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  • 1
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    Niche construction by non-diazotrophs for N2 fixers in the eastern tropical North Atlantic Ocean (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 44 (13). pp. 6904-6913.
    Details
    Publication Date: 2020-02-06
    Description: Diazotrophic dinitrogen (N2) fixation contributes ~76% to "new" nitrogen inputs to the sunlit open ocean, but environmental factors determining N2 fixation rates are not well constrained. Excess phosphate (phosphate-nitrate/16 〉 0) and iron availability control N2 fixation rates in the eastern tropical North Atlantic (ETNA), but it remains an open question how excess phosphate is generated within or supplied to the phosphate-depleted sunlit layer. Our observations in the ETNA region (8°N-15°N, 19°W-23°W) suggest that Prochlorococcus and Synechococcus, the two ubiquitous non-diazotrophic cyanobacteria with cellular N:P ratios higher than the Redfield ratio, create an environment of excess phosphate, which cannot be explained by diapycnal mixing, atmospheric, and riverine inputs. Thus, our results unveil a new biogeochemical niche construction mechanism by non-diazotrophic cyanobacteria for their diazotrophic phylum group members (N2 fixers). Our observations may help to understand the prevalence of diazotrophy in low-phosphate, oligotrophic regions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2017GL074218
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    In situ imaging reveals the biomass of giant protists in the global ocean (2016)
    Nature Research
    In:  Nature, 532 (7600). pp. 504-507.
    Details
    Publication Date: 2019-09-23
    Description: Planktonic organisms play crucial roles in oceanic food webs and global biogeochemical cycles(1,2). Most of our knowledge about the ecological impact of large zooplankton stems from research on abundant and robust crustaceans, and in particular copepods(3,4). A number of the other organisms that comprise planktonic communities are fragile, and therefore hard to sample and quantify, meaning that their abundances and effects on oceanic ecosystems are poorly understood. Here, using data from a worldwide in situ imaging survey of plankton larger than 600 mu m, we show that a substantial part of the biomass of this size fraction consists of giant protists belonging to the Rhizaria, a super-group of mostly fragile unicellular marine organisms that includes the taxa Phaeodaria and Radiolaria ( for example, orders Collodaria and Acantharia). Globally, we estimate that rhizarians in the top 200 m of world oceans represent a standing stock of 0.089 Pg carbon, equivalent to 5.2% of the total oceanic biota carbon reservoir(5). In the vast oligotrophic intertropical open oceans, rhizarian biomass is estimated to be equivalent to that of all other mesozooplankton ( plankton in the size range 0.2-20 mm). The photosymbiotic association of many rhizarians with microalgae may be an important factor in explaining their distribution. The previously overlooked importance of these giant protists across the widest ecosystem on the planet(6) changes our understanding of marine planktonic ecosystems.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature17652
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Springtime zooplankton size structure over the continental shelf of the Bay of BiscaY (2014)
    Copernicus Publications (EGU)
    In:  Ocean Science, 10 (5). pp. 821-835.
    Details
    Publication Date: 2019-09-23
    Description: Linking lower and higher trophic levels requires special focus on the essential role played by mid-trophic levels, i.e., the zooplankton. One of the most relevant pieces of information regarding zooplankton in terms of flux of energy lies in its size structure. In this study, an extensive data set of size measurements is presented, covering parts of the western European continental shelf and slope, from the Galician coast to the Ushant front, during the springs from 2005 to 2012. Zooplankton size spectra were estimated using measurements carried out in situ with the Laser Optical Plankton Counter (LOPC) and with an image analysis of WP2 net samples (200 μm mesh size) performed following the ZooScan methodology. The LOPC counts and sizes particles within 100–2000 μm of spherical equivalent diameter (ESD), whereas the WP2/ZooScan allows for counting, sizing and identification of zooplankton from ~ 400 μm ESD. The difference between the LOPC (all particles) and the WP2/ZooScan (zooplankton only) was assumed to provide the size distribution of non-living particles, whose descriptors were related to a set of explanatory variables (including physical, biological and geographic descriptors). A statistical correction based on these explanatory variables was further applied to the LOPC size distribution in order to remove the non-living particles part, and therefore estimate the size distribution of zooplankton. This extensive data set provides relevant information about the zooplankton size distribution variability, productivity and trophic transfer efficiency in the pelagic ecosystem of the Bay of Biscay at a regional and interannual scale.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/os-10-821-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 27 (3). pp. 871-881.
    Details
    Publication Date: 2018-03-19
    Description: A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO4), and the 300 km2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to ≥0.40. Silicic acid (〈2 µmol L−1) limited diatoms, which contributed 〈10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC m−2 d−1, probably ±20%. 234Th profiles implied constant export of ~6.3 mmol POC m−2 d−1 in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly 〈1.1 mmol POC m−2 d−1, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/gbc.20077
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Nitrogen Fuelling of the Pelagic Food Web of the Tropical Atlantic (2015)
    Public Library of Science
    In:  PLoS ONE, 10 (6). e0131258.
    Details
    Publication Date: 2019-09-23
    Description: We estimated the relative contribution of atmosphere (ic Nitrogen (N) input (wet and dry deposition and N fixation) to the epipelagic food web by measuring N isotopes of different functional groups of epipelagic zooplankton along 23°W (17°N-4°S) and 18°N (20-24°W) in the Eastern Tropical Atlantic. Results were related to water column observations of nutrient distribution and vertical diffusive flux as well as colony abundance of Trichodesmium obtained with an Underwater Vision Profiler (UVP5). The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values. Atmospheric N input was highest (61% of total N) in the strongly stratified and oligotrophic region between 3 and 7°N, which featured very high depth-integrated Trichodesmium abundance (up to 9.4×104 colonies m-2), strong thermohaline stratification and low zooplankton δ15N (~2‰). Relative atmospheric N input was lowest south of the equatorial upwelling between 3 and 5°S (27%). Values in the Guinea Dome region and north of Cape Verde ranged between 45 and 50%, respectively. The microstructure-derived estimate of the vertical diffusive N flux in the equatorial region was about one order of magnitude higher than in any other area (approximately 8 mmol m-2 d 1). At the same time, this region received considerable atmospheric N input (35% of total). In general, zooplankton δ15N and Trichodesmium abundance were closely correlated, indicating that N fixation is the major source of atmospheric N input. Although Trichodesmium is not the only N fixing organism, its abundance can be used with high confidence to estimate the relative atmospheric N input in the tropical Atlantic (r2 = 0.95). Estimates of absolute N fixation rates are two- to tenfold higher than incubation-derived rates reported for the same regions. Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N. In a global analysis, it may thus help to close the gap in oceanic N budgets.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: text
    Format: text
    DOI: 10.1371/journal.pone.0131258
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX (2013)
    AMER GEOPHYSICAL UNION
    In:  EPIC3Global Biogeochemical Cycles, AMER GEOPHYSICAL UNION, 27, pp. 1-11, ISSN: 0886-6236
    Details
    Publication Date: 2019-07-16
    Description: A closed eddy core in the Atlantic Subantarctic Southern Ocean was fertilized twice with two tons of iron (as FeSO4) to test whether iron addition enhances downward particle flux into the deep ocean. The ~300 km2 fertilized patch was occupied for 39 d. Chlorophyll-a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to ≥0.40. Silicic acid was at limiting concentrations (〈2 µmol L-1), diatoms contributed 〈10% of phytoplankton biomass, and copepods exerted high grazing pressure. This is the first study of downward particle flux out of an artificially-fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch estimated from O2:Ar ratios averaged 21 mmol POC m−2 d−1, probably ±20%. Export flux at 100 m calculated from 234Th profiles remained constant inside the patch (∼6.3 mmol POC m−2 d−1) and was similar to unfertilized adjacent waters. The difference between NCP and 234Th-derived export implies organic carbon accumulation in the mixed layer, and remineralization between the mixed layer and 100 m. Fluxes caught in neutrally buoyant sediment traps at 200 m and 450 m inside and outside the patch were mostly 〈1.1 mmol POC m−2 d−1, predominantly of fecal material, and did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon-limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 7
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    Net community production, Thorium-234 activity and particle flux during the Southern Ocean iron fertilization experiment LOHAFEX (2013)
    PANGAEA
    In:  Supplement to: Martin, Patrick; Rutgers van der Loeff, Michiel M; Cassar, Nicolas; Vandromme, Pieter; d'Ovidio, Francesco; Stemmann, Lars; Rengarajan, Ramabadran; Soares, Melena; González, Humberto E; Ebersbach, Friederike; Lampitt, Richard Stephen; Sanders, Richard J; Barnett, Bruce A; Smetacek, Victor; Naqvi, Syed Wajih Ahmad (2013): Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX. Global Biogeochemical Cycles, 27(3), 871-881, https://doi.org/10.1002/gbc.20077
    Details
    Publication Date: 2023-11-09
    Description: A closed eddy core in the Subantarctic Atlantic Ocean was fertilized twice with two tons of iron (as FeSO4), and the 300 km**2 fertilized patch was studied for 39 days to test whether fertilization enhances downward particle flux into the deep ocean. Chlorophyll a and primary productivity doubled after fertilization, and photosynthetic quantum yield (FV/FM) increased from 0.33 to 〉0.40. Silicic acid (〈2 µmol/L) limited diatoms, which contributed 〈10% of phytoplankton biomass. Copepods exerted high grazing pressure. This is the first study of particle flux out of an artificially fertilized bloom with very low diatom biomass. Net community production (NCP) inside the patch, estimated from O2:Ar ratios, averaged 21 mmol POC/m**2/d, probably ±20%. 234Th profiles implied constant export of ~6.3 mmol POC/m**2/d in the patch, similar to unfertilized waters. The difference between NCP and 234Th-derived export partly accumulated in the mixed layer and was partly remineralized between the mixed layer and 100 m. Neutrally buoyant sediment traps at 200 and 450 m inside and outside the patch caught mostly 〈1.1 mmol POC/m**2/d, predominantly of fecal origin; flux did not increase upon fertilization. Our data thus indicate intense flux attenuation between 100 and 200 m, and probably between the mixed layer and 100 m. We attribute the lack of fertilization-induced export to silicon limitation of diatoms and reprocessing of sinking particles by detritus feeders. Our data are consistent with the view that nitrate-rich but silicate-deficient waters are not poised for enhanced particle export upon iron addition.
    Keywords: AWI_MarGeoChem; Marine Geochemistry @ AWI
    Type: Dataset
    Format: application/zip, 7 datasets
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 8
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    Giant protists in the global ocean (2016)
    PANGAEA
    In:  Supplement to: Biard, Tristan; Stemmann, Lars; Picheral, Marc; Mayot, Nicolas; Vandromme, Pieter; Hauss, Helena; Gorsky, G; Guidi, Lionel; Kiko, Rainer; Not, Fabrice (2016): In situ imaging reveals the biomass of giant protists in the global ocean. Nature, 532(7600), 504-507, https://doi.org/10.1038/nature17652
    Details
    Publication Date: 2023-11-09
    Description: Planktonic organisms play crucial roles in oceanic food webs and global biogeochemical cycles. Most of our knowledge about the ecological impact of large zooplankton stems from research on abundant and robust crustaceans, and in particular copepods. A number of the other organisms that comprise planktonic communities are fragile, and therefore hard to sample and quantify, meaning that their abundances and effects on oceanic ecosystems are poorly understood. Here, using data from a worldwide in situ imaging survey of plankton larger than 600 µm, we show that a substantial part of the biomass of this size fraction consists of giant protists belonging to the Rhizaria, a super-group of mostly fragile unicellular marine organisms that includes the taxa Phaeodaria and Radiolaria (for example, orders Collodaria and Acantharia). Globally, we estimate that rhizarians in the top 200 m of world oceans represent a standing stock of 0.089 Pg carbon, equivalent to 5.2% of the total oceanic biota carbon reservoir. In the vast oligotrophic intertropical open oceans, rhizarian biomass is estimated to be equivalent to that of all other mesozooplankton (plankton in the size range 0.2-20 mm). The photosymbiotic association of many rhizarians with microalgae may be an important factor in explaining their distribution. The previously overlooked importance of these giant protists across the widest ecosystem on the planet changes our understanding of marine planktonic ecosystems.
    Type: Dataset
    Format: application/zip, 3 datasets
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 9
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    Biological and physical influences on marine snowfall at the equator - data collection (2017)
    PANGAEA
    In:  Supplement to: Kiko, Rainer; Biastoch, Arne; Brandt, Peter; Cravatte, Sophie; Hauss, Helena; Hummels, Rebecca; Kriest, Iris; Marin, Frédéric; McDonnell, Andrew; Oschlies, Andreas; Picheral, Marc; Schwarzkopf, Franziska; Thurnherr, Andreas M; Stemmann, Lars (2017): Biological and physical influences on marine snowfall at the equator. Nature Geoscience, https://doi.org/10.1038/NGEO3042
    Details
    Publication Date: 2023-11-09
    Description: High primary productivity in the equatorial Atlantic and Pacific oceans is one of the key features of tropical ocean biogeochemistry and fuels a substantial flux of particulate matter towards the abyssal ocean. How biological processes and equatorial current dynamics shape the particle size distribution and flux, however, is poorly understood. Here we use high-resolution size-resolved particle imaging and Acoustic Doppler Current Profiler data to assess these influences in equatorial oceans. We find an increase in particle abundance and flux at depths of 300 to 600 m at the Atlantic and Pacific equator, a depth range to which zooplankton and nekton migrate vertically in a daily cycle. We attribute this particle maximum to faecal pellet production by these organisms. At depths of 1,000 to 4,000 m, we find that the particulate organic carbon flux is up to three times greater in the equatorial belt (1° S–1° N) than in off-equatorial regions. At 3,000 m, the flux is dominated by small particles less than 0.53 mm in diameter. The dominance of small particles seems to be caused by enhanced active and passive particle export in this region, as well as by the focusing of particles by deep eastward jets found at 2° N and 2° S. We thus suggest that zooplankton movements and ocean currents modulate the transfer of particulate carbon from the surface to the deep ocean.
    Keywords: Climate - Biogeochemistry Interactions in the Tropical Ocean; SFB754
    Type: Dataset
    Format: application/zip, 8 datasets
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    DATA PANGAEA
  • 10
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    Net community production estimates from underway O2:Ar measurement during POLARSTERN cruise ANT-XXV/3 (LOHAFEX) (2013)
    PANGAEA
    Details
    Publication Date: 2023-11-09
    Keywords: ANT-XXV/3; AWI_MarGeoChem; Comment; CT; DATE/TIME; DEPTH, water; LATITUDE; LONGITUDE; Marine Geochemistry @ AWI; Net community production of oxygen; Polarstern; PS73/3-track; PS73 LOHAFEX; South Atlantic Ocean; Underway cruise track measurements
    Type: Dataset
    Format: text/tab-separated-values, 62614 data points
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    DATA PANGAEA
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