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Mineralogy and Mg, Sr and Na uptake in charophyte gyrogonites from culture experiments. Paleolimnological implications.
|Authors:||Anadón, Pere ; Utrilla, Rosa ; Martín, M.; Robles, F.; Rodríguez-Lázaro, Julio; Vázquez, Antonio|
|Citation:||5th International Limnogeological Congress: 162 (2011)|
|Abstract:||Charophytes are aquatic non -marine green algae which include taxa that live in brackish waters. The enseathing cells of the female reproductive organ or oogonium of some taxa are able to calcify, producing the so called gyrogonite which may be fossilized. The interest of the geochemical studies on the gyrogonites is because the calcification process happens in few weeks during summer while the incrustation of the charophyte stems, when it occurs, usually takes place along several months of the growing season (spring to fall). Gyrogonites therefore may provide precise indications of summer limnic conditions. Three Chara species (C. vulgaris,C. hispida and C. globularis) and Lamprothamnium papulosum have been grown under controlled conditions of water chemistry, temperature (T) and light period (12h/12h) in laboratory aquaria to examine the mineralogical composition and Mg, Sr and Na uptake features of the gyrogonite calcite. Four types of water at 18, 20, 25 and 28°C were used for the cultures. The conductivity ranged from 0.8 mS/cm to 47 mS/cm; molar Mg/Ca w: 0.40 -11, Sr/Caw: 0.0030 -0.0070 and Na/Caw: 0.60 -26.3. The carbonate from the gyrogonites was analized by XR diffraction and ICP-OMS. The mineralogy of gyrogonites for the three Chara species varies from low magnesian calcite (LMC, 1 .7-4% Mg mol) to high magnesian calcite (HMC, 4.3-26% Mg mol) and to a mixture of HMC and aragonite. At low water conductivity, temperature is the main factor controlling the Mg content in the calcite; at higher T values HMC is formed in C. hispida and C. globularis gyrogonites. At moderate conductivity (5.5 mS/cm) the gyrogonites from C. hispida and C. globularis mostly consist of a mixture of HMC and aragonite; the latter increases with the water T, reaching 48-53% at 25-28°C in both species. The gyrogonites fromL. papulosum, which formed at 22 and 47 mS/cm, are made of HMC or a mixture of HMC and aragonite. Our data suggest that Mg/Ca and T of the water are not the unique factors that control the mineralogy of the obtained gyrogonites. The results for the trace-element analyses in monomineralic gyrogonites indicate that the Mg/Ca in the calcite gyrogonite is directly related to the Mg/Ca and T of the water but there is a species-specific control at low Mg/Ca w and some influence of the conductivity. In contrast, Sr/Cagyris not related with the Sr/Ca and conductivity of the water, although Sr uptake is species-specific controlled. On the other hand, the Na/Ca from gyrogonites is directly related to the water conductivity. There is no noticeable species-specific control of the Na/Cawand T in the Na uptake except for Na/CawforC. hispida|
|Appears in Collections:||(Geo3Bcn) Comunicaciones congresos|