Stable carbon isotopic compositions of individual n-fatty acids and n-alkanes were determined in six sediments from the Ohtsuchi River to the Pacific Ocean at north Honshu Island, Japan. Long-chain n-fatty acids (LCFAs) ranging from C20 to C30 and long-chain n-alkanes (LCALs) ranging from C23 to C33 have large isotopic variations from -35 to -25‰ and -35 to -29‰, respectively, although the molecular distributions of LCFAs and LCALs are almost identical in all analyzed samples. LCFAs are more depleted in 13C than total organic carbon (TOC) by about 5 to 12‰. The δ13C values are relatively similar between n-C20 and n-C26, and gradually decrease with increasing molecular weight to n-C30 by 3 to 5‰. Each n-fatty acid component shows a systematic enrichment in 13C from river to open ocean by up to 6‰ (from -32.5 to -26‰ for n-C26), and a similar isotopic composition in the open ocean (∼-26‰ for n-C26). LCALs are also more depleted in 13C than TOC by about 6 to 12‰. The δ13C values gradually decrease from n-C19 to n-C31 by up to 6‰, then increase for >n-C31. Abundant LCALs, such as n-C29 and n-C31, show a systematic enrichment in 13C from river to open ocean by up to 3% (from -34.6 to -31.9‰ for n-C31), and a similar isotopic composition in the open ocean (∼-31.5‰ for n-C31). On the other hand, C35n-alkane has a relatively uniform isotopic composition (∼-29‰) for all sediments. Such isotopic variations exhibit good correlations with δ13CTOC (-26.4 to -20.4‰) and C/N ratio (12 to 7 by atom) variations as well as amount of sedimentary cutin- and lignin-derived organic compounds of terrestrial higher plant origin. The isotopic distributions can be explained by a two-component mixture model involving isotopically different terrestrial and marine LCFAs and LCALs as endmember components. Although LCFAs (>n-C20) and LCALs (>n-C23) in marine sediments have been previously presumed to be derived from terrestrial higher plants, the results presented here may indicate that some of the LCFAs and LCALs in marine sediments are actually originated in the marine environment. Compound-specific isotope signature is important for evaluating the sources, as well as transport and mixing processes for the LCFAs and LCALs in a terrestrial-marine system.
Concentrations of platinum-group elements (PGEs) and gold in basalts from Kilauea and Mauna Loa, Hawaii, were determined by ICP-MS, using an improved fire-assay and tellurium coprecipitation technique for preconcentrating the metals. Major and trace elements, together with Pb-Sr isotope compositions of basalt samples confirmed that these samples are typical Hawaiian tholeiites. The abundances of the PGEs and Au in Hawaiian tholeiites are rather constant during magmatic differentiation processes, whereas MORBs show strong fractionation of those elements. The distinctive behaviour of these PGEs in Hawaiian tholeiites cannot be explained solely via. fractionation of those elements by separation of crystallizing phases such as chromite, olivine and clinopyroxene. Oversaturation of sulfur and separation of sulfides from magmas are required for elucidating PGEs and Au concentrations in Hawaiian tholeiites.
Thermochemical data for solution at 25°C and 1 atm (ΔGs°, ΔHs° and ΔSs°) of fully isomorphous LnES3·9H2O (ES = C2H5SO4-) and partly isomorphous LnCl3·nH2O (n = 7 for La-Pr and n = 6 for Nd-Lu) are discussed, because they provide important clues to understand the tetrad effects in REE patterns of geochemical samples. All the differences in ΔHs°, ΔGs° and ΔSs° between LnCl3·6H2O and LnES3·9H2O show convex tetrad effects, and they correspond to ΔHr, ΔGr and ΔSr for the reaction series: LnCl3·6H2O (c) + 3(ES-)(aq) + 3H2O(l) = LnES3·9H2O(c) + 3Cl-(aq). The convex tetrad effects are explained by the refined spin-pairing energy theory (RSPET) and thermodynamic principles: LnES3·9H2O have larger Racah (E1 and E3) parameters than LnCl3·6H2O by about 0.5% and 1%, respectively. The differences in E1 and E3 relate to minute but significant differences in dissociation energies for bondings of Ln3+ ions with ligands, and then to ΔHr and the vibrational entropy differences of ΔSr(vib). They emerge as convex tetrad effects in ΔHr and ΔSr. A similar tetrad effect is seen in ΔGr, because ΔHr dominates in ΔGr = ΔHr - TΔSr for the low temperature reactions. Each series variation of ΔHs°, ΔGs° or ΔSs° for LnES3·9H2O or LnCl3·6H2O consists of (i) a tetrad effect due to the differences in Racah parameters between Ln3+(aq) and each isomorphous Ln(III) hydrate series, (ii) an irregularity caused by the hydration change of light Ln3+(aq) from nonahydrate to octahydrate with going from La to Tb, and (iii) the smooth residual variation. Concave tetrad effects are seen in ΔHs°, ΔGs° and ΔSs° for heavy LnES3·9H2O, but no such variations in those for heavy LnCl3·6H2O. This means the Racah parameters decreasing in the order: LnES3·9H2O > LnCl3·6H2O ≈ Ln3+(aq, octahydrate). The RSPET makes it possible to determine the irregularity due to the hydration change of light Ln3+(aq) from ΔHs°, ΔGs° or ΔSs° for the two isomorphous Ln(III) hydrate series. The irregularity is the thermodynamic parameter (ΔHh∗, ΔSh∗ or ΔGh∗) for the stabilization of real light Ln3+(aq) relative to octahydrate Ln3+(aq).
Lanthanide(III)-carbonate complexes, LnCO3+(aq) and Ln(CO3)2-(aq), are the principal Ln(III) species in seawater. Their logarithmic stability constants, logβ1(Ln(CO3)+) and logβ2(Ln(CO3)2-) defined by total carbonate ion concentration, are known to show “irregular” variations across the series. The irregularities are explained by the hydration change of light Ln3+(aq) and the refined spin-pairing energy theory (RSPET). The hydration change of Ln3+(aq) affects the stability constants, because they are given by the reactions of Ln3+(aq) With CO32-(aq) and 2CO32-(aq), respectively. However, it does not affect their ratio of [β2(Ln(CO3)2-)/β1(LnCO3+)] which is the stepwise stability constant of Ln(CO3)2-(aq) for the reaction: LnCO3+(aq) + CO32-(aq) = Ln(CO3)2-(aq). Only when corrected for the hydration change of Ln3+(aq), the logβ1(Ln(CO3)+) values exhibit a regular convex tetrad effect across the series. Similarly corrected logβ2(Ln(CO3)2-) values also show a convex tetrad effect with a small break at Pr. The log [β2 (Ln(CO3)2-)/β1(LnCO3+)] values are fairly constant, but display a small octad effect with convexity and the small break at Pr. The LnCO3+(aq) series appears to be an isomorphous complex series, but the Ln(CO3)2-(aq) series involves a structural change between the three lightest Ln members and the others. The RSPET analysis has been made for the tetrad effects after the correction for hydration change of Ln3+(aq), in which the small break at Pr in logβ2(Ln(CO3)2-) has also been corrected successfully. It was revealed that Racah E1 and E3 parameters decrease in the order that Ln3+(aq, octahydrate) >> LnCO3+(aq) > Ln(CO3)2-(aq). This corresponds to the nephelauxetic effect known in spectroscopic studies of Ln(III) complexes.
Concentration and stable carbon isotopic composition (δ13C) of CH4 are determined in a water column of an 327 m deep oxic oligotrophic crater lake, Lake Towada in Japan. The results of CTD measurements show relatively high temperature and high conductivity in the lower part of the column, possibly derived from hot springs at the crater wall approximately 150 m deep. The vertical profile of CH4 concentration shows two sharp maxima of 68 and 69 nmol/kg at depths of 20 and 150 m, respectively. The δ13C value of CH4 at 20 m is -55‰PDB, suggesting microbial production in and around the lake. In contrast, the δ13C value of CH4 at 150 m is +11‰PDB, which suggests some secondary isotopic alternation processes peculiar to hot spring-derived CH4 in the oxic water column, such as rapid aerobic microbial oxidation.