scholarly journals Symbioses of Ciliates (Ciliophora) and Diatoms (Bacillariophyceae): Taxonomy and Host–Symbiont Interactions

Oceans ◽  
2020 ◽  
Vol 1 (3) ◽  
pp. 133-155 ◽  
Author(s):  
Fernando Gómez
Keyword(s):  
Boundary Layer ◽  
Atlantic Ocean ◽  
Competitive Advantage ◽  
Large Species ◽  
Diffusive Boundary Layer ◽  
Pelagic Environment ◽  
Diffusive Boundary ◽  
Diazotrophic Cyanobacteria ◽  
Vorticella Oceanica ◽  
Facultative Symbiosis

The nature of the plankton symbioses between ciliates and diatoms has been investigated from the tropical South Atlantic Ocean, and Mediterranean and Caribbean Seas. The obligate symbioses of the diatoms Chaetoceros dadayi or C. tetrastichon with the tintinnid Eutintinnus spp., and Chaetoceros coarctatus with the peritrich ciliate Vorticella oceanica are the most widespread, and the consortium of Chaetoceros densus and Vorticella sp. have been rediscovered. Facultative symbioses between Eutintinnus lususundae and Chaetoceros peruvianus, Hemiaulus spp., and Thalassionema sp. are less frequent, often containing three or four partners because Hemiaulus can also harbor the diazotrophic cyanobacteria Richelia intracellularis. Another three-partner consortium is the peritrich ciliate Zoothamnium pelagicum, ectobiont bacteria, and the diatom Licmophora sp. The predominantly oligotrophic conditions of tropical seas do not favor the survival of large diatoms, but large species of Coscinodiscus and Palmerina in facultative symbiosis with Pseudovorticella coscinodisci have a competitive advantage over other diatoms (i.e., reduction of sinking speed and diffusive boundary layer). Symbioses allow sessile peritric ciliates to extend their distribution in the pelagic environment, permit boreal-polar related diatoms such as C. coarctatus or Fragilariopsis doliolus to inhabit tropical seas, and help large diatoms to extend their survival under unfavorable conditions.

Countercurrent convection in a double-diffusive boundary layer

1985 ◽  
Vol 160 ◽  
pp. 181-210 ◽  
Author(s):  
R. H. Nilson
Keyword(s):  
Boundary Layer ◽  
Vertical Wall ◽  
Similarity Solutions ◽  
Relative Strength ◽  
Diffusive Boundary Layer ◽  
Buoyancy Forces ◽  
Diffusive Boundary ◽  
Laminar Convection ◽  
Similar Solutions ◽  
Double Diffusive

Countercurrent flow may be induced by opposing buoyancy forces associated with compositional gradients and thermal gradients within a fluid. The occurrence and structure of such flows is investigated by solving the double-diffusive boundary-layer equations for steady laminar convection along a vertical wall of finite height. Non-similar solutions are derived using the method of matched asymptotic expansions, under the restriction that the Lewis and Prandtl numbers are both large. Two sets of asymptotic solutions are constructed, assuming dominance of one or the other of the buoyancy forces. The two sets overlap in the central region of the parameter space; each set matches up with neighbouring unidirectional similarity solutions at the respective borderlines of incipient counterflow.Interaction between the buoyancy mechanisms is controlled by their relative strength R and their relative diffusivity Le. Flow in the outer thermal boundary layer deviates from single-diffusive thermal convection, depending upon the magnitude of the parameter RLe. Flow in the inner compositional boundary layer deviates from single-diffusive compositional convection, depending upon the magnitude of $RLe^{\frac{1}{3}}$.

Kinetic aspects of major and trace elements in olivines from variably cooled basaltic melts

2020 ◽  
Author(s):  
Sarah Lang ◽  
Silvio Mollo ◽  
Lyderic France ◽  
Manuela Nazzari ◽  
Valeria Misiti ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Trace Elements ◽  
Crystal Growth ◽  
Cooling Rate ◽  
Crystallization Kinetics ◽  
Growth Rates ◽  
Crystal Surface ◽  
Major And Trace Elements ◽  
Diffusive Boundary Layer ◽  
Diffusive Boundary

<p>Olivine is an important mineral phase in naturally cooled basaltic rocks. The texture and composition of olivine are strictly related to the interplay between the degree of magma undercooling and crystal growth rate. Crystals formed at low undercoolings and growth rates generally show polyhedral-hopper textures and quite homogeneous compositions, while skeletal-dendritic textures and evident crystal zonations occur at high undercoolings and growth rates. In this context, we have performed equilibrium and disequilibrium (i.e., cooling rate) experiments to better understand, by a comparatively approach, the effects of crystallization kinetics on the incorporation of major and trace cations in olivine lattice. The experiments were carried out in a 1 atm vertical tube CO-CO2 gas-mixing furnace to perform experiment at atmospheric pressure and oxygen fugacity of QFM-2 using a basaltic glass (i.e., OIB) as starting materials. The equilibrium experiment was performed at 1175 °C. These target temperatures were kept constant for 240 h and then quenched. Conversely, the disequilibrium experiments were performed at the superliquidus temperature of 1250, and 1300 °C, which was kept constant for 2 h before cooling. The final target temperatures of 1150 (undercooling -ΔT = 50 °C), and 1175 °C (-ΔT = 25 °C) were attained by applying cooling rates of 2 °C/h, 20 °C/h, and 60 °C/h. Then the experimental charges were quenched. Results show that the olivine texture shifts from euhedral (i.e., equilibrium) to anhedral (i.e., disequilibrium) under the effect of cooling rate and rapid crystal growth. In equilibrium experiments, the composition of olivine is homogeneous and non chemical gradients are found in the melt next to the crystal surface. In contrast, a diffusive boundary layer develops in the melt surrounding the olivine crystals growing rapidly under the effect of cooling rate and degree of undercooling. The compositional gradient in the melt increases with increasing cooling rate and undercooling, causing the diffusive boundary layer to expand towards the far field melt. Because of the effects of crystallization kinetics, skeletal-dendritic olivines incorporates higher proportions of major and trace elements that are generally incompatible within their crystal lattice under equilibrium conditions.</p>

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