No abstract

Chalcedony is a porous spatial arrangement of hydroxylated nanometre sized α-quartz (SiO(2)) crystallites. Due to micro-structural transformations upon heat treatment, the optical and mechanical properties of the rock are modified. We investigated these transformations in sedimentary length-fast chalcedony through Fourier Transform near- and mid-infrared spectroscopy using direct transmission and the reflectivity. Chemical adsorption potential and absorption of H(2)O by pores was studied after heat treatment. We found that water held in open porosity is reduced upon heat treatment to temperatures above 150°C. Silanole is noticeably lost from 250 to 300°C upwards and new bridging Si-O-Si further reduces the surface of open pores, creating a less porous material. Molecular water, resulting from the reaction Si-OH HO-Si→Si-O-Si+H(2)O creates new isolated pores within the material. At temperatures above 500°C, the samples start internal fracturing, permitting water held in isolated pores to be evacuated. These results shed light on thermal transformations in chalcedony and allow for a better understanding of mechanical transformations after heat treatment.

Ocean acidification is a major global stressor that leads to substantial changes in seawater carbonate chemistry, with potentially significant consequences for calcifying organisms. Marine shelled mollusks are ecologically and economically important species providing essential ecosystem services and food sources for other species. Because they use calcium carbonate (CaCO 3) to produce their shells, mollusks are among the most vulnerable invertebrates to ocean acidification, with early developmental stages being particularly sensitive to pH changes. This study investigated the effects of CO 2-induced ocean acidification on larval development of the European abalone Haliotis tuberculata, a commercially important gastropod species. Abalone larvae were exposed to a range of reduced pHs (8.0, 7.7 and 7.6) over the course of their 2 development cycle, from early-hatched trochophore to pre-metamorphic veliger. Biological responses were evaluated by measuring the survival rate, morphology and development, growth rate and shell calcification. Larval survival was significantly lower in acidified conditions than in control conditions. Similarly, larval size was consistently smaller under low pH conditions. Larval development was also affected, with evidence of a developmental delay and an increase in the proportion of malformed or unshelled larvae. In shelled larvae, the intensity of birefringence decreased under low pH conditions, suggesting a reduction in shell mineralization. Since these biological effects were observed for pH values expected by 2100, ocean acidification may have potentially negative consequences for larval recruitment and persistence of abalone populations in the near future.