Kinetic and equilibrium mass-dependent isotope fractionation laws in nature and their geochemical and cosmochemical significance

The mass-dependent fractionation laws that describe the partitioning of isotopes are different for kinetic and equilibrium reactions. These laws are characterized by the exponent relating the fractionation factors for two isotope ratios such that α_2/1 = α_3/1^β. The exponent β for equilibrium exchange is (1/m₁ − 1/m₂)/(1/m₁ − 1/m₃), where m_i are the atomic masses and m₁ < m₂ < m₃. For kinetic fractionation, the masses used to evaluate β depend upon the isotopic species in motion. Reduced masses apply for breaking bonds whereas molecular or atomic masses apply for transport processes. In each case the functional form of the kinetic β is ln(M₁/M₂)/ln(M₁/M₃), where M_i are the reduced, molecular, or atomic masses. New high-precision Mg isotope ratio data confirm that the distinct equilibrium and kinetic fractionation laws can be resolved for changes in isotope ratios of only 3‰ per amu. The variability in mass-dependent fractionation laws is sufficient to explain the negative Δ¹⁷O of tropospheric O₂ relative to rocks and differences in Δ¹⁷O between carbonate, hydroxyl, and anhydrous silicate in Martian meteorites. (For simplicity, we use integer amu values for masses when evaluating β throughout this paper.)     

The distribution of chlorophylla,protein, RNA and DNA in the North Pacific Ocean

Chla, protein, RNA and DNA were measured in 400 samples taken from the surface down to 5,000 m at 27 oceanographical stations in the North Pacific Ocean. Two section diagrams of these cellular constituents were given along 155°E and 155°W meridians, and several vertical profiles of the four constituents were also given at some stations near Japan. The average concentration ranges of Chla, protein, RNA and DNA obtained in this study area were 0.025–0.862, 11.4–88.1, 1.36–35.3 and 0.13–5.24g/l, respectively. Chla was distributed mostly in the photic zone as we would expect. However protein, RNA were in high concentrations within the photic zone and sometimes extremely high concentrations in the deep aphotic zone.     

Al-Mg systematics of chondrules in a primitive CO chondrite

We have conducted systematic investigations of formation age, chemical compositions, and mineralogical characteristics of ferromagnesian chondrules in Yamato-81020 (CO3.05), one of the most primitive carbonaceous chondrites, to get better understanding of the origin of chemical groups of chondrites. The ²⁶Al-²⁶Mg isotopic system were measured in fourteen FeO-poor (Type I), six FeO-rich (Type II) and two aluminum-rich (Al-rich) chondrules using a secondary ion mass spectrometer. Excesses of ²⁶Mg in plagioclase (1.0-13.5‰) are resolved with sufficient precision (mostly 0.4-6.6‰ at 2σ level) in all the chondrules studied except one. Chemical zoning of Mg and Na in plagioclase were investigated in detail in order to evaluate the applicability of ²⁶Al-²⁶Mg chronometer. We conclude that the Al-Mg isotope system of the chondrules in Y-81020 have not been disturbed by parent-body metamorphism and can be used as chronometer assuming homogeneous distribution of ²⁶Al. Assuming an initial ²⁶Al/²⁷Al ratio of 5 × 10⁻⁵ in the early solar system, ²⁶Al-²⁶Mg ages were found to be 1.7-2.5 Ma after CAI formation for Type I, 2.0-3.0 Ma for Type II and 1.9 and 2.6 Ma for Al-rich chondrules.The formation ages of ferromagnesian chondrules in Y-81020 are in good agreement with those of L and LL (type 3.0-3.1) chondrites in the literature, which indicates that common chondrules in the CO chondrite were formed contemporaneously with those in L and LL chondrites. The concurrent formation of chondrules of CO and L/LL chondrites suggests that the chemical differences between CO and L/LL chondrites might be caused by spatial separation of chondrule formation environments in the protoplanetary disk.     

Use of a time-domain electromagnetic method with geochemical tracers to explore the salinity anomalies in a small coastal aquifer in north-eastern Tunisia

The study area is a small coastal plain in north-eastern Tunisia. It is drained by an ephemeral stream network and is subject to several pollutant discharges such as oilfield brine coming from a neighboring oil company and wastewater from Somâa city, located in the upstream of the plain. Furthermore, a hydraulic head near the coastal part of the aquifer is below sea level, suggesting that seawater intrusion may occur. A time-domain electromagnetic (TDEM) survey, based on 28 soundings, was conducted in Wadi Al Ayn and Daroufa plains to delineate the saline groundwater. Based on longitudinal and transversal resistivity two-dimensional pseudosections calibrated with boring data, the extent of saline water was identified. Geochemical tracers were combined with the resistivity dataset to differentiate the origin of groundwater salinization. In the upstream part of the plain, the infiltration of oilfield brine through the sandy bed of Wadi Al Ayn seems to have a considerable effect on groundwater salinization. However, in the coastal part of the aquifer, groundwater salinization is due to seawater intrusion and the saltwater is reaching an inland extent around 1.3 km from the shoreline. The contribution ratios of saline water bodies derived from the inverted chloride data vary for the oilfield brine from 1 to 13 % and for the seawater from 2 to 21 %.     

Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings

In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. Measurements of radiocarbon content in absolutely dated tree-rings provide a calibration curve for accurate dating of archaeological matters, but at the same time, enable us to examine the variations of solar magnetic activity in the pre-historical period. The Sun holds several long-term quasi-cyclic variations in addition to the fundamental 11-year sunspot activity cycle and the 22-year polarity reversal cycle, and it is speculated that the property of the 11-year and the 22-year solar cycle varies in association with such long-term quasi-cycles. It is essential to reveal the details of solar variations around the transition time of solar dynamo for illuminating the mechanisms of the long-term solar variations. We therefore have investigated the property of the 11-year and 22-year cycles around the two grand solar minima; the Maunder Minimum (1645–1715 AD) and the Spoerer Minimum (1415–1534 AD), the periods of prolonged sunspot minima. As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima. It suggests the inverse correlation between the solar cycle length and solar magnetic activity level, and also the change of meridional flow during the grand solar activity minima. Further measurements for the beginning of the grand solar minima will provide a clue to the occurrence of such prolonged sunspot disappearance. We also discuss the effect of solar variations to radiocarbon dating.     

Parameters of the Magnetic Flux inside Coronal Holes

The parameters of the magnetic flux distribution inside low-latitude coronal holes (CHs) were analyzed. A statistical study of 44 CHs based on Solar and Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284?Å images showed that the density of the net magnetic flux, B _net, does not correlate with the associated solar wind speeds, V _x . Both the area and net flux of CHs correlate with the solar wind speed and the corresponding spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A possible explanation for the low correlation between B _net and V _x is proposed. The observed non-correlation might be rooted in the structural complexity of the magnetic field. As a measure of the complexity of the magnetic field, the filling factor, f(r), was calculated as a function of spatial scales. In CHs, f(r) was found to be nearly constant at scales above 2 Mm, which indicates a monofractal structural organization and smooth temporal evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller than 2 Mm, the filling factor decreases rapidly, which means a multifractal structure and highly intermittent, burst-like energy release regime. The absence of the necessary complexity in CH magnetic fields at scales above 2 Mm seems to be the most plausible reason why the net magnetic flux density does not seem to be related to the solar wind speed: the energy release dynamics, needed for solar wind acceleration, appears to occur at small scales below 1 Mm.     

Trace elements and stable isotope ratios (δC and δN) in fish from deep-waters of the Sulu Sea and the Celebes Sea

Trace elements (TEs) and stable isotope ratios (δ¹⁵N and δ¹³C) were analyzed in fish from deep-water of the Sulu Sea, the Celebes Sea and the Philippine Sea. Concentrations of V and Pb in pelagic fish from the Sulu Sea were higher than those from the Celebes Sea, whereas the opposite trend was observed for δ¹³C. High concentrations of Zn, Cu and Ag were found in non-migrant fish in deep-water, while Rb level was high in fish which migrate up to the epipelagic zone, probably resulting from differences in background levels of these TEs in each water environment or function of adaptation to deep-water by migrant and non-migrant species. Arsenic level in the Sulu Sea fish was positively correlated with δ¹⁵N, indicating biomagnification of arsenic. To our knowledge, this is the first study on relationship between diel vertical migration and TE accumulation in deep-water fish.     

Experimental study of incongruent evaporation kinetics of enstatite in vacuum and in hydrogen gas

Variations in bulk Mg/Si ratios in the various groups of chondritic meteorites indicate that Mg/Si fractionation occurred in the primitive solar nebula. Enstatite (MgSiO₃) evaporates incongruently forming forsterite (Mg₂SiO₄) as an evaporation residue; therefore, evaporation of enstatite produces Mg/Si variations in solid (Mg-rich) and gas (Si-rich) and must be considered as a probable process responsible for Mg/Si fractionation recorded in chondrites. To understand the evaporation kinetics of enstatite, incongruent evaporation experiments on enstatite single crystals have been carried out in vacuum and in hydrogen gas at temperatures of 1300 to 1500°C. A polycrystalline forsterite layer is formed on the surface of enstatite by preferential evaporation of the SiO₂ component, both in vacuum and in hydrogen gas. The thickness of the forsterite layer in vacuum increases with time in the early stage of evaporation and later the thickness of the forsterite layer remains constant (several microns). This is due to the change in the rate limiting process from surface reaction plus nucleation and growth to diffusion in the surface forsterite layer. The activation energy of the diffusion-controlled evaporation rate constant of enstatite is 457 (±58) kJ/mol. A thinner forsterite layer is formed on the surface of enstatite in hydrogen gas than in vacuum. Evaporation of enstatite in hydrogen gas is also considered to be controlled by diffusion of ions through the forsterite layer. The thin forsterite layer formed in hydrogen gas is ascribed to the enhanced evaporation rate of forsterite in the presence of hydrogen gas.The results are applied to incongruent evaporation under the solar nebular conditions. The steady thickness of the forsterite of nebular pressure-temperature conditions is estimated to be submicron because of the enhanced evaporation rate of forsterite under hydrogen-rich nebular conditions if evaporated gases are taken away immediately and no back reaction occurs (an open system). Because enstatite grains in the solar nebula would be comparable to the estimated steady thickness of forsterite, evaporation of such enstatite grains under kinetic conditions could play an important role in producing variations in Mg/Si ratios between solid and gas in the solar nebula.