Geochemical and Microstructural Signals in Giant ClamTridacna maximaRecorded Typhoon Events at Okinotori Island, Japan

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AbstractTo validate the usability of the giant clam shell as a recorder of short‐term environmental changes such as typhoons, we collected a liveTridacna maximafrom Okinotori Island, Japan, on 15 June 2006. Growth increment thickness, stable isotope ratio (δ18Oshell, δ13Cshell), and the barium/calcium ratio (Ba/Ca) in theT. maximashell sample were measured and compared to Okinotori Island instrumental environmental data. In the outer layer of the shell sample, there were 365 ± 6 growth increments per year, as estimated by the δ18Oshellprofile compared with sea surface temperature. The growth increments in the specimen were formed daily, and thus, we can determine the date of the sampling points of δ18Oshell, δ13Cshelland the Ba/Ca ratio by counting growth increments. After typhoon approach, there is a decrease in increment thickness and some disturbed growth increments. The positive peaks in the shell Ba/Ca ratio and δ18Oshellcorresponded to lower sea surface temperature caused by typhoons. These results indicated that the microstructural and geochemical record inTridacna maximashells could be useful for detecting past typhoon events.