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  • 2010-2014  (30)
  • 2014  (30)
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  • 2010-2014  (30)
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  • 1
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    Stimulated Bacterial Growth under Elevated p Co2: Results from an Off-Shore Mesocosm Study (2014)
    Public Library of Science
    In:  PLoS ONE, 9 (6). e99228.
    Details
    Publication Date: 2019-09-23
    Description: Marine bacteria are the main consumers of freshly produced organic matter. Many enzymatic processes involved in the bacterial digestion of organic compounds were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years but the consequences for microbial physiology, organic matter cycling and marine biogeochemistry are still unresolved. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging initially from ca. 280 to 3000 µatm and sampled every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During the first phytoplankton bloom, 5–10% more transparent exopolymer particles were formed in the high pCO2 mesocosms. Simultaneously, the efficiency of the protein-degrading enzyme leucine aminopeptidase increased with decreasing pH resulting in up to three times higher values in the highest pCO2/lowest pH mesocosm compared to the controls. In general, total and cell-specific aminopeptidase activities were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported up to 28% higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean.
    Type: Article , PeerReviewed
    Format: text
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    DOI: 10.1371/journal.pone.0099228
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Impact of CO2 enrichment on organic matter dynamics during nutrient induced coastal phytoplankton blooms (2014)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 36 (3). pp. 641-657.
    Details
    Publication Date: 2019-09-23
    Description: A mesocosm experiment was conducted to investigate the impact of rising fCO2 on the build-up and decline of organic matter during coastal phytoplankton blooms. Five mesocosms (∼38 m³ each) were deployed in the Baltic Sea during spring (2009) and enriched with CO2 to yield a gradient of 355–862 µatm. Mesocosms were nutrient fertilized initially to induce phytoplankton bloom development. Changes in particulate and dissolved organic matter concentrations, including dissolved high-molecular weight (〉1 kDa) combined carbohydrates, dissolved free and combined amino acids as well as transparent exopolymer particles (TEP), were monitored over 21 days together with bacterial abundance, and hydrolytic extracellular enzyme activities. Overall, organic matter followed well-known bloom dynamics in all CO2 treatments alike. At high fCO2, higher ΔPOC:ΔPON during bloom rise, and higher TEP concentrations during bloom peak, suggested preferential accumulation of carbon-rich components. TEP concentration at bloom peak was significantly related to subsequent sedimentation of particulate organic matter. Bacterial abundance increased during the bloom and was highest at high fCO2. We conclude that increasing fCO2 supports production and exudation of carbon-rich components, enhancing particle aggregation and settling, but also providing substrate and attachment sites for bacteria. More labile organic carbon and higher bacterial abundance can increase rates of oxygen consumption and may intensify the already high risk of oxygen depletion in coastal seas in the future.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/plankt/fbt125
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Enhanced calcite dissolution in the presence of the Aerobic Methanotroph Methylosinus trichosporium (2014)
    Taylor & Francis
    In:  Geomicrobiology Journal, 31 (4). pp. 325-337.
    Details
    Publication Date: 2017-09-28
    Description: Microbial aerobic methane oxidation (MOx) is intrinsically coupled to the production of carbon dioxide, favoring carbonate dissolution. Recently, microbial organic polymers were shown to be able to induce carbonate dissolution. To discriminate between different mechanisms causing calcite dissolution, experiments were conducted in the presence of solid calcite with (1) actively growing cells (2) starving cells, and (4) dead cells of the methanotrophic bacterium Methylosinus trichosporium under brackish conditions (salinity 10) near calcite saturation (saturation state (Ω) 1.76 to 2.22). Total alkalinity and the amount of dissolved calcium markedly increased in all experiments containing M. trichosporium cells. After initial system equilibration, similar calcite dissolution rates, ranging between 14.9 (dead cells) and 29.6 μmol l−1 d−1 (actively growing cells), were observed. While concentrations of transparent exopolymer particles declined with time in the presence of actively growing and starving cells, they increased in experiments with dead cells. Scanning electron microscopy images of calcite crystals revealed visible surface corrosion after exposure to live and dead M. trichosporium cells. The results of this study indicate a strong potential for microbial MOx to affect calcite stability negatively, facilitating calcite dissolution. In addition to CO2 production by methanotrophically active cells, we suggest that the release of acidic or Ca2+-chelating organic carbon compounds from dead cells could also enhance calcite dissolution.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1080/01490451.2013.834007
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Changes in organic matter cycling in a plankton community exposed to warming under different light intensities (2014)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 36 (3). pp. 658-671.
    Details
    Publication Date: 2018-06-06
    Description: To investigate the combined effect of temperature and light availability on organic matter production and degradation during a winter/spring phytoplankton bloom in Kiel Bight, we conducted a mesocosm study applying two temperature regimes, ambient (T + 0) and plus 6°C (T + 6) and three irradiance levels. Rising temperature accelerated the onset of the phytoplankton bloom, while light intensity played only a minor role for the timing and bloom development. Maximum build-up of chlorophyll a and particulate organic carbon were ∼20% lower at T + 6 compared with T + 0, probably caused by a combination of elevated heterotrophic processes and enhanced sedimentation during the bloom. The latter is supported by increased TEP concentrations at T + 6 (TEP/POC 0.18 mol C/mol C) compared with T + 0 (0.11 mol C/mol C) during bloom conditions, which may have promoted cell aggregation and sinking. Dissolved organic carbon concentrations increased more rapidly at elevated temperature. For a warmer future ocean, we can hence expect two counteracting mechanisms controlling organic matter flow during phytoplankton blooms: (1) enhanced processing of organic matter via the microbial loop resulting in a faster recycling and (2) depending on the dominating phytoplankton species, enhanced TEP formation resulting in increased particle aggregation and thus export of carbon and nutrients.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/plankt/fbu005
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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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
  • 6
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    No detectable effect of CO2 on elemental stoichiometry of Emiliania huxleyi in nutrient-limited, acclimated continuous cultures (2014)
    Inter Research
    In:  Marine Ecology Progress Series, 507 . pp. 15-30.
    Details
    Publication Date: 2019-09-23
    Description: Effects of CO2 concentration on elemental composition of the coccolithophore Emiliania huxleyi were studied in phosphorus-limited, continuous cultures that were acclimated to experimental conditions for 30 d prior to the first sampling. We determined phytoplankton and bacterial cell numbers, nutrients, particulate components like organic carbon (POC), inorganic carbon (PIC), nitrogen (PN), organic phosphorus (POP), transparent exopolymer particles (TEP), as well as dissolved organic carbon (DOC) and nitrogen (DON), in addition to carbonate system parameters at CO2 levels of 180, 380 and 750 µatm. No significant difference between treatments was observed for any of the measured variables during repeated sampling over a 14 d period. We considered several factors that might lead to these results, i.e. light, nutrients, carbon overconsumption and transient versus steady-state growth. We suggest that the absence of a clear CO2 effect during this study does not necessarily imply the absence of an effect in nature. Instead, the sensitivity of the cell towards environmental stressors such as CO2 may vary depending on whether growth conditions are transient or sufficiently stable to allow for optimal allocation of energy and resources. We tested this idea on previously published data sets where PIC and POC divided by the corresponding cell abundance of E. huxleyi at various pCO2 levels and growth rates were available.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps10824
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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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
  • 8
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    Regulation of bacterioplankton activity in Fram Strait (Arctic Ocean) during early summer: The role of organic matter supply and temperature (2014)
    Elsevier
    In:  Journal of Marine Systems, 132 . pp. 83-94.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Activity of Arctic bacterioplankton in summer is regulated by concentration and composition of organic matter. • Bacterial production in Fram Strait is significantly related to concentrations of total amino acids. • Bacterioplankton in Polar Water show enhanced enzymatic hydrolysis of combined carbohydrates compared to Atlantic Water. Abstract The bacterial turnover of organic matter was investigated in Fram Strait at 79°N. Both Atlantic Water (AW) inflow and exported Polar Water (PW) were sampled along a transect from Spitsbergen to the eastern Greenland shelf during a late successional stage of the main annual phytoplankton bloom in summer. AW showed higher concentrations of amino acids than PW, while organic matter in PW was enriched in combined carbohydrates. Bacterial growth and degradation activity in AW and PW were related to compositional differences of organic matter. Bacterial production and leucine-aminopeptidase along the transect were significantly correlated with concentrations of amino acids. Activity ratios between the extracellular enzymes β-glucosidase and leucine-aminopeptidase indicate the hydrolysis potential for polysaccharides relative to proteins. Along the transect, these ratios showed a higher hydrolysis potential for polysaccharides relative to proteins in PW than in AW, thus reflecting the differences in organic matter composition between the water masses. Q10 values for bacterial production ranged from 2.4 (± 0.8) to 6.0 (± 6.8), while those for extracellular enzymes showed a broader range of 1.5 (± 0.5) to 23.3 (± 11.8). Our results show that in addition to low seawater temperature also organic matter availability contributes to the regulation of bacterial growth and enzymatic activity in the Arctic Ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.jmarsys.2014.01.003
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    A semi-quantitative spectrophotometric, dye-binding assay for determination of Coomassie Blue stainable particles (2014)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 12 . pp. 604-616.
    Details
    Publication Date: 2019-09-23
    Description: Coomassie stainable particles (CSP) are protein-containing transparent particles that can be stained with Coomassie brilliant blue (CBB) and are found abundantly in aquatic systems; however, their distribution and role remain poorly known, in part due to the lack of an efficient method to study them. We developed a new, simple, and low cost semi-quantitative spectrophotometric method for determination of CSP in aquatic systems. The method is analogous to that used to quantify polysaccharide-rich gel particles called transparent exopolymeric particles (TEP). CSP concentration is determined relative to bovine serum albumin (BSA) standard aggregates (in a manner similar to how TEP is quantified relative to xanthan gum). The method is based on the linear relationship between CSP concentration and the absorbance of the eluted dye from a CBB-protein complex, which has an absorbance maximum (λmax) at 615 nm. The limit of detection and the precision (%RSD) for the proposed method are 6 μg BSA equivalent and 11%, respectively. The new spectrophotometric method was validated with the existing microscopic method. This new method to quantify CSP is simple, enables rapid measurements, and allows a more efficient comparison with TEP concentrations than the present microscopic method. The spectrophotometric analyses will further the investigation of the abundance, distribution, and role of CSP in the biogeochemistry of the ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.4319/lom.2014.12.604
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Characteristics of marine aggregates during the phytoplankton spring bloom in a temperate tidal basin (2014)
    In:  [Poster] In: Ocean Sciences Meeting 2014, 23.-28.02.2014, Honululu, Hawaii, USA .
    Details
    Publication Date: 2014-03-10
    Description: High abundance of aggregates has often been related to high primary production and phytoplankton blooms. Especially in shallow and turbid coastal regions the formation of aggregates and their sinking velocities also depends on the interaction between primary produced organic matter and lithogenic particles. Nine roller tank experiments were conducted during spring 2012 in the Northern Wadden Sea (Germany) to determine temporal dynamics of formation, composition, and sinking velocity of aggregates, in relation to the wax and wane of the phytoplankton bloom. Highest sinking velocities (June-July) did not coincide with highest SPM concentrations (January-March). After the diatom bloom almost 80% of SPM was rapidly settling in aggregates but only 10% rapidly settled during the subsequent Phaeocystis bloom. The results suggest interactive effects of particle size, specific density and the availability of organic and inorganic particulate matter. Our study underlines the importance of marine aggregates as carrier of organic matter and of lithogenic particles as ballasting material for sedimentation in tidal basins.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
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