Marine bivalve geochemistry and shell ultrastructure from modern low pH environments

Abstract. Bivalve shells can provide excellent archives of past environmental change but have not been used to interpret ocean acidification events. We investigated carbon, oxygen and trace element records from different shell layers in the mussels Mytilus galloprovincialis (from the Mediterranean) and M. edulis (from the Wadden Sea) combined with detailed investigations of the shell ultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy) were transplanted and grown in water with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the east coast of the island of Ischia. The shells of transplanted mussels were compared with M. edulis collected at pH ~8.2 from Sylt (German Wadden Sea). Most prominently, the shells recorded the shock of transplantation, both in their shell ultrastructure, textural and geochemical record. Shell calcite, precipitated subsequently under acidified seawater responded to the pH gradient by an in part disturbed ultrastructure. Geochemical data from all test sites show a strong metabolic effect that exceeds the influence of the low-pH environment. These field experiments showed that care is needed when interpreting potential ocean acidification signals because various parameters affect shell chemistry and ultrastructure. Besides metabolic processes, seawater pH, factors such as salinity, water temperature, food availability and population density all affect the biogenic carbonate shell archive.</jats:p

number 2 OPTICS COMMUNICATIONS

Holographically made zone plates are described. Imaging properties and spectrometric applications are discussed. Experimental results with soft X-radiation are given

Biodegradation of textile waste by marine bacterial communities enhanced by light

Knowledge of biofilm formation on pollutants in the marine realm is expanding, but how communities respond to substrates during colonization remains poorly understood. Here, we assess community assembly and respiration in response to two different micropollutants, virgin high‐density polyethylene (HDPE) microbeads and textile fibres under different light settings. Raman characterization, high‐throughput DNA sequencing data, quantitative PCR, and respiration measurements reveal how a stimulation of aerobic respiration by micropollutants is translated into selection for significantly different communities colonizing the substrates. Despite the lack of evidence for biodegradation of HDPE, an increased abundance and respiration of bacterial taxa closely related to hydrocarbonoclastic Kordiimonas spp. and Alteromonas spp. in the presence of textile waste highlights their biodegradation potential. Incubations with textile fibres exhibited significantly higher respiration rates in the presence of light, which could be partially explained by photochemical dissolution of the textile waste into smaller bioavailable compounds. Our results suggest that the development and increased respiration of these unique microbial communities may potentially play a role in the bioremediation of the relatively long‐lived textile pollutants in marine habitats, and that the respiration of heterotrophic hydrocarbon‐degrading bacteria colonizing marine pollutants can be stimulated by light

A Study on Ikaite Growth in the Presence of Phosphate

Phosphate is a common component in natural growth solutions of ikaite. Although phosphate often occurs as a minor constituent, its presence may promote the formation of ikaite as it significantly inhibits the precipitation of calcite. The interactions of phosphate with ikaite and the role of a potential uptake of phosphate by ikaite, however, are poorly understood. In this study, the influence of phosphate on ikaite growth at 1 °C was investigated. Ikaite and calcite seeded growth experiments were conducted in cryo-mixed-flow reactors at saturation ratios 1.5 ≤ Ωikaite ≤ 2.9 (Ω = ionic activity product/solubility product). From these growth experiments, the rate constant k = 0.10 ± 0.03 µmol/m2/s and the reaction order n = 0.8 ± 0.3 were derived for ikaite. The reaction order implies a transport or adsorption controlled growth mechanism which supports a low energy pathway of ikaite growth via an attachment of hydrous CaCO30 complexes without any extensive dehydration of aqueous species as, for instance, required for calcite growth. A potential depletion of aqueous phosphate due to an uptake by ikaite growth was not detectable. Furthermore, growth retardation by phosphate, as known for calcite growth, was not evident. Thus, a significant incorporation of phosphate into growing ikaite could be precluded for the conditions applied in this study. The observed lack of incorporation of phosphate agrees with the previously suggested growth mechanism via the attachment of hydrous CaCO30 complexes which likely does not facilitate substantial substitution of carbonate by phosphate ions

Micromechanical properties and structural characterization of modern inarticulated brachiopod shells

[1] We investigated micromechanical properties and ultrastructure ofthe shells of the modern brachiopod species Lingula anatina, Disciniscalaevis, and Discradisca stella with scanning electron microscopy (SEM,EDX), transmission electron microscopy (TEM) and Vickers microhardnessindentation analyses. The shells are composed of two distinct layers, anouter primary layer and an inner secondary layer. Except for the primarylayer in Lingula anatina, which is composed entirely of organic matter,all other shell layers are laminated organic/inorganic composites. Theorganic matter is built of chitin fibers, which provide the matrix forthe incorporation of calcium phosphate. Amorphous calcium phosphate inthe outer, primary layer and crystalline apatite is deposited into theinner, secondary layer of the shell. Apatite crystallite sizes in theumbonal region of the shell are about 50 x 50 nm, while within thevalves crystallite sizes are significantly smaller, averanging 10 x 25nm. There is great variation in hardness values between shell layers andbetween the investigated brachiopod species. The microhardness of theinvestigated shells is significantly lower than that of inorganichydroxyapatite. This is caused by the predominantly organic materialcomponent that in these shells is either developed as purely organiclayers or as an organic fibrous matrix reinforced by crystallites. Ourresults show that this particular fiber composite material is veryefficient for the protection and the support of the soft animal tissue.It lowers the probability of crack formation and effectively impedescrack propagation perpendicular to the shell by crack-deviationmechanisms. The high degree of mechanical stability and toughness isachieved by two design features. First, there is the fiber compositematerial which overcomes some detrimental and enhances some advantageousproperties of the single constituents, that is the softness andflexibility of chitin and the hardness and brittleness of apatite.Second, there is a hierarchical structuring from the nanometer to amicrometer level. We could identify at least seven levels of hierarchywithin the shells

A rotating condenser and off-axis zone plate monochromator for the TXM at the undulator U41 at BESSY II

Abstract The G . ottingen transmission X-ray microscope at the low emittance electron storage ring BESSY II uses the concept of dynamical aperture synthesis (Reynolds, DeVelis, Parrent, Thomson (Eds.), The New Physical Optics Notebook, SPIE, 1990, pp. 536-548) for the object illumination. The concept is well suited as a condenser, as it can match any required numerical aperture of the TXM objective. Furthermore, a novel off-axis transmission zone-plate monochromator is included, which can generate a monochromaticity of several thousand in the object illumination.

Marine bivalve shell geochemistry and ultrastructure from modern low pH environments: environmental effect versus experimental bias

Bivalve shells can provide excellent archives of past environmentalchange but have not been used to interpret ocean acidification events.We investigated carbon, oxygen and trace element records from differentshell layers in the mussels Mytilus galloprovincialis combined withdetailed investigations of the shell ultrastructure. Mussels from theharbour of Ischia (Mediterranean, Italy) were transplanted and grown inwater with mean pHT 7.3 and mean pHT 8.1 near CO2 vents on the eastcoast of the island. Most prominently, the shells recorded the shock oftransplantation, both in their shell ultrastructure, textural andgeochemical record. Shell calcite, precipitated subsequently underacidified seawater responded to the pH gradient by an in part disturbedultrastructure. Geochemical data from all test sites show a strongmetabolic effect that exceeds the influence of the low-pH environment.These field experiments showed that care is needed when interpretingpotential ocean acidification signals because various parameters affectshell chemistry and ultrastructure. Besides metabolic processes,seawater pH, factors such as salinity, water temperature, foodavailability and population density all affect the biogenic carbonateshell archive

Inhomogeneous magnetization in dipolar ferromagnetic liquids

At high densities fluids of strongly dipolar spherical particles exhibit spontaneous long-ranged orientational order. Typically, due to demagnetization effects induced by the long range of the dipolar interactions, the magnetization structure is spatially inhomogeneous and depends on the shape of the sample. We determine this structure for a cubic sample by the free minimization of an appropriate microscopic density functional using simulated annealing. We find a vortex structure resembling four domains separated by four domain walls whose thickness increases proportional to the system size L. There are indications that for large L the whole configuration scales with the system size. Near the axis of the mainly planar vortex structure the direction of the magnetization escapes into the third dimension or, at higher temperatures, the absolute value of the magnetization is strongly reduced. Thus the orientational order is characterized by two point defects at the top and the bottom of the sample, respectively. The equilibrium structure in an external field and the transition to a homogeneous magnetization for strong fields are analyzed, too.Comment: 17 postscript figures included, submitted to Phys. Rev.