11:45 AM - 12:15 PM
★ [U04-06] Ultra-high resolution past environmental reconstruction-Insolation extracted from giant clam shells-
Keywords:past marine environment, insolation, NanoSIMS, giant clam shell
We have measured minor (Mg and Sr) and trace (Ba) elements of living giant clam and fossil clam shells. Living sample (Tridacna derasa) was cultivated from March 2002 to October 2005 at Kabira coral reef of Ishigaki Island in the southwestern part of the Ryukyu Archipelago, southern Japan. A clear seasonal variation in Sr/Ca ratio is observed in longer set of measurements with 50 micron resolution. In addition the ratio exhibits striking diurnal variations by 2 micron resolution, reflecting the daily light cycle. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these annual and diurnal variations . About 5000 years old fossil sample (Tridacna gigas) was collected in August 2007 at Shiraho coast of the same island. The Sr/Ca ratios in the winter layers of the sample are characterized by a striking diurnal cycle consisting of narrow growth lines with high Sr/Ca ratios and broad growth bands with low Sr/Ca ratios. These variations, which are consistent with those of the cultivated clam shell, indicate the potential for the reconstruction of the variation in solar insolation during the middle Holocene at a few hours resolution .
 Henderson (2002) Earth Planet. Sci. Lett. 203, 1-3.  Sano et al. (2005) Anal. Sci. 21, 1091-1097.  Sano et al. (2012) Nature Commun. 3, 761.  Hori et al. (2015) Scientific Reports, in press.