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  • 1
    Electronic Resource
    Electronic Resource
    Carbon dioxide limitation of marine phytoplankton growth rates (1993)
    [s.l.] : Nature Publishing Group
    Nature 361 (1993), S. 249-251 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Dissolved inorganic carbon in sea water exists in three inter-changeable forms: CO2, HCO^ and COl~. Despite its low concentration (0.5%-1% of DIG, corresponding to 10-15 jjiM CO2 at pH 8.2), CO2 is the main source of inorganic carbon for phytoplankton growth in the natural environment. This is ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/361249a0
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    Paper (German National Licenses)
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  • 2
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    Dust deposition: iron source or sink? A case study (2011)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 8 (8). pp. 2107-2124.
    Details
    Publication Date: 2019-07-05
    Description: A significant decrease of dissolved iron (DFe) concentration has been observed after dust addition into mesocosms during the DUst experiment in a low Nutrient low chlorophyll Ecosystem (DUNE), carried out in the summer of 2008. Due to low biological productivity at the experiment site, biological consumption of iron can not explain the magnitude of DFe decrease. To understand processes regulating the observed DFe variation, we simulated the experiment using a one-dimensional model of the Fe biogeochemical cycle, coupled with a simple ecosystem model. Different size classes of particles and particle aggregation are taken into account to describe the particle dynamics. DFe concentration is regulated in the model by dissolution from dust particles and adsorption onto particle surfaces, biological uptake, and photochemical mobilisation of particulate iron. The model reproduces the observed DFe decrease after dust addition well. This is essentially explained by particle adsorption and particle aggregation that produces a high export within the first 24 h. The estimated particle adsorption rates range between the measured adsorption rates of soluble iron and those of colloidal iron, indicating both processes controlling the DFe removal during the experiment. A dissolution timescale of 3 days is used in the model, instead of an instantaneous dissolution, underlining the importance of dissolution kinetics on the short-term impact of dust deposition on seawater DFe. Sensitivity studies reveal that initial DFe concentration before dust addition was crucial for the net impact of dust addition on DFe during the DUNE experiment. Based on the balance between abiotic sinks and sources of DFe, a critical DFe concentration has been defined, above which dust deposition acts as a net sink of DFe, rather than a source. Taking into account the role of excess iron binding ligands and biotic processes, the critical DFe concentration might be applied to explain the short-term variability of DFe after natural dust deposition in various different ocean regions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-8-2107-2011
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory site (2009)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 6 (10). pp. 2041-2061.
    Details
    Publication Date: 2012-12-12
    Description: A one-dimensional model of Fe speciation and biogeochemistry, coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model, is applied for the Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) site. Among diverse processes affecting Fe speciation, this study is focusing on investigating the role of dust particles in removing dissolved iron (DFe) by a more complex description of particle aggregation and sinking, and explaining the abundance of organic Fe-binding ligands by modelling their origin and fate. The vertical distribution of different particle classes in the model shows high sensitivity to changing aggregation rates. Using the aggregation rates from the sensitivity study in this work, modelled particle fluxes are close to observations, with dust particles dominating near the surface and aggregates deeper in the water column. POC export at 1000 m is a little higher than regional sediment trap measurements, suggesting further improvement of modelling particle aggregation, sinking or remineralisation. Modelled strong ligands have a high abundance near the surface and decline rapidly below the deep chlorophyll maximum, showing qualitative similarity to observations. Without production of strong ligands, phytoplankton concentration falls to 0 within the first 2 years in the model integration, caused by strong Fe-limitation. A nudging of total weak ligands towards a constant value is required for reproducing the observed nutrient-like profiles, assuming a decay time of 7 years for weak ligands. This indicates that weak ligands have a longer decay time and therefore cannot be modelled adequately in a one-dimensional model. The modelled DFe profile is strongly influenced by particle concentration and vertical distribution, because the most important removal of DFe in deeper waters is colloid formation and aggregation. Redissolution of particulate iron is required to reproduce an observed DFe profile at TENATSO site. Assuming colloidal iron is mainly composed of inorganic colloids, the modelled colloidal to soluble iron ratio is lower that observations, indicating the importance of organic colloids.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/bg-6-2041-2009
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    On the role of heat fluxes in the uptake of anthropogenic carbon in the North Atlantic (2002)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 16 (4). pp. 85-1.
    Details
    Publication Date: 2018-03-15
    Description: The influence of the overturning circulation on the anthropogenic carbon sink in the North Atlantic is investigated with a simple box model. The net air-sea flux of anthropogenic carbon in the North Atlantic is the result of two opposing fluxes: The first is the uptake caused by the disequilibrium between the rapidly rising atmospheric pCO2 and the dissolved carbon content in the ocean, depending mainly on the water exchange rate between mixed layer and interior North Atlantic ocean. Superimposed is a second flux, related to the northward transport of heat within the Atlantic basin, that is directed out of the ocean, contrary to conventional wisdom. It is caused by a latitudinal gradient in the ratio of seawater alkalinity to total dissolved inorganic carbon that in turn is related to the cooling and freshening of surface water on its way north. This flux depends strongly on the vertical structure of the upper branch of the overturning circulation and on the distribution of undersaturation and supersaturation of CO2 in Atlantic surface waters. A data-based estimate of anthropogenic carbon inventory in the North Atlantic is consistent with a dominance of the disequilibrium flux over the heat-flux-related outgassing at the present time, but, in our model, does not place a strong constraint on the net anthropogenic air-sea flux. Stabilization of the atmospheric pCO2 on a higher level will change the relative role of the two opposing fluxes, making the North Atlantic a source of anthropogenic carbon to the atmosphere. We discuss implications for the interpretation of numerical carbon cycle models.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2002GB001897
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Modeling the speciation and biogeochemistry of iron at the Bermuda Atlantic Time-series Study site (2005)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 19 (1). GB1019.
    Details
    Publication Date: 2018-03-16
    Description: By means of numerical modeling, we analyze the cycling of iron between its various physical (dissolved, colloidal, particulate) and chemical (redox state and organic complexation) forms in the upper mixed layer. With our proposed model it is possible to obtain a first quantitative assessment of how this cycling influences iron uptake by phytoplankton and its loss via particle export. The model is forced with observed dust deposition rates, mixed layer depths, and solar radiation at the site of the Bermuda Atlantic Time-series Study (BATS). It contains an objectively optimized ecosystem model which yields results close to the observational data from BATS that has been used for the data-assimilation procedure. It is shown that the mixed layer cycle strongly influences the cycling of iron between its various forms. This is mainly due to the light dependency of photoreductive processes, and to the seasonality of primary production. The daily photochemical cycle is driven mainly by the production of superoxide, and its amplitude depends on the concentration and speciation of dissolved copper. Model results are almost insensitive to the dominant form of dissolved iron within dust deposition, and also to the form of iron that is taken up directly during algal growth. In our model solutions, the role of the colloidal pumping mechanism depends strongly on assumptions on the colloid aggregation and photoreduction rate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GB002340
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The effect of iron availability on the regulation of inorganic carbon acquisition in the coccolithophore Emiliania huxleyi and the significance of cellular compartmentation for stable carbon isotope fractionation (2007)
    Elsevier
    In:  Geochimica et Cosmochimica Acta, 71 (22). pp. 5301-5312.
    Details
    Publication Date: 2019-09-23
    Description: Iron is limiting phytoplankton productivity in large parts of today's oceans, the so-called HNLC (high nutrient low chlorophyll) areas. It is a key component in photosynthesis during which inorganic carbon fixation in most phytoplankton species is sustained by so-called carbon concentrating mechanisms (CCMs). Here we investigate CCM regulation in the coccolithophore Emiliania huxleyi in response to varying degrees of iron limitation by means of membrane-inlet mass spectrometry. Compared to iron replete conditions rates of both active CO2 and HCO-3 uptake were markedly reduced under iron limitation leading to significantly diminished growth rates. Moreover, there was a concomitant decrease in CCM efficiency, reflected in an increased CO2 loss from the cell in relation to carbon fixation. Under such conditions higher values for carbon isotope fractionation (∈P) would be expected. However, direct measurements of ∈P showed that carbon isotope fractionation was insensitive to changes in growth rates and CCM activity. This can be explained by concomitant changes in internal DIC fluxes in and out of the chloroplast as demonstrated with a simple cell model comprising two compartments. Thus, carbon isotope fractionation reflects the ability of phytoplankton to actively control their inorganic carbon acquisition depending on environmental conditions. The insensitivity of carbon isotope fractionation to changes in the availability of iron could be of interest for paleoreconstructions in the HNLC areas of today's oceans.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.gca.2007.09.012
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Simulating the modern δ30Si distribution in the oceans and in marine sediments (2016)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-08-01
    Description: The δ30Si of biogenic silica ( urn:x-wiley:gbc:media:gbc20388:gbc20388-math-0001) in marine sediments is a promising proxy for the reconstruction of silicic acid utilization by diatoms in the geological past. The application of this proxy, however, requires an understanding of the modern δ30Si distributions and their controlling mechanisms. Here we present results from a modern climate simulation with a coupled ocean‐sediment model that includes a prognostic formulation of biogenic silica production with concurrent silicon isotopic fractionation. In agreement with previous studies, biological fractionation combined with physical transport and mixing determines the oceanic distribution of simulated δ30Si. A new finding is a distinct seasonal cycle of δ30Si in the surface ocean, which is inversely related to that of silicic acid concentration and mixed layer depth. We also provide the first simulation results of sedimentary δ30Si, which reveal that (1) the urn:x-wiley:gbc:media:gbc20388:gbc20388-math-0002 distribution in the surface sediment reflects the exported urn:x-wiley:gbc:media:gbc20388:gbc20388-math-0003 signal from the euphotic zone and (2) the dissolution of biogenic silica in the sediment acts as a source of relatively light δ30Si into the bottom waters of the polar oceans, while it is a source of heavier δ30Si to the subtropical South Atlantic and South Pacific.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Reply to Schuiling et al.: Different processes at work [Letters (Online Only)] (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-03-23
    Description: Schuiling et al. (1) question our conclusion (2) that the annual dissolution rate of olivine is limited by the saturation of waters with silicic acid (H4SiO4), which is one product of the dissolution reaction of olivine. In support of this point they discuss findings of CO2 sequestration in a mine in Yukon, Canada, claiming that a minimum of 1,700 g C m−2 y−1 was sequestered between 1978 and 2004 by silicate weathering and precipitation of (mainly) magnesium carbonates (3). This value is approximately 20 times larger than the 85 g C m−2 y−1 calculated in our study for the Amazon...
    Keywords: Letters, Sustainability Science
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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    PAPER CURRENT
  • 9
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    Sinkers or floaters? Contribution from salp pellets to the export flux during a large bloom event in the Southern Ocean (2016)
    In:  EPIC3Deep-Sea Research II
    Details
    Publication Date: 2021-01-26
    Description: Salp fecal pellets are rich in organic matter and have been shown to sink at very high velocities. In recent years, salp abundances have been increasing in the Southern Ocean where they seem to be replacing krill as the dominant grazers on phytoplankton. As salps can form large swarms with high pellet production rates, it has been suggested that they will become increasingly important for the vertical export of particulate organic matter in the Southern Ocean. However, detailed studies combining both investigations of pellet production rates, turnover, and export are still needed in order to determine whether salp pellets are important for export (‘sinkers’) or recycling (‘floaters’) of organic matter. Our results suggest that pellets are produced at high rates in the upper few hundred meters of the water column. Although we observed high sinking velocities and low microbial degradation rates of the produced salp pellets, only about one third of the produced pellets were captured in sediment traps placed at 100 m and about ~13% of the produced pellets were exported to sediment traps placed at 300 m. The high retention of these fast-settling pellets seems to be caused by break-up and loosening of the pellets, possibly by zooplankton and salps themselves. We measured 3-fold lower size-specific sinking velocities in loosened and fragmented compared to freshly produced intact pellets-. This enhanced the residence times ( 〉 1 day) of both small and large pellets in the upper water column. We postulate that the fragile nature of salp pellets make them more important for recycling of organic matter in the upper mesopelagic layer rather than as a conduit for export of particulate organic matter to the seafloor.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 10
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    Simulating the modern δ30Si distribution in the oceans and in marine sediments (2016)
    In:  EPIC3Global Biogeochemical Cycles, 30(2), pp. 120-133, ISSN: 08866236
    Details
    Publication Date: 2016-04-13
    Description: The δ30Si of biogenic silica ( inline image) in marine sediments is a promising proxy for the reconstruction of silicic acid utilization by diatoms in the geological past. The application of this proxy, however, requires an understanding of the modern δ30Si distributions and their controlling mechanisms. Here we present results from a modern climate simulation with a coupled ocean-sediment model that includes a prognostic formulation of biogenic silica production with concurrent silicon isotopic fractionation. In agreement with previous studies, biological fractionation combined with physical transport and mixing determines the oceanic distribution of simulated δ30Si. A new finding is a distinct seasonal cycle of δ30Si in the surface ocean, which is inversely related to that of silicic acid concentration and mixed layer depth. We also provide the first simulation results of sedimentary δ30Si, which reveal that (1) the inline image distribution in the surface sediment reflects the exported inline image signal from the euphotic zone and (2) the dissolution of biogenic silica in the sediment acts as a source of relatively light δ30Si into the bottom waters of the polar oceans, while it is a source of heavier δ30Si to the subtropical South Atlantic and South Pacific.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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