Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in ¹¹B relative to ¹⁰B (δ¹¹B = −1.2 to +7.7) and ⁷Li relative to ⁶Li (δ⁷Li = −1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (δ¹¹B = −16.6 to −2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle.     

Application of a 3-D chemical fate prediction model (FATE3D) to predict dioxin concentrations in the Tokyo Bay

A 3-D chemical fate prediction model (FATE3D) was applied to predict the dioxin concentrations in the seawater of Tokyo Bay, Japan. The simulations were carried out for a period of one year (from September 2002 to August 2003). Parameters such as meteorological data, flow field conditions, concentrations and sinking rates of organic particulate matter, initial and boundary conditions, and loading fluxes and physico-chemical properties of dioxins were used as the model inputs.The simulation results compared favorably with the field measurements of dioxin concentrations in the bay for both the particulate and dissolved phases, indicating the validity and predictive capability of the model. Furthermore, the differences in the seasonal cycles and distributions between the particulate- and dissolved-phase dioxins in the bay were estimated from the simulation results.However, the particulate-phase dioxin concentrations in the bottom layers (+1 m from the bottom) were underestimated, probably because the resuspension process was not taken into account in the model. The improvement of the model's predictive capability, including the resuspension process, shall be the focus of our next study.     

Global distribution and atmospheric transport of chlorinated hydrocarbons: HCH (BHC) isomers and DDT compounds in the Western Pacific,Eastern Indian and Antarctic Oceans

Concentrations of chlorinated hydrocarbons such as HCH isomers and DDT compounds were determined in air and surface water samples taken from the Western Pacific, Eastern Indian and Antarctic Oceans. The most interesting finding was their presence in measurable concentrations in the Antarctic Ocean. Chlorinated hydrocarbon pesticides are widely distributed in the open ocean environment over both the northern and southern hemispheres, and some characteristic distribution patterns of pesticide species in different oceanic regions were observed both in air and water samples. HCH residues found in the northern hemisphere were much higher in concentration than those in the southern hemisphere. On the other hand, higher concentrations of DDT residues were found in the tropical regions, but their levels were not so different between both the northern and southern hemispheres. HCH isomers found in the northern hemisphere had the following order of concentrations:-HCH> HCH>-HCH, while in the southern hemisphere-HCH was apparently dominant. DDT compound compositions were rather uniform in all the oceans surveyed, and more than 50% wasp,p-DDT. These facts can be explained by the world wide situation regarding pesticide use and the physicochemical properties of the pesticides such as their vapor pressures and water solubilities. In addition, the meridional circulation of the atmosphere, particularly the mass flows of the Hadley and Ferrel cells in the troposphere, also contributes to the atmospheric transport and global distribution of these pesticides.     

Chlorinated hydrocarbons in the North Pacific and Indian Oceans

PCBs, DDT compounds and HCH isomers were detected in the air and surface waters of the North Pacific and Indian Oceans, including the Bering Sea, East China Sea, South China Sea, Bay of Bengal and the Arabian Sea. The general concentrations of each chlorinated hydrocarbon were as follows: water PCBs 0.1 to 1.0, DDT 0.01 to 1.0, HCH 1.0 to 10 ngl ^–1; air DDT 0.01 to 1.0, HCH 0.1 to 10 ng m^–3. PCB concentrations in surface waters were slightly lower than those of the North Atlantic and North Sea previously reported, while DDT concentrations in the air and water were higher. Remarkably high concentrations of DDT and HCH were found in the air off the western coast of India. Also in the Pacific site off Central America, a fairly high concentration of DDT was observed in an air sample. These data suggest that large amounts of DDT and HCH are being used in the tropical zone, especially in southern Asia. Furthermore, high concentrations were observed both in the air and water of the Northwest Pacific between 30°N and 40°N latitude. There is a possibility that both pesticides are not only still being used in lower latitude countries but also in the mid-latitude ones of the Asian continent excluding Japan. In addition to this atmospheric circulation may also contribute to the concentration of these pesticides in the mid-latitudinal zone.     

Can the visualization of rip currents prevent drowning accidents? Consideration of the effect of optimism bias

Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.

     

Farm income,inequality, and poverty among farm families of a flood-prone area in Bangladesh: climate change vulnerability assessment

GeoJournal - This paper examines the farm income differences, income inequality of farm households, parameters of income variability that ascertain vulnerability levels, and cost-income variability...     

Wavenumber spectra of planetary-scale disturbances in the Mars atmosphere

Wavenumber spectra of the martian atmosphere covering zonal wavenumbers s=1-6 were obtained as a function of latitude and season for the first time from the temperatures measured by the Thermal Emission Spectrometer onboard the Mars Global Surveyor. The stationary component tends to peak at s=2, where the martian topography has large amplitude, and drops rapidly at higher wavenumbers. The transient component in the middle and high latitudes tends to peak at s=1, which is lower than the most unstable wavenumber based on linear theories, and exhibits spectral slopes much flatter than the stationary component. In the equatorial region, the spectra of the transient component are almost flat, indicating that the organization of large-scale structures is less efficient in this region. The spectral shapes are similar between the 0.5 and 2.2 hPa surfaces, except that the slopes are slightly steeper at 0.5 than at 2.2 hPa, probably due to selective vertical transmission at low wavenumbers. The seasonal variation is relatively large in the middle and high latitudes, where the maximum power occurs in winter and the minimum occurs in summer, with an exception that the transient component is maximum in spring in the southern hemisphere. Intensification of s=1 transient waves is observed around the period of the initiation of global dust storms.