The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Reinhard Miller - One of the best experts on this subject based on the ideXlab platform.
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Surface shear rheological studies of marine phytoplankton cultures - Nitzschia closterium, Thalassiosira rotula, Thalassiosira punctigera and Phaeocystis sp.
Colloids and surfaces. B Biointerfaces, 2006Co-Authors: Verena Kuhnhenn, Jürgen Krägel, Ulrich Horstmann, Reinhard MillerAbstract:The study of interfacial properties in the marine environment is important for the understanding of air-sea gas exchange processes, especially with respect to the behaviour of entrained air bubbles. Seawater contains surfactant material, much of which is thought to origin from the exudation of dissolved organic material (DOM) by phytoplankton. This study aims at investigating the influence of different phytoplankton species on the surface shear viscosity of an air-water interface. Measurements of surface shear viscosity were carried out with the ISR1 interfacial shear rheometer. Surface shear viscosities of stock cultures of Phaeocystis sp., Thalassiosira rotula, Thalassiosira punctigera and Nitzschia closterium as well as of F/2 nutrient medium and seawater were measured. The surface shear viscosity of N. closterium was investigated during different stages of its growth as well as for an unfiltered stock culture sample and its filtrate. Results reveal that the influence of phytoplankton on the surface shear viscosity is species specific. An increase in surface shear viscosity occurred for the N. closterium stock culture only. The remaining cultures showed similar behaviour to F/2 nutrient medium. The increase of surface shear viscosity during the growth of N. closterium occurred mainly during the exponential growth phase. The increases in surface shear viscosity depend on the presence of phytoplankton cells in the sample. The formation of compact mechanical structures at the air-water interface originating from the aggregation of DOM released by N. closterium as a cause for the observed increases in surface shear viscosity is discussed.
Bokun Chen - One of the best experts on this subject based on the ideXlab platform.
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photoperiod mediates the differential physiological responses of smaller Thalassiosira pseudonana and larger Thalassiosira punctigera to temperature changes
Journal of Applied Phycology, 2020Co-Authors: Jihua Liu, Bokun ChenAbstract:Global warming is altering both phytoplankton-experienced temperature and light-exposure duration through shifting their niches from low to high latitudes. We explored the growth, physiology, and compositions of a smaller Thalassiosira pseudonana and a larger Thalassiosira punctigera, temperate marine centric diatoms, in responses to a matrix of temperatures (12, 15, 18, and 21 °C) and photoperiods (light:dark cycles of 4:20, 8:16, 16:8, and 24:0). Both T. pseudonana and T. punctigera grew faster under medium temperature and longer photoperiod, under the expected optimal instantaneous light intensity. The biovolume-based pigments content of T. pseudonana responded largely to temperature, while that of T. punctigera responded more to photoperiod duration than to temperature. In T. pseudonana, shortest photoperiod enhanced cellular protein content and alleviated their temperature dependency. Continuous growth light reduced the photosynthetic capacity of T. pseudonana at the lowest temperature and reduced that of T. punctigera across temperatures. Moreover, we found the increasing temperature linearly increased the dark respiration rate (Rd) and molar ratio of carbon to nitrogen (C:N) of T. pseudonana but decreased that of T. punctigera, with the scattered effects of photoperiod. Our results demonstrated that responses of diatoms Thalassiosira across photoperiods and temperatures vary with species and possibly with cell size, suggesting that the poleward shift of the niches of phytoplankton in nature might cause a change in community structure.
Verena Kuhnhenn - One of the best experts on this subject based on the ideXlab platform.
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Surface shear rheological studies of marine phytoplankton cultures - Nitzschia closterium, Thalassiosira rotula, Thalassiosira punctigera and Phaeocystis sp.
Colloids and surfaces. B Biointerfaces, 2006Co-Authors: Verena Kuhnhenn, Jürgen Krägel, Ulrich Horstmann, Reinhard MillerAbstract:The study of interfacial properties in the marine environment is important for the understanding of air-sea gas exchange processes, especially with respect to the behaviour of entrained air bubbles. Seawater contains surfactant material, much of which is thought to origin from the exudation of dissolved organic material (DOM) by phytoplankton. This study aims at investigating the influence of different phytoplankton species on the surface shear viscosity of an air-water interface. Measurements of surface shear viscosity were carried out with the ISR1 interfacial shear rheometer. Surface shear viscosities of stock cultures of Phaeocystis sp., Thalassiosira rotula, Thalassiosira punctigera and Nitzschia closterium as well as of F/2 nutrient medium and seawater were measured. The surface shear viscosity of N. closterium was investigated during different stages of its growth as well as for an unfiltered stock culture sample and its filtrate. Results reveal that the influence of phytoplankton on the surface shear viscosity is species specific. An increase in surface shear viscosity occurred for the N. closterium stock culture only. The remaining cultures showed similar behaviour to F/2 nutrient medium. The increase of surface shear viscosity during the growth of N. closterium occurred mainly during the exponential growth phase. The increases in surface shear viscosity depend on the presence of phytoplankton cells in the sample. The formation of compact mechanical structures at the air-water interface originating from the aggregation of DOM released by N. closterium as a cause for the observed increases in surface shear viscosity is discussed.
Jean-jacques Pichon - One of the best experts on this subject based on the ideXlab platform.
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The biogeography of major diatom taxa in Southern Ocean sediments: 2. Open ocean related species
Palaeogeography Palaeoclimatology Palaeoecology, 2005Co-Authors: Xavier Crosta, Oscar Romero, Leanne Armand, Jean-jacques PichonAbstract:Diatom assemblages from 228 core-top samples were investigated to determine the modern geographic distributions of 10 major open ocean species or species groups in the Atlantic and Indian sectors of the Southern Ocean. Our study gives a more comprehensive view of the relationships between diatom distribution and environmental pressures than previous studies, as our modern database covers a much wider area, and additionally highlights the relationships with sea ice cover and concentration. The 10 species or species categories can mainly be lumped into three groupings. First, a cool open ocean grouping composed of Rhizosolenia pointed group, Thalassiosira gracilis group and Trichotoxon reinboldii with maximum relative abundances occurring within the maximum winter sea-ice edge. Second, a pelagic open ocean grouping composed of Fragilariopsis kerguelensis, Thalassiosira lentiginosa, Thalassiosira oliverana and Thalassiothrix spp. group with maximum occurrences at the Antarctic Polar Front. Third, a warm open ocean grouping with maximum abundances observed within the Polar Front Zone and composed of the Rhizosolenia rounded group, the Thalassionema nitzschioides var. nitzschioides group and the Thalassionema nitzschioides var. lanceolata. Comparisons of the abovementioned 10 species or species groups with modern February sea-surface temperatures and sea-ice duration and concentration reveal species-specific sedimentary distributions regulated both by sea-surface temperatures and sea ice conditions that support the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches.
Jürgen Krägel - One of the best experts on this subject based on the ideXlab platform.
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Surface shear rheological studies of marine phytoplankton cultures - Nitzschia closterium, Thalassiosira rotula, Thalassiosira punctigera and Phaeocystis sp.
Colloids and surfaces. B Biointerfaces, 2006Co-Authors: Verena Kuhnhenn, Jürgen Krägel, Ulrich Horstmann, Reinhard MillerAbstract:The study of interfacial properties in the marine environment is important for the understanding of air-sea gas exchange processes, especially with respect to the behaviour of entrained air bubbles. Seawater contains surfactant material, much of which is thought to origin from the exudation of dissolved organic material (DOM) by phytoplankton. This study aims at investigating the influence of different phytoplankton species on the surface shear viscosity of an air-water interface. Measurements of surface shear viscosity were carried out with the ISR1 interfacial shear rheometer. Surface shear viscosities of stock cultures of Phaeocystis sp., Thalassiosira rotula, Thalassiosira punctigera and Nitzschia closterium as well as of F/2 nutrient medium and seawater were measured. The surface shear viscosity of N. closterium was investigated during different stages of its growth as well as for an unfiltered stock culture sample and its filtrate. Results reveal that the influence of phytoplankton on the surface shear viscosity is species specific. An increase in surface shear viscosity occurred for the N. closterium stock culture only. The remaining cultures showed similar behaviour to F/2 nutrient medium. The increase of surface shear viscosity during the growth of N. closterium occurred mainly during the exponential growth phase. The increases in surface shear viscosity depend on the presence of phytoplankton cells in the sample. The formation of compact mechanical structures at the air-water interface originating from the aggregation of DOM released by N. closterium as a cause for the observed increases in surface shear viscosity is discussed.
