted a small DOC increase during the bloom period; this increase was similar in magnitude to observations in other areas and produced a good fit with the other data. Major conclusions: (1) gross primary production (GPP) was over twice the measured 14 C production estimates; (2) phytoplankton exudation was a major source of DOC, and 35% of the GPP flowed through the DOC and was utilized by the bacteria, with a low gross growth efficiency (17%); (3) 62% of the community respiration came from organisms ,5 mm in size; (4) the major source of food for microzooplankton was phytoplankton 1‐5 mm in size, but the mesozooplankton ingested more microzooplankton than phytoplankton; and (5) only 8% of the total net primary production was grazed by mesozooplankton. These results provide quantitative support to the emerging consensus on the relative roles of large and small organisms in the euphotic zone and demonstrate the necessity of measuring DOC to constrain the carbon budget within the euphotic zone.

The copepod Calanus finmarchicus is the major contributor to zooplankton biomass in the North Atlantic and Norwegian Sea, but recent studies have shown a 70% decrease in abundance as well as a northward shift in the species’ range. Insights into dispersal capabilities gained from population genetic studies will be crucial in predicting the response of C. finmarchicus communities to climate change and, consequently, we have developed a set of expressed sequence tag-derived microsatellite markers to allow fine-scale elucidation of population structuring and dispersal. Ten polymorphic markers displayed between two and 19 alleles, with levels of expected heterozygosity ranging from 0.044 to 0.924.

Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature of the production system was a rapid retreat of the ice-edge, which uncoupled the marginal ice zone from a phytoplankton bloom which remained associated with a frontal system. This bloom was maintained, and probably initiated, in an unusual environment generated by the interaction between the marginal ice zone and the front. Size-based analyses of the microbial system were derived for ice-covered, recently ice-covered and open water sites. Estimates of standing stocks and key rate processes were combined to produce a single food web network for each station. The under-ice system was one of low production and low recycling but apparently high retention. As the ice retreated the microbial systems to the north began to develop, but these were constrained by grazing pressure. The bloom in the area appeared to be sustained even though estimated losses were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relation to the environmental changes and the interaction of the marginal ice zone and the frontal system appears crucial to the phytoplankton. Microzooplankton grazing is implicated as a major controlling factor. The local microbial dynamics are strongly influenced by material which was produced at an earlier time and somewhere else in the Southern Ocean.

The Southern Ocean is the largest of the high-nutrient, low-chlorophyll (HNLC) regions of the world ocean. Phytoplankton production fails to utilise completely the pool of inorganic nutrients in the euphotic zone, giving rise to low phytoplankton bio-mass and leaving relatively high summer nutrient concentrations. This enigma is of considerable significance for our understanding of the role of the oceans in the global carbon cycle. Various limiting factors have been considered: low light, low temperature, absence of necessary trace elements, grazing pressure and other means of biomass removal. The dynamics of nitrogen uptake by phytoplankton are of particular importance. Classically, nitrate mixed into the surface layer during winter provides the nitrogen pool for growth in the spring bloom. Some organic material is exported to depth, whilst the remainder is recycled, providing ammonium and other reduced species as nitrogenous substrates for growth during the remainder of the season. The oxidation state of the inorganic nitrogen supply thus identifies new and recycled carbon fixation. Whilst this is convenient “shorthand” for the nitrogen nutrition of carbon export in much of the ocean, it is an inappropriate model for the Southern Ocean. Here, nitrate and ammonium use are simultaneous, and nitrate is never exhausted by the annual phytoplankton production. We speculate that a range of environmental factors combine to make the large pool of nitrate partially inaccessible to phytoplankton. in addition to the documented effects of low iron availability and high ammonium concentrations, the low temperatures characteristic of the Southern Ocean may decrease nitrate availability because of the increased energetic overheads in its uptake and reduction. This in turn makes ammonium an important nitrogenous substrate, and its production by zooplankton and heterotrophic microorganisms is an important component of the plankton nitrogen cycle. There is some evidence that ammonium production by large grazing animals may stimulate phytoplankton growth. Microbial removal of nitrogen from sedimenting phytoplankton cells may result in local decoupling between the carbon and nitrogen cycles, allowing some reduced nitrogen to remain in the euphotic zone whilst carbon is exported to depth.

The background to and outcomes of the Environmental Monitoring Programme (EMP) required by statutory regulators for the deployment of the SeaGen tidal turbine in Strangford Lough, Northern Ireland, an area with many conservation designations, are described. The EMP, which was set within the context of an adaptive management approach, considered possible effects of the device on local populations of seals and harbour porpoises, representative seabirds and benthic communities. The studies on seals were carried out on both local and regional scales. The ecological studies were complemented by detailed field and hydrodynamic modelling investigations together with a programme of mitigation measures designed to reduce collisions between seals and turbine rotors. In general only minor statistically significant changes in abundance, distribution and animal behaviour patterns were recorded, principally associated with small distributional shifts close to the turbine structure and with the likelihood that these changes were ecologically of little significance. The seal–rotor collision mitigation studies provided a base for the establishment of acceptable collision risk strategies. The EMP highlighted observational, methodological and statistical challenges in assessing the environmental consequences of marine energy devices. A brief review of related studies in Strangford Lough is included.

A study of carbon and nitrogen uptake by phytoplankton was conducted at two sites in the subpolar northeast Atlantic during July 1991. The main study site at 61°N, 20°W was located within a cyclonic warm core eddy, and the other site was at 62°30′N, 20°W. Based on evidence of coccolithophore sedimentation and the relatively slow movement of the eddy, this structure was probably within the bounds of a mesoscale coccolithophore bloom that was in decline 10–20 days before the present study. As little is known about the conditions leading to the onset or collapse of such a bloom, the data presented here are, to our knowledge, the first to quantify phytoplankton dynamics following such an event. In addition, data from the main site provide one of the first assessments of the carbon and nitrogen dynamics within a cyclonic eddy that is typically observed in the northeast Atlantic. The findings at both sites revealed relatively high rates of primary production and concomitant uptake of inorganic nitrogen, suggesting that production rates were not enhanced within the eddy relative to the surrounding waters. These rates were comparable with those noted in late spring in the northeast Atlantic at lower latitudes (47°N, 20°W; 0.7 g C m −2 day −1 ) and are slightly in excess of modelled estimates of production for the subpolar North Atlantic in midsummer (0.5–0.6 g C m −2 day −1 ), but less than estimates based on functional photosynthetically active radiation (PAR)-productivity relationships derived from the North Atlantic Bloom Experiment (NABE) (greater than 1.0 g C m −2 day −1 ). Such functional relationships, derived at lower latitudes, may not be applicable to the subpolar northeast Atlantic. The findings of this study concur with the previous suggestion that the subpolar Atlantic is indeed productive at this time and may deserve further attention from modellers. A comparison of physical, chemical and biological conditions during the coccolithophore bloom and post-bloom periods indicates little change in environment and suggests the role of some self-regulatory mechanism, such as cell self-shading, as the cause of the collapse of the bloom. Invoking such a non-environmental factor may also explain the observed high rates of post-bloom production.

Time series measurements of size-fractionated chlorophyll a concentrations and primary production were made over the course of the spring bloom in and adjacent to a mesoscale eddy in the N.E. Atlantic as part of the U.K. Biogeochemical Ocean Flux Study 1990 Lagrangian Bloom Experiment. Substantial production, dominated by the >5μm and >1–5,μm fractions, was recorded before the main growth phase of the bloom, although total chlorophyll a concentrations varied little over this period. The main growth phase of the bloom, which occurred over approximately one week, was dominated by the > 1–5 μm fraction; a principal constituent was the small diatom Nanoneis hasleae, which almost entirely displaced larger diatoms more typical of a spring bloom population. The >5 um phytoplankton fraction became dominant for approximately two weeks following the main bloom growth phase but was replaced at the end of the observation period by the > 1–5 μm and 0.2-1 μm fractions. Phytoplankton taxonomic data for the 1990 bloom period were very different to the more typical bloom conditions of 1989. An intercomparison of14C production measurements made by U.K. and Dutch participants during the period of the Experiment using common samples gave total column productivities differing by

The findings of a cruise to study the phytoplankton bloom dynamics associated with the marginal ice zone (MIZ) in the Bellingshausen Sea during Austral spring (November-December) 1992 are reported. Biomass and rate process measurements were carried out at stations located in the ice, ice edge and open water along the 85°W meridian in order to establish the productivity of the microalgae associated with sea-ice and in the water column. In addition, a series of transects along 85°W from sea-ice to open water conditions enabled an assessment of the development of phytoplankton populations. Low phytoplankton biomass and production were noted at ice-covered and ice-edge stations and in the open water close to the ice edge. Observations from the transects indicated no development of a classical ice edge bloom despite evidence that sea-ice had retreated more than 100 km during the study period. Survey data along the 85°W line revealed a region of high chlorophyll, centred on 67.5°S, which was initially observed during brash ice conditions. This feature, which remained geographically consistent, persisted for at least 25 days and was thought to be associated with a frontal region. Water column primary production ( 14 C) in this high chlorophyll region was ca 0.8 g C m −2 day − , more than 8 times higher than noted in the MIZ. Phytoplankton photosynthetic characteristics within this region indicated that cells were adapted to a low light regime. A critical depth of 80 m, estimated directly from oxygen flux measurements, was sufficient to permit the initiation and net growth of phytoplankton standing stocks in a mixed layer of ca 70 m. A modelling approach using 14 C observations suggested that phytoplankton growth was less than the sum of the algal loss terms within this feature. An advective supply of cells therefore would be required to sustain the observed high and constant algal biomass. In addition, although this high chlorophyll feature was initially observed during brash-ice conditions, the available data suggest that it was initiated under open water conditions.

Samples were taken from the open water region directly north of the ice-edge zone between 65.5 and 69.0°S, 83.5 and 88.0°W by R.R.S. Discovery between 23 November and 8 December 1992 for estimates of size-fractionated chlorophyll a concentrations and primary production and also for data on phytoplankton taxonomic distributions. The size-fractions (SF) considered were >18 μm, 2–18μm and 0.2–2 μm. The data confirmed the presence of a high chlorophyll zone (HCZ) immediately south of the surface boundary of the Southern Polar Front and also the absence of a classical stability induced ice-edge bloom, as inferred from a concurrent hydrographic survey. Chlorophyll a concentrations both within and without the HCZ were dominated by the >18 μm SF, with this fraction consistently comprising >75% of the total chlorophyll biomass within the HCZ. Although maximal productivity also was associated with the > 18μm SF, at the majority of locations its relative contribution to the total was generally less than for the comparable chlorophyll a samples, indicating a reduced photosynthetic efficiency for this SF compared to the smaller SFs. To the north of the HCZ, primary production was approximately equal between the three SFs. Data from a transect across the HCZ showed the phytoplankton to be dominated by larger diatoms, although a maximum in Phaeocystis was present immediately to the north of the frontal boundary. A succession in the phytoplankton taxa was inferred northwards from the ice-edge to the frontal boundary. A steady-state modelling approach indicated a loss rate of the phytoplankton from the HCZ by mesoscale activity of 0.071 day−. Extrapolation of the data obtained during the survey gave an estimate of primary production within the HCZ associated with the Southern Polar Front between longitudes 135-75°W in the Bellingshausen Sea, that is over an approximate distance of 2470 km, of 50 × 103 tonnes C day−1.

Size-fractionated primary productivity measurements were done in the northeast Atlantic from May to July 1989 as part of the Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment. Samples were taken on the 20°W meridian at 47, 52, 56 and 60°N, with most intensive sampling at 47 and 60°N. At the time of the first sampling at 47°N, the bloom was over but, at the other stations, substantial phytoplankton biomass and productivity were measured. The northward progression in maximum phytoplankton biomass was associated with increasing water stability and resulted in a decline in the concentration of nitrate and silicate in the surface mixed layer. The maxima in phytoplankton biomass and productivity were associated with phytoplankton cells that were larger than 5 μm diameter, but the immediate pre-bloom conditions at 60°N were dominated by small nanoplankton ( 50% of the daily productivity of 500–800 mgC m−2 day−1. In the post-bloom conditions at 47°N, nanophytoplankton again became increasingly important. Picophytoplankton (

A manual method for the quantitative determination of urea in seawater was developed based on the reaction of urea with diacetylmonoxime. Critical factors include the treatment of collection bottles, sample storage, pre-filtration techniques, water purification, reaction temperature and reproducible cooling of samples during analysis. The limit of detection was 0·14 μg-at urea-N 1 −1 with Beer's Law being obeyed in the range tested of 0–15 μg-at urea-N 1 −1 . The precision (±1 SD) of replicate samples of 1,2 and 15 μg-at urea-N 1 -1 was 0·024, 0·019 and 0·03 μg-at urea-N 1 −1 ( n = 10) respectively.

The overall background to the U.K. BOFS (Biogeochemical Ocean Flux Study) Project, designed to investigate oceanic carbon flux processes throughout the water column, is briefly described together with the strategy for the 1990 BOFS Spring Bloom Experiment. The Experiment involved two ships and was carried out in the northeast Atlantic between 46–50°N, 14–22°W in the period 18 April – 25 June 1990 with the objective of monitoring and quantifying the major carbon flux changes associated with the succession of the spring bloom. Sampling was carried out over a 7 week period adjacent to a Lagrangian buoy drogued at 30m. The spatial fields of the major variables were characterized from box grid surveys around the position of the marker drogue at the beginning and end of the time series observations with the time series hydrographical changes being related to features observed in the spatial surveys. The hydrographical and core biological observations made in the Experiment are described and interpreted. The reference drogue was deployed within an anticyclonic eddy in which initially there was little evidence of seasonal thermocline or phytoplankton develooment. The majority of an array of 30m drogues placed around the reference drogue drifted between 75–150km north and east of their origin, probably exiting from the original eddy system after the first 6 days of deployment. The reference drogue moved anticyclonically around the eddy centre for the first 13 days before exiting from the eddy system and becoming entrained in a discontinuity zone located between discrete warmer and cooler water bodies defined between 50–200m. During this latter period, which continued through to the end of the Experiment, the drogue tracked SE overall and alternately grazed the margins of the two water bodies with greater drift speeds being associated with the influence of the cooler water. Phytoplankton development proceeded slowly over the period that the drogue remained in the original eddy and paralleled the gradual development of the seasonal thermocline. A marked increase in phytoplankton occurred concurrently with the exit of the buoy from the eddy system into the boundary region of the cooler water where increased stratification prevailed. The phytoplankton increase persisted for only 6 days and declined sharply, primarily owing to advective influences, as the buoy moved away from the cool water influence with chlorophyll values remaining low for the remainder of the Experiment. Mesoscale influences were observed to have a major influence on the development sequence of the spring bloom in this area of the northeast Atlantic.

The cool-water copepodCalanus finmarchicusis a key species in North Atlantic marine ecosystems since it represents an important food resource for the developmental stages of several fish of major economic value. Over the last 40 years, however, data from the Continuous Plankton Recorder survey have highlighted a 70 per cent reduction inC. finmarchicusbiomass, coupled with a gradual northward shift in the species's distribution, which have both been linked with climate change. To determine the potential forC. finmarchicusto track changes in habitat availability and maintain stable effective population sizes, we have assessed levels of gene flow and dispersal in current populations, as well as using a coalescent approach together with palaeodistribution modelling to elucidate the historical population demography of the species over previous changes in Earth's climate. Our findings indicate high levels of dispersal and a constant effective population size over the period 359 000–566 000 BP and suggest thatC. finmarchicuspossesses the capacity to track changes in available habitat, a feature that may be of crucial importance to the species's ability to cope with the current period of global climate change.

A shore-based survey of hydrographic variables along the southern Oman coast between 16°55′N, 53°55′E and 17°23′N, 55°17.5′E was carried out between August and November 1985 during the southwest monsoon season and the succeeding period marked by the onset of the northeast winds. During the monsoon season strong evidence of upwelling based on temperature and nutrient data was apparent for the eastern half of the survey area which was distinguished by severe coastal relief and a steeply shelving bathymetry. The upwelled water appeared to be advected westwards into the shallower waters of Salalah Bay which comprised the western part of the survey area. Maximum stratification as inferred from increased temperatures and decreased nutrient concentrations was recorded at the western end of Salalah Bay. Marked increases in chlorophylla were apparent within the Bay at the boundary between the stratified and upwelled waters but concentrations were low within the main bodies of the two water types. The upwelling process was discontinuous in time but the intensity of the upwelling was not apparently related to variation in wind strength; only minimal variations in the velocity of the prevailing southwest wind were recorded during the major part of the survey period. Regular diurnal changes of variable amplitude were observed for all properties sampled with the exception of salinity.

Diatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the 'biological pump' than they have previously been attributed1, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate2, 3, but northern Atlantic waters are richer in nitrate than silicate4. Following the spring stratification, diatoms are the first phytoplankton to bloom2, 5. Once silicate is exhausted, diatom blooms subside in a major export event6, 7. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by 'mining' deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere.

UPTAKE of atmospheric CO2 by the ocean's 'biological pump' is driven by export of carbon from the euphotic zone to deeper waters1,2. As nitrate is a limiting nutrient in large regions of the ocean, measurements of nitrate uptake are often used to estimate the amount of carbon exported in this way3–6. This presupposes knowledge of the molar C: N ratio in the organic material exported from the upper waters, which is usually taken to be 6.6 (the Redfield ratio7,8). Recent studies have suggested, however, that the consumption ratio of C:N may deviate from this value in coastal waters9–11. Here we present time-series from both coastal waters and open-ocean sites which demonstrate that net organic carbon production greatly exceeded that predicted from nitrate consumption and the Redfield C:N ratio. We found a similar discrepancy in sections across broad regions of the North Atlantic during eutrophic periods. Our results suggest that extrapolating from nitrate consumption using the Redfield ratio leads to significant underestimates of organic carbon export from the euphotic zone.

16 pages, 7 figures, 3 tables., An intensive study of pelagic primary production and microplankton community respiration was carried out during an entire upwelling season in the Ria de Vigo (NW Spain). From April to November measurements of oxygen production and respiration using the light-dark bottle technique were made twice a week at the surface, 1% light depth (1% LD, 12 ± 4 m) and 40 m (8 m above sea floor) alongside routine physical, chemical and biological measurements. During the major part of the survey period intermittent intrusions of cold, nutrient-rich upwelled water were observed in the ria with a periodicity of about 2 wk. Rates of gross primary production (GPP) were high but variable averaging 37.3 ± 30.7 µM O2 d-1 and 3.6 ± 4.8 µM O2 d-1 at the surface and 1% LD respectively over the period of survey (n = 50). Rates of dark community respiration (DCR) were also high and variable with maximum values being observed in the surface layer where the seasonal average was 12.2 ± 9.8 µM O2 d-1. At the 1% LD and 40 m, DCR averaged 5.3 ± 4.4 and 2.8 ± 3.0 µM O2 d-1 respectively. Although seasonal average and maximal DCR (up to 46.5 µM O2 d-1) were among the highest reported for coastal areas, microplankton production over the period of survey was dominated by autotrophic processes. Respiration losses by the microplankton community in the euphotic zone represented on average 43% of estimated mean seasonal water column GPP (2.1 to 2.7 g C m-2 d-1). Net heterotrophy in the aphotic layer consumed the equivalent of a further 25% of estimated water column GPP. The degree of coupling between primary production and respiration was primarily controlled by upwelling. During upwelling events respiration was generally low in the water column but it increased as a linear function of chlorophyll a concentration (R2 = 0.55, n = 13) and GPP (R2 = 0.47, n = 13) in the surface layer. Under such condition phytoplankton appears as the dominant component of community respiration consuming 14% of GPP. During periods of upwelling relaxation respiration was high relative to GPP. High water column respiration rates extending occasionally down to 40 m took place at the expense of organic matter trapped inside the bay. The seasonal breakdown of thermal stratification in autumn presented a relationship between surface respiration and chlorophyll a or GPP similar to that observed during upwelling events. The large excess primary production during this period was not remineralised inside the ria, suggesting that a large fraction may be exported towards the shelf., The project was funded by the EU MAST Contract CT90-0017 'Control of Phytoplankton Dominance'. G.M. is grateful to the British Council for a 6 mo fellowship which enabled her to continue her study at the Queen's University of Belfast. X.A.A.-S. acknowledges support from a visiting fellowship of the Departamento de Postgrado y Especializacion (CSIC) during the preparation of the paper. The authors thank the staff of Queen's University Marine Laboratory in Portaferry and of the Grupo de Oceanoloxia at the Instituto de Investigacions Marbias in Vigo for their help and support during the project.

The main features of the relationships between the distribution of phytoplankton and the hydrography of north-west Scottish waters were determined in May and August 1983. A complex but marked salinity boundary separated coastal and oceanic shelf waters to the west of Barra Head whilst a zone of active vertical mixing associated with strong tidal currents was located immediately adjacent to the Barra Head headland. Increased chlorophyll concentrations were observed adjacent to the salinity boundary, discontinuously within the coastal water, and also in the vicinity of the thermocline in the deeper off-shelf water. Low concentrations were typical of the shelf-break and Barra Head mixing zones. The main salinity boundary and shelf-break zone delineated marked changes in the phytoplankton taxonomic compositions and nutrient status of the bounding waters. Diatoms were the chief floral constituents of the coastal water in both spring and summer. Enhanced ammonium concentrations were consistently located beneath the shallow inshore boundary of the coastal current adjacent to the mainland coast. The spring bloom utilized nitrate for growth although a part of the increase was likely to have been supported by ammonium nitrogen. Increases in bottom water nitrate concentrations over the shelf were observed in summer, and may represent a potentially important additional source of nitrogen to assist in the maintenance of shelf productivity during the summer.

Growth rates, cell chlorophyll a concentrations, and carbon uptake rates of Phaeodactylum tricornutum Bohlin grown in cyclical and constant light regimes at three mean irradiances (PFD) were compared. Light cycles with periods 5–38 min were used. Under high PFD the cyclical light regime resulted in both increased and decreased growth rates dependent on the signal frequency. Growth rates were universally depressed under mid and low PFD. Minimal influence of the light field was apparent on cell chlorophyll concentrations. The most marked effect of the fluctuating light was recorded on the carbon uptake rates with maximal influence demonstrated in those samples both grown and incubated in fluctuating light at high as opposed to mid and low PFDs. From the combination of light fields employed, the existence of both short and long term physiological controls of the carbon uptake rates were deduced, these being related to the time scales of carbon uptake and cell growth. A partial explanation to account for the observed increases in carbon uptake in terms of short period non-linear uptake kinetics was derived from two further experiments.

Planktonic populations from three contrasting sites collected in March, May, and August, 1976, were fractionated by differential filtration into a larger fraction (LF) and smaller fraction (SF) and the kinetics of remineralization and assimilation of 14 C urea in the dark by these fractions and the total populations examined. The data were plotted according to the treatment of Wright & Hobbie. Linear kinetics was generally found for total 14 C turnover by the LF and SF collectively. Turnover times of the in situ urea were greatest in March when minimal phytoplankton was present and least in May at the time of the spring bloom of phytoplankton. Lowest turnover times were always found at the station in open water outside the Lough. There was no relation between turnover time and in situ urea concentrations. Maximum velocity of uptake of urea ( V ) was greatest in May and least in August: the lowest values of V were always encountered in the main water body of the Lough. Comparable data for the LF followed a similar pattern. Linear kinetics of 14 C urea turnover was not shown by the SF, a fraction which accounted for up to 40 % of 14 C turnover. The proportion of 14 C utilized by the SF increased with increasing concentration of added urea. 14 C was only assimilated by the LF, the amount being 10 % or less of the total 14 C turnover.

The variability of primary productivity in surface waters was continuously recorded during spatial and sectional surveys of the Irish Sea in the summer of 1977. Localized patches of intense productivity were found, not in the frontal region of the western Irish Sea, but farther east. Subsurface distributions of physical, chemical and biological characteristics through a latitudinal section of the Irish Sea are reported. These data showed that the productivity peaks occurred at the boundaries of a water type exhibiting properties uncharacteristic of Irish Sea waters.

An island in a stratified region of the shelf seas creates a local increase in tidal mixing. The influences of the enhanced mixing on both the physical structure and phytoplankton biomass distribution have been assessed in a detailed survey of the Scilly Isles region of the Celtic Sea. Marked asymmetries in the observed pattern of stratification and sea surface temperature are in accord with the h/u3 distribution which predicts low stability regions occurring on the sides of the island. Displacement of the low stability regions relative to the h/u3 minima is consistent with a northward mean flow. Levels of biomass and primary productivity were found to be increased by a factor ∼5 over a large region (∼20 ×island area) surrounding the islands with particularly intense concentrations of phytoplankton in the pycnocline where chlorophyll levels up to 30 mg m−3 were observed. The location of these maxima at some distance from the islands is suggestive of an intrusive flow of mixed water into the pycnocline. Estimates of nitrate flux, associated with the production of mixed water by stirring, are of the right order to sustain the observed levels of production.

A part of the western Irish Sea is strongly stratified during the summer months, with the boundary of stratification marked by a front with horizontal temperature gradients. Continuous on-line analysis has been used to record the surface water variability of nine characteristics along a cruise path in this area. Multivariate analysis (principal component) indicates the presence of four distinct water types separated by thermal gradients. Two of these water types show land mass influence and two illustrated the effects of the mixed and stratified regimes. The stratified surface waters had a marked degree of homogeneity with respect to the measured characteristics, while the mixed surface waters exhibited greater variability. Marked micro-variations in chlorophyll a concentrations were observed in the latter water type. No consistent relationships were observed among the physical, chemical, and biological variables across the front because of the gradual change in the gross properties of the mixed surface water during its northward passage through the Irish Sea.

Distributions of physical, chemical and biological characteristics observed in the frontal region of the western Irish Sea during July 1977 are presented. High chlorophyll concentrations and phytoplankton cell numbers were associated with the lateral thermal discontinuity. The characteristics of the stratified and mixed waters varied along the length of the front, such that the changes recorded across each frontal transect were unique. The qualitative composition of the diatom population on either side of the front, however, was distinctive. Observations, concentrated on one transect, showed that the diatom population at the front was a mixture of the populations on either side, and that the high phytoplankton standing crop there was predominantly stimulated by nutrient complementation.

The work described in this paper was produced as part of SuperGen Marine Energy Research Consortium II, which was funded by the UK Engineering and Physical Science Research Council (grant number EP/E040136/1). The shallow water kelp Laminaria digitata, abundant in coastal zones of the North Atlantic, is exposed to a range of hydrodynamic environments that makes it ideal for assessing the role of water motion on their growth rate. Here we quantify the growth of L. digitata, as a factor of blade and stipe elongation, at sites adjacent to Strangford Lough, Northern Ireland under different hydrodynamic conditions over a one year period. A modelling approach was used to numerically determine both the temporal and spatial variability of the hydrodynamic environment. Ambient seawater nutrient concentrations, temperature and irradiance were measured as well as the internal nutrient status of the L. digitata populations. Kelp populations growing in the greatest and lowest water motion showed the lowest growth rates. Differences observed in growth rate could not be attributed to seawater nutrient availability, temperature or light. The internal nutrient status also suggested no influence on the observed differences in growth rate. Therefore if there are minimal differences in light, temperature and nutrients between sites, then populations of L. digitata exposed to different water motions are likely to exhibit different growth rates. It is suggested that the growth rate differences observed were a function of water motion with the possibility that, in response to the hydrodynamic forces experienced by the algal cells, L. digitata kelps in the high energy environments were putting more energy into strengthening cell walls rather than blade elongation. Publisher PDF

SEASONAL thermal fronts which occur in coastal waters are typified by sharp lateral gradients of temperature at the sea surface resulting from a surface outcropping of the thermocline. The frontal regions are areas of considerable physical and biological activity; in the case of the fronts in the Celtic and Irish Seas this increase in biological activity is reflected in marked increases of chlorophyll a at the sea surface1. Considerable data on the spatial distribution of physical and chemical characteristics of the water and chlorophyll a concentrations in the vicinity of these and other fronts are now available2–5. But, few observations have been made either on the temporal variability of these characteristics or on the more detailed distribution of phytoplankton productivity. During a survey of the Celtic Sea in September 1976 we made consecutive crossings of the frontal region in order to investigate the small-scale distributions of chlorophyll a and primary productivity and their interrelationships with selected physical and chemical variables.

The dense phytoplankton blooms observed in earlier studies in the Southern Ocean Marginal Ice Zone (MIZ) may not be representative of all regions, so that some previous assessments of the overall importance of this system in total primary production may have been overestimated. Recent observations have shown that increased phytoplankton production may not always be associated with the retreating ice-edge, due to the unpredictability of meltwater-induced stability. Complex interactions between the MIZ and hydrographic fronts have also been indicated. A range of simple simulations, based on biomass inventories for the major biogeochemical systems in the Southern Ocean, show that the greater part of chlorophyll biomass is located in the extensive regions between the major fronts. Consideration of the fronts and the MIZ only, which we surmize may be the principal sites of export production, indicates that the MIZ is clearly the most important single feature. Even if the occurrence of MIZ blooms in the simulations is reduced dramatically, such blooms still appear to make a substantial contribution to production and, by implication, carbon export.

A full understanding of the biogeochemical cycling of silica in the North Atlantic is hampered by a lack of estimates of silica uptake by phytoplankton. We applied the 32 Si radiotracer incubation technique to determine silica uptake rates at 10 sites during the UK-(Natural Environment Research Council) Faroes‐Iceland‐Scotland hydrographic and environmental survey (FISHES) cruise in the Northeast Atlantic, May 2001. Column silica uptake rates ranged between 6 and 166 mmol Si m 22 d 21 ; this data set was integrated with concurrent hydrographic, chemical, and primary productivity data to explain these changes in silica uptake in terms of the progress of the spring bloom. In order to interpret data covering a relatively large spatial and temporal scale, we used mean photic zone silica concentration as a proxy time-series measure of diatom bloom progression. Both absolute and specific silica uptake rates were highest at dissolved silica concentrations .2 mmol L 21 . Si and C uptake were vertically decoupled at those stations where surface silica was strongly depleted. Absolute primary productivity was not strongly correlated with dissolved silica concentrations, owing to either exhaustion of silica at diatom-dominated stations or to dominance of the community by other phytoplankton. Silica uptake as a function of increased substrate concentration was linear up to 25 mmol L 21 ; we consider some possible reasons for the nonhyperbolic response.

Jickells, T.D. ... et. al.-- 34 pages, 6 tables, 10 figures We report the results of an experiment in the Northeast Atlantic in which sulphur hexafluoride (SF6) was released within an eddy and the behaviour of trace gases, nutrients and productivity followed within a Lagrangian framework over a period of 24 days. Measurements were also made in the air above the eddy in order to estimate air–sea exchange rates for some components. The physical, biological and biogeochemical properties of the eddy resemble those of other eddies studied in this area, suggesting that the results we report may be applicable beyond the specific eddy studied. During a period of low wind speed at the start of the experiment, we are able to quantitatively describe and balance the nutrient and carbon budgets for the eddy. We also report concentrations of various trace gases in the region which are similar to those observed in other studies and we estimate exchange rates for several trace gases. We show that the importance of gas exchange over other loss terms varies with time and also varies for the different gases. We show that the various trace gases considered (CO2, dimethyl sulphide (DMS), N2O, CH4, non-methane-hydrocarbons, methyl bromide, methyl iodide and volatile selenium species) are all influenced by physical and biological processes, but the overall distribution and temporal variability of individual gases are different to one another. A storm disrupted the stratification in the eddy during the experiment, resulting in enhanced nutrient supply to surface waters, enhanced gas exchange rates and a change in plankton community, which we quantify, although overall productivity was little changed. Emphasis is placed on the regularity of storms in the temperate ocean and the importance of these stochastic processes in such systems This is contribution no. ACP175 of the NERC ACSOE Thematic Programme. NERC grants GST/02/1276 supported the work of Jickells and Spokes, GST/02/1278 the work of Liss and Nightingale together with core funding to the Plymouth Marine Laboratory (PML) while the ACSOE core programme supported Broadgate and the shiptime costs, NERC grant GR9/3467 to G.S. supported Moncoiffé and Gilpin. Steinke was supported by NERC grant GR3/10956. The University of Newcastle upon Tyne Research Committee provided funding to support T. Frost. The work of Simó and Pedrós-Alió was supported by the Spanish McyT grant MAR97-1885-E

Comprehensive distribution patterns of physical and chemical characteristics have been obtained from a series of cruises in Liverpool Bay. The marked feature of these distributions was their temporal variability, suggesting that the surface residual circulation is also temporally variable. The influence of wind stress upon the circulation pattern and hence water quality of this sea area is illustrated.