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  • AGU (American Geophysical Union)  (3)
  • 2015-2019  (1)
  • 2005-2009  (2)
  • 1
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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
  • 2
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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
  • 3
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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
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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