Abstract
We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. Mg/Ca ratios of the inner surface of the outer shell layer, corresponding to the most recent date, show cyclic changes at 25–90 μm intervals, while no interpretable variations are observed in Sr/Ca and Ba/Ca ratios. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, therefore serving a proxy of the past tsunami. Following the tsunami, periodic peaks and troughs in Mg/Ca continued, perhaps due to a biological memory effect as an endogenous clock.
Highlights
We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan
There are a couple of analytical methods which permit trace element determination with both detection limits in the ppb to ppm range and a lateral spatial resolution better than 200 μm scale such as Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES) with a micro-drill sampling technique, Inductively Coupled Plasma Mass Spectrometry (ICPMS) carried out with a laser-ablation sampling technique and Secondary Ion Mass Spectrometry (SIMS)
Using a NanoSIMS, high-resolution analysis of a giant clam shell has provided an environmental proxy of the finest published temporal resolution Sr/Ca ratios produced by daily light c ycles[7] and Fe/Ca ratios produced by extreme weather e vents[8]; data at this short temporal scale of a bivalve shell appear to be occasionally influenced by unexpected biological controls on an organism’s physiology and not directly related to the ambient seawater temperature[9]
Summary
We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, serving a proxy of the past tsunami. Based on observation, we discuss an hourly Mg/Ca anomaly possibly derived from a great tsunami induced by the 2011 Tohoku earthquake
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