Short-term flow fluctuations in Onagawa Bay,Japan, as revealed by long-term mooring observation

Short-term flow fluctuations in the southern central part of Onagawa Bay were examined using long-term mooring and hydrographic data observed during the period from May 2013 to April 2014. The short-term flow fluctuations were dominant in the periodic bands of 15–27 days and shorter than 10 days. The principal and minor components of these flow fluctuations were respectively along and across the local isobaths, which are almost parallel in the north direction. The northward flow fluctuations along the local isobaths were correlated with the northeastward wind fluctuations in both periodic bands, and these correlations were more evident from fall to winter. On the basis of these results, the northward flows are regarded as wind-induced barotropic coastal jets. On other hand, the eastward flow fluctuations across the local isobaths were related to inflow and outflow via the bay mouth or the Izushima Channel. Inflow and outflow with reverse flow at lower depths formed in summer, but those with vertically uniform flow tended to form in winter. The main summertime inflow and outflow were driven by horizontal gradients in density. These permit us to regard the main summertime inflow and outflow as gravitational circulation. Also, the summertime inflow can be intermittently caused by internal waves.     

Isotopic composition of dissolved inorganic carbon in subsurface sediments of gas hydrate-bearing mud volcanoes, Lake Baikal: implications for methane and carbonate origin

We report on the isotopic composition of dissolved inorganic carbon (DIC) in pore-water samples recovered by gravity coring from near-bottom sediments at gas hydrate-bearing mud volcanoes/gas flares (Malenky, Peschanka, Peschanka 2, Goloustnoe, and Irkutsk) in the Southern Basin of Lake Baikal. The δ¹³C values of DIC become heavier with increasing subbottom depth, and vary between ?9.5 and +21.4‰ PDB. Enrichment of DIC in ¹³C indicates active methane generation in anaerobic environments near the lake bottom. These data confirm our previous assumption that crystallization of carbonates (siderites) in subsurface sediments is a result of methane generation. Types of methanogenesis (microbial methyl-type fermentation versus CO₂-reduction) were revealed by determining the offset of δ¹³C between dissolved CH₄ and CO₂, and also by using δ¹³C and δD values of dissolved methane present in the pore waters. Results show that both mechanisms are most likely responsible for methane generation at the investigated locations.     

Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer

The maximum uptake rate (_max) and affinity constant (K _s) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average _max/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average _max/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the _max/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of new production to total production was estimated by _max[_max–No₃/(_max–NO₃+_max–NH₄)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04).     

Geographical Variations in Prosome Length and Body Weight of Neocalanus Copepods in the North Pacific

Geographical variations in prosome length and body weight of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were investigated on samples from North-South and East-West transects in the North Pacific during spring to early summer in 1998 and 1999. Southward and eastward increasing patterns were pronounced for water temperature, although no significant pattern was observed for chlorophyll a concentrations. All Neocalanus species showed large geographical variations in prosome length and body weight, being smaller in the southern and eastern waters. Comparing the relationship between prosome length and body weight, large deviations (lower body weight at a given prosome length) were evident for the eastern specimens of N. cristatus and N. plumchrus. In stepwise regression analysis, the geographical variations of prosome length and body weight revealed a significantly negative correlation with temperature variations. These results suggest that temperature is a more important environmental factor than chlorophyll a concentration in its effect on geographical variations in prosome length and body weight of Neocalanus copepods in the North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stability of genetic diversity in an intertidal goby population after exposure to tsunami disturbance

Massive tsunami disturbances have potentially detrimental effects on genetic diversity and effective population size of coastal marine species, and evaluating these effects can be useful for devising conservation strategies for coastal marine environments. Local populations of the intertidal goby Chaenogobius annularis, which are distributed on scattered rocky beaches of the Japanese Archipelago, show demographic independence without overlapping generations, making this an ideal species with which to study the effects of tsunami disturbance on genetic diversity. Some of these populations were affected by the tsunami of the 2011 off the Pacific coast of Tohoku Earthquake. Here, we investigated the change in genetic diversity of a local population of this species, which was located close to the epicenter of the earthquake, across the cohorts before and after the tsunami and evaluated the impact of the tsunami disturbance. Genetic diversity was maintained after the tsunami, and no change in the effective population size was observed. Our results suggest that the tsunami disturbance has had no marked impact on the genetic diversity of C. annularis.     

P–V–T equation of state of Mn3Al2Si3O12 spessartine garnet

The thermoelastic parameters of synthetic Mn₃Al₂Si₃O₁₂ spessartine garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1,100 K, by synchrotron radiation energy dispersive X-ray diffraction within a DIA-type multi-anvil press apparatus. The analysis of room temperature data yielded K ₀ = 172 ± 4 GPa and K ₀ ^′  = 5.0 ± 0.9 when V _0,300 is fixed to 1,564.96 Å³. Fitting of P–V–T data by means of the high-temperature third-order Birch–Murnaghan EoS gives the thermoelastic parameters: K ₀ = 171 ± 4 GPa, K ₀ ^′  = 5.3 ± 0.8, (?K _0,T /?T) _P  = ?0.049 ± 0.007 GPa K^?1, a ₀ = 1.59 ± 0.33 × 10^?5 K^?1 and b ₀ = 2.91 ± 0.69 × 10^?8 K^?2 (e.g., α _0,300 = 2.46 ± 0.54 × 10^?5 K^?1). Comparison with thermoelastic properties of other garnet end-members indicated that the compression mechanism of spessartine might be the same as almandine and pyrope but differs from that of grossular. On the other hand, at high temperature, spessartine softens substantially faster than pyrope and grossular. Such softening, which is also reported for almandine, emphasize the importance of the cation in the dodecahedral site on the thermoelastic properties of aluminosilicate garnet.     

Phytotoxicity assessment of γ-Fe2O3 nanoparticles on root elongation and growth of rice plant

This study was conducted to determine the phytotoxicity of 6 nm γ-Fe₂O₃ nanoparticles (IONPs) in terms of root elongation and the physiological performance of rice plants. Rice seeds (Oryza sativa L. var. Koshihikari) exposed to IONPs at 500, 1,000 and 2,000 mg/L, had a significantly higher root elongation than the control and its bulk counterparts (IOBKs), indicating that the effect can be nanospecific. In a 14-week greenhouse pot experiment, the CO₂ assimilation rate in IOBK and IONP-treated pots (500 and 1,000 mg/pot) decreased over time, with the decline (maximum 42.5 %) being less pronounced for IONPs, indicating that the effect cannot be inferred from the toxicity of nanoscale size iron oxide. Excessive adsorption of IONPs onto soil colloids with subsequent low water extractable iron was responsible for the unremarkable phytotoxic nature of IONPs in the rice plants. Amendment of IONPs coated with 20 mmol citric acid (IONPs-Cit) significantly diminished the CO₂ assimilation rate and the decrease was similar to its bulk counterpart (IOBKs-Cit). However, maximum shoot growth inhibition (37 %) was associated with the application of IOBKs-Cit. It was concluded that massive accumulations of Fe plaque on the root surfaces of IOBKs-Cit treatments due to a decline in the pH of rhizoplane soils compared to the IONPs-Cit treatments were responsible for the remarkable shoot growth reduction. This study provided evidence of the phytotoxicity of γ-Fe₂O₃ nanoparticles, demonstrating the lower toxicity of nanosized iron oxide compared to a microsized preparation under reductive conditions.     

Upper Eocene travertine-lacustrine carbonate in the Jianchuan basin,southeastern Tibetan Plateau: Reappraisal of its origin and implication for the monsoon climate

The Asian monsoon is one of the largest climatic systems in the world, but age of its onset has been estimated differently ranging from the late Eocene to the Quaternary. We investigated the sedimentology and stable isotopic compositions of the upper Eocene Jiuziyan Formation, a terrestrial limestone unit in the Jianchuan basin, Yunnan Province in China. This limestone formation is restricted in several localities in the central part of the basin. Previously, this has been characterized as palustrine carbonate and the transition to the sublacustrine deposit of the overlying Shuanghe Formation was interpreted as the appearance of wetter climate during the late Eocene. Our observations of macro- and microfacies revealed sedimentary fabrics indicating rapid CaCO₃ precipitation, such as dendritic calcite and calcified reed stems, which are unlikely to develop in a simple lacustrine setting. High carbonate content (mostly >90 %) and restricted distribution of the Jiuziyan limestone indicate a depositional setting spatially limited and isolated from clastic influx. These findings, together with clearly higher δ¹³C values (−0.7 ‰ to +6.9 ‰) and lower δ¹⁸O values (−14.6 ‰ to −10.5 ‰) than those of the Shuanghe Formation, indicate that the limestone was mainly travertine, carbonate formed from endogenic spring water. The elevated δ¹³C resulted from a large amount of CO₂ degassing from spring water with high pCO₂. In addition, the occurrence of centimeter-scale lamination coupled with cyclic changes in δ¹³C and δ¹⁸O is almost identical with the modern annually-laminated travertine reported from Baishuitai in northern Yunnan Province, implying comparable amplitude of seasonal temperature and precipitation changes to the record of the modern travertine at Baishuitai. Our results do not contradict the previous interpretation of late Eocene wetting and additionally suggest the existence of the late Eocene monsoon climate in the Jianchuan basin.