title: Past daily light cycle recorded in the strontium/calcium ratios of giant clam shells.
abstract: The historical record of daily light cycle in tropical and subtropical regions is short. Moreover, it remains difficult to extract this cycle in the past from natural archives such as biogenic marine carbonates. Here we describe the precise analysis of Sr/Ca, Mg/Ca, and Ba/Ca ratios in a cultivated giant clam shell, using a laterally high-resolution secondary ion mass spectrometer with 2 μm resolution. The Sr/Ca ratio exhibits striking diurnal variations, reflecting the daily light cycle. A clear seasonal variation in Sr/Ca is also observed in another longer set of measurements with 50 μm resolution. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these diurnal and annual variations. This opens the possibility to develop the Sr/Ca ratio from a giant clam shell as an effective proxy for parameters of the daily light cycle.
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba 277-8564, Japan. ysano@aori.u-tokyo.ac.jp
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sano
authors.forename: Sayumi
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Kotaro
authors.initials: K
authors.lastname: Shirai
authors.forename: Naoto
authors.initials: N
authors.lastname: Takahata
authors.forename: Katsumi
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Kohki
authors.initials: K
authors.lastname: Sowa
authors.forename: Kenji
authors.initials: K
authors.lastname: Iwai
mesh_terms: D060105:Animal Shells / Q000737:chemistry* / Q000502:physiology; D000818:Animals; D059001:Aquatic Organisms / Q000502:physiology; D001464:Barium / Q000032:analysis; D049872:Bivalvia / Q000502:physiology*; D002118:Calcium / Q000032:analysis*; D002254:Carbonates / Q000032:analysis; D002940:Circadian Rhythm; D004777:Environment; D008274:Magnesium / Q000032:analysis; D017440:Photoperiod; D012621:Seasons; D012758:Shellfish; D018629:Spectrometry, Mass, Secondary Ion; D013324:Strontium / Q000032:analysis*; D014329:Tropical Climate
chemical_list: D002254:Carbonates; D001464:Barium; D008274:Magnesium; D002118:Calcium; D013324:Strontium