Estimation of groundwater residence time using the 36Cl bomb pulse

We propose a methodology for estimating the residence time of groundwater based on bomb-produced (36)Cl. Water samples were collected from 28 springs and 2 flowing wells located around Mt. Fuji, Central Japan. (36)Cl/Cl ratios in the water samples, determined by accelerator mass spectrometry (AMS), were between 43 × 10(-15) and 412 × 10(-15). A reference time series of the above-background (i.e., bomb-derived) (36)Cl concentration was constructed by linearly scaling the background-corrected Dye-3 data according to the estimated total bomb-produced (36)Cl fallout in the Mt. Fuji area. Assuming piston flow transport, estimates of residence time were obtained by comparing the measured bomb-derived (36)Cl concentrations in spring water with the reference curve. The distribution of (36)Cl-based residence times is basically consistent with that of tritium-based estimates calculated from data presented in previous studies, although the estimated residence times differ between the two tracers. This discrepancy may reflect chlorine recycling via vegetation or the relatively small change in fallout rate, approximately since 1975, which would give rise to large uncertainties in (36)Cl-based estimates of recharge for the period, approximately since 1975. Given the estimated ages for groundwater from flowing wells, dating based on a (36)Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s.     

Movement of radiocaesium fallout released by the 2011 Fukushima nuclear accident

The moment magnitude (M _w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of ¹³⁴Cs and ¹³⁷Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of ¹³⁴Cs and ¹³⁷Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs.     

Shock compression of zirconia ZrO2 and zircon ZrSiO4 in the pressure range up to 150 GPa

The shock compression state of zirconia ZrO₂ and zircon ZrSiO₄ in the pressure range up to 150 GPa (1.5 Mbar) are studied on the basis of the measurements of shock velocities, particle-velocity histories, free surface motions, and electrical conductivities. Zircon transforms, and zirconia probably does, to high pressure phases up to 90 GPa. The shock velocity (U _s ) — particle velocity (U _p ) Hugoniots can be described as U _s =4.38+1.37 U _p km/s above 90 GPa for ZrO₂, and U _s =6.50+0.49 U _p km/s (mixed phase region), and U _s =1.54+2.30 U _p km/s (high pressure phase region) for ZrSiO₄. The corrected isothermal densities of the high pressure phase ZrSiO₄ are roughly consistent with the isothermal ones of mixtures of ZrO₂ and SiO₂. Bulk sound velocities in the high-pressure phase region of these oxides are discussed in comparison with other dioxides. Electrical conductivities of these oxides increase from lower than 10^?12 S/m to greater than 10⁰ S/m in the shock-stress range up to 70 GPa, and remain as constant values up to higher than 100 GPa.     

菲律宾地热场中矿物和地球化学条件对砷迁移的制约

砷总是与硫化物共同形成于地热环境中。然而,在地表氧化条件下硫化物与雨水接触后易溶解。在地热环境中硫化物溶解后的二次沉淀物对砷的迁移有着重大的影响。溶解的砷酸盐易被铁的氢氧化物固定,且铁的氢氧化物在大多数的地表氧化条件下都可以稳定存在。地热流体中无定形SiO_2的迅速沉淀和高岭石化可以固定大量的砷。这些硅酸盐可以稳定的存在于较宽泛的pH和氧化还原条件下。菲律宾地热场中矿物和地球化学条件对砷迁移的制约@Chelo PASCUA$Graduate School of Natural Scienceand Technology,Kanazawa University,Ishikawa,Japan …     

Simulating the carbon balance of a temperate larch forest under various meteorological conditions

This editorial provides a subject index from published articles, active researchers, and published papers in the field of carbon balance and management.     

A site effect study of the Adapazari basin,Turkey, from strong- and weak-motion data

Approximately 4000 people were killed due to collapse of buildings in downtown Adapazari during the 1999 Izmit, Turkey earthquake (Mw = 7.4). The downtown is located on a deep sedimentary basin, so-called Adapazari basin. We study site effects of the Adapazari basin based on strong- and weak-motion data obtained by a temporary array observation deployed in and around the Adapazari basin after the earthquake. Four moderate-size aftershocks (M4.6–M5.8) are selected in our study. We evaluate the S-wave amplifications in the basin by using the traditional spectral ratio method. The spectral ratios show that the S waves are considerably amplified in the frequency range of 0.5 to about 5 Hz at the basin sites, but are apparently de-amplified at frequencies higher than about 10 Hz. We make a quantitative interpretation of the empirical amplifications based on the S-wave velocity structures at the stiff-soil reference site as well as at the basin sites; these structures were estimated by the microtremor array measurements. Through the interpretation, we confirm that the amplifications at low frequencies are attributed to the thick sedimentary layers in the Adapazari basin and that the apparent de-amplifications at high frequencies are partly due to the reference site response. In addition to the considerable S-wave amplifications, the basin site records show long-period (about 2 sec) later phases after the S-wave arrival; these later phases are basin-transduced surface waves that are originated from the source and transmitted into the basin. The predominant period of these waves apparently depends on the earthquake magnitude. We conclude that heavy damage in downtown Adapazari during the 1999 Izmit earthquake was caused not only by strongly amplified S-waves but also by long-period basin surface waves of long duration.     

Upper limit of heaving pressure derived by pore-water pressure measurements of partially frozen soil

Experiments were conducted to estimate heaving pressures of saturated soil partially frozen in a closed system. Temperatures at both ends of a specimen were kept constant, i.e., positive at the top and negative at the bottom. When the overburden pressure P was maintained at a constant value, the pore-water pressure P_w, which showed a certain value before freezing, decreased gradually as freezing progressed, finally attaining a specific value, whereafter the specimen ceased taking water into it. The pressure difference between P and P_w, at this stage was defined as the upper limit of heaving pressure σ_u, which evidently depended on the temperature θ_c of the cooling end, in accordance with the relation: σ_u = −11.4 θ_c (kg/cm²)

It corresponds to the modified Clausius-Clapeyron's formula, which gives the freezingpoint depression of an ice—water system, where the pressure acting on the ice differs from that on the water. This is the same as the value obtained by Radd and Oertle (1973). It is considered, however, that, when θ_c lowers, the value of θ_u reaches finally a constant value smaller than the one obtained by the above equation. Denoted by σ_{u max}, it was defined as a maximum heaving pressure. The value of σ_{u max} depended on soil type.     

Geoarchaeological investigations at the upper Paleolithic site of Kamihoronai‐Moi,Hokkaido, Japan

In order to better understand modern human behavioral variability in Hokkaido, Japan, we consider the geoarchaeology of the Kamihoronai‐Moi site in terms of its geochronology, stratigraphy, depositional environments, and post‐depositional disturbances. A Paleolithic component is stratigraphically situated between the Eniwa‐a (15,000–17,000 ¹⁴C yr B.P.) and the Tarumae‐d (8000–9000 ¹⁴C yr B.P.) tephras. Moreover, six AMS ¹⁴C ages on charcoal from a Pleistocene‐aged hearth feature are between 14,400 and 14,800 ¹⁴C yr B.P. Quantitative examinations of patterns in artifact distributions show a low degree of vertical and horizontal displacement of chipped‐stone artifacts, suggesting that post‐depositional movement of the cultural material was insufficient to disrupt the original pattern of artifact distribution. © 2009 Wiley Periodicals, Inc.