Distinctive copepod community of the estuarine turbidity maximum: comparative observations in three macrotidal estuaries (Chikugo, Midori, and Kuma Rivers), southwestern Japan

Copepods are considered to be a vital component connecting the unique macrotidal environment to the high productivity and high biodiversity of the Ariake Sea. To examine the spatiotemporal succession of copepod communities, we conducted monthly sampling (vertical hauls of a 100-μm mesh plankton net) in three neighboring macrotidal estuaries between 2005 and 2006. Irrespective of the season, three copepod communities were recognized in relation to the relatively long gradients of salinity and turbidity along the Chikugo and Midori River estuaries. The oligohaline community (salinity 1–10) was observed at higher turbidities (>100 NTU), whereas the freshwater (salinity <1) and meso/polyhaline (salinity >10) communities were associated with lower turbidities (<100 NTU). The oligohaline calanoid Sinocalanus sinensis occurred only in the Chikugo River estuary, maintaining a large biomass (dry weight >10 mg m^?3) in or close to the well-developed estuarine turbidity maximum (ETM) throughout the year. In the Midori River estuary, the oligohaline community lacked S. sinensis and showed a minimum biomass during winter (<10 mg m^?3). In both estuaries, the freshwater community always remained at a small biomass (<1 mg m^?3), whereas the meso/polyhaline community showed marked seasonal changes in biomass (0.1–657 mg m^?3). The prevalence of higher salinities allowed only the meso/polyhaline community to occur in the Kuma River estuary. In summary, S. sinensis characterized the copepod community distinctive of the well-developed ETM, potentially serving as an important link to higher trophic levels during winter when copepods are scarce in other areas.     

Seasonal variation in the Ra/Ra ratio of coastal water within the Sea of Japan: Implications for the origin and circulation patterns of the Tsushima Coastal Branch Current

In the current study, low-background γ-spectrometry was employed to determine the ²²⁸Ra/²²⁶Ra activity ratio and ¹³⁷Cs activity of 84 coastal water samples collected at six sites along the main island of Japan (Honshu Island) within the Sea of Japan, including the Tsushima Strait, and two other representative sites on Honshu Island (a Pacific shore and the Tsugaru Strait) at 1-month intervals in 2006.The ²²⁸Ra/²²⁶Ra ratio of coastal waters in the Sea of Japan exhibited similar patterns of seasonal variation, with minimum values during early summer (²²⁸Ra/²²⁶Ra = 0.6–0.8), maximum values during autumn (²²⁸Ra/²²⁶Ra = 1.5–3), and a time lag in their temporal changes ( 2.5 months and over  1300 km distance). However, the 2 other sites represented no clear periodic variation.In contrast to the positive correlation between ¹³⁷Cs activity (0.6–1.7 mBq/L) and salinity (15–35), the ²²⁸Ra/²²⁶Ra ratio of coastal water samples from the Sea of Japan was not observed to correlate with salinity, and the increase in the ²²⁸Ra/²²⁶Ra ratio was not as marked (0.5–1; May–June 2004 and 2005) during the migration along Honshu Island. The input of land-derived water and/or the diffusion of radium from coastal sediments is unlikely to have affected the wide seasonal variation in the ²²⁸Ra/²²⁶Ra ratio observed in these water samples.The seasonal variation in the ²²⁸Ra/²²⁶Ra ratio recorded for the coastal waters of the Sea of Japan is considered to be mainly controlled by the remarkable changes in the mixing ratio of the ²²⁸Ra-poor Kuroshio and the ²²⁸Ra-rich continental shelf waters within the East China Sea (ECS). After passing through the Tsushima Strait, this water mass moves northeast along the coastline of the Sea of Japan as the Tsushima Coastal Branch Current (TCBC).     

Phytoplankton assemblage in the Plio-Pleistocene record of Lake Baikal as indicated by sedimentary steryl chlorin esters

Past changes in phytoplankton assemblages in Lake Baikal over the last 4.5 Ma, both in population and composition, are inferred from the downcore profiles of the relatively stable chlorophyll derivatives steryl esters of pyropheophorbides a and b (steryl chlorine esters; SCEs) in the 0–200 m section of the BDP-98 drill core, supplemented by the data on biogenic silica (BSi) and total organic carbon (TOC) contents. SCEs-a and -b dominate among sedimentary chlorophyll derivatives in the BDP-98 sediments except for the upper few meters, indicating their high stability during diagenetic alteration of sediments. The depth (age) profiles of SCEs-a are consistent with BSi and TOC profiles and are interpreted as reflecting primary productivity of the lake in the past. Baikal proxies reveal close correlation with marine oxygen isotope records (MIS stratigraphy). These observations confirm that climate change in the northern hemisphere has been a primary factor controlling the total phytoplankton productivity in Lake Baikal during the last several million years.Among SCEs-a, C₃₀ (dinostanol)-SCE-a, a marker of dinoflagellates was identified by GC–MS analysis. SCE-b, a marker of green algae, was identified by its UV–vis spectrum. The ratio of C₃₀-SCE-a to total SCEs-a (TSCEs-a) was higher during 4.5–4.2 and 1.7–1.3 Ma, suggesting that dinoflagellates proliferated preferentially in those periods. The early Pleistocene maximum of this ratio corresponds to the broad minimum of diatom abundance previously suggested to have recorded a prolonged regional cooling. An abrupt increase in the SCE-b/TSCEs-a ratio was observed at 2.5–2.6 Ma, indicating that green algae containing chlorophyll b have proliferated in Lake Baikal during this period. This interval has also been suggested to contain evidence for a significant regional cooling based on minima of diatom abundance and BSi in sediments. The depth profile of C₂₇Δ⁵ (cholesterol)-SCE-a relative to TSCEs-a showed a trend similar to that of BSi, suggesting that C₂₇Δ⁵-SCE-a/TSCEs-a ratio is a potential marker of diatoms in Lake Baikal.Certain mismatches between the Lake Baikal profiles of biological indicators and the marine oxygen isotope records, as well as the slight temporal offsets between different Lake Baikal biological marker signals suggest that the regional component of climatic and/or lacustrine environmental changes also have played a role in determining the composition of the Lake Baikal Plio-Pleistocene phytoplankton assemblage.     

Long-range transport of particulate polycyclic aromatic hydrocarbons at Cape Hedo remote island site in the East China Sea between 2005 and 2008

Particle-associated polycyclic aromatic hydrocarbons (PAHs) in outflow from East Asia were observed at Cape Hedo, Okinawa, Japan between 2005 and 2008. The filter samples of the total suspended particles were analyzed by means of gas chromatography-mass spectrometry. The total concentration of fourteen 3–7-ring PAHs was 0.01–24 ng m^?3 (average 1.6 ng m^?3). The average PAH concentration increased in the winter-spring season and decreased in the summer-fall season. The average benzo(a)pyrene to benzo(e)pyrene ratio was 0.49 in the winter-spring season and was lower than the literature values for East Asian cities in the same season. This result shows that aging of organic aerosol particles proceeds during long-range transport from East Asia. In the Asian Pacific region, these pollutants are transported from East Asia in the winter-spring season, whereas clean air mass is transported from the Pacific Ocean in the summer-fall season.     

Swell-dominant surface waves observed by a moored buoy with a GPS wave sensor in Otsuchi Bay,a ria in Sanriku,Japan

Real-time monitoring of wind and surface waves in Otsuchi Bay, Iwate, Tohoku, Japan, commenced in October 2012, using a mooring buoy with an ultrasonic anemometer and a single-mode GPS wave sensor. Wind and wave data are distributed hourly in real time via the Internet along with a chart of their time series. We analyzed data monitored in the first 3 months in order to assess the variability and occurrence of wind and waves and to elucidate the main reasons for wave variation in Otsuchi Bay. The monitoring data revealed that surface waves in the bay were predominantly affected by swells propagated from the northeastern offshore region and that the wave height was significantly correlated with the component of wind velocity toward Otsuchi Bay in the northeastern offshore region that faces the bay mouth. The offshore wind field was expected to provide information useful for predicting coastal waves in a ria bay in Sanriku such as Otsuchi Bay. However, it should be emphasized that the horizontal distribution of the offshore wind field which has a significant effect on the surface waves in a ria bay depends heavily on the topographic shape of the bay.     

New record of <Emphasis Type="Italic">Lobophora rosacea</Emphasis> (Dictyotales; Phaeophyceae) from the South China Sea

Lobophora rosacea C.W. Vieira, Payri et De Clerck is reported from the South China Sea for the first time. Our specimens are very similar to L. rosacea recently described from New Caledonia, not only in morphology but also in rbcL and cox3 gene sequences. The fan-shaped thallus grows erectly, attaching to the substrate by a basal holdfast. The thallus is composed of a single layer of large medullary cells and three to four layers of cortical cells on both sides of the medulla. Mature sporophytes are detected, with sporangium sori scattered on both surfaces of the thallus.     

Liquefaction Analysis Using Viscoplastic Kinematic Hardening Constitutive Model

The dynamic response analysis combined with the generalized return-mapping algorithm is applied to the integration algorithms of viscoplastic constitutive relations including the effect of the shear band. The kinematic hardening model based on modified and extended soil model with isotropic strain-hardening–softening is employed. In this paper, the TESRA (temporary effect of strain rate and acceleration) model is employed for the nonlinear viscosity of sand. The constitutive equations of rate-dependent plasticity originally proposed by Duvaut–Lions are employed as the base of the solutions. Liquefaction of a buried pipe is analyzed by finite element method by employing the above mentioned constitutive relations and the calculated results are compared with experimental results. The dynamic response analysis is applied to the solutions of the problems. The kinematic hardening–softening viscoplastic constitutive relations for geomaterials are promising for the predictions of cumulative deformations and liquefaction of the buried pipe. A great deal of experimental results indicate that the stress is a unique function of irreversible strain and its rate.     

EXAFS study on the cause of enrichment of heavy REEs on bacterial cell surfaces

Rare earth element (REE) pattern is a unique geochemical tracer and has been measured for various natural materials. Among these, the REE distribution pattern between bacteria and water exhibits anomalous enrichment in the heavy REE (HREE) part, which can act as a signature of bacteria-related materials in natural samples. In this study, the REE binding site on the cell surface of a Gram-positive bacterium (Bacillus subtilis) responsible for HREE enrichment has been identified using extended X-ray absorption fine structure (EXAFS) coupled with a study of the variation in REE distribution patterns. The EXAFS data showed that the HREEs form complexes with multiple phosphate site (including phosphoester site) with a larger coordination number (CN) at lower REE-bacteria ratios ([REE]/[bac]), while light and middle REEs form complexes to the phosphate site with a lower CN. The fraction coordinated to carboxylate increased for all REEs with increasing [REE]/[bac] ratio. On the other hand, the enrichment of HREE in the REE distribution patterns of the bacteria was less marked with increasing [REE]/[bac] ratio. This result is consistent with the EXAFS data, because the REE pattern of surface complex with multiple phosphate in a reference material exhibits a monotonous increase for heavier REE, while phosphate surface complex with a low CN and a carboxylate site reach a maximum around Sm and Eu. Based on these results, it is clear that the REE are primarily bound to the phosphate site and subsequently to the carboxylate site on the bacterial cell surface.Regarding the pH dependence in the range (3 < pH < 7), both the EXAFS and REE pattern data indicate that the fraction of REE-carboxylate increased as the pH increases. The results above obtained for B. subtilis were also valid for Escherichia coli, a Gram-negative bacterium, showing that similar phosphate and carboxylate sites are also available in the cell walls of E. coli, or other Gram negative bacteria. In all our results, the variation in REE patterns correlated with the binding site indicated by EXAFS, showing that the REE pattern itself reflects the binding site of the REE at the bacterial surface for various parameters (pH and [REE]/[bac] ratio). Thus, the REE patterns can be used to estimate the binding sites for lower [REE]/[bac] ratios where spectroscopic techniques cannot be applied.The average bond length between the REE and oxygen was compared for various REE sorbed on bacteria, showing that the bond length for HREE (Er to Lu) was much shorter than those extrapolated from the trend between La and Dy, because of the selective binding of the HREE as the multiple phosphate surface complexes. Our results are consistent with the selective enrichment of the HREE at the bacterial cell surfaces, considering that chemical species with a shorter bond length are more stable. Thus, it is clear that the HREE enrichment at the bacterial cell surfaces is caused by the formation of the multiple phosphate surface complexes. Based on these results, it is suggested that materials having such phosphate sites such as bacteria and bacteria-related materials can induce anomalous HREE enrichment in natural systems.     

Does black carbon abatement hamper CO 2 abatement?

Concerns have been raised that near-term black carbon abatement strategies for global warming mitigation would interfere with the longer-term CO₂ abatement efforts. In response, we put forward a “combined target and metric approach”, a theoretical framework, in which the time horizon of the metric is linked to the specific target of the climate policy. In this approach, a shorter time horizon for the metric is justified only when the overall climate policy is tightened; the lower the target level of the climate policy, the earlier the year of the target. Employing a consistent time perspective for the metric and target means that enhanced near-term reduction of short-lived climate forcers does not reduce the importance of the CO₂ abatement, since the overall climate target is stricter.     

The structure and behavior of the arctic cyclone in summer analyzed by the JRA-25/JCDAS data

In this study, three-dimensional structures and the life-time behavior of arctic cyclones are investigated as case studies, using reanalysis data of JRA-25 and JCDAS. In recent years, arctic region has undergone drastic warming in conjunction with the reduced sea ice concentration in summer. The rapid reduction of the sea ice concentration is explained, to some extent, by a pressure dipole of the arctic cyclone and Beaufort high over the Arctic Ocean. This paper presents some case studies for the structure of the arctic cyclone.It is found by the analysis of this study that the arctic cyclone indicates many differences in structure and behavior compared with the mid-latitude cyclone. The arctic cyclones move rather randomly in direction over the Arctic Ocean. The arctic cyclone has a barotropic structure in the vertical from the surface to the stratosphere. The arctic cyclone detected at the sea level pressure is connected with the polar vortex at the 500 hPa level and above. Importantly, the arctic cyclone has a cold core in the troposphere and a warm core around the 200 hPa level. The mechanism of the formation is discussed based on the analyzed structure of the arctic cyclones.