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  • AGU (American Geophysical Union)  (5)
  • ASLO (Association for the Sciences of Limnology and Oceanography)  (3)
  • Wissenschaftliche Auswertungen  (2)
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  • 1
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    The modulating effect of light intensity on the response of the coccolithophore Gephyrocapsa oceanicato ocean acidification (2015)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 60 (6). pp. 2145-2157.
    Details
    Publication Date: 2018-10-01
    Description: Global change leads to a multitude of simultaneous modifications in the marine realm among which shoaling of the upper mixed layer, leading to enhanced surface layer light intensities, as well as increased carbon dioxide (CO2) concentration are some of the most critical environmental alterations for phytoplankton. In this study, we investigated the responses of growth, photosynthetic carbon fixation and calcification of the coccolithophore Gephyrocapsa oceanica to elevated inline image (51 Pa, 105 Pa, and 152 Pa) (1 Pa ≈ 10 μatm) at a variety of light intensities (50–800 μmol photons m−2 s−1). By fitting the light response curve, our results showed that rising inline image reduced the maximum rates for growth, photosynthetic carbon fixation and calcification. Increasing light intensity enhanced the sensitivity of these rate responses to inline image, and shifted the inline image optima toward lower levels. Combining the results of this and a previous study (Sett et al. 2014) on the same strain indicates that both limiting low inline image and inhibiting high inline image levels (this study) induce similar responses, reducing growth, carbon fixation and calcification rates of G. oceanica. At limiting low light intensities the inline image optima for maximum growth, carbon fixation and calcification are shifted toward higher levels. Interacting effects of simultaneously occurring environmental changes, such as increasing light intensity and ocean acidification, need to be considered when trying to assess metabolic rates of marine phytoplankton under future ocean scenarios.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/lno.10161
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2levels (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Biogeosciences, 119 (6). pp. 1216-1230.
    Details
    Publication Date: 2020-10-20
    Description: A large-scale multidisciplinary mesocosm experiment in an Arctic fjord (Kongsfjorden, Svalbard; 78°56.2′N) was used to study Arctic marine food webs and biogeochemical elements cycling at natural and elevated future carbon dioxide (CO2) levels. At the start of the experiment, marine-derived chromophoric dissolved organic matter (CDOM) dominated the CDOM pool. Thus, this experiment constituted a convenient case to study production of autochthonous CDOM, which is typically masked by high levels of CDOM of terrestrial origin in the Arctic Ocean proper. CDOM accumulated during the experiment in line with an increase in bacterial abundance; however, no response was observed to increased pCO2 levels. Changes in CDOM absorption spectral slopes indicate that bacteria were most likely responsible for the observed CDOM dynamics. Distinct absorption peaks (at ~ 330 and ~ 360 nm) were likely associated with mycosporine-like amino acids (MAAs). Due to the experimental setup, MAAs were produced in absence of ultraviolet exposure providing evidence for MAAs to be considered as multipurpose metabolites rather than simple photoprotective compounds. We showed that a small increase in CDOM during the experiment made it a major contributor to total absorption in a range of photosynthetically active radiation (PAR, 400–700 nm) and, therefore, is important for spectral light availability and may be important for photosynthesis and phytoplankton groups composition in a rapidly changing Arctic marine ecosystem.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2013JG002587
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Between- and within-population variations in thermal reaction norms of the coccolithophore Emiliania huxleyi (2014)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 59 (5). pp. 1570-1580.
    Details
    Publication Date: 2017-09-02
    Description: Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist–specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between-population variation, we also found variation within populations. Genotype-by-environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2014.59.5.1570
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Effects of ocean acidification on the biogenic composition of the sea-surface microlayer: Results from a mesocosm study (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (11). pp. 7911-7924.
    Details
    Publication Date: 2019-09-23
    Description: The sea-surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, proteins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean-atmosphere interactions, still little is known about its structural characteristics and sensitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here we report results of a large-scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynamics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emissions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2014JC010188
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Distinguishing between the effects of ocean acidification and ocean carbonation in the coccolithophore Emiliania huxleyi (2011)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 56 (6). pp. 2040-2050.
    Details
    Publication Date: 2020-10-16
    Description: The coccolithophore Emiliania huxleyi was cultured under a broad range of carbonate chemistry conditions to distinguish the effects of individual carbonate system parameters on growth, primary production, and calcification. In the first experiment, alkalinity was kept constant and the fugacity of CO2 (fCO2) varied from 2 to 600 Pa (1 Pa ≈ 10 µatm). In the second experiment, pH was kept constant (pHfree = 8) with fCO2 varying from 4 to 370 Pa. Results of the constant-alkalinity approach revealed physiological optima for growth, calcification, and organic carbon production at fCO2 values of ∼ 20 Pa, ∼ 40 Pa, and ∼ 80 Pa, respectively. Comparing this with the constant-pH approach showed that growth and organic carbon production increased similarly from low to intermediate CO2 levels but started to diverge towards higher CO2 levels. In the high CO2 range, growth rates and organic carbon production decreased steadily with declining pH at constant alkalinity while remaining consistently higher at constant pH. This suggests that growth and organic carbon production rates are directly related to CO2 at low (sub-saturating) concentrations, whereas towards higher CO2 levels they are adversely affected by the associated decrease in pH. A pH dependence at high fCO2 is also indicated for calcification rates, while the key carbonate system parameter determining calcification at low fCO2 remains unclear. These results imply that key metabolic processes in coccolithophores have their optima at different carbonate chemistry conditions and are influenced by different parameters of the carbonate system at both sides of the optimum.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2011.56.6.2040
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Influence of plankton community structure on the sinking velocity of marine aggregates (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 30 (8). pp. 1145-1165.
    Details
    Publication Date: 2019-09-23
    Description: About 50 Gt of carbon is fixed photosynthetically by surface ocean phytoplankton communities every year. Part of this organic matter is reprocessed within the plankton community to form aggregates which eventually sink and export carbon into the deep ocean. The fraction of organic matter leaving the surface ocean is partly dependent on aggregate sinking velocity which accelerates with increasing aggregate size and density, where the latter is controlled by ballast load and aggregate porosity. In May 2011, we moored nine 25 m deep mesocosms in a Norwegian fjord to assess on a daily basis how plankton community structure affects material properties and sinking velocities of aggregates (Ø 80–400 µm) collected in the mesocosms' sediment traps. We noted that sinking velocity was not necessarily accelerated by opal ballast during diatom blooms, which could be due to relatively high porosity of these rather fresh aggregates. Furthermore, estimated aggregate porosity (Pestimated) decreased as the picoautotroph (0.2–2 µm) fraction of the phytoplankton biomass increased. Thus, picoautotroph-dominated communities may be indicative for food webs promoting a high degree of aggregate repackaging with potential for accelerated sinking. Blooms of the coccolithophore Emiliania huxleyi revealed that cell concentrations of ~1500 cells/mL accelerate sinking by about 35–40%, which we estimate (by one-dimensional modeling) to elevate organic matter transfer efficiency through the mesopelagic from 14 to 24%. Our results indicate that sinking velocities are influenced by the complex interplay between the availability of ballast minerals and aggregate packaging; both of which are controlled by plankton community structure.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GB005372
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Auswirkungen der Ozeanversauerung auf marine Lebensprozesse (2011)
    Wissenschaftliche Auswertungen
    In:  In: Warnsignal Klima: Die Meeres – Änderungen und Risiken. , ed. by Lozan, J. L., Graßl, H., Karbe, L. and Reise, K. Buchreihe "Warnsignale" . Wissenschaftliche Auswertungen, Hamburg, Germany, pp. 172-176.
    Details
    Publication Date: 2019-02-13
    Description: Consequences of the ocean acidification to biological processes: The dissolution of anthropogenic carbon dioxide (CO2 ) into the ocean is causing a series of chemical changes: an increase in CO2 concentration, a decrease in calcium carbonate saturation and pH, and a change in the chemistry of many biologically important chemical species (see Chapter 3.9 for details). These chemical changes will affect a range of biological processes in marine organisms, including the precipitation of calcium carbonate, fixation of CO_2 and nitrogen, pumping of hydrogen ions to regulate internal pH, and uptake of nutrients for growth. This chapter focuses on biological processes that are likely to be affected by acidification and how these effects on individual organisms may scale up to the ecosystem level.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 8
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    Unexpected consequences of increasing CO2 and ocean acidity on marine production of DMS and CH2ClI: Potential climate impacts (2007)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 34 (L05710).
    Details
    Publication Date: 2018-02-15
    Description: Increasing atmospheric mixing ratios of CO2 have already lowered surface ocean pH by 0.1 units compared to preindustrial values and pH is expected to decrease an additional 0.3 units by the end of this century. Pronounced physiological changes in some phytoplankton have been observed during previous CO2 perturbation experiments. Marine microorganisms are known to consume and produce climate-relevant organic gases. Concentrations of (CH3)2S (DMS) and CH2ClI were quantified during the Third Pelagic Ecosystem CO2 Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO2. Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO2 treatments, and 18% (±10%) higher in the 3xCO2 mesocosms. For CH2ClI the 2xCO2 treatments were 46% (±4%) greater than the controls and the 3xCO2 mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006GL028139
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Versauerung des Meerwassers durch anthropogenes CO2 (2011)
    Wissenschaftliche Auswertungen
    In:  In: Warnsignal Klima: Die Meeres – Änderungen und Risiken. , ed. by Lozan, J. L., Graßl, H., Karbe, L. and Reise, K. Buchreihe "Warnsignale" . Wissenschaftliche Auswertungen, Hamburg, Germany, pp. 159-162.
    Details
    Publication Date: 2019-02-13
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 10
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    Effect of rising atmospheric carbon dioxide on the marine nitrogen fixer Trichodesmium (2007)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 21 (2). GB2028.
    Details
    Publication Date: 2018-03-20
    Description: Diazotrophic (N2-fixing) cyanobacteria provide the biological source of new nitrogen for large parts of the ocean. However, little is known about their sensitivity to global change. Here we show that the single most important nitrogen fixer in today's ocean, Trichodesmium, is strongly affected by changes in CO2 concentrations. Cell division rate doubled with rising CO2 (glacial to projected year 2100 levels) prompting lower carbon, nitrogen and phosphorus cellular contents, and reduced cell dimensions. N2 fixation rates per unit of phosphorus utilization as well as C:P and N:P ratios more than doubled at high CO2, with no change in C:N ratios. This could enhance the productivity of N-limited oligotrophic oceans, drive some of these areas into P limitation, and increase biological carbon sequestration in the ocean. The observed CO2 sensitivity of Trichodesmium could thereby provide a strong negative feedback to atmospheric CO2 increase.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006GB002898
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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