Novel analytical approach to bivalve shell biogeochemistry: A case study of hydrothermal mussel shell

抄録

To study the mechanism of element incorporation into bivalve shells living in hydrothermal environments, the chemical composition of deep-sea mussel (Bathymodiolus platifrons) shell was analyzed using three microanalytical techniques. Mg/Ca, Sr/Ca, Mn/Ca, and Ba/Ca ratios were measured in ∼8-μm-diameter spots by secondary ion mass spectrometry (NanoSIMS). Mg, Sr, Ca, and S distributions were analyzed by electron probe microanalyzer (EPMA; spatial resolution, ∼2 μm). Micro-scale shell structures were observed by SEM and optical microscope. The inner aragonitic layer comprised three sublayer types. The thick organic sublayers and homogeneous sublayers were interlaminated sporadically among usually deposited nacreous layers. Elemental compositions were significantly associated with shell sublayer types. The thick organic sublayers contained higher Mg/Ca, Sr/Ca and Ba/Ca ratios by factors of up to 3.0, 2.6 and 3.2, respectively, compared to the adjacent nacreous layers. On the other hand, Mn/Ca ratios in homogeneous sublayers were depleted down to one third of those in adjacent nacreous layers. Our data suggest that biological effects are significant for micro scale elemental distributions.