Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba 277-8564, Japan.
Nat Commun. 2012 Mar 27;3:761. doi: 10.1038/ncomms1763.
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.
热带和亚热带地区的日光照周期历史记录很短。此外，从生物成因的海洋碳酸盐等自然档案中提取过去的这种周期仍然很困难。在这里，我们使用分辨率为 2 微米的横向高分辨率二次离子质谱仪，详细分析了养殖巨蚌壳中的 Sr/Ca、Mg/Ca 和 Ba/Ca 比值。Sr/Ca 比值呈现出显著的日变化，反映了日光照周期。在分辨率为 50 微米的另一组更长的测量中，也观察到 Sr/Ca 的明显季节性变化。巨蚌和共生藻类中的光增强钙化和元素运输过程可能解释了这些昼夜和年度变化。这为从巨蚌壳中开发 Sr/Ca 比值作为日光照周期参数的有效替代物提供了可能性。
