Intercolony variability of skeletal oxygen and carbon isotope signatures of cultured Porites corals: Temperature-controlled experiments

The skeletal oxygen isotope ratio of Porites corals is the most frequently used proxy of past seawater temperature and composition for tropical and subtropical oceans. However, field calibration of the proxy signals is often difficult owing to the dual dependence of skeletal oxygen isotope ratio on temperature and the oxygen isotope composition of water. We conducted tank experiments in which we grew Porites spp. colonies for 142 d in thermostated seawater at five temperature settings between 21°C and 29°C under moderate light intensity of 250 μmol m⁻² s⁻¹ with a 12:12 light:dark photoperiod. A skeletal isotope microprofiling technique applied along the major growth axis of each colony revealed that the oxygen isotope ratios of newly deposited skeleton in most colonies remained almost constant during tank incubation, thus providing an ideal situation for precise calibration of oxygen isotope ratio proxy signals. However, the oxygen isotope ratios displayed an unusually large intercolony variability (∼1‰) at each temperature setting although the mean slope (∼0.15‰ °C⁻¹) obtained for the temperature-skeletal oxygen isotope ratio relationship was close to previous results. The intercolony variations in the oxygen isotope ratios were apparently caused by kinetic isotope effects related to variations in the skeletal growth rate rather than by species-specific variability or genetic differences within species. No correlation was found between skeletal carbon isotope ratios and temperature. The carbon isotope ratios showed significantly inverse correlation with linear growth rates, suggesting a kinetic isotope control at low growth rates. Observed intercolony variability in skeletal carbon isotope ratios (∼5‰) can be partly attributed to growth-rate-related kinetic isotope effects.     

Solid‐state 13C NMR characterization of insoluble organic matter from Antarctic CM2 chondrites: Evaluation of the meteoritic alteration level

Abstract— Chemical structures of the insoluble organic matter (IOM) from the Antarctic CM2 chondrites (Yamato [Y‐] 791198, 793321; Belgica [B‐] 7904; Asuka [A‐] 881280, 881334) and the Murchison meteorite were analyzed by solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Different types of carbons were characterized, such as aliphatic carbon (Ali‐C), aliphatic carbon linked to hetero atom (Hetero‐Ali‐C), aromatic carbon (Aro‐C), carboxyls (COOR), and carbonyls (C=O). The spectra of the IOM from Murchison and Y‐791198 showed two major peaks: Ali‐C and Aro‐C, while the spectra from the other meteorites showed only one major peak of Aro‐C. Carbon distribution was determined both by manual integration and deconvolution. For most IOM, the Aro‐C was the most abundant (49.8–67.8%) of all carbon types. When the ratios of Ali‐C to Aro‐C (Ali/Aro) were plotted with the atomic hydrogen to carbon ratio (H/C), a correlation was observed. If we use the H/C as a parameter for the thermal alteration event on the meteorite parent body, this result shows a different extent of thermal alteration. In addition, IOM with a lower Ali/Aro showed a lower ratio of Ali‐C to COOR plus C=O (Ali / (COOR + C=O)). This result suggests that the ratio of CO moieties to aliphatic carbon in IOM might reflect chemical oxidation that was involved in hydrothermal alteration.     

Long-term patterns in the diets of Japanese temperate bassLateolabrax japonicus larvae and juveniles in Chikugo estuarine nursery ground in Ariake Bay, Japan

Larval and juvenile Japanese temperate bass (Lateolabrax japonicus) samples were collected from a wide range of spatial gradients (covering a distance of approximately 30 km) in Chikugo estuary, Ariake Bay, Japan over a period of 8 yr (1997–2004) in order to observe changes in diet. Gut contents were studied by separating, identifying, counting, and estimating the dry weight of prey organisms. Copepod samples were collected during each cruise to observe the numerical composition, abundance, and biomass in the estuary. Considerable spatial and temporal variations were observed in copepod distributions in ambient water and the diets of the fish. Two distinctly different copepod assemblages were identified in the estuary: One in the upper estuarine turbidity maximum (ETM), dominated by a single speciesSinocalanus sinensis and the other in the lower estuary consisting of a multispecies assemblage, dominated byOithona davisae, Acartia omorii, Paracalanus parvus, andCalanus sinicus. The gut content composition of the fish in the upper estuary was dominated byS. sinensis, while in the lower estuary, it consisted ofP. parvus, O. davisae, andA. omorii. Within the size group analyzed (13.0–27.0 mm SL), the smaller individuals were found to feed on a mixed diet composed of smaller prey. The diets gradually shifted to bigger prey composed predominantly ofS. sinensis for larger size groups. Greater proportions of empty guts were recorded in the smaller individuals and dropped with increasing fish size. Higher dry biomass of copepods in the environment, as well as higher dry weights of gut contents, were recorded in the upper estuary, indicating that the upper estuarine ETM areas are important nursery grounds for the early life stages of the Japanese temperate bass. The early life stages of the Japanese temperate bass are adapted to use the upstream nursery grounds and ascending to the nursery areas to useS. sinensis is one of the key survival strategies of the Japanese temperate bass in the Chikugo estuary.     

Exploratory study on improving the benthic environment in sediment by sediment microbial fuel cells

Benthos cannot survive in strongly reduced sediments, in which the redox potential is around ?400 mV. Such sediments are typically found in inner harbors that are exposed to wastewater discharges. Field experiments were conducted to investigate the potential of sediment microbial fuel cells (SMFCs) for improving the benthic environment in such sediments. To the best of our knowledge, this has not been reported in any previous literature. Bottom sediment was collected and used to fuel an SMFC suspended 500 mm below the water surface. The sediments then were collected one year after installation, and their benthos environment was investigated. The most remarkable results are that the diversity and growth of benthos were higher in the SMFC-applied sediment than in a control sediment. The results have further strengthened that the sediment remediation was enhanced, in which the oxygen consumption rate of the sediment was reduced, and the mineralization of the organic matter was increased. Our findings suggest that SMFCs are a promising technology for the remediation of strongly reduced sediment and for the improvement of the benthic environment.     

Field experiments on remediation of coastal sediments using granulated coal ash

Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L⁻¹ in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment.     

Increase in medium-size rainfall events will enhance the C-sequestration capacity of biological soil crusts

Biological soil crusts(BSCs) play important roles in the carbon(C) balance in arid regions. Net C balance of BSCs is strongly dependent on rainfall and consequent activation of microbes in the BSCs. The compensation-rainfall size for BSCs(the minimum rainfall amount for a positive net C balance) is assumed to be different with BSCs of different developmental stages. A field experiment with simulated rainfall amount(SRA) of 0, 1, 5, 10, 20, and 40 mm was conducted to examine the C fluxes and compensation-rainfall size of BSCs in different parts of fixed dunes in the ecotone between the Badain Jaran Desert and the Minqin Oasis. We found algae-lichen crust on the interdunes and crest, algae crust on the leeward side, and lichen-moss crust on the windward. Even a small rainfall(1 mm) can activate both photosynthesis and respiration of all types of BSCs. The gross ecosystem production, ecosystem respiration, and net ecosystem exchange were significantly affected by SRA, hours after the simulated rainfall, position on a dune, and their interactions. The rapid activation of photosynthesis provides a C source and therefore could be responsible for the increase of C efflux after each rewetting. C-uptake and-emission capacity of all the BSCs positively correlated with rainfall size, with the lowest C fluxes on the leeward side. The compensation rainfall for a net C uptake was 3.80, 15.54, 8.62, and 1.88 mm for BSCs on the interdunes, the leeward side, the crest, and the windward side, respectively. The whole dune started to show a net C uptake with an SRA of 5 mm and maximized with an SRA of about 30 mm. The compensation-rainfall size is negatively correlated with chlorophyll content. Our results suggest that BSCs will be favored in terms of C balance, and sand dune stabilization could be sustained with an increasing frequency of 5-10 mm rainfall events in the desert-oasis transitional zone.-     

Equivalent linear method considering frequency dependent characteristics of stiffness and damping

Equivalent linear dynamic response analysis of ground is based on complex moduli and Fourier series expansion; therefore, it is not an equivalent method but an approximate method. Two deficiencies in the conventional equivalent linear method represented by SHAKE are described first. The maximum shear strength is overestimated, resulting in overestimation of the peak acceleration under a strong ground motion, and the amplification is underestimated at high frequency. The latter sometimes results in underestimation of the peak acceleration under weak ground shaking, and gives an incident wave with unrealistic large accelerations or a divergence of analysis in deconvolution analysis under strong ground motion. Both deficiencies are shown to come from the same cause, i.e. computing the effective strain as a constant fraction of the maximum strain. Since this is a key concept of the equivalent linear analysis, one cannot overcome both deficiencies at the same time in the conventional method. An apparent frequency dependence in stiffness and damping is shown to appear in the dynamic response, although soil itself does not show frequency dependent characteristics. Following this observation, the effective strain is expressed in terms of frequency from the similarity concept of the strain–frequency relationship between time domain and frequency domain. This enables the reduction of both deficiencies at the same time, resulting in a marked improvement in the equivalent linear analysis. The accuracy of the proposed method is examined by the simulations of three vertical array records during large earthquakes. The proposed method always gives much better prediction than conventional equivalent linear methods for both convolution and deconvolution analyses, and it is confirmed to be applicable at more than 1% shear strain.     

The design of diamond Compton telescope

We have developed radiation detectors using the new synthetic diamonds. The diamond detector has an advantage for observations of “low/medium” energy gamma rays as a Compton telescope. The primary advantage of the diamond detector can reduce the photoelectric effect in the low energy range, which is background noise for tracking of the Compton recoil electron. A concept of the Diamond Compton Telescope (DCT) consists of position sensitive layers of diamond-striped detector and calorimeter layer of CdTe detector. The key part of the DCT is diamond-striped detectors with a higher positional resolution and a wider energy range from 10 keV to 10 MeV. However, the diamond-striped detector is under development. We describe the performance of prototype diamond detector and the design of a possible DCT evaluated by Monte Carlo simulations.