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  • 1
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    Phytoplankton Blooms at Increasing Levels of Atmospheric Carbon Dioxide: Experimental Evidence for Negative Effects on Prymnesiophytes and Positive on Small Picoeukaryotes (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 . Art.Nr. 64.
    Details
    Publication Date: 2020-02-06
    Description: Anthropogenic emissions of carbon dioxide (CO2) and the ongoing accumulation in the surface ocean together with concomitantly decreasing pH and calcium carbonate saturation states have the potential to impact phytoplankton community composition and therefore biogeochemical element cycling on a global scale. Here we report on a recent mesocosm CO2 perturbation study (Raunefjorden, Norway), with a focus on organic matter and phytoplankton dynamics. Cell numbers of three phytoplankton groups were particularly affected by increasing levels of seawater CO2 throughout the entire experiment, with the cyanobacterium Synechococcus and picoeukaryotes (prasinophytes) profiting, and the coccolithophore Emiliania huxleyi (prymnesiophyte) being negatively impacted. Combining these results with other phytoplankton community CO2 experiments into a data-set of global coverage suggests that, whenever CO2 effects are found, prymnesiophyte (especially coccolithophore) abundances are negatively affected, while the opposite holds true for small picoeukaryotes belonging to the class of prasinophytes, or the division of chlorophytes in general. Future reductions in calcium carbonate-producing coccolithophores, providing ballast which accelerates the sinking of particulate organic matter, together with increases in picoeukaryotes, an important component of the microbial loop in the euphotic zone, have the potential to impact marine export production, with feedbacks to Earth's climate system.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    DOI: 10.3389/fmars.2017.00064
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Variations of the Organic Matter Composition in the Sea Surface Microlayer: A Comparison between Open Ocean, Coastal, and Upwelling Sites Off the Peruvian Coast (2017)
    Frontiers
    In:  Frontiers in Microbiology, 8 . Art.No. 2369.
    Details
    Publication Date: 2020-02-06
    Description: The sea surface microlayer (SML) is the thin boundary layer between the ocean and the atmosphere, making it important for air-sea exchange processes. However, little is known about what controls organic matter composition in the SML. In particular, there are only few studies available on the differences of the SML of various oceanic systems. Here, we compared the organic matter and neuston species composition in the SML and the underlying water (ULW) at 11 stations with varying distance from the coast in the Peruvian upwelling regime, a system with high emissions of climate relevant trace gases, such as N2O and CO2. In the open ocean, organic carbon, and amino acids were highly enriched in the SML compared to the ULW. The enrichment decreased at the coastal stations and vanished in the upwelling regime. At the same time, the degradation of organic matter increased from the open ocean to the upwelling stations. This suggests that in the open ocean, upward transport processes or new production of organic matter within the SML are faster than degradation processes. Phytoplankton was generally not enriched in the SML, one group though, the Trichodesmium-like TrL (possibly containing Trichodesmium), were enriched in the open ocean but not in the upwelling region indicating that they find a favorable habitat in the open ocean SML. Our data show that the SML is a distinct habitat; its composition is more similar among different systems than between SML and ULW of a single station. Generally the enrichment of organic matter is assumed to be reduced when encountering low primary production and high wind speeds. However, our study shows the highest enrichments of organic matter in the open ocean which had the lowest primary production and the highest wind speeds.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3389/fmicb.2017.02369
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Microbial Communities in the East and West Fram Strait During Sea Ice Melting Season (2018)
    Frontiers
    In:  Frontiers in Marine Science, 5 . Art.Nr. 429.
    Details
    Publication Date: 2021-02-08
    Description: Climate models project that the Arctic Ocean may experience ice-free summers by the second half of this century. This may have severe repercussions on phytoplankton bloom dynamics and the associated cycling of carbon in surface waters. We currently lack baseline knowledge of the seasonal dynamics of Arctic microbial communities, which is needed in order to better estimate the effects of such changes on ecosystem functioning. Here we present a comparative study of polar summer microbial communities in the ice-free (eastern) and ice-covered (western) hydrographic regimes at the LTER HAUSGARTEN in Fram Strait, the main gateway between the Arctic and North Atlantic Oceans. Based on measured and modeled biogeochemical parameters, we tentatively identified two different ecosystem states (i.e., different phytoplankton bloom stages) in the distinct regions. Using Illumina tag-sequencing, we determined the community composition of both free-living and particle-associated bacteria as well as microbial eukaryotes in the photic layer. Despite substantial horizontal mixing by eddies in Fram Strait, pelagic microbial communities showed distinct differences between the two regimes, with a proposed early spring (pre-bloom) community in the ice-covered western regime (with higher representation of SAR11, SAR202, SAR406 and eukaryotic MALVs) and a community indicative of late summer conditions (post-bloom) in the ice-free eastern regime (with higher representation of Flavobacteria, Gammaproteobacteria and eukaryotic heterotrophs). Co-occurrence networks revealed specific taxon-taxon associations between bacterial and eukaryotic taxa in the two regions. Our results suggest that the predicted changes in sea ice cover and phytoplankton bloom dynamics will have a strong impact on bacterial community dynamics and potentially on biogeochemical cycles in this region.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.3389/fmars.2018.00429
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Bacterial Colonization and Vertical Distribution of Marine Gel Particles (TEP and CSP) in the Arctic Fram Strait (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 (Art.No. 166).
    Details
    Publication Date: 2020-02-06
    Description: Gel particles—a class of abundant transparent organic particles—have increasingly gathered attention in marine research. Field studies on the bacterial colonization of marine gels however are still scarce. So far, most studies on respective particles have focused on the upper ocean, while little is known on their occurrence in the deep sea. Here, we report on the vertical distribution of the two most common gel particle types, which are polysaccharide-containing transparent exopolymer particles (TEP) and proteinaceous Coomassie stainable particles (CSP), as well as numbers of bacteria attached to gel particles throughout the water column, from the surface ocean down to the bathypelagial (〈 3,000 m). Our study was conducted in the Arctic Fram Strait during northern hemispheres' summer in 2015. Besides data on the bacterial colonization of the two gel particle types (TEP and CSP), we present bacterial densities on different gel particle size classes according to 12 different sampling depths at four sampling locations. Gel particles were frequently abundant at all sampled depths, and their concentrations decreased from the euphotic zone to the dark ocean. They were colonized by bacteria at all sampled water depths with risen importance at the deepest water layers, where fractions of bacteria attached to gel particles (%) increased within the total bacterial community. Due to the omnipresent bacterial colonization of gel particles at all sampled depths in our study, we presume that euphotic production of this type of organic matter may affect microbial species distribution within the whole water column in the Fram Strait, down to the deep sea. Our results raise the question if changes in the bacterial community composition and functioning on gel particles occur over depth, which may affect microbial respiration and remineralization rates of respective particles in different water layers.
    Type: Article , PeerReviewed
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    DOI: 10.3389/fmars.2017.00166
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Organic Matter in the Surface Microlayer: Insights From a Wind Wave Channel Experiment (2018)
    Frontiers
    In:  Frontiers in Marine Science, 5 . Art.Nr. 182.
    Details
    Publication Date: 2021-03-18
    Description: The surface microlayer (SML) is the uppermost thin layer of the ocean and influencing interactions between the air and sea, such as gas exchange, atmospheric deposition and aerosol emission. Organic matter (OM) plays a key role in air-sea exchange processes, but studying how the accumulation of organic compounds in the SML relates to biological processes is impeded in the field by a changing physical environment, in particular wind speed and wave breaking. Here, we studied OM dynamics in the SML under controlled physical conditions in a large annular wind wave channel, filled with natural seawater, over a period of 26 days. Biology in both SML and bulk water was dominated by bacterioneuston and -plankton, respectively, while autotrophic biomass in the two compartments was very low. In general, SML thickness was related to the concentration of dissolved organic carbon (DOC) but not to enrichment of DOC or of specific OM components in the SML. Pronounced changes in OM enrichment and molecular composition were observed in the course of the study and correlated significantly to bacterial abundance. Thereby, hydrolysable amino acids, in particular arginine, were more enriched in the SML than combined carbohydrates. Amino acid composition indicated that less degraded OM accumulated preferentially in the SML. A strong correlation was established between the amount of surfactants coverage and γ-aminobutric acid, suggesting that microbial cycling of amino acids can control physiochemical traits of the SML. Our study shows that accumulation and cycling of OM in the SML can occur independently of recent autotrophic production, indicating a widespread biogenic control of process across the air-sea exchange.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3389/fmars.2018.00182
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Bacterial Community Composition in the Sea Surface Microlayer Off the Peruvian Coast (2018)
    Frontiers
    In:  Frontiers in Microbiology, 9 . Art.Nr. 2699.
    Details
    Publication Date: 2021-03-19
    Description: The sea surface microlayer (SML) is located at the air-sea interface, with microorganisms and organic matter in the SML influencing air-sea exchange processes. Yet understanding of the SML bacterial (bacterioneuston) community composition and assembly remains limited. Availability of organic matter, UV radiation and wind speed have previously been suggested to influence the community composition of bacterioneuston. Another mechanism potentially controlling bacterioneuston dynamics is bacterioplankton attached to gel-like particles that ascend through the water column into the SML. We analyzed the bacterial community composition, Transparent Exopolymer Particles (TEP) abundance and nutrient concentrations in the surface waters of the Peruvian upwelling region. The bacterioneuston and bacterioplankton communities were similar, suggesting a close spatial coupling. Four Bacteroidetes families were significantly enriched in the SML, two of them, the Flavobacteriaceae and Cryomorphaceae, were found to comprise the majority of SML-enriched operational taxonomic units (OTUs). The enrichment of these families was controlled by a variety of environmental factors. The SML-enriched bacterial families were negatively correlated with water temperature and wind speed in the SML and positively correlated with nutrient concentrations, salinity and TEP in the underlying water (ULW). The correlations with nutrient concentrations and salinity suggest that the enriched bacterial families were more abundant at the upwelling stations.
    Type: Article , PeerReviewed
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    Format: other
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    Format: other
    Format: archive
    DOI: 10.3389/fmicb.2018.02699
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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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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  • 8
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    Variations in the elemental ratio of organic matter in the central Baltic Sea: Part I—Linking primary production to remineralization (2015)
    Elsevier
    In:  Continental Shelf Research, 100 . pp. 25-45.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Elemental C:N:P variations of organic matter are simulated at monitoring site BY15. • No N2 fixation needed to explain observed PO4PO4 and pCO2pCO2 levels after spring bloom. • Model features relevance of DOP production and remineralization for N2 fixation. • Model estimates of annual N2 fixation are View the MathML source297±24mmolNm-2a-1. • Model estimates of annual total production are View the MathML source14.16±0.71molCm-2a-1. Abstract: For most marine ecosystems the growth of diazotrophic cyanobacteria and the associated amount of nitrogen fixation are regulated by the availability of phosphorus. The intensity of summer blooms of nitrogen (N2) fixing algae in the Baltic Sea is assumed to be determinable from a surplus of dissolved inorganic phosphorus (DIP) that remains after the spring bloom has ended. But this surplus DIP concentration is observed to continuously decrease at times when no appreciable nitrogen fixation is measured. This peculiarity is currently discussed and has afforded different model interpretations for the Baltic Sea. In our study we propose a dynamical model solution that explains these observations with variations of the elemental carbon-to-nitrogen-to-phosphorus (C:N:P) ratio during distinct periods of organic matter production and remineralization. The biogeochemical model resolves seasonal C, N and P fluxes with depth at the Baltic Sea monitoring site BY15, based on three assumptions: (1) DIP is utilized by algae though not needed for immediate growth, (2) the uptake of dissolved inorganic nitrogen (DIN) is hampered when the algae׳s phosphorus (P) quota is low, and (3) carbon assimilation continues at times of nutrient depletion. Model results describe observed temporal variations of DIN, DIP and chlorophyll-a concentrations along with partial pressure of carbon dioxide (pCO2)(pCO2). In contrast to other model studies, our solution does not require N2 fixation to occur shortly after the spring bloom to explain DIP drawdown and pCO2pCO2 levels. Model estimates of annual N2 fixation are View the MathML source297±24mmolNm-2a-1. Estimates of total production are View the MathML source14200±700mmolCm-2a-1, View the MathML source1400±70mmolNm-2a-1, and View the MathML source114±5mmolPm-2a-1 for the upper 50 m. The models C, N and P fluxes disclose preferential remineralization of P and of organic N that was introduced via N2 fixation. Our results are in support of the idea that P uptake by phytoplankton during the spring bloom contributes to the consecutive availability of labile dissolved organic phosphorus (LDOP). The LDOP is retained within upper layers and its remineralization affects algal growth in summer, during periods of noticeable N2 fixation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.csr.2014.06.015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    The influence of extracellular polysaccharides, growth rate, and free coccoliths on the coagulation efficiency of Emiliania huxleyi (2015)
    Elsevier
    In:  Marine Chemistry, 175 . pp. 5-17.
    Details
    Publication Date: 2019-09-23
    Description: Highlights: • Coagulation efficiency of the coccolithophorid Emiliania huxleyi was determined with Couette flow devices. • Higher coagulation efficiencies of cells were observed at lower growth rates. • Coagulation efficiency increases with the extracellular polysaccharides fraction. Abstract: Coagulation of small particles results in the formation of larger aggregates that play an important role in the biological pump, moving carbon and other elements from the surface to the deep ocean and seafloor. In this study, we estimated the efficiency of particle coagulation of the coccolithophore Emiliania huxleyi at different growth rates using Couette flow devices at a natural shear rate. To determine the impacts of chemical and biological factors involved in aggregate formation, we investigated how variance in organic matter composition, and in particular the presence of extracellular polysaccharides (EP), including transparent exopolymer particles (TEP) and acidic polysaccharides attached to the coccolith surface, affect the coagulation efficiency (α). When E. huxleyi was grown in a chemostat at different growth rates, coagulation efficiency increased from ~ 0.40 to 1 as cell growth rates declined and nutrients became more limited. With declining growth rate the concentration of EP and the number of detached coccoliths increased. Overall a close correlation between coagulation efficiency of E. huxleyi and the ratio of EP to total particle volume was observed. The minimum value of α of ~ 0.4 determined during this study is higher than estimates published for other phytoplankton cells, and may be related to the presence of EP attached to coccoliths. Based on our findings, we suggest that E. huxleyi is more prone to form aggregates, particularly during the decline of blooms, when increased production of EP and enhanced shedding of coccoliths coincide. This may be one explanation for why blooms of E. huxleyi play an important role in the biological carbon pump, efficiently enhancing the vertical flux of particles, as has been suggested by sediment trap studies.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marchem.2015.04.010
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    A novel protocol for determining the concentration and composition of sugars in particulate and in high molecular weight dissolved organic matter (HMW-DOM) in seawater (2011)
    Elsevier
    In:  Marine Chemistry, 127 . pp. 180-191.
    Details
    Publication Date: 2019-09-23
    Description: A method is described to simultaneously determine the neutral, amino, and acidic sugar content of combined carbohydrates in high molecular weight (HMW, 〉 1 kDa) dissolved organic matter and in particles from seawater samples. Monomeric sugars are determined after acid hydrolysis and neutralization through acid evaporation using high performance anion exchange chromatography (HPAEC) coupled with pulsed amperometric detection (PAD). The separation of sugars during chromatography is achieved in two steps, an isocratic elution (18 mM NaOH) followed by a gradient course of two mobile eluent phases (NaOH and CH3COONa). HPAEC-PAD has previously been applied to measure neutral and amino sugars in marine samples. Since salt anions interfere with the measurement, some of the earlier studies used ion exchange resins for seawater desalting. Thereby, variable losses of neutral and amino sugars, and the complete removal of acidic sugars have been reported. Here, we show that desalting by membrane dialysis (1 kDa) is an efficient alternative to ion exchange resins and yields recoveries of 〉 90% for HMW carbohydrates. We conducted several tests to determine the accuracy and reproducibility of the method. Sugar concentrations determined with our protocol were compared to results obtained with the colorimetric TPTZ-method, and with earlier HPAEC-PAD protocols using cation/ anion exchange resins. Applications of our protocol to field samples indicated that acidic sugars can comprise a substantial fraction (30-50%) of HMW dissolved carbohydrates in seawater. The simultaneous analysis of the three classes of sugars appears promising to detect a larger fraction of marine combined carbohydrates, and thus to improve our understanding of organic matter cycling in the ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.marchem.2011.09.004
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