[Corrigendum to] Effects of small-scale turbulence on lower trophic levels under different nutrient conditions [vol 32, pg 197, 2010]

Small-scale turbulence affects the pelagic food web and energy flow in marine systems and the impact is related to nutrient conditions and the assemblage of organisms present. We generated five levels of turbulence (2*10 29 to 1*10 24 W kg 21 ) in land-based mesocosms (volume 2.6 m 3 ) with and without additional nutrients (31:16:1 Si:N:P m M) to asses the effect of small-scale turbulence on the lower part of the pelagic food web under different nutrient conditions. The ecological influence of nutrients and small-scale turbulence on lower trophic levels was quantified using multivariate statistics (RDA), where nutrients accounted for 31.8% of the observed biological variation, while 7.2% of the variation was explained by small-scale turbulence and its interaction with nutrients. Chlorophyll a, primary production rates, bacterial production rates and diatom and dinoflagellate abundance were positively correlated to turbulence, regardless of nutrient conditions. Abundance of autotrophic flagellates, total phytoplankton and bacteria were positively correlated to turbulence only when nutrients were added. Impact of small-scale turbulence was related to nutrient con- ditions, with implications for oligotrophic and eutrophic situations. The effect on community level was also different compared to single species level. Microbial processes drive biogeochemical cycles, and nutrient-controlled effects of small-scale turbulence on such processes are relevant to foresee altered carbon flow in marine systems

Increased CO2 and iron availability effects on carbon assimilation and calcification on the formation of Emiliania huxleyi blooms in a coastal phytoplankton community

In the present work, we exposed a natural phytoplankton community to either present (390-μatm, LC) or future CO2 levels predicted for year-2100 (900-μatm, HC) combined with ambient (4.5 nmol L−1, −DFB) or high (12 nmol L−1, +DFB) dissolved iron (dFe) levels, during 25 days by using mesocosms. We report on changes in carbon assimilation processes (acquisition, fixation, and calcification) of the phytoplankton community due to increased dissolved CO2 and dFe and to the interaction of both factors. The isotopic disequilibrium assay results showed that inorganic carbon (Ci) acquisition by the community was unaffected by CO2 and Fe availability. The main Ci source for photosynthesis was bicarbonate and external carbonic anhydrase activity was only detected at the beginning of the experiment, suggesting a relevant role for bicarbonate transporters in the phytoplankton community developed in all treatments. However, there was a significant effect of both factors on particulate organic carbon (POC) content, particulate calcium production and carbon fixation rates. Increased dFe at LC conditions led to the highest values of carbon fixation and POC of all treatments, promoting a massive Emiliania huxleyi bloom. This response was not observed in the HC treatments. The latter indicates a negative impact of increased CO2 on the formation of E. huxleyi blooms, in agreement with the observed significant reduction in calcium production under HC. Our results suggest that ocean acidification can decrease primary production under iron-replete conditions in E. huxleyi blooming areas, affecting the biological carbon pump in coastal ecosystems

Can silicate and turbulence regulate the vertical flux of biogenic matter? A mesocosm study

The effects of silicate and turbulence on the vertical flux of biogenic matter were studied in mesocosms. The experiment consisted of eight 27 m3 enclosures all fertilised with nitrate and phosphate (NP), while 4 of the enclosures were supplied with silicate as well (NPS). A 2-layer density gradient was created, and turbulence was generated at 2 intensity levels in the upper layer of the enclosures by a vertically moving grid. We tested the hypotheses that: (1) dissolved silicate (DSi) has a strong regulating effect on biogenic sedimentation by favouring the growth of diatoms instead of flagellates; (2) there is a positive linear relationship between DSi consumption and carbon export; and (3) elevated levels of turbulence would further increase the loss rates of diatoms through aggregate formation. Addition of DSi caused higher primary production and a shift from a flagellate to diatom-dominated phytoplankton community. However, contrary to expectations, sedimentation of chla was lower (<15 mg m–2 d–1) where diatoms dominated than where flagellates prevailed (≤80 mg m–2 d–1). The hypothesised linear relationship between addition of DSi and vertical export was thus not found in this experiment. The 2 levels of turbulence caused no statistically significant differences in the suspended concentrations or sedimentation rates of phytoplankton groups. In conclusion, DSi triggered a diatom bloom with stable sedimentation rates in the NPS replicates, while comparatively higher loss rates were found in the flagellate-dominated NP enclosures. Turbulence had little effect on the phytoplankton community and sedimentation of biogenic matter

Suplementos constantes vs pulsos de nutrientes (N, P y Si): efecto sobre el fitoplancton, mesozooplancton y en el flujo de materia biogénica

An experiment with eight vertically stratified seawater enclosures of 27 m3 (depth 9.3 m, diameter 2 m, 90% penetration of PAR) was run in order to test whether pulsed addition of nutrients may cause: 1, higher primary production; 2, higher build-up of phytoplankton biomass; 3, larger temporal mismatch between herbivores and phytoplankton biomass; and 4, higher sedimentation rates, distinguishing in each case between silicate and non-silicate fertilised systems. Nitrate and phosphate were added to all enclosures (NP), while silicate was added to four of the enclosures (NPS). Each enclosure received the same total amount of nutrients, but the nutrients were supplied at four different intervals ranging from one single load to continuous additions. Spring bloom-like systems developed where nutrients were added in one or two pulses as they were characterised by high primary production, high suspended biomass of chlorophyll a (Chl a) and particulate organic carbon (POC) and high sedimentation rates. In contrast, the seawater enclosures receiving nutrients about every third day or in a continuous supply resembled regenerated systems with low concentrations of suspended Chl a and POC and with low and stable loss rates. Due to a typical autumn inoculum with dominance of dinoflagellates and flagellates, diatoms did not dominate the NPS enclosures. The only significant effect of the silicate addition was higher vertical flux of particulate organic nitrogen in the NPS enclosures, and higher microzooplankton biomass. The mesozooplankton did not show responses to the different frequencies of nutrient additions. However, accumulation of mesozooplankton biomass was higher in the NP-mesocosms, probably reflecting better feeding conditions. We conclude that the frequency of nutrient additions had a stronger influence on the development of the phytoplankton and vertical flux of carbon than the +/- silicate treatment in this experiment.Se realizó un experimento en agua de mar verticalmente estratificada y confinada en ocho mesocosmos de 27 m3 (9.3 m de profundidad, 2 m de diámetro, 90% de penetración de luz), con el fin de comprobar si la adición de pulsos de nutrientes puede causar: 1. Un incremento de la producción primaria, 2. Un incremento en la biomasa de fitoplancton, 3. Aumento temporal de la desincronización entre los hervíboros y la biomasa de fitoplancton. 4. Aumento de la tasa de sedimentación y si la respuesta de 1-4 puede ser distinta en sistemas fertilizados con y sin silicato. A todos los mesocosmos se añadía nitrato y fosfato (NP), mientras que el silicato solo se añadió a cuatro de los mesocosmos (NPS). Cada mesocosmo recibía la misma cantidad total de nutrientes, pero los nutrientes eran administrados en 4 intervalos diferentes, variando desde una única adición a adiciones en continuo. En los mesocosmos donde los nutrientes se habían añadido en uno o dos pulsos se desarrollaba una proliferación algal semejante a la de primavera, caracterizado por una elevada producción primaria, una elevada biomasa suspendida de clorofila a (chl a) y carbono orgánico particulado (POC) y una elevada tasa de sedimentación. En cambio los mesocosmos que recibían nutrientes una vez cada tres días o en adiciones continuadas, se comportaban como sistemas regenerados con bajas concentraciones de Chl a y POC suspendidos y bajas y estables tasas de pérdidas. Debido a un inóculo típico de otoño con dominancia de dinoflagelados y flagelados, las diatomeas no dominaban los mesocosmos NPS. El único efecto significativo de las adiciones de silicato era el de incrementar el flujo vertical de nitrógeno orgánico en los mesocosmos NPS y aumentar la biomasa de microzooplancton. El mesozooplancton no mostraba ninguna respuesta a las diferentes frecuencias de adición de nutrientes. Sin embargo, la acumulación de biomasa de mesozooplancton era más elevada en los NP-mesocosmos, probablemente reflejando mejores condiciones de alimentación. Concluimos que la frecuencia en la adición de nutrientes tenía una influencia más acusada en el desarrollo del fitoplancton y del flujo vertical de carbono que la adición o no adición de silicato en este experimento

Viral, bacterial and ciliate abundance and viral-bacterial diversity in mesocosm experiments, 2007-2008, Kongsfjorden

Two mesocosm experiments, PAME-I and PAME-II were conducted in 2007 and 2008 to investigate fate of organic carbon in the arctic microbial food web. Mesocosms were nutrient fertilized initially to induce phytoplankton bloom development. In PAME-I eight units (each 700 L) formed two four point gradients of additional DOC in form of glucose (0, 0.5, 1 and 3 times Redfield ratio in terms of carbon relative to the nitrogen and phosphorus additions) (Fig. 1). All the eight units also got a daily dose of NH4+ and PO4**3- in Redfield ratio. Two gradients were set up, one with silicate addition, performed in the Arctic location Ny Ålesund, Svalbard, have previously been reported to give different food-web level responses to similar nutrient perturbations. In PAME-II all ten units (each 900 L) formed two four point gradients of additional DOC in form of glucose (0, 0.5, 1, 2 and 3 times Redfield ratio in terms of carbon relative to nitrogen and phosphorus additions). The two gradients in glucose were kept silicate replete. NH4+ was used as the DIN source in one gradient (units 1 to 5) and NO3- in the other (units 6-9). All units got a daily dose of PO4**3- in Redfield ratio. Prokaryotes and viruses were measured by flow cytometry, while ciliate abundances were counted using a Flow Cam. Viral and bacterial diversity was measured by PFGE and DGGE, respectively. In PAME-II the abundance of ciliates was lower than in PAME-I, presumably caused by higher copepod grazing. The abundances of prokaryotes and viruses were also lower in PAME-II compared to PAME-I. Further, less diversity was detected in the viral community (FCM and PFGE) in PAME-II, and no response was observed in the bacterial community structure due to addition of organic carbon

CarbonBridge 2014: Physical oceanography and microorganism composition during 5 cruises (Jan, March, May, August, Nov 2014) on and off the shelf northwest of Svalbard in 2014

Data were collected on and off the shelf northwest of Svalbard during cruises in January, March, May, August and November 2014. The sampling depths were 1, 5, 10, 20, 30, 50, 100, 200, 500, 750, and 1000 m, as well as at the depth of the Chl a maximum. The sampling concentrated on the core of the northwards drifting warm Atlantic water, which enters the Arctic Ocean north of Svalbard either south or north of the Yermark plateau. Transects were sampled across the core of the Atlantic water inflow at 79N, and additionally at 79.4N in May and August. Heavy drift ice restricted the sampling to the shelf and shelf-break in May and August 2014. During January, March, and November, the area north of Svalbard was largely ice-free, which allowed sampling off the shelf-break into the Arctic Ocean during winter. At all stations, depth profiles of temperature, salinity and fluorescence were taken with a CTD (Seabird SBE 911 plus). Water was sampled with Niskin bottles from discrete depths for analysis of inorganic nutrients, chlorophyll a (Chl a), microbial abundance, bacterial production (BP), as well as DOM and POM. In May and August, three process stations each (in datasheet referred to as P-stations: P1, P3, P4 in May, and P5, P6, P7 in August, at these stations more time-demanding processes were investigated, such as in situ primary production and vertical export of POM. Chl a was determined by filterig 100-500mL water onto Whatmann GF/F glass fiber filters. Chl a was determined fluorometrically (10-AU, Turner Designs) from triplicates of each filter type after extraction in 5 mL methanol at room temperature in the dark for 12 h without grinding. Abundances of microorganisms: picophytoplankton, nanophytoplankton, virus, heterotrophic bacteria, and heterotrophic nanoflagellates were determined on an Attune(R) Focusing Flow Cytometer (Applied Biosystems by Life technologies) with a syringe-based fluidic system and a 20 mW 488 nm (blue) laser. Samples were fixed with glutaraldehyde (0.5% final conc.) at 4°C for minimum 2 h, shock frozen in liquid nitrogen, and stored at -80 °C until analysis. Total organic carbon (TOC) in unfiltered seawater was analyzed by high temperature combustion using a Shimadzu TOC-VCSH. All samples were acidified with HCl (to a pH of around 2) and bubbled with pure N2 gas in order to remove any inorganic carbon. Calibration was performed using deep seawater and low carbon reference waters. A blank consisting of milliQ water was analyzed every eighth sample to assess the day-to-day instrument variability. Concentration of total nitrogen (TN) was determined simultaneously by high temperature combustion using a CPH-TN nitrogen analyzer. Total organic nitrogen (TON) was calculated by subtracting the inorganic nitrogen (NOx = NO3 + NO2 + NH4+) measured from parallel nutrient samples. The instrument was calibrated using a standard series of acetoanilide and the accuracy of the instrument was evaluated using seawater reference material provided by the Hansell CRM (consensus reference material) program. For analysis of particulate organic carbon (POC) and particulate organic nitrogen (PON), triplicate subsamples (100 - 500 mL) were filtered onto precombusted Whatman GF/F glass-fibre filters (450°C for 5 h), dried at 60°C for 24 h and analyzed on-shore with a Leeman Lab CEC 440 CHN analyzer. Prior to analysis, the dried samples were fumed by concentrated HCl in 24 h before re-drying at 60°C for 24 h to remove inorganic carbon. Unfiltered seawater was filled directly from the Niskin bottles into 30 mL acid washed HDPE bottles and stored at -20°C. Nitrite and nitrate (NO-2 + NO- 3 ), phosphate (PO3- 4 ) and silicic acid (H4SiO4) were measured on a Smartchem200 (by AMS Alliance) autoanalyser following procedures as outlined in Wood et al. (1967) for NO-3 + NO-2 , Murphy and Riley (1962) for PO3-4 and Koroleff (1983) for the determination of H4SiO4. The determination of NO-3 was done by reduction to NO-2 on a built-in cadmium column, which was loaded prior to every sample run. Seven-point standard curves were made prior to every run. Two internal standards and one blank were inserted for every 8 samples and these were used to correct for any drift in the measurements. Concentration of NH+4 was determined directly in fresh samples using ortho-phthaladehyde according to Holmes et al. (1999

Effects of small-scale turbulence on lower trophic levels under different nutrient conditions

Small-scale turbulence affects the pelagic food web and energy flow in marine systems and the impact is related to nutrient conditions and the assemblage of organisms present. We generated five levels of turbulence (2*10−9 to 1*10−4 W kg−1) in land-based mesocosms (volume 2.6 m3) with and without additional nutrients (31:16:1 Si:N:P μM) to asses the effect of small-scale turbulence on the lower part of the pelagic food web under different nutrient conditions. The ecological influence of nutrients and small-scale turbulence on lower trophic levels was quantified using multivariate statistics (RDA), where nutrients accounted for 31.8% of the observed biological variation, while 7.2% of the variation was explained by small-scale turbulence and its interaction with nutrients. Chlorophyll a, primary production rates, bacterial production rates and diatom and dinoflagellate abundance were positively correlated to turbulence, regardless of nutrient conditions. Abundance of autotrophic flagellates, total phytoplankton and bacteria were positively correlated to turbulence only when nutrients were added. Impact of small-scale turbulence was related to nutrient conditions, with implications for oligotrophic and eutrophic situations. The effect on community level was also different compared to single species level. Microbial processes drive biogeochemical cycles, and nutrient-controlled effects of small-scale turbulence on such processes are relevant to foresee altered carbon flow in marine systems