Recent seismic monitoring mainly by the Hi-net High sensitivity seismograph network in Japan for the last decade has been revealing the 3D structure of velocity anomaly in the crust and mantle due to heterogeneous presence of deep-seated fluids and fluid-related deep low frequency earthquakes in subduction zones of Japan arc. Petrological water circulation models combined with geophysical subduction models quantitatively show the water budget in the solid earth. The recent findings infer the importance of deep hydrothermal fluid on the occurrence of inland earthquakes. As the models are built with the result obtained by monitoring, experimental techniques or simulations, implications from evidence-based geochemical and geological studies are expected for the proof of water circulation models. Hence, we examined chemical features of deep groundwaters in SW Japan arc, and showed spatial distribution of deep-seated fluid mixed into groundwater. We found that the deep-seated fluid, whose isotopic composition is similar to magmatic, has the high Li/Cl ratio 0.001 in wt. ratio and concluded that Li/Cl is a good indicator for detecting the slab-related deep-seated fluid in groundwaters. Spatial distribution of Li/Cl reveals that slab-related deep-seated fluid upwells along the faults and tectonic lines, and at close to Quaternary volcanoes in SW Japan arc. In most cases, upwelling places are found close to the areas where deep low frequency DLF earthquakes are occurring, implying that deep-seated fluid causes DLF events.
Aegagropila linnaei is a freshwater green alga, which at one time was distributed widely in the northern hemisphere. The aggregate often forms beautiful spherical shapes known as “lake balls” or “Marimo”. The population of Marimo has been rapidly decreasing worldwide, and today the large Marimo, with a diameter of more than 12 cm, exit only in Lake Akan in Japan. However, how Marimo grow and maintain their unique spherical shape in natural habitats remains unsolved. Here we show that Marimo are “polished” into spheres by the rotation induced by wind waves. Such a process enhances the water exchange between the interior and exterior of the Marimo, thereby recycling nutrients for growth. Our results provide an intriguing model of a physical environment interacting with biological processes in a self-sustaining ecosystem. We also demonstrate that Marimo have a spherical annual ring structure, and their growth rate is associated with ice cover. The balance between the ecology of Marimo and the water environment in Lake Akan is highly vulnerable and at risk of irreversible degradation. We must endeavor to rescue Marimo from the fate of a "canary in the coal mine" of global climate change.
Satellite remote sensing is a highly useful tool for monitoring chlorophyll-a concentration (Chl-a) in water bodies. Remote sensing algorithms based on near-infrared-red (NIR-red) wavelengths have demonstrated great potential for retrieving Chl-a in inland waters. This study tested the performance of a recently developed NIR-red based algorithm, SAMO-LUT (Semi-Analytical Model Optimizing and Look-Up Tables), using an extensive dataset collected from five Asian lakes. Results demonstrated that Chl-a retrieved by the SAMO-LUT algorithm was strongly correlated with measured Chl-a (R 2 = 0.94), and the root-mean-square error (RMSE) and normalized root-mean-square error (NRMS) were 8.9 mg•m −3 and 72.6%, respectively. However, the SAMO-LUT algorithm yielded large errors for sites where Chl-a was less than 10 mg•m −3 (RMSE = 1.8 mg•m −3 and NRMS = 217.9%). This was because differences in water-leaving radiances at the NIR-red wavelengths (i.e., 665 nm, 705 nm and 754 nm) used in the SAMO-LUT were too small due to low concentrations of water constituents. Using a blue-green algorithm (OC4E) instead of the SAMO-LUT for the waters with low constituent concentrations would have reduced the RMSE and NRMS to 1.0 mg•m −3 and 16.0%, respectively. This indicates(1) the NIR-red algorithm does not work well when water constituent concentrations are
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