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The spring bloom on the Scotian Shelf is examined using a mooring array deployed from 18 March 2002 to 18 April 2002 to provide physical, chemical, and biological measurements with high temporal and vertical resolution. These measurements are complemented by the Atlantic Zone Monitoring Program (AZMP) biweekly occupations of a station near the mooring site (HL2). Results from AZMP sampling and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color imagery in early March show that coastal upwelling played an important role in the initiation of the spring bloom near the coast. This was a period of very strong horizontal gradients in surface chlorophyll. The main bloom at HL2 was sustained for most of the mooring period with peak chlorophyll levels reaching 6 mg m-3. Following the drawdown of nutrients in the upper 20 m, the bloom continued for 9 d and then disappeared at the surface but remained at the depth of the nutricline (30-50 m). The onset and evolution of the spring bloom on the inner Scotian Shelf is a complex process in which nutrient inventory, vertical mixing, and coastal upwelling play roles of varying importance throughout its lifetime. Mesozooplankton biomass does not change significantly until the very end of the mooring period indicating the grazing by this component of the zooplankton did not have as important a role in the termination of the bloom as the exhaustion of near-surface nutrients.

The magnitude of the flux of biogenic particulate organic carbon (POC) exported from the surface waters of the world ocean and remineralized at depth is critical to constraining models of the global carbon cycle, yet remains controversial. The use of upper ocean sediment traps is still one of the primary tools for determining this export flux, although trap fluxes have been shown to vary significantly because of hydrodynamic and sample collection biases. Over the past decade, 234 Th increasingly has been used as a tracer to estimate POC export from the euphotic zone by multiplying the depth-integrated 234 Th flux by the POC/ 234 Th ratio of sinking particles. The accuracy of this technique is highly dependent on the natural variability in the POC/ 234 Th ratio and 234 Th flux, yet the significance of this variability to estimates of POC export remains uncertain. Based on an analysis of new 234 Th and POC data from the Labrador Sea and a review of 25 previous independent field studies, we report that POC export fluxes can vary 2-10 times or more solely because of variability in the POC/ 234 Th ratio and procedures used to estimate the 234 Th flux. Recommended improvements include studies of the biological, chemical, and physical mechanisms controlling 234 Th-organic matter interactions in seawater; detailed comparisons of POC/ 234 Th ratios in size-fractionated and sediment trap material; increased spatial and temporal sampling density of 234 Th; and more standardized procedures to calculate the 234 Th export flux.

Three trans-Atlantic oceanographic surveys (Nova Scotia to Canary Islands) were carried out during fall 1992 and spring 1993 to describe the large-scale variability in hydrographic, chemical and biological properties of the upper water column of the subtropical gyre and adjacent waters. Significant spatial and temporal variability characterized a number of the biological pools and rate processes whereas others were relatively invariant. Systematic patterns were observed in the zonal distribution of some properties. Most notable were increases (eastward) in mixed-layer temperature and salinity, depths of the nitracline and chlorophyll- a maximum, regenerated production (NH 4 uptake) and bacterial production. Dissolved inorganic carbon (DIC) concentrations, phytoplankton biomass, mesozooplankton biomass and new production (NO 3 uptake) decreased (eastward). Bacterial biomass, primary production, and community respiration exhibited no discernible zonal distribution patterns. Seasonal variability was most evident in hydrography (cooler/fresher mixed-layer in spring), and chemistry (mixed-layer DIC concentration higher and nitracline shallower in spring) although primary production and bacterial production were significantly higher in spring than in fall. In general, seasonal variability was greater in the west than in the east; seasonality in most properties was absent west of Canary Islands (∼20°W). The distribution of autotrophs could be reasonably well explained by hydrography and nutrient structure, independent of location or season. Processes underlying the distribution of the microheterophs, however, were less clear. Heterotrophic biomass and metabolism was less variable than autotrophs and appeared to dominate the upper ocean carbon balance of the subtropical North Atlantic in both fall and spring. Geographical patterns in distribution are considered in the light of recent efforts to partition the ocean into distinct “biogeochemical provinces”.

A comparative ecology of chlorophyll, bacteria and picophytoplankton is presented for seven ecological provinces in the North Atlantic. Depth-integrated standing stocks of these biota were measured from boreal polar to subtropical gyral regions. Averaging over all sampling times and locations within each province, it appeared that the integrated biomass of bacteria did not exceed that of phytoplankton in any province. Although this biomass ratio often exceeded unity in surface waters of the subtropical gyral provinces, the ratio for the upper water column as a whole was lowered by the subsurface chlorophyll layer. Bacteria and picophytoplankton, as the potential food resource of micrograzers, appeared to complement each other such that their total biomass did not vary much more than 2-fold amongst the seven provinces. Characteristic parameters of the biotic depth profiles, namely surface concentrations, integrated stocks and depth of maximum, were used to cluster the provinces. The original classification of provinces based on surface chlorophyll fields and characteristic regional physics was reinforced by the inclusion of bacteria and picophytoplankton.

Natural 15 N / 14 N ( δ 15 N) was determined in suspended particulate matter (SPM) and plankton tow samples (20- and 233-μm mesh nets) during extensive surveys along E–W transects from Halifax, Nova Scotia, to the Canary Islands in the fall of 1992 and the spring of 1993. This is the first study reporting δ 15 N measurements along with NO − 3 and NH + 4 uptake rates in the North Atlantic. During both cruises, the δ 15 N of SPM and net-plankton was lower in oligotrophic waters compared with values in eutrophic areas. The lack of correlation between the euphotic zone integrated δ 15 N SPM and NH + 4 concentration and NH + 4 uptake rate at both times suggested that the contrast between regions could not be explained by regenerated production, even though NH + 4 was the preferred N substrate in most regions. In fact, based on a correlation analysis, this study suggested that isotope fractionation during nitrate uptake and the residence time of N in SPM ( τ ) were the two major factors controlling the δ 15 N SPM in 1992. During the fall of 1992, the δ 15 N SPM of the oligotrophic region ( τ of 100–170 d) was consistent with the accumulated product equation in closed systems and a δ 15 N of new nitrate of 4–5‰. In contrast, in eutrophic regions ( τ of 7–40 d), the δ 15 N SPM was consistent with an open system equation. Isotope fractionation ( e ) for growth on nitrate was estimated to be 2.4‰ in the upwelling off Morocco. In 1993, no correlations were observed between δ 15 N SPM and nitrate dynamics, probably because of horizontal advection. Based on the low τ of 5–30 d, an open system equation was used with nitrate as the reactant, and it suggested variations of 2–3‰ in either the δ 15 N NO3 or e .

Using ship-based phytoplankton fluorescence techniques on a 9-d transect of the North Atlantic Ocean, we have produced the first synoptic view of variations in the maximum quantum yield of photosynthetic energy conversion (4,) on an ocean-wide basis. Based on our 4, measurements, the North Atlantic can be divided into two basins. The southeastern basin (from the African coast to the midocean ridge) is characterized by relatively little horizontal variation in 4, over vast stretches of the ocean. In the northwestern basin (from the midocean ridge to the Canadian coast), we measured lower values of 4, than in the eastern basin, particularly in the upper water column. Lowest surface values were found in an area of strong horizontal flow. Our results suggest that nutrient supply limits phytoplankton productivity over vast stretches of the North Atlantic in this period (early summer). However, surface values of 4, across the North Atlantic appear to be independent of nutrient concentration and distance to nitrate supply. We propose that horizontal advection may play an important role in determining the local conditions to which phytoplankton productivity parameters respond. Our results also suggest that an apparent relationship between remotely sensed variables (ocean color, sea surface height) and phytoplankton photosynthetic parameters exists that may provide the basis for the development of new algorithms used to estimate phytoplankton productivity from satellites.

The concentration-dependent uptake of nitrate (NO,) and its inhibit ion by ammonium (NH,) were surveyed in surface waters of the North Atlantic Ocean. Low-level NO, determinations combined with conventional tracer methods provided the first comprehensive data set on NO, utlization kinetics at nanomolar concentrations. Uptake followed saturation kinetics described by the Michaeli s-Menten equation. The half-saturation parameter for uptake (KN) ranged 2-3 orders of magnitude, covarying with ambient NO, concentrations. KN concentrations in oceanic waters averaged -20-30 nM. NH, half-saturation parameters could only be approximated (i.e. KA + A), but observations suggested that KA and K,, were of similar magnitude in oceanic waters. Maximum uptake rates of nitrate, prntN), and ammonium, prncA), covaried, but prncA) almost always exceeded prncN); in oceanic waters, the disparity was an order of magnitude or greater. Most of the variability in A,,(~ and prncA) could be explained by variations in phytoplankton biomass and temperature. The slope of the uptake vs. concentration relationship, CX, was also investigated but was highly variable and could not be related to any of the oceanographic properties observed; cr, was generally greater than ayN. Kinetics analysis showed that NH4 is preferentially utilized over NO3 over the full spectrum of nitrogen concentrations, nanomolar to micromolar. The inhibition of NO3 uptake by NH,, was also parameterized using the Michaelis-Menten expression. The inhibition half-saturation parameter (KJ covaried with KN, but Kj concentrations in oceanic waters (N 4050 nM) always exceeded KW Maximum inhibition (1,) was rarely complete (i.e. I,,., < I), even at 2,000 nM ammonium. Overall, results suggest that nitrogen utilization parameters currently used in ecosystem models of the open ocean should be re-examined. The mechanisms of supply and the kinetics of utilization of dissolved inorganic nitrogen are believed to play a critical role in determining the productivity, size structure, and species succession of phytoplankton communities in much of the world’s oceans. Dugdale (1967) was the first to propose a theoretical framework for nitrogen acquisition by phytoplankton at steady state based on the concentration-dependent uptake of nitrate and ammonium and represented by the well-known Michaelis-Menten equation of enzyme kinetics

During the 1989 spring bloom in the western North Atlantic, we estimated the biomass and productivity of bacteria and phytoplankton at two sites (40 and 45°N) representing different water masses. At 40°N, almost all of the phytoplankton carbon could be accounted for by photosynthetic nanoplankton and picoplankton; in contrast, at 45°N, only about half was thus accounted, implying a substantial contribution by photosynthetic microplankton. At both sites, bacterial abundance was quite high (up to 2 × 109 cells l−1), and the rates of bacterial production assessed by incorporation of [3H]thymidine (up to 8 pmol l−1 h−1) and [3H]leucine (up to 240 pmol l−1h−1) were significant. Specific growth rates of bacteria based on [3H]thymidine incorporation were 0.08–0.25 day−1. Taken together, our measurements and assumptions implied a demand for primary production in the order of 16–36% over the euphotic zone or 24–78% over the upper 100 m in the water column. We conclude that ultraphytoplankton and bacteria played significant roles in the flux of carbon during the 1989 North Atlantic spring bloom.

An investigation of the spring bloom was carried out in the western North Atlantic (40–50°W) as one component of the multi-nation Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment (NABE). The cruise track included an extended hydrographic section from 32 to 47°N and process studies at two week-long time-series stations at 40 and 45°N. Biological and chemical data collected along the transect indicated that the time-series stations were located in regions where the spring bloom was well developed; algal biomass was high and surface nutrient concentrations were reduced from maximum wintertime levels. Despite similarities in the vertical structure and magnitude of phytoplankton biomass and productivity, the two stations clearly differed in physical, chemical and other biological characteristics. Detailed depth profiles of the major autotrophic and heterotrophic microplankton groups (bacteria, phytoplankton, microzooplankton) revealed a strong vertical coherence in distribution at both sites, with maximum concentrations in the upper 50 m being typical of the spring bloom. Ultraplankton (< 10 μm) were an important component of the primary producers at 40°N, whereas larger netplankton (diatoms, dinoflagellates) were more important at 45°N. Silicate depletion was clearly evident in surface waters at 45°N, where diatoms were most abundant. Despite the relative importance of diatoms at 45°N, dinoflagellates dominated the biomass of the netplankton at both sites; however, much of this community may have been heterotrophic. Bacterial biomass and production were high at both stations relative to phytoplankton levels, particularly at 45°N, and may have contributed to the unexpectedly high residual ammonium concentrations observed below the chlorophyll maximum layer at both stations. Microzooplankton grazing dominated phytoplankton losses at both stations, with consumption as high as 88% of the daily primary production. Grazing losses to the mesozooplankton, on the other hand, were small (

Euphotic zone concentrations and fluxes of nitrate, ammonium, particulate and dissolved organic nitrogen were measured over an 18 month period at the VERTEX time-series site in the oligotrophic northeast Pacific (33°N, 139°W). Variations in all N-forms were significant but not clearly linked to the temporal hydrographic cycle. Inorganic-N uptake (nitrate + ammonium) from 15 N tracer experiments generally paralleled primary productivity variations, peaking in summer; ammonium accounted for most of the uptake (∼90%) and temporal variability. Comparisons of 15 N results with estimates of autotropic N-uptake from 14 C incorporation into protein suggest that as much as 40% of the annual inorganic-N uptake was due to microheterotrophs; peak heterotrophic N-uptake occurred in summer when heterotrophic biomass was at its maximum. Nitrate uptake (new production) was less variable than ammonium uptake and annually equivalent to particulate nitrogen export from sediment traps. Dissolved organic-N (DON) represented the largest and most variable N-pool, accounting for 80–90% of the total nitrogen in the euphotic zone. Vertical DON gradients, however, were small and temporally invariant, implying little contribution to the biogenic nitrogen export from the euphotic zone.

Compound remote sensing, a technique for estimating oceanic new production using remotely sensed data on ocean color and temperature, is discussed. This approach, which depends on parameterizations developed from ship observations as well as on satellite data, yields more representative estimates of the large-scale average new production than those calculated from ship data alone. The approach is illustated with data for the Georges Bank.

Temperature, light and dissolved nutrients are considered the “master” abiotic properties controlling primary production in the ocean. Each of these properties, in turn, is influenced by water column stability Sustained research over the past several decades has endeavored to ascertain which of these properties is most important in regulating phytoplankton growth. In no region has this research effort been more evident than at high latitudes. For both polar regions, extremes in each of these properties are the rule in surface waters where phytoplankton grows: the lowest ocean temperatures, the greatest seasonal excursion in incident solar radiation, and the highest dissolved nutrient concentrations. Based largely on indirect evidence, early researchers speculated that polar primary production was high relative to production at lower latitudes. This was commonly attributed to the abundant surface “macronutrients” (NO3, PO4, H4SiO4) since physiological adaptations to the suboptimum temperatures and light were thought to characterize these high latitude populations. Intensification of polar research since the late 1960's has in many respects modified this view. Current perspectives are that important differences exist between the Arctic and Antarctic with regard to the availability and role nutrients play in regulating primary production. In general much less emphasis is now placed on the significance of the macronutrients in the Antarctic although there is speculation and some evidence that “micronutrients” (Fe) may be important. Macronutrient availability appears to play a more important, though secondary, role in the Arctic, that of sustaining rather than initiating phytoplankton growth. This paper reviews early, contemporary, and present research addressing the question, “What role does nutrient availability play in the distribution and magnitude of primary production in Arctic and Antarctic waters?” Emphasis is placed on new research on under-ice communities as well as on the historically studied pelagic communities.

Particulat organic carbon and nitrogen fluxes measured with free-floating seediment traps deployed six times over an 18-month period were combined with 14C primary production and 15N uptake measurements in order to obtain annual estimates of new production (NP) and associted f-ratios at the VERTEX time-series site. The site, located in the northeast Pacific Ocean at 33°N, 139°W, was occuped at trimonthly intervals to conduct water column studies and to recover/redeploy the sediment traps. The upper 250m of the VERTEX site exhibited considerable variability in some biological properties over seasonal time scales. While integrated photoautotrophic biomass remained relatively constant (0.57 ± 0.1 g C m−2) during the 18-month period, both integrated primary production and particulate ATP varied approximately 2.5-fold, ranging from 220 to 550 mg C m−2d−1 and 0.6–1.5 g C m−2, respectively. There was also considerable variation in both NP and f-ratios over the 18-month sampling period, although most of the NP variability was associated with short-term (i.e

Interzonal diel migrant plankton and nekton obtain organic carbon by feeding at night above the main pycnoline of subtropical and tropical oceans, and respire part of it by day in the interior of the ocean below the pycnocline. Using data from seven oceanic stations, and conservative models to compute respiration at depth, we show that this flux of respiratory carbon ranged from 20 to 430 mg C m−2 d−1 or 13–58% of computed particulate sinking flux across the pycnocline. If this flux occurs consistently between 50°N and 50°S, it will add about 5–20% (depending on method of calculation) to current estimates of global sinking flux of organic carbon across the pycnocline.

This is a personal account of the history, accomplishments and future of biological oceanography in Canada with emphasis on Canadian government research. Canadian biological oceanographers have a rich history pre-dating the formal beginning of marine scientific research in the country with the establishment of the St Andrews and Nanaimo field stations in the early 1900s. Over the years, they have distinguished themselves by being leaders in the early developments of the discipline, including methodologies, concepts and understanding of both the pelagic and benthic ecosystems. In more recent years, Canadian biological oceanographers have led in the conceptualization,planning and implementation of major interdisciplinary/international research initiatives on climate change and ecosystem dynamics. Additionally, they are making important contributions to ecosystem and climate monitoring, research aimed at understanding the influence of ecosystems on harvestable living resource variability and on climate change, and development and application of ecosystem and climate models. Canadian biological oceanographers have made and continue to make significant contributions to the understanding of the biology of the oceans and its interactions with the physical, chemical and geological world. The challenge of solving the complex scientific and societal problems of the future will require better planning, coordination and strongercommitment to the ocean sciences by universities and government than is currently in place. Strategic planning to define goals and responsibilities is urgently needed and should include not only government and universities, but also private sector research and industry.Ceci est une vue personnelle de l’historique, des réussites et de l’avenir del’océanographie biologique au Canada qui met l’accent sur la recherche gouvernementale canadienne. Les océanographes biologiques canadiens ont un passé riche qui pré date le début officiel de la recherche scientifique marine dans ce pays avec la fondation des stations marines St. Andrews et Nanaimo au début des années 1900. Au fil des ans ils se sont distingués par leur rôle de chef de file dans le développement de cette discipline, couvrant les méthodes, les concepts et la compréhension des écosystèmes pélagiques et benthiques. Les océanographes biologiques canadiens ont mené dans la conceptualisation, la planification et la mise en place d’initiatives majeures en recherche multidisciplinaire et internationale sur le changement climatique et ladynamique des écosystèmes. De plus, ils font actuellement des contributions importantes à la surveillance du climat et des écosystèmes, à la recherche visant à comprendre l’influence des écosystèmes sur la variabilité des ressources marines exploitables et sur le changement climatique, et au développement et à l’application des modèles climatiques et écosystémiques. Les océanographes biologiques canadiens ont fait (et continuent à faire) des contributions significatives à notre compréhension de la biologie des océans et de ses interactions avec la physique, la chimie et la géologie. Les défis soulevés par les problèmes scientifiques et socio-économiques complexes de l’avenir exigent une meilleure planification et coordination et un engagement plus fort envers les sciences océaniques que démontré présentement par les universités et les gouvernements. Il est urgent de développer une planification stratégique quidéfinit les objectifs et les responsabilités pour rencontrer les défis de l’avenir et qui inclue non seulement les gouvernements et les universités, mais aussi la recherche privée et l’industrie.

Results from several years of oceanographic cruises are reported which show that the parameters of the photosynthesis-light curve of the flora of the North Sargasso Sea are remarkably constant in magnitude, except during the spring phytoplankton bloom when their magnitudes are noticeably higher. These results are interpreted as providing direct evidence for nutrient control of photosynthesis in the open ocean. The findings also reinforce the plausibility of using biogeochemical provinces to partition the ocean into manageable units for basin- or global-scale analysis. They show that seasonal changes in critical parameter should not be overlooked if robust carbon budgets are to be constructed, and illustrate the value of attacking the parameters that control the key fluxes, rather than the fluxes themselves, when investigating the ocean carbon cycle.

Since the advent of antituberculous therapy, tuberculosis of the ear has decreased in incidence; but of late, cases of both pulmonary and otologic tuberculosis are on the rise. In addition, the treatment of aural tuberculosis is now more difficult due to resistance to one or more of the routinely used antituberculous pharmacotherapeutic agents. Urban areas and selected populations have been particularly endangered by the re-emergence of this disease. In light of this developing situation, three cases of aural tuberculous infections are presented. Typical and atypical presentations of the disease, including history, signs, symptoms, and radiographic findings are discussed, as are treatment options. The importance of aural tuberculosis as part of the general increase in incidence and resistance of the disease is examined.

Deep profiles of particulate organic matter, microplankton (phytoplankton and bacteria), zooplankton and their metabolic activities were investigated during two summer voyages to the eastern Canadian Arctic. Magnitudes and depth distributions were similar in many respects to observations from temperate and tropical waters. Strong gradients in most properties were observed in the upper 50–100 m and subsurface maxima were generally associated with the upper mixed-layer (>50 m). In addition to the general vertical decreases in plankton biomass and metabolic activity there was evidence for both rapid transport (sinking) of organic matter and for enhanced (above background) levels of microbial metabolic activity in deep waters (>500 m). Zooplankton depth distributions differed from the pattern generally observed at lower latitudes; in the Arctic, zooplankton abundance decreased to a lesser degree with depth than particulate organics and microplankton. The overwintering behavior of high-latitude zooplankton appeared to be the best explanation for their relatively high abundance at depth. Despite this, however, zooplankton apparently contributed little to the total column community metabolism.

We measured simultaneously the size-distribution of oxygen consumption, inorganic and orgamc dissolved carbon assimilation, and the standing stocks of phytoplankton and bacteria, to develop simple carbon budgets and "C exchange models for the microplankton communities of a large conhnental shelf system. In spring samples (dominated by large-celled dlatoms) community respiration consumed 33 to 100 % or more of the gross primary production (GPP) measured by the 0,-light-anddark-bottle technique and was apparently due entirely to microheterotrophs. In fall samples (dominated by flagellates) community respiration consumed 100 % or more of the measured GPP, and appeared on average to be due equally to autotrophs and heterotrophs. Pnmary production, estimated by 14C-CO2 assimilation into particulate matter, often greatly underestimated GPP and community metabolism measured by the 0, technique, with apparent photosynthetic quotients (PQ) of about 5.0 in the spring samples. Modelling of the tracer dynamics suggested large rates of DOC release (> particulate production) from a small and rapidly cycling pool w i t h the autotrophs as the cause of the large apparent PQ's. The large share of primary production consumed by small microheterotrophs ( c 5 or l p) and frequent lack of positive net community production suggested a low efficiency for the transfer of microheterotrophic production to larger or.;a~isn?s.

Tracer exchange kinetics were consistent with the view that microplankton of waters near Hawaii produced and assimilated dissolved orthophosphate and dissolved compounds other than orthophosphate at roughly equal rates in experiments conducted in September, 1982. Using simple exchange models plus chemical measurements, we inferred that material other than orthophosphate could sometimes dominate the soluble molybdate-reactive pool (SRP), as is frequently the case in fresh waters. Where phosphorus exchange was most rapid, the tracer kinetics suggested that some fraction of the plankton community was disproportionately responsible for dissolved phophorus exchange. Comparisons against independent measurements of rapid phytoplankton turnover in these communities supported the conclusion that dissolved compounds other than orthophosphate were rapidly cycled and formed an important substrate for plankton growth.

In the Canadian high arctic, in summer, in situ profiles of oxygen evolution and carbon fixation by phytoplankton showed excellent qualitative and quantitative agreement with an apparent photosynthetic quotient in the range from 1.3 to 1.8. Water column photosynthesis was linear in the available light at the surface. Daily rates photosynthesis exceeded 1 mg C m-2 d-1, implying a minimal estimate for annual production in the range from 35 to 70 g C m-2 y-1.

In phytoplankton of the eastern tropical Pacific Ocean from 25 to 90 percent of the biomass (measured as chlorophyll a) and 20 to 80 percent of the inorganic carbon fixation were attributable to particles that could pass a screen with a 1-micrometer pore diameter. Evidence is presented that these are indeed autotrophic cells and not cell fragments.

A high field nuclear magnetic resonance spectrometer has been put into operation at the MIT, Francis Bitter National Magnet Laboratory. The spectrometer is built around a high homogeneity magnet, the design field of which was 11.74 T, and which in fact operates in persistent mode at a field of 11.71 T. The magnet is wound using niobium–titanium superconductor cooled to 2.3 K and is housed in a special dewar designed to permit continuous subatmospheric cryogenic operation and to minimize helium consumption. This and a companion paper describe the analysis, design, and construction of the magnet.

At a station (NFLUX), occupied for 10 days in the northern Sargasso Sea, we assembled data to test the hypothesis that diel migrant biota in the open ocean induce a downward flux of dissolved inorganic nitrogen that is significant in relation to the passive flux under gravity of particulate organic nitrogen at the base on the photic zone. We founf taht NH4+ excretion rates by day at depths below the photic zone were approximately 8% of particulate nitrogen flux obtained by a sediment trap array at the same depth. This figure is in the lower part of the range of values calculated previously for 10 published station data sets; we attribute this to the quite high rate of passive flux relative to primary production at the NFLUX station.

A study of phosphate assimilation by coastal marine plankton revealed that both phytoplankton and microheterotrophs incorporated radioactive phosphorus (33P). Size fractionation of the particulate matter (using 1 μm pore diameter Nucleopore® membrane filters), antibiotic treatment (using garamycin), and independent estimaties of photoautotrophic (14CO2 uptake) and heterotrophic (3H-glucose uptake) activities were employed to separate phyto- and bacterioplankton phosphate uptake. Results indicated that phytoplankton 33P-uptake was best estimated by the fraction of particulate matter retained on the 1 μm membrane filters. Usually, less than 10% of the phytoplankton (based on chlorophyll a measurements) passed the 1 μm pore-diameter filters, whereas about 90% of the heterotrophic activity passed. At least 50% of the 33P-uptake was associated with the 1 μm fraction.

Uptake of inorganic (NO3‒, NH4+) and organic (urea) nitrogen compounds by arctic phytoplankton was linear for at least 30 h of incubation under natural temperature and light conditions. Extrapolation of linear fits of the data showed positive ordinal intercepts for NH4+, suggesting relatively more rapid uptake early in the incubation period. Short term uptake experiments confirmed this; rates computed from 20-min incubations were on the average 3-fold higher than 24-h uptake rates. The transient nature of these enhanced uptake rates resulted in their contributing little (

In Baffin Bay, phytoplankton populations from the 1% light level were susceptible to photoinhibition whereas populations from the 50% light level were not. Both the initial slope of the light saturation curve and the assimilation number were smaller for the deep samples than for the shallow ones. The optimal irradiance for photosynthesis by the near-surface populations was comparable to the maximum irradiance to which they might be exposed in situ , but that for the populations near the bottom of the photic zone was higher than the populations could experience in situ . The general magnitudes of the photosynthesis parameters for these late summer arctic populations fell towards the low end of the range observed in temperate waters.

Properties of the light saturation curve of photosynthesis and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity are shown to change qualitatively in a natural population of marine phytoplankton during a spring bloom. Evidence is presented to show that these changes constitute photoadapative responses to increasing irradiance. As irradiance increased during the bloom, both the level of light-saturated photosynthesis ( P m ) and the initial slope of the light saturation curve ( α = photosynthetic efficiency) increased whether those parameters were normalized to chlorophyll a concentration ( P m b , α b ) or to cell numbers ( P m c , α c ). The magnitudes of these changes were such that I k (= P m / α , the photoadaptation parameter) did not change, but I m , the light intensity at which photosynthesis becomes saturated, increased. RuBPC activity, both chlorophyll a (RuBPC b ) and cell number normalized (RuBPC c ), also increased during the bloom. We suggest that these adaptations were achieved by simultaneously increasing the number of photosynthetic units, proportionately decreasing the photosynthetic unit size, and increasing both the concentrations of the enzymes of the dark reactions and possibly also of photosynthetic electron transport components. We also observed diminished levels of photoinhibition in the high light adapted cells late in the bloom and have suggested that this was a consequence of the same suite of physiological changes. In situ carbon fixation per cell increased during the bloom whereas no change occurred in this parameter when normalized to chlorophyll a concentration. Although these photoadaptive responses thus permitted carbon to be fixed in situ more rapidly per cell, at a constant efficiency with respect to investment of energy in the photosynthetic apparatus, they did not result in a change in growth rate. Based on consideratios of the role of time scale in physiological adaptation, however, it is suggested that the observed alterations in photosynthesis with increasing irradiance might permit a cell to more rapidly fill an energy quota for division, possibly an advantage in a mixing environment in which energy is patchily distributed, both spatially and temporalyy. Phosphoenolpyruvate carboxylase activity when normalized to chlorophyll a (PEPC b ) did not change during the bloom while chlorophyll a normalized dark carbon fixation decreased sharply and was quantitatively small compared to PEPC b . On this basis and considering that RuBPC b increased during the bloom, it is suggested that, although PEPC may be involved in dark carbon fixation, its most important quantitative role is probably an indirect one in light dependent photosynthesis. We have also considered the relevance of laboratory results on photoadaptation to interpretations of field studies and have suggested that batch culture studies must be treated with caution but that turbidistat and semi-continuous methods provide reasonable simulations of natural conditions.

Analyses of some 700 photosynthesis-irradiance (P-I) experiments made on natural marine phytoplankton assemblages in over six years of field work are summarized. Observed variations in P-I parameters are discussed in relation to geographical location, sample depth and temporal cycles (diel to interannual). Results suggest that P-I characteristics and therefore regional primary production are largely under physical control; temperature and light appear to be the most important environmental covariables.

During a cruise to the eastern Canadian Arctic (Northern Baffin Bay) in the summer of 1980, we took advantage of the 24-h photoperiod to conduct a 32-h time course experiment of 14C accumulation under natural solar radiation. The degree of non-linearity in the time course was judged against a time-dependent curve of radioactivity constructed by cumulatively adding the amount of 14C taken up in sequential short (2 h) incubations of plankton held in a replicate bottle but left unlabelled until removed for assay. Departure from linearity was due first to decreasing rates of 14C incorporation into polysaccharides and then into lipids. There was a close correspondence between 14C incorporation into proteins in the 32-h incubation and in the sequence of short incubations. These observations are consistent with patterns in utilization of photosynthetic end-products established from laboratory studies of unicellular algal cultures. Based on parallel or independent control experiments, it was judged that complicating factors such as diel light changes, nitrogenous nutrient exhaustion, bottle size effects or inhibitory conterminants in NaH14CO3 stock solutions would not seriously affect our interpretation that non-linearity resulted from catabolic loss of radiocarbon.

Nitrogen cycling in a natural planktonic food chain was followed before and after perturbation by copper (10 μg l-1). Observations were separated into effects from artificial containment of the food chain and effects from the addition of copper. An initial reduction of seston-N and subsequent recovery, uniformly high settling rates of suspended particulate-N, and general decrease in zooplankton-N were attributed to the physical limitations imposed by the enclosures (e.g. elimination of normal mixing processes). Acute inhibition of nitrate assimilation by the seston, acute elevation of seston-N settling and chronic inhibition of zooplankton feeding, along with accelerated decline in zooplankton stocks, were attributed to copper stress. Since zooplankton stocks and fluxes were most drastically affected by copper, its overall effect on N-cycling through the planktonic food chain would depend largely upon the importance of zooplankton in regulating the production of the remaining seston.

On precise les interrelations entre l'environnement physique et les processus de productivite primaire et secondaire et l'on discute les relations possibles entre la production de larve de poissons et celle de langoustes dans cette baie

The spatial distribution and size-dependence of oxygen consumption (respiration) and production by microplankton in near surface waters of the Canadian Arctic were measured during summer, 1983. High oxygen flux rates (consumption and production) were observed near surface (upper 20–30 m) and were generally associated with high phytoplankton biomass (chlorophyll a) levels. A substantial portion of the respiration (>50%), however, was below the euphotic zone. Integrated oxygen fluxes (0–100 m) were approximately in balance (i.e., net oxygen production ≈ 0) at most locations sampled. In general, oxygen fluxes were higher than have been observed in the Southern Ocean but in the same range as found in temperate coastal waters. Size-fractionation studies showed that most (>60%) of the oxygen production and phytoplankton biomass (chlorophyll a) were associated with organisms greater than 35 μm. On the other hand, more than 70% of the respiration was associated with organisms less than 35 μm; on average, more than 50% of the respiration was associated with organisms less than 1 μm. These results are consistent with theoretical studies and with experimental observations from temperate waters.

Rates of oxygen utilization (OUR) at depth in the ocean have been interpreted as showing that rates of carbon fixation by phytoplankton, as estimated by 14CO2 assimilation in vitro, must be in error1. The oxygen is consumed in the decomposition of organic matter sinking from the photic zone: there is a stoichiometrically equivalent flux of nitrate from the deep water towards the surface2. For comparison with the 14C data, it is conventional to extrapolate OUR to total equivalent phytoplankton production through a constant factor f, the ratio of nitrate based production (Pnew) to total production (Pt) as defined by Dugdale and Goering3. The alternative hypothesis, that scaling up OUR by a constant factor f is inappropriate, has not been examined in detail. We show here that f is variable in space and time for most provinces of the ocean. Furthermore, we show that in nitrogen-limited systems, such as the pelagic of the open ocean, Pt and f should be positively correlated. Applying these results to data from the Sargasso Sea, we find that the carbon fluxes estimated by 14C assimilation are consistent with the oxygen fluxes estimated by OUR. The conclusion is of profound importance for understanding the major biogeochemical cycles of the ocean.

A comparison of nitrogen assimilation rates based on uptake of 15 NH 4 + and incorporation of 14 CO 2 into protein at three stations near the Hawaiian Islands indicates that heterotrophic processes accounted for at least 50 to 75% of the NH 4 + uptake. These results suggest that bacteria may compete effectively with phytoplankton for inorganic nutrients in the sea.

Urea concentrations, uptake, and excretion were measured at various locations in northern Baffin Bay and surrounding waters during the summer of 1980. Concentrations were variable ( 2.00 mg-at. N m−3) but followed patterns of decreasing concentration with depth in the euphotic zone and with distance from land. Urea accounted for > 50% of the total dissolved nitrogen in the upper mixed layer at most stations. Urea uptake rates showed generally the same distributional patterns as did concentrations and on the average accounted for 32% of the total nitrogen (NO3− + NH4+ + urea) productivity in the eupholic zone. Ammonium, and frequently NO3−, were utilized in preference to urea. Dual isotope (14C and 15N-urea) labelling experiments suggested that most urea-C was respired as CO2 while 50 to 80% of the urea-N was incorporated by the phytoplankton. Excretion measurements suggested that the four dominant macrozooplankton species (Calanus hyperboreus, C. finmarchicus, C. glacialis, and Metridia sp.) supplied only −3% of the urea-N but –40% of the NH4+-N requirements of the primary producers.

In the castcrn Canadian arctic the photosynthesis-irradiance curves of phytoplankton from the 50% and 1% light levels differ mainly in their susceptibility to photoinhibition. The photoinhibition parameters of deep poplllations and the intensity of the deep chlorophyll maximum were correlated with N2, the bulk stratification parameter of the water column. Comparison of data from the same region in different periods suggests that the characteristic susceptibility to photoinhibition requires 2-6 weeks to develop once a population is isolated below a pycnocline. Insensitivity to photoinhibition developed much more quickly when a population from the chlorophyll maximum was exposed to surface light. The threshold of photoinhibition increased rapidly, reaching surface intensities within 4-6 h. The adaptation is sufficiently rapid that phytoplankton from the chlorophyll maximum should be stressed only briefly when transported to the surface by a mixed-layer-deepening event.

Phytoplankton biomass (chlorophyll a) and primary production rates in Baffin Bay during summer 1978 were comparable to levels reported for other open water arctic and subarctic regions. Values were moderately high ([Formula: see text] mg Chl∙m−2; 227 mg C-fixed∙m−2∙d−1) considering the low mixed-layer nutrient (nitrogen) concentrations, low ambient temperatures ([Formula: see text] euphotic zone = −0.2 °C), and variable and moderately low daily solar radiation ([Formula: see text] MW∙m−2). Biomass maxima were consistently found at or near the bottom of the euphotic zone, and were 6 times higher than surface values on the average. Nitrate and ammonium were assimilated in approximately equal proportions despite the relatively greater abundance of nitrate in the euphotic zone, particularly below the mixed layer. Average C:N assimilation ratios were slightly lower (5:1) than the chemical composition ratio of the particulate matter (7:1). High phosphate assimilation rates reflected the abundance of this nutrient in the euphotic zone and resulted in low C:P (22:1) and N:P (6:1) assimilation ratios. Growth rates computed from carbon and nitrogen (NO3− + NH4+) assimilation rates averaged 0.31 and 0.35 doublings∙d−1, respectively, for the euphotic zone, and were half the maximum expected growth rates for prevailing water temperatures and optimal conditions of light and nutrients. Baffin Bay phytoplankton populations exhibited no obvious signs of severe nitrogen limitation despite low euphotic zone concentrations of the nutrient. Furthermore, the strong correspondence between: (1) normalized primary production rates (photosynthetic index) and incident solar radiation and (2) growth rates and incubation temperatures suggests that nutrients may play a relatively less important role in controlling arctic primary production than previously considered.Key words: phytoplankton, primary production, nutrients, arctic, light, and temperature

Plankton biomass, material fluxes, e.g. 14C uptake, and specific growth rates are related quantities. In the course of comparing various methods of measuring these properties in September 1982 off Oahu, Hawaii, we found specific growth rates of l-2.d-I. Such rates approach the maximum expected values observed in laboratory cultures. Plankton production is reported to be low in subtropical oceanic gyres compared with coastal waters at similar latitudes (Steemann Nielsen 1955; Koblentz-Mishke et al. 1970). Standing stocks, e.g. chlorophyll concentrations, are lower in the gyres, and plant nutrient levels are scarcely detectable by standard methods. We report here on a