A Worldwide Groundwater Isoscape: history of cycle stored in the bottles

Isoscape is a mapping of large scale spatiotemporal distributions of stable isotope, and its use has spread into many disciplines. Groundwater records the history of precipitation of the region, and therefore, a worldwide groundwater isoscape will be useful tool to consider global water cycle under climate change condition. However, it is not so easy to collect samples worldwide without observation network. Here, we propose the global isotope map of groundwater with the measurements of worldwide bottled waters. We collected over 400 bottles from Japan and over 400 bottles from 76 nations except Japan. The oxygen and hydrogen isotope ratios of the measured bottled water range from -21.18 to -0.22 ‰ and from -162.9 to 5.0 ‰, respectively. The delta diagram showed clear liner relationship between δ2H and δ18O: δ2H = 8.11 × δ18O + 14.2 (r2= 0.97). The continental effect was clear in European region on the δ18O isoscape, except for the higher elevation points (>2000m), the isotope value clearly decreased from west to east. In Japan, the latitude effect from south to north was clear, and the elevation effect was also clear at the Japan Alps mountains locate at the central part of Japan. These patterns are similarly found in the global maps of delta18O in precipitation derived from the Global Network for Isotopes in Precipitation (GNIP). However, we successfully proposed the map with higher spatial resolutions. In addition to the spatial distribution, we investigated time sequential variation of monthly samples from 5 sources in Japan for 5 years. The coefficient of variations were less than 1.8 and this fact suggest that the groundwater bodies were stable for the years. Our findings suggest that the commercial bottled waters will be a good proxy of natural environmental water, and the bottled water isoscapes can be a snapshot of the current status of the water cycle in the world as well as of the groundwater resources.