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The effects of large scale tidal energy device (TED) arrays on phytoplankton processes owing to the changes in hydrodynamic flows are unknown. Coupled two-dimensional biogeochemical and hydrodynamic models offer the opportunity to predict potential effects of large scale TED arrays on the local and regional phytoplankton dynamics in coastal and inshore environments. Using MIKE 21 Software by DHI (https://www.dhigroup.com), coupled two-dimensional biogeochemical and hydrodynamic models were developed with simulations including no turbines or an array of 55 turbines with four solar radiation scenarios to assess the temporal and spatial changes of phytoplankton dynamics in an idealised domain. Results suggest that the effect of TEDs on phytoplankton dynamics accounted for up to 25% of the variability in phytoplankton concentrations, most likely associated with an increased residence time in an inshore basin. However, natural variation, such as the intensity of photosynthetically active radiation, had a larger effect on phytoplankton dynamics than an array of TEDs.

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.

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.

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 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.

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 (

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.

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.

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 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.