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  • Open Access
    Authors: 
    Marta Rodrigo-Gámiz; Sebastiaan W Rampen; H. de Haas; Marianne Baas; Stefan Schouten; J.S. Sinninghe Damsté;
    Publisher: Copernicus GmbH
    Project: NWO | Sedimentary long-chain, m... (6761), EC | PACEMAKER (226600)

    Abstract. Subpolar regions are key areas for studying natural climate variability due to their high sensitivity to rapid environmental changes, particularly through sea surface temperature (SST) variations. Here, we have tested three independent organic temperature proxies (UK'37; TEX86; and the long-chain diol index, LDI) regarding their potential applicability for SST reconstruction in the subpolar region around Iceland. UK'37, TEX86 and TEXL86 temperature estimates from suspended particulate matter showed a substantial discrepancy with instrumental data, while long-chain alkyl diols were below the detection limit at most of the stations. In the northern Iceland Basin, sedimenting particles revealed a seasonality in lipid fluxes, i.e., high fluxes of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) were measured during late spring and during summer and high fluxes of long-chain alkyl diols during late summer. The flux-weighted average temperature estimates had a significant negative (ca. 2.3 °C for UK'37) and positive (up to 5 °C for TEX86) offset with satellite-derived SSTs and temperature estimates derived from the underlying surface sediment. UK'37 temperature estimates from surface sediments around Iceland correlate well with summer mean sea surface temperatures, while TEX86-derived temperatures correspond with both annual and winter mean 0–200 m temperatures, suggesting a subsurface temperature signal. Anomalous LDI-SST values in surface sediments and low mass flux of 1,13- and 1,15-diols compared to 1,14-diols suggest that Proboscia diatoms are the major sources of long-chain alkyl diols in this area rather than eustigmatophyte algae, and therefore the LDI cannot be applied in this region.

  • Open Access English
    Authors: 
    Melchor González-Dávila; Juana Magdalena Santana-Casiano; Rana A. Fine; J. Happell; Bruno Delille; Sabrina Speich;
    Publisher: HAL CCSD
    Countries: France, Belgium

    Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT) and total alkalinity (AT) offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation. Here we present data that suggest that south of 55° S, surface water will be under-saturated with respect to aragonite within the next few decades. Belcanto

  • Open Access
    Authors: 
    Gerald Langer; Gernot Nehrke; Ian Probert; J. Ly; Patrizia Ziveri;
    Publisher: Copernicus GmbH
    Project: EC | EPOCA (211384)

    Abstract. Four strains of the coccolithophore E. huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 μatm to ~1200 μatm. Growth rate, particulate organic carbon content, and particulate inorganic carbon content were measured, and organic and inorganic carbon production calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the analysed parameters and none of the four strains displayed a response pattern previously described for this species. We conclude that the sensitivity of different strains of E. huxleyi to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature.

  • Open Access
    Authors: 
    Sandra Martínez-García; Emilio Fernández; Alejandra Calvo-Díaz; Emilio Marañón; Xosé Anxelu G. Morán; Eva Teira;
    Publisher: Centro Oceanográfico de Gijón
    Country: Spain

    Abstract. Atmospheric nutrient deposition into the open ocean increased over the past decades as a result of human activity and water-soluble organic nitrogen accounts for up to 30% of the total nitrogen inputs. The effects of inorganic and/or organic nutrient inputs on phytoplankton and heterotrophic bacteria have never been concurrently assessed in open ocean oligotrophic communities over a wide spatial gradient. We studied the effects of potentially limiting inorganic (nitrate, ammonium, phosphate, silica) and organic nutrient (glucose, aminoacids) inputs on microbial plankton biomass, community structure and metabolism in five microcosm experiments conducted along a latitudinal transect in the Atlantic Ocean (from 26° N to 29° S). Primary production rates increased up to 1.8-fold. Bacterial respiration and microbial community respiration increased up to 14.3 and 12.7-fold, respectively. Bacterial production and bacterial growth efficiency increased up to 58.8-fold and 2.5-fold, respectively. The largest increases were measured after mixed inorganic-organic nutrients additions. Changes in microbial plankton biomass were small as compared with those in metabolic rates. A north to south increase in the response of heterotrophic bacteria was observed, which could be related to a latitudinal gradient in phosphorus availability. Our results suggest that organic matter inputs associated with atmospheric deposition into the Atlantic Ocean will result in a predominantly heterotrophic versus autotrophic response and in increases in bacterial growth efficiency, particularly in the Southern Hemisphere. Subtle differences in the initial environmental and biological conditions are likely to result in differential microbial responses to inorganic and organic matter inputs.

  • Open Access English
    Authors: 
    Fernández, A.; Mouriño-Carballido, B. (Beatriz); Bode, A. (Antonio); Varela, M.; Marañón, E.;
    Publisher: Copernicus Publications
    Country: Spain

    We have determined the latitudinal distribution of Trichodesmium spp. abundance and community N2 fixation in the Atlantic Ocean along a meridional transect from ca. 30° N to 30° S in November–December 2007 and April–May 2008. The observations from both cruises were highly consistent in terms of absolute magnitude and latitudinal distribution, showing a strong association between Trichodesmium abundance and community N2 fixation. The highest Trichodesmium abundances (mean = 220 trichomes L−1,) and community N2 fixation rates (mean = 60 μmol m−2 d−1) occurred in the Equatorial region between 5° S–15° N. In the South Atlantic gyre, Trichodesmium abundance was very low (ca. 1 trichome L−1) but N2 fixation was always measurable, averaging 3 and 10 μmol m2 d−1 in 2007 and 2008, respectively. We suggest that N2 fixation in the South Atlantic was sustained by other, presumably unicellular, diazotrophs. Comparing these distributions with the geographical pattern in atmospheric dust deposition points to iron supply as the main factor determining the large scale latitudinal variability of Trichodesmium spp. abundance and N2 fixation in the Atlantic Ocean. We observed a marked South to North decrease in surface phosphate concentration, which argues against a role for phosphorus availability in controlling the large scale distribution of N2 fixation. Scaling up from all our measurements (42 stations) results in conservative estimates for total N2 fixation of ∼6 TgN yr−1 in the North Atlantic (0–40° N) and ~1.2 TgN yr−1 in the South Atlantic (0–40° S).

  • Open Access English
    Authors: 
    M. Stabholz; X. Durrieu de Madron; Miquel Canals; Alexis Khripounoff; Isabelle Taupier-Letage; Pierre Testor; Serge Heussner; Philippe Kerhervé; N. Delsaut; Loïc Houpert; +2 more
    Publisher: HAL CCSD
    Countries: Spain, Spain, United Kingdom, France
    Project: EC | HERMIONE (226354)

    The deep outer margin of the Gulf of Lions and the adjacent basin, in the western Mediterranean Sea, are regularly impacted by open-ocean convection, a major hydrodynamic event responsible for the ventilation of the deep water in the western Mediterranean Basin. However, the impact of open-ocean convection on the flux and transport of particulate matter remains poorly understood. The variability of water mass properties (i.e., temperature and salinity), currents, and particle fluxes were monitored between September 2007 and April 2009 at five instrumented mooring lines deployed between 2050 and 2350-m depth in the deepest continental margin and adjacent basin. Four of the lines followed a NW–SE transect, while the fifth one was located on a sediment wave field to the west. The results of the main, central line SC2350 ("LION") located at 42°02.5&prime; N, 4°41&prime; E, at 2350-m depth, show that open-ocean convection reached mid-water depth (&asymp; 1000-m depth) during winter 2007–2008, and reached the seabed (&asymp; 2350-m depth) during winter 2008–2009. Horizontal currents were unusually strong with speeds up to 39 cm s<sup>−1</sup> during winter 2008–2009. The measurements at all 5 different locations indicate that mid-depth and near-bottom currents and particle fluxes gave relatively consistent values of similar magnitude across the study area except during winter 2008–2009, when near-bottom fluxes abruptly increased by one to two orders of magnitude. Particulate organic carbon contents, which generally vary between 3 and 5%, were abnormally low (&le; 1%) during winter 2008–2009 and approached those observed in surface sediments (&asymp; 0.6%). Turbidity profiles made in the region demonstrated the existence of a bottom nepheloid layer, several hundred meters thick, and related to the resuspension of bottom sediments. These observations support the view that open-ocean deep convection events in the Gulf of Lions can cause significant remobilization of sediments in the deep outer margin and the basin, with a subsequent alteration of the seabed likely impacting the functioning of the deep-sea ecosystem.

  • Open Access English
    Authors: 
    Albert-Miquel Sánchez; Jaume Piera;
    Publisher: Copernicus Publications
    Country: Spain
    Project: EC | CITCLOPS (308469)

    The scattering properties of aquatic suspended particles have many optical applications. Several data inversion methods have been proposed to estimate important features of particles, such as their size distribution or their refractive index. Most of the proposed methods are based on the Lorenz–Mie theory to solve Maxwell's equations, where particles are considered homogeneous spheres. A generalization that allows consideration of more complex-shaped particles is the T-matrix method. Although this approach imposes some geometrical restrictions (particles must be rotationally symmetrical) it is applicable to many life forms of phytoplankton. In this paper, three different scenarios are considered in order to compare the performance of several inversion methods for retrieving refractive indices. The error associated with each method is discussed and analyzed. The results suggest that inverse methods using the T-matrix approach are useful to accurately retrieve the refractive indices of particles with complex shapes, such as for many phytoplankton organisms This work was supported by the Spanish National Research Council (CSIC) under the EU Citclops Project (FP7-ENV-308469), the MESTRAL project (CTM2011-30489-C02-01), and the CSIC ADOICCO project (Ref 201530E063) 18 pages, 19 figures, 2 tables Peer Reviewed

  • Open Access English
    Authors: 
    L. T. Bach; A. J. Paul; T. Boxhammer; E. von der Esch; M. Graco; K. G. Schulz; E. Achterberg; P. Aguayo; J. Arístegui; P. Ayón; +41 more
    Publisher: Copernicus Publications
    Countries: Germany, Peru, Denmark

    Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.

  • Publication . Article . Other literature type . Preprint . 2013
    Open Access
    Authors: 
    Raquel Vaquer-Sunyer; Carlos M. Duarte; Aurore Regaudie-de-Gioux; Johnna Holding; Lara S. Garcia-Corral; Marit Reigstad; Paul Wassmann;
    Publisher: Copernicus GmbH
    Countries: Norway, France, Spain
    Project: EC | ATP (226248)

    The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer), one in 2010 (spring) and one in 2011 (spring). The results show that the metabolism of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom and water temperature. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis of metabolic rates in the Arctic Ocean, and especially in the European Arctic corridor. Additionally, a rough annual metabolic estimate for this area of the Arctic Ocean was calculated, resulting in a net community production of 108 g C m−2 yr−1 Hay una corrección que solo implica el orden de los autores (Biogeosciences 10: 2347 [2013]; DOI 10.5194/bg-10-2347-2013) Peer reviewed

  • Publication . Article . Other literature type . Preprint . 2019
    Open Access English
    Authors: 
    E. A. Courtois; E. A. Courtois; C. Stahl; B. Burban; J. Van den Berge; D. Berveiller; L. Bréchet; L. Bréchet; J. L. Soong; J. L. Soong; +4 more
    Countries: France, United States, Belgium, Spain
    Project: EC | IMBALANCE-P (610028), ANR | ANAEE-FR (ANR-11-INBS-0001), EC | RainForest-GHG (796438)

    Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.

Advanced search in Research products
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The following results are related to European Marine Science. Are you interested to view more results? Visit OpenAIRE - Explore.
112 Research products, page 1 of 12
  • Open Access
    Authors: 
    Marta Rodrigo-Gámiz; Sebastiaan W Rampen; H. de Haas; Marianne Baas; Stefan Schouten; J.S. Sinninghe Damsté;
    Publisher: Copernicus GmbH
    Project: NWO | Sedimentary long-chain, m... (6761), EC | PACEMAKER (226600)

    Abstract. Subpolar regions are key areas for studying natural climate variability due to their high sensitivity to rapid environmental changes, particularly through sea surface temperature (SST) variations. Here, we have tested three independent organic temperature proxies (UK'37; TEX86; and the long-chain diol index, LDI) regarding their potential applicability for SST reconstruction in the subpolar region around Iceland. UK'37, TEX86 and TEXL86 temperature estimates from suspended particulate matter showed a substantial discrepancy with instrumental data, while long-chain alkyl diols were below the detection limit at most of the stations. In the northern Iceland Basin, sedimenting particles revealed a seasonality in lipid fluxes, i.e., high fluxes of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) were measured during late spring and during summer and high fluxes of long-chain alkyl diols during late summer. The flux-weighted average temperature estimates had a significant negative (ca. 2.3 °C for UK'37) and positive (up to 5 °C for TEX86) offset with satellite-derived SSTs and temperature estimates derived from the underlying surface sediment. UK'37 temperature estimates from surface sediments around Iceland correlate well with summer mean sea surface temperatures, while TEX86-derived temperatures correspond with both annual and winter mean 0–200 m temperatures, suggesting a subsurface temperature signal. Anomalous LDI-SST values in surface sediments and low mass flux of 1,13- and 1,15-diols compared to 1,14-diols suggest that Proboscia diatoms are the major sources of long-chain alkyl diols in this area rather than eustigmatophyte algae, and therefore the LDI cannot be applied in this region.

  • Open Access English
    Authors: 
    Melchor González-Dávila; Juana Magdalena Santana-Casiano; Rana A. Fine; J. Happell; Bruno Delille; Sabrina Speich;
    Publisher: HAL CCSD
    Countries: France, Belgium

    Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT) and total alkalinity (AT) offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation. Here we present data that suggest that south of 55° S, surface water will be under-saturated with respect to aragonite within the next few decades. Belcanto

  • Open Access
    Authors: 
    Gerald Langer; Gernot Nehrke; Ian Probert; J. Ly; Patrizia Ziveri;
    Publisher: Copernicus GmbH
    Project: EC | EPOCA (211384)

    Abstract. Four strains of the coccolithophore E. huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 μatm to ~1200 μatm. Growth rate, particulate organic carbon content, and particulate inorganic carbon content were measured, and organic and inorganic carbon production calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the analysed parameters and none of the four strains displayed a response pattern previously described for this species. We conclude that the sensitivity of different strains of E. huxleyi to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature.

  • Open Access
    Authors: 
    Sandra Martínez-García; Emilio Fernández; Alejandra Calvo-Díaz; Emilio Marañón; Xosé Anxelu G. Morán; Eva Teira;
    Publisher: Centro Oceanográfico de Gijón
    Country: Spain

    Abstract. Atmospheric nutrient deposition into the open ocean increased over the past decades as a result of human activity and water-soluble organic nitrogen accounts for up to 30% of the total nitrogen inputs. The effects of inorganic and/or organic nutrient inputs on phytoplankton and heterotrophic bacteria have never been concurrently assessed in open ocean oligotrophic communities over a wide spatial gradient. We studied the effects of potentially limiting inorganic (nitrate, ammonium, phosphate, silica) and organic nutrient (glucose, aminoacids) inputs on microbial plankton biomass, community structure and metabolism in five microcosm experiments conducted along a latitudinal transect in the Atlantic Ocean (from 26° N to 29° S). Primary production rates increased up to 1.8-fold. Bacterial respiration and microbial community respiration increased up to 14.3 and 12.7-fold, respectively. Bacterial production and bacterial growth efficiency increased up to 58.8-fold and 2.5-fold, respectively. The largest increases were measured after mixed inorganic-organic nutrients additions. Changes in microbial plankton biomass were small as compared with those in metabolic rates. A north to south increase in the response of heterotrophic bacteria was observed, which could be related to a latitudinal gradient in phosphorus availability. Our results suggest that organic matter inputs associated with atmospheric deposition into the Atlantic Ocean will result in a predominantly heterotrophic versus autotrophic response and in increases in bacterial growth efficiency, particularly in the Southern Hemisphere. Subtle differences in the initial environmental and biological conditions are likely to result in differential microbial responses to inorganic and organic matter inputs.

  • Open Access English
    Authors: 
    Fernández, A.; Mouriño-Carballido, B. (Beatriz); Bode, A. (Antonio); Varela, M.; Marañón, E.;
    Publisher: Copernicus Publications
    Country: Spain

    We have determined the latitudinal distribution of Trichodesmium spp. abundance and community N2 fixation in the Atlantic Ocean along a meridional transect from ca. 30° N to 30° S in November–December 2007 and April–May 2008. The observations from both cruises were highly consistent in terms of absolute magnitude and latitudinal distribution, showing a strong association between Trichodesmium abundance and community N2 fixation. The highest Trichodesmium abundances (mean = 220 trichomes L−1,) and community N2 fixation rates (mean = 60 μmol m−2 d−1) occurred in the Equatorial region between 5° S–15° N. In the South Atlantic gyre, Trichodesmium abundance was very low (ca. 1 trichome L−1) but N2 fixation was always measurable, averaging 3 and 10 μmol m2 d−1 in 2007 and 2008, respectively. We suggest that N2 fixation in the South Atlantic was sustained by other, presumably unicellular, diazotrophs. Comparing these distributions with the geographical pattern in atmospheric dust deposition points to iron supply as the main factor determining the large scale latitudinal variability of Trichodesmium spp. abundance and N2 fixation in the Atlantic Ocean. We observed a marked South to North decrease in surface phosphate concentration, which argues against a role for phosphorus availability in controlling the large scale distribution of N2 fixation. Scaling up from all our measurements (42 stations) results in conservative estimates for total N2 fixation of ∼6 TgN yr−1 in the North Atlantic (0–40° N) and ~1.2 TgN yr−1 in the South Atlantic (0–40° S).

  • Open Access English
    Authors: 
    M. Stabholz; X. Durrieu de Madron; Miquel Canals; Alexis Khripounoff; Isabelle Taupier-Letage; Pierre Testor; Serge Heussner; Philippe Kerhervé; N. Delsaut; Loïc Houpert; +2 more
    Publisher: HAL CCSD
    Countries: Spain, Spain, United Kingdom, France
    Project: EC | HERMIONE (226354)

    The deep outer margin of the Gulf of Lions and the adjacent basin, in the western Mediterranean Sea, are regularly impacted by open-ocean convection, a major hydrodynamic event responsible for the ventilation of the deep water in the western Mediterranean Basin. However, the impact of open-ocean convection on the flux and transport of particulate matter remains poorly understood. The variability of water mass properties (i.e., temperature and salinity), currents, and particle fluxes were monitored between September 2007 and April 2009 at five instrumented mooring lines deployed between 2050 and 2350-m depth in the deepest continental margin and adjacent basin. Four of the lines followed a NW–SE transect, while the fifth one was located on a sediment wave field to the west. The results of the main, central line SC2350 ("LION") located at 42°02.5&prime; N, 4°41&prime; E, at 2350-m depth, show that open-ocean convection reached mid-water depth (&asymp; 1000-m depth) during winter 2007–2008, and reached the seabed (&asymp; 2350-m depth) during winter 2008–2009. Horizontal currents were unusually strong with speeds up to 39 cm s<sup>−1</sup> during winter 2008–2009. The measurements at all 5 different locations indicate that mid-depth and near-bottom currents and particle fluxes gave relatively consistent values of similar magnitude across the study area except during winter 2008–2009, when near-bottom fluxes abruptly increased by one to two orders of magnitude. Particulate organic carbon contents, which generally vary between 3 and 5%, were abnormally low (&le; 1%) during winter 2008–2009 and approached those observed in surface sediments (&asymp; 0.6%). Turbidity profiles made in the region demonstrated the existence of a bottom nepheloid layer, several hundred meters thick, and related to the resuspension of bottom sediments. These observations support the view that open-ocean deep convection events in the Gulf of Lions can cause significant remobilization of sediments in the deep outer margin and the basin, with a subsequent alteration of the seabed likely impacting the functioning of the deep-sea ecosystem.

  • Open Access English
    Authors: 
    Albert-Miquel Sánchez; Jaume Piera;
    Publisher: Copernicus Publications
    Country: Spain
    Project: EC | CITCLOPS (308469)

    The scattering properties of aquatic suspended particles have many optical applications. Several data inversion methods have been proposed to estimate important features of particles, such as their size distribution or their refractive index. Most of the proposed methods are based on the Lorenz–Mie theory to solve Maxwell's equations, where particles are considered homogeneous spheres. A generalization that allows consideration of more complex-shaped particles is the T-matrix method. Although this approach imposes some geometrical restrictions (particles must be rotationally symmetrical) it is applicable to many life forms of phytoplankton. In this paper, three different scenarios are considered in order to compare the performance of several inversion methods for retrieving refractive indices. The error associated with each method is discussed and analyzed. The results suggest that inverse methods using the T-matrix approach are useful to accurately retrieve the refractive indices of particles with complex shapes, such as for many phytoplankton organisms This work was supported by the Spanish National Research Council (CSIC) under the EU Citclops Project (FP7-ENV-308469), the MESTRAL project (CTM2011-30489-C02-01), and the CSIC ADOICCO project (Ref 201530E063) 18 pages, 19 figures, 2 tables Peer Reviewed

  • Open Access English
    Authors: 
    L. T. Bach; A. J. Paul; T. Boxhammer; E. von der Esch; M. Graco; K. G. Schulz; E. Achterberg; P. Aguayo; J. Arístegui; P. Ayón; +41 more
    Publisher: Copernicus Publications
    Countries: Germany, Peru, Denmark

    Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.

  • Publication . Article . Other literature type . Preprint . 2013
    Open Access
    Authors: 
    Raquel Vaquer-Sunyer; Carlos M. Duarte; Aurore Regaudie-de-Gioux; Johnna Holding; Lara S. Garcia-Corral; Marit Reigstad; Paul Wassmann;
    Publisher: Copernicus GmbH
    Countries: Norway, France, Spain
    Project: EC | ATP (226248)

    The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer), one in 2010 (spring) and one in 2011 (spring). The results show that the metabolism of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom and water temperature. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis of metabolic rates in the Arctic Ocean, and especially in the European Arctic corridor. Additionally, a rough annual metabolic estimate for this area of the Arctic Ocean was calculated, resulting in a net community production of 108 g C m−2 yr−1 Hay una corrección que solo implica el orden de los autores (Biogeosciences 10: 2347 [2013]; DOI 10.5194/bg-10-2347-2013) Peer reviewed

  • Publication . Article . Other literature type . Preprint . 2019
    Open Access English
    Authors: 
    E. A. Courtois; E. A. Courtois; C. Stahl; B. Burban; J. Van den Berge; D. Berveiller; L. Bréchet; L. Bréchet; J. L. Soong; J. L. Soong; +4 more
    Countries: France, United States, Belgium, Spain
    Project: EC | IMBALANCE-P (610028), ANR | ANAEE-FR (ANR-11-INBS-0001), EC | RainForest-GHG (796438)

    Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.