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[1] Spatial and temporal variations of submarine groundwater discharge (SGD) have been evaluated by automated seepage meters from the Yellow River delta to 7 km offshore in the Bohai Sea, China. We identified three zones from the coast to offshore based on different relationships between tidal and SGD changes. Our results indicate that the point of maximum SGD shifted 2 km offshore from September 2004 to September 2006. This spatial change is thought to be caused by sediment deposition near the coast. Integrating submarine fresh groundwater discharge (SFGD) along the coastline of the Yellow River delta using measured values of SFGD per unit length of shoreline shows that discharge of fresh groundwater along the entire delta would be equivalent to 4.5 to 7.0 % of the river discharge.

[1] Precipitation samples were collected during 45 events at 18 stations in the Kanto Plain, Japan, during June-September 1997. The hydrogen and oxygen isotope ratios were measured for each event and then the deuterium-excess parameter d was determined. Spatial variability (a few per mil) of the deuterium excess was significantly less than its temporal variability (20%). Spatially averaged d was highly correlated with vapor pressure, temperature, and wind vector in the lower atmosphere. The observed d (except for that influenced by evaporation from falling raindrops) was compared to d estimated using meteorological data from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. Estimation of d was based on a simple relationship between the deuterium excess and humidity condition over sea surface. The source area of precipitated water, as indicated by its isotopic footprint, was recognized over seas near Japan as an area where excellent agreement was found between estimated and observed values (e.g., root mean square difference <1). The location of the estimated source area appears to be quite reasonable considering with the direction of the water vapor advection in the lower atmosphere. These results suggest that event-based d values are useful for tracing the hydrological cycle in the atmosphere.INDEX TERMS: 1040 Geochemistry: Isotopic composition/ chemistry; 1655 Global Change: Water cycles (1836); 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); KEYWORDS: hydrogen and oxygen isotopes, deuterium excess, tracer, precipitation, source area, hydrological cycle Citation: Yamanaka, T., J. Shimada, and K. Miyaoka, Footprint analysis using event-based isotope data for identifying source area of precipitated water,

Large year-to-year variations of δ18O were found in the precipitation recorded in the International Atomic Energy Agency/Global Network of Isotopes in Precipitation (IAEA/GNIP) database for February at Cuiabá, located on the northern fringe of Pantanal, Brazil. Three depleted years (1963, 1978, and 1968) and three enriched years (1966, 1984, and 1983) were chosen to investigate this phenomenon and to correlate the amount of precipitation, the occurrences of storm precipitation, and the vapor flux field. In the depleted years, precipitation exceeding the long-term mean was observed at Cuiabá, while the southward vapor flux from the Amazon basin was less than the long-term mean. Since d-excesses in these years were large in general, fast evaporation must contribute to the greater precipitation observed in these depleted years. In contrast, such common features were not found in the vapor flux field in the enriched years. The occurrences of storm precipitation are important in 1966, while the amount effect is responsible for 1984. In 1983, enriched meteoric water is attributed to both the occurrences of storm precipitation and vapor flux field.