Estimates Of New Production Research Articles

Scaling up taxon-specific microbial traits to predict community-level microbial activity in agricultural systems

Soil microorganisms perform many important ecosystem functions including nitrogen (N) cycling which dictates plant productivity in agricultural ecosystems. Despite the importance of these communities, connecting microbial composition with ecosystem function has been a long standing challenge. Taxon-specific substrate assimilation traits, measured with quantitative stable isotope probing (qSIP), may provide a means to scale from microbial community composition to community-level process rates. To test the potential for scaling up taxon-specific N assimilation to predict community-level rates of carbon mineralization, N mineralization, and N immobilization we measured soil properties, microbial activity, and N assimilation using 15N qSIP in soils from six distinct farm systems. N assimilation, measured as DNA 15N enrichment, varied among taxa and within taxa across farms. Taxon specific N assimilation was aggregated to calculate a community-weighted mean, which when combined with measures of microbial biomass was used to estimate new microbial biomass N production. This estimate of new microbial biomass production reflects the growth of active microbes over the incubation period and related to microbial activity. The new microbial biomass N produced was predictive of soil C and N mineralization rates, explaining 37–47% of the observed variation across the six farming systems. This approach highlights the ability of trait-based methods to relate microbial community structure data to microbially mediated functional process rates. Such advances may enhance our ability to understand and manage microbially mediated processes, such as N cycling, in both natural and agricultural ecosystems.

Distribution of 210Pb and 210Po in the Arctic water column during the 2007 sea-ice minimum: Particle export in the ice-covered basins

210Pb and 210Po are naturally occurring radionuclides that are commonly used as a proxy for particle and carbon export. In this study, the distribution of the 210Po/210Pb pair was investigated in the water column of the Barents, Kara and Laptev Seas and the Nansen, Amundsen and Makarov Basins in order to understand the particle dynamics in the Arctic Ocean during the 2007 sea-ice minimum (August–September). Minimum activities of total 210Pb and 210Po were found in the upper and lower haloclines (approx. 60–130 m), which are partly attributed to particle scavenging over the shelves, boundary current transport and subsequent advection of the water with low 210Pb and 210Po activities into the central Arctic. Widespread and substantial (> 50%) deficits of 210Po with respect to 210Pb were detected from surface waters to 200 m on the shelves, but also in the basins. This was particularly important in the Makarov Basin where, despite very low chlorophyll-a levels, estimates of annual new primary production were three times higher than in the Eurasian Basin. In the Nansen, Amundsen and Makarov Basins, estimates of annual new primary production correlated with the deficits of 210Po in the upper 200 m of the water column, suggesting that in situ production and subsequent export of biogenic material were the mechanisms that controlled the removal of 210Po in the central Arctic. Unlike 210Po, 234Th deficits measured during the same expedition were found to be very small and not significant below 25 m in the basins (Cai et al., 2010), which indicates, given the shorter half-life of 234Th, that particle export fluxes in the central Arctic would have been higher before July–August in 2007 than later in the season.

An organic carbon budget for coastal Southern California determined by estimates of vertical nutrient flux, net community production and export

Organic carbon export and burial in coastal upwelling regions is an important mechanism for oceanic uptake of atmospheric CO2. In order to understand how these complex systems will respond to future climate forcing, further studies of nutrient input, biological production and export are needed. Using a 7Be-based approach, we produced an 18-month record of upwelling velocity estimates at the San Pedro Ocean Time-series (SPOT), Southern California Bight. These upwelling rates and vertical nutrient distributions have been combined to make estimates of potential new production (PNP), which are compared to estimates of net community oxygen production (NOP) made using a one-dimensional, two-box non-steady state model of euphotic zone biological oxygen supersaturation. NOP agrees within uncertainty with PNP, suggesting that upwelling is the dominant mechanism for supplying the ecosystem with new nutrients in the spring season, but negligible in the fall and winter. Combining this data set with estimates of sinking particulate organic carbon (POC) flux from water column 234Th:238U disequilibrium and sediment trap deployments, and an estimate of the ratio of dissolved organic carbon (DOC):POC consumption rates, we construct a simple box model of organic carbon in the upper 200m of our study site. This box model (with uncertainties of ±50%) suggests that in spring, ~28% of net production leaves the euphotic zone as DOC, of this, ~12% as horizontal export and ~16% via downward mixing. The remaining ~72% of net organic carbon export exits as sinking POC, with only ~10% of euphotic zone export reaching 200m. We find the metabolic requirement for the local heterotrophic community below the euphotic zone, but above 200m, is ~105±50mmolCm−2d−1, or ~80% of net euphotic zone production in spring.

Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic

Estimates of carbon flux to the deep oceans are essential for our understanding of global carbon budgets. Sinking of detrital material ("biological pump") is usually thought to be the main biological component of this flux. Here, we identify an additional biological mechanism, the seasonal "lipid pump," which is highly efficient at sequestering carbon into the deep ocean. It involves the vertical transport and metabolism of carbon rich lipids by overwintering zooplankton. We show that one species, the copepod Calanus finmarchicus overwintering in the North Atlantic, sequesters an amount of carbon equivalent to the sinking flux of detrital material. The efficiency of the lipid pump derives from a near-complete decoupling between nutrient and carbon cycling—a "lipid shunt," and its direct transport of carbon through the mesopelagic zone to below the permanent thermocline with very little attenuation. Inclusion of the lipid pump almost doubles the previous estimates of deep-ocean carbon sequestration by biological processes in the North Atlantic.

Ammonium uptake by phytoplankton regulates nitrification in the sunlit ocean.

Nitrification, the microbial oxidation of ammonium to nitrate, is a central part of the nitrogen cycle. In the ocean’s surface layer, the process alters the distribution of inorganic nitrogen species available to phytoplankton and produces nitrous oxide. A widely held idea among oceanographers is that nitrification is inhibited by light in the ocean. However, recent evidence that the primary organisms involved in nitrification, the ammonia-oxidizing archaea (AOA), are present and active throughout the surface ocean has challenged this idea. Here we show, through field experiments coupling molecular genetic and biogeochemical approaches, that competition for ammonium with phytoplankton is the strongest regulator of nitrification in the photic zone. During multiday experiments at high irradiance a single ecotype of AOA remained active in the presence of rapidly growing phytoplankton. Over the course of this three day experiment, variability in the intensity of competition with phytoplankton caused nitrification rates to decline from those typical of the lower photic zone (60 nmol L−1 d−1) to those in well-lit layers (<1 nmol L−1 d−1). During another set of experiments, nitrification rates exhibited a diel periodicity throughout much of the photic zone, with the highest rates occurring at night when competition with phytoplankton is lowest. Together, the results of our experiments indicate that nitrification rates in the photic zone are more strongly regulated by competition with phytoplankton for ammonium than they are by light itself. This finding advances our ability to model the impact of nitrification on estimates of new primary production, and emphasizes the need to more strongly consider the effects of organismal interactions on nutrient standing stocks and biogeochemical cycling in the surface of the ocean.

Estimates of potential new production (PNP) for the waters off the western Antarctic Peninsula (WAP) region

Potential new production (PNP) can be used as a proxy for new primary production (nPP) and sets the upper bound limit of nitrate-derived primary production (PP). For this study, we estimate PNP by employing a one-dimensional analytical model using in situ and model data for the waters off the western Antarctica Peninsula (WAP) for midsummer, centered around January. Field observations were made during the Palmer Long Term Ecological Research (Palmer LTER) program. A decade long time-series of NO3 vertical profile data (1998–2007, N=516) was used for PNP computations.PNP was calculated for the WAP region by subdividing it into three sub-regions i.e. Coastal, Shelf and Slope based on bathymetry and water mass properties. The Coastal sub-region includes waters with bathymetric depths of 450m or less with Slope water accounting for the oceanic region greater than 750m water depth, while the extensive Shelf region occupies the area between these depth limits. Mean PNP estimates were computed to be 2482.6±197.5, 384.5±61.7, and 891.1±81.8mgCm−2d−1 for the Coastal, Shelf and Slope sub-regions, respectively. The estimated overall mean PNP rate for the entire Palmer LTER WAP region during midsummer (January) was 1257.5±113.6mgCm−2d−1. The mean potential f-ratio (PNP:PP) for the WAP region was closer to unity (potential f-ratio=1.2) indicating that nPP (as opposed to recycled production) plays a major role in sustaining this sporadic but highly productive Antarctic ecosystem during mid-summer. We have also analyzed a longer time series from oceanic sampling stations off Palmer Station, Anvers Island, Antarctica spanning yeardays 310–45 (late November–mid February, 1994–2007). Harmonic regression fit of PNP data from all stations within this nearshore sampling grid of the Palmer LTER Program during the growth season provides maximum and minimum PNP rates of 2181.78 and 14.69mgCm−2d−1 on yeardays 335 (late November) and 43 (mid February), respectively. The overall mean PNP for this region was estimated to be 1040.93±764.58mgCm−2d−1 by employing a constant Kz value of 10−5ms−2. The maximum and minimum PNP values coincide approximately with the onset and demise of annual algal bloom.Analysis of the terms used in the PNP equation indicate that both NO3 drawdown rates (mean=13.25±9.57mmolm−2d−1, N=156) and NO3 flux into the euphotic layer (mean=1.36±1.79mmolm−2d−1, N=156) have high temporal and spatial variability. NO3 drawdown rates were higher than NO3 flux into the control volume by approximately an order of magnitude. Sensitivity analyses of the model using two extreme values of Kz, (10−4 and 10−5ms−2) that are widely reported in the literature for the WAP region, yielded a PNP range of 97.13mgCm−2d−1. The latter accounted for approximately 10% of the overall computed PNP. PNP estimates for the coastal sub-region which includes Marguerite Bay agreed well with estimates of nPP from north Marguerite Bay in a recent study which employed different datasets and research approach.

Euphotic zone nitrification in the NE subarctic Pacific: Implications for measurements of new production

Ammonium (NH4+) oxidation rates, nitrate (NO3−) uptake rates and dissolved nutrient concentrations were measured throughout the euphotic zone along the Line P oceanographic transect in the NE subarctic Pacific, on three cruises (winter, spring and late-summer) in 2009. NH4+ oxidation was found to proceed throughout the euphotic zone and rates ranged from undetectable to 97nmolL−1d−1. Evidence was found to suggest that both light and NH4+ concentrations played a role in regulating NH4+ oxidation rates, with rates increasing as light decreased and NH4+ concentrations increased. The observation that NH4+ oxidation was a ubiquitous process throughout the euphotic zone demonstrates that not all NO3− present in this region of the water column should be considered new nitrogen, and has important implications for estimates of new production in the NE subarctic Pacific. Depth-integrated NO3− uptake rates ranged from 0.65 to 6.0mmolm−2d−1, and we found that euphotic zone NH4+ oxidation could have supported between 3 and 100% of the phytoplankton NO3− demands along Line P. Taking potential euphotic zone NO3− regeneration into account resulted in new production estimates being reduced by an average of ~50%. During spring and late-summer, the degree by which new production was reduced, when euphotic zone NO3− regeneration was taken into consideration, was tightly anti-correlated to total NO3− uptake rates. This indicates that the implications of euphotic zone nitrification for estimates of new production are greatest in the less productive regions of the oceans.

The contribution of the deep chlorophyll maximum to primary production in a seasonally stratified shelf sea, the North Sea

Results from extensive cruises in the years 2000 and 2001 throughout distinct ecohydrodynamic regions of the central and southern North Sea are presented and used to generate estimates of gross primary production and new production. An undulating CTD fitted with a fluorometer was towed over a distance of 12,000 kms. Fluorescence data were used to determine the chlorophyll distribution and derive estimates of phytoplankton biomass. These results were combined with estimates of primary production (new and regenerated) from experiments from one cruise in order to estimate gross production for a greater geographical extent. Results from repeat inter-annual transects showed that the strength of the thermocline and the associated deep chlorophyll maximum were variable. However, when the primary production was integrated over the 15–40 m depth, the variability between years was low. While the depth and strength of the deep chlorophyll maximum varied across the region, a deep chlorophyll maximum (DCM) is a consistent and widespread feature of this region at around 30 m depth. In 2001 the calculated average primary production rate in summer for the whole area surveyed was 0.91 g C m−2 day−1. This daily production equates to ~130 g C m−2 for the summer stratified period. In the offshore stratified regions around the Dogger Bank and Eastern Central North Sea primary production of 64 g C m−2 associated with the deep chlorophyll maximum (15–40 m) accounted for 60 % of total primary production during the summer stratified period (after the spring bloom). Approximately 66 % of new production in these areas occurred in the DCM. This study shows the extent of the DCM in the North Sea and demonstrates its importance in sustaining primary production after the spring bloom.

Estimates of potential new production in the Java-Sumatra upwelling system

The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profiles to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×103 mol/s and potential new production of 1.02×1014 gC/a.

Estimates of New and Total Productivity in Central Long Island Sound from In Situ Measurements of Nitrate and Dissolved Oxygen

Biogeochemical cycles in estuaries are regulated by a diverse set of physical and biological variables that operate over a variety of time scales. Using in situ optical sensors, we conducted a high-frequency time-series study of several biogeochemical parameters at a mooring in central Long Island Sound from May to August 2010. During this period, we documented well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into various signal components, we estimated the amount of variation that could be ascribed to each process. Primary production and surface wind stress explained 59 and 19 %, respectively, of the variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and sunlight on about one quarter of study days. Daytime nitrate minima and dissolved oxygen maxima occurred nearly simultaneously on the majority (>80 %) of days during the study period; both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the following night. Changes in nitrate concentrations were used to generate daily estimates of new primary production (182 ± 37 mg C m−2 day−1) and the f ratio (0.25), i.e., the ratio of production based on nitrate to total production. These estimates, the first of their kind in Long Island Sound, were compared to values of community respiration, primary productivity, and net ecosystem metabolism, which were derived from in situ measurements of oxygen concentration. Daily averages of the three metabolic parameters were 1,660 ± 431, 2,080 ± 419, and 429 ± 203 mg C m−2 day−1, respectively. While the system remained weakly autotrophic over the duration of the study period, we observed very large day-to-day differences in the f ratio and in the various metabolic parameters.

Dissolved O2/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean

We use continuous and discrete measurements of the dissolved O2/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O2/Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O2/Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on‐deck 24 h 14C incubations and gross carbon production values from photosynthesis‐irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5–4.2 times higher but with uncertainties in that ratio near ±2. These comparisons show that the photosynthesis‐irradiance experiments based on 1–2 h 14C incubations underestimated gross carbon production.

Designing workshop management system supporting decision making with OODB

In this study, a workshop production management system supporting decision making is designed for use in small and medium-sized machine workshops. Small and medium sized companies’ quality, price, and delivery time issues are in a tough competitive environment. Especially such as the orders which cannot be delivered to customers in time, disruptions in production schedules and low production performance seem to be the major problems facing in this type of sector. Through this research it is aimed to design software to keep all the needed information in a suitable database and give the customers fast and accurate information. In order to support future implementation of decision support system, the software is designed such that it will enable the user to easily analyze its production parameters such as efficiency, cost deviation of production from planned cost, cost estimation of new production, etc. Due to the natural structure of this project Object Oriented database is chosen for implementation. These databases can be constructed through object-oriented language and in the scope of this work .NET based db4o is used. For software development, Unified Modelling Language (UML) is used since by using UML the database system is well defined, visualized, generated and specified considering complete project. The user interfaces are designed by using ASP.NET for easy access of the user location independently. It is seen that without using so much coding load, an effective object-oriented database can be designed. It is possible to use the same language for both application and object-oriented databases in contrast to relational databases. The designed database can be used in different machine workshops with small modifications depending on the specifications of workshops.

Simple equations to estimate ratios of new or export production to total production from satellite‐derived estimates of sea surface temperature and primary production

Two simple equations with sea surface temperature and total primary production as independent variables were used to estimate ratios of new or export production to total primary production (ef‐ratios) in the ocean. Both equations assume that ef‐ratios are negatively correlated with temperature in a linear manner and positively correlated with total primary production in a curvilinear manner characteristic of a Holling type II function. The two equations were parameterized based on different sets of field data: in one case entirely from estimates of new production based on nitrate uptake, and in the other case based on a comprehensive summary of new and export production estimates derived from a combination of techniques. Estimates of global export production based on satellite observations and use of the two equations were 9–13 Gt C per year. The form of both equations likely captures the principal effects of temperature and total production on ef‐ratios, and their mathematical simplicity should facilitate their prognostic application in climate change research and studies of the ocean's carbon cycle.

Nitrification from the lower euphotic zone to the sub-oxic waters of a highly productive British Columbia fjord

Nitrification rates were measured monthly from April to October 2008, at depths ranging from the lower euphotic zone to the sub-oxic waters of Saanich Inlet. Ammonium (NH 4 +) and nitrite (NO 2 −) oxidation rates ranged from undetectable to 0.319 and 0.478 μmol L − 1 d − 1 , respectively. NH 4 + oxidation rates and concentrations were positively correlated at substrate concentrations less than 0.8 μmol NH 4 + L − 1 . Positive correlations between NH 4 + oxidation rates, NO 2 − concentrations, and NO 2 − oxidation rates were also observed, highlighting the important role that NH 4 + oxidation plays in supporting NO 2 − oxidation in Saanich Inlet. Despite the apparent dependence of NO 2 − oxidation rates on NH 4 + oxidation rates, the former was still 44% higher than the latter and we concluded that Saanich Inlet NO 2 − oxidation rates were augmented by fortnightly spring-tide nutrient renewal. From May to October, sub-oxic zone waters were isolated from any significant mixing events, and we estimated that nitrification was responsible for approximately 25% of dissolved oxygen consumption. This estimate is in close agreement with that calculated using Redfield stoichiometry, and as such highlights the accuracy with which nitrification rates can be quantified using incubation techniques. Finally, nitrification rates in the euphotic zone were at times substantial, and we suggest that earlier estimates of new production in Saanich Inlet may have been overestimated by approximately 15%.

Estimation of new primary production in the Benguela upwelling area, using ENVISAT satellite data and a model dependent on the phytoplankton community size structure

The spatial and temporal variations of oceanic new primary production have a crucial importance for the study of biogeochemical fluxes in the ocean; however, they have been poorly documented. In this paper, we propose a revision of the “shift‐up” new production model developed for upwelling areas by Dugdale et al. (1989), and later adapted by Kudela and Dugdale (1996), using ocean color and sea surface temperature satellite data as inputs. The major improvement of the model is that the estimation of nitrogen uptake rates takes into account the phytoplankton community size structure, estimated for each pixel using the method of Uitz et al. (2006). Appropriate physiological parameters are then used for each size class. This revised model has been applied to Medium‐Resolution Imaging Spectrometer and Advanced Along Track Scanning Radiometer data acquired over the year 2003, using the Benguela upwelling area as a test site. The combination of the new production model with a total production model allows the seasonal variations of new and total productions (including the respective contributions of the three size classes) to be estimated and compared. Even though microphytoplankton are generally considered to be responsible for new production, our results show that the contribution of small cells should not be overlooked in the upwelling‐affected areas.

The consumption of zooplankton by early life stages of fish in the North Sea

Abstract Heath, M. R. 2007. The consumption of zooplankton by early life stages of fish in the North Sea. – ICES Journal of Marine Science, 64: 1650–1663. Previous work has shown that during the 1970s, fish and carnivorous macrozooplankton together consumed ∼22 gC m−2 year−1 of mesozooplankton, principally copepods. Consumption declined to ∼17 gC m−2 year−1 during the 1990s, mainly because of a reduction in fish production. The zooplankton production required to meet this demand seems to be approximately accounted for by estimates of new primary production, but there are additional sinks for zooplankton production attributable to predation by, for example, gelatinous species. Additionally, the consumption of zooplankton by early life stages of fish is difficult to assess and could be larger than implied by the earlier analysis. Here, the role of fish early life stages in zooplankton consumption is re-assessed, and found to be approximately double that previously estimated. Some 28% of the zooplankton consumption by fish is now estimated to be attributable to early life stages, resulting in an estimate of zooplankton consumption by the fish community as a whole 14% higher. Taken overall, the consumption of zooplankton production by fish and other planktivorous predators is now estimated to be 19–25 gC m−2 year−1.

New and regenerated production during a late summer bloom in an Arctic polynya

New and regenerated production were estimated from nitrate, ammonium and urea uptake in the highly productive North Water region (NOW, northern Baffin Bay) during the late summer bloom and its decline in early autumn 1999. Nitrogen uptake rates decreased due to a significant 4-fold reduction of the average irradiance in the euphotic zone between these 2 periods. Nitrate availability also regulated the relative uptake of nitrate (ratio of nitrate uptake to total nitrogen uptake, or f-ratio) over spatial scales in early autumn. Stations located along the Greenland coast, which had relatively warm (-0.5°C) and saline (32.5) waters, had higher nitrate concentrations (153 vs. 51 mmol N m -2 ) and f-ratios (0.36 vs. 0.16) than those of stations located on the Canadian side, where the euphotic zone was relatively colder (-1.4°C) and less saline (30.6). The f-ratios were also corrected for nitrogen uptake by heterotrophic bacteria using the results from experiments that employed specific metabolic inhibitors. The corrected f-ratio range of 0.24 to 0.41 considered only the fraction of the nitrogen uptake due to phytoplankton in order to obtain a more accurate estimate of new production. Based on this range, new production varied from 203 to 346 and 85 to 145 mg C m -2 d -1 in late summer and early autumn, respectively. For the entire sampling period, averaged new production was 132 to 228 mg C m -2 d -1 ; however, when the dissolved form was included, we estimated that new production may double to between 262 and 452 mg C m -2 d -1 . This estimate illustrates that dissolved forms can be significant and need to be considered. When combining our results with those from the literature, new production in the NOW in 1998 - 99 amounted to between 143 and 152 g C m -2 yr -1 , suggesting that 60% of the total annual primary production may potentially be exported from the euphotic zone. This study completes the first annual time series of new production in a high-latitude ecosystem.

234Th-derived particulate organic carbon export from an island-induced phytoplankton bloom in the Southern Ocean

It has long been recognised that some oceanic regions have persistently low-chlorophyll levels, even though there are abundant inorganic nutrients. Studies have shown that these high-nutrient low-chlorophyll (HNLC) areas are depleted in iron, an essential micronutrient. In these regions biological production can be enhanced with artificial mesoscale iron fertilisation. However, the ability of iron-induced blooms to efficiently sequester carbon to mesopelagic depths is still an open question. It is hypothesised that sub-Antarctic islands in the HNLC Southern Ocean are also a source of iron and thus fuel the natural phytoplankton blooms observed in their proximity, thereby enhancing levels of particulate organic carbon (POC) export. To test the third part of this hypothesis, POC export was measured in the Southern Ocean region of the Crozet Islands (52°E, 46°S) during the austral summer of 2004/2005 as part of the CROZEX project. Based on satellite imagery, a high-chlorophyll region (maximum concentration=4 μg l−1) north and downstream of the islands was distinguished from a low-chlorophyll region (typical concentration=0.3 μg l−1) south and upstream of the islands. POC export estimates were obtained by using the naturally occurring particle-reactive radionuclide tracer 234Th. POC export was initially 15 mmol C m−2 d−1 in the high-chlorophyll bloom region, compared with 5 mmol C m−2 d−1 in the low-chlorophyll, non-bloom region. After a moderately small bloom at the southern control stations (max concentration=0.7 μg l−1) the spatial variability in POC export was lost, resulting in equally high levels of POC export (ca. 20 mmol C m−2 d−1) throughout the study region. Comparison of 234Th-derived POC export with estimates of new production, calculated from nitrate budgets, revealed evidence for a decoupling of new and export production, with this effect most apparent within the northern bloom area. In addition to methodological issues this apparent decoupling of new and export production could be due to a buildup of dissolved organic nitrogen within the bloom region, thus reducing the amount of POC available for export to mesopelagic depths.

Nitrogen uptake by heterotrophic bacteria and phytoplankton in Arctic surface waters

We estimated rates of heterotrophic bacterial and phytoplankton uptake of nitrate, ammonium, and urea using 15 N-labelled nitrogen and specific metabolic inhibitors of prokaryote and eukaryote nitrogen metabolism in the surface waters of the North Water (northern Baffin Bay) during autumn that were charactenzed by the absence of cyanobactena (comprising prochlonphytes). The percentage of nitrate + ammonium uptake by heterotrophic bacteria ranged between 44 and 78% of the measured total uptake and was the highest when the phytoplankton biomass was relatively low (<2 μg Chlorophyll a L -1 ). Phytoplankton accounted for a larger fraction (e.g., 58-95%) of urea uptake than heterotrophic bacteria. When our results are combined with those from previous studies carried out in diverse temperate and polar areas, it appears that heterotrophic bacteria account for ∼25% (14-40%; median and interquartile range) of the total nitrate uptake in surface waters with chlorophyll biomass <2 μgL -1 . Estimates of new production computed from phytoplankton carbon uptake and f-ratios may be strongly overestimated in regions where nitrate uptake by heterotrophic bacteria is high and the biomass of phytoplankton is low.

An estimation of annual new production and carbon fluxes in the northeast Atlantic Ocean during 2001

A dual 13C/15N isotopic technique was used to estimate carbon and nitrogen uptake rates during the 1‐year‐long Programme Océan Multidisciplinaire Méso Echelle (POMME) experiment in the northeast basin of the Atlantic Ocean (16°–22°W, 38°–45°N). Rates of primary production ranged from 2.26 μmoles L−1 d−1 in winter to maximum surface values of 7.8 μmoles L−1 d−1 during the spring season. Nitrate assimilation was intense since the beginning of winter and accounted for 3–7 mmoles m−2 d−1 in the first 80 m depth of the water column. Rates increased to 5–9 mmoles m−2 d−1 during the spring season. NO3− uptake rates during the late summer season were close to winter values. Ammonium assimilation activity balanced the uptake of nitrate for all seasons. The seasonal f ratio was close to 0.28 in winter, increased to 0.34 in spring, and, finally, decreased to 0.25 in late summer. Annual carbon uptake rates for the entire POMME area accounted for 16.9 moles C m−2 yr−1. From this result, annual new production could be estimated to 5.7 moles C m−2 yr−1.