ALBERT

Description: A program of geophysical research was carried out as a preliminary stage of study of the Santorini volcanic group. This area is of remarkable geothermal and volcanological interest, and the definition of a volcanological structural model is the starting point for an understanding of the local geodynamic processes. Gravity, magnetic and geoelectrical data proved that: (i) the core of the volcanic edifice consists of a sedimentary-metamorphic basement; (ii) the basement is tectonically disturbed and a linear tectonic system produces a graben-type structure in the middle part of the area.

Description: The strontium, magnesium, and calcium contents of the shells of the planktonic foraminifer Globorotalia truncatulinoides from continental rise sediments were determined by electron microprobe. This species spends the early part of its life cycle in the upper water column where it precipitates the lamellar portion of its shell. It then sinks below the permanent thermocline where it is secondarily calcified with a blocky calcite coating. This change of environments through the organism’s life allows a test of the hypothesis that an individual can change the composition of the carbonate material secreted in response to changes in the temperature of of the water mass in which it lives. All individuals except a juvenile showed decreasing magnesium contents in the outermost portion of their shells, corresponding to decreasing temperature in successively deeper water. The juvenile form showing no secondary calcification was uniform in composition. Because the Mg/Ca ratio in seawater is constant, this differentiation strongly supports the contention that an individual organism, as it precipitates shell material, can regulate its composition in response to environmental changes in temperature. No significant differences in composition were found between left- and right-coiling specimens. The difference between lamellar and blocky calcite was found to be significantly less in a sample from 10 cm below the top of the piston core than those from above or below this level. This difference is produced by a decrease in the magnesium content of the lamellar calcite and may correspond to a surface water temperature 2.5°C lower approximately 1,100 years ago.

Description: A small collection of otoliths was obtained from scatsof sub-adult male Antarctic fur seals Arctocephalus gazella at Bird Island, South Georgia. A reference collection of otoliths from South Georgia fish was used to identify the material and to derive relationships between otolith length and fish weight which were then applied to the sample otolith, after correcting for loss of material during digestion. The pelagic icefish Chamsocephalus gunnari was the main prey, in terms of numbers (55%) and weight (76%) of fish consumed. Other species taken include thelantern fish Gymnoscoscopelus nicholsi, the nototheniids Notothenia rossii. Notothenia gibberifrons, and Patagonotothen larseni and Pseudochaenichthys georgianus. The estimated mean weight of the C. gunnari specimens was 160kg (range 45-560g) and most were young adults aged 3-5 years; individuals of other species were mainly much smaller.

Description: Infrared and Mössbauer spectroscopy show that the extent of the reduction of nontronite is dependent on the chemical composition of the nontronite and on the nature of the reducing agent. Hydrazine reversibly reduces about 10% of the iron in all of the nontronites studied irrespective of composition and it is suggested that the resulting ferrous iron occurs only in distorted octahedral sites. Similar conclusions are reached for the dithionite reduction of the nontronites containing little tetrahedral iron, but for those with more than one in eight silicons replaced by iron, changes brought about by dithionite treatment are irreversible due to dissolution of appreciable quantities of iron. Results from both spectroscopic techniques suggest that iron in tetrahedral sites is preferentially dissolved and that up to 80% of the structural iron can be reduced. Evidence is presented for the formation in these extensively reduced nontronites of a small amount of a mica-like phase resembling celadonite or glauconite, and, as dithionite is used for the pretreatment of soils, the implication of this observation is briefly discussed. The use of deuterated hydrazine as a reducing agent has enabled the nontronite absorption band near 850 cm-1 to be assigned to a Si-O (apical) stretching vibration, which is inactive in the infrared for perfect hexagonal symmetry, but which is activated by distortions in the tetrahedral layer

Description: The internal shell of the cuttlefish, which acts as a rigid buoyancy tank, is structured to combine high compressive strength — since it must withstand the external hydrostatic pressure — with minimum weighT. The micro-architecture of cuttlebone has been examined by electron microscopy and the relevance of the structure to the mechanical duties required of the shellin vivo are briefly discussed. The inorganic calcareous structure is associated with an organic component which may act as a template for mineralization.