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.     

Potential of mosques to serve as evacuation shelters for foreign Muslims during disasters: a case study in Gunma,Japan

Natural Hazards - Foreigners tend to be vulnerable to disasters due to religious and cultural differences. In Japan, Muslim foreign residents, who are minorities, likely face difficulties in terms...     

Changes in the abundance and composition of picophytoplankton in relation to the occurrence of a Kyucho and a bottom intrusion in the Bungo Channel,Japan

The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 °C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel.     

Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.     

Mesozoic radiolarians and radiolarian-bearing sequences in the circum-Pacific regions: A report of the symposium-'Radiolarians and Orogenic Belts'

Abstract This paper contains extended abstracts of the seven papers presented at the symposium 'Radiolarians and Orogenic Belts' held at the seventh meeting of the International Association of Radiolarian Paleontologists (INTERRAD). Important results of the symposium include the following: (1) Upper Paleozoic and Mesozoic cherts are widely distributed within accretionary complexes in the circum-Pacific orogenic belt. Radiolarian dating reveals that long durations of chert sedimentation in a pelagic environment are recorded on both sides of Pacific-rim accretionary complexes (e.g. New Zealand, Japan, Russian Far East, Canadian Cordillera). (2) Triassic radiolarian faunas from New Zealand and the Omolon Massif, northeast Siberia are similar in composition and are characterized by the absence of typical Tethyan elements. This suggests that radiolarian faunal provincialism may have been established as early as the Triassic. High-latitude radiolarian taxa exhibit a bi-polar distribution pattern. (3) The Lower Triassic interval in chert dominant pelagic sequences is mechanically weaker than other levels and acted as a décollement in accretionary events. This lithologic. contrast in physical property is considered to reflect radiolarian evolution, such as the end-Permian mass extinction.     

Solar Wind Speed and Expansion Rate of the Coronal Magnetic Field in Solar Maximum and Minimum Phases

Relationships between solar wind speed and expansion rate of the coronal magnetic field have been studied mainly by in-ecliptic observations of artificial satellites and some off-ecliptic data by Ulysses. In this paper, we use the solar wind speed estimated by interplanetary scintillation (IPS) observations in the whole heliosphere. Two synoptic maps of SWS estimated by IPS observations are constructed for two Carrington rotations CR 1830 and 1901; CR 1830 starting on the 11th of June, 1990 is in the maximum phase of solar activity cycle and CR 1901 starting on the 29th of September, 1995 is in the minimum phase. Each of the maps consist of 64800 (360×180) data points. Similar synoptic maps of expansion rate of the coronal magnetic field (RBR) calculated by the so-called potential model are also constructed under a radial field assumption for CR 1830 and CR1901. Highly significant correlation (r=–0.66) is found between the SWS and the RBR during CR1901 in the solar minimum phase; that is, high-speed winds emanate from photospheric areas corresponding to low expansion rate of the coronal magnetic field and low speed winds emanate from photospheric areas of high expansion rate. A similar result is found during CR 1830 in solar maximum phase, though the correlation is relatively low (r=–0.29). The correlation is improved when both the data during CR 1830 and CR 1901 are used together; the correlation coefficient becomes –0.67 in this case. These results suggest that the correlation analysis between the SWS and the RBR can be applied to estimate the solar wind speed from the expansion rate of the coronal magnetic field, though the correlation between them may depend on the solar activity cycle. We need further study of correlation analysis for the entire solar cycle to get an accurate empirical equation for the estimation of solar wind speed. If the solar wind speed is estimated successfully by an empirical equation, it can be used as an initial condition of a solar wind model for space weather forecasts.     

Enhanced chlorophyll associated with island-induced cyclonic eddies in the eastern channel of the Tsushima Straits

The relationship between island-induced cyclonic eddies and chlorophyll a (chl-a) was investigated using field data and satellite images in the eastern channel of the Tsushima Straits. The maximum chl-a concentration around the leeward eddy of the Tsushima Islands was two or three times greater than that of outside the eddy. Two different mechanisms of chl-a enhancement associated with island-induced cyclonic eddies were found in the post-bloom periods. In summer, when nutrients were depleted in the surface layer, eddy pumping increased the nutrient supply in the euphotic zone, resulting in enhanced chl-a around the shallow thermocline near the eddy core. In late autumn, when the mixed layer deepened over the euphotic zone, the mixed layer depth became shallow due to the doming effect of the cyclonic eddy, therefore, the improved irradiance condition led to an increase in the chl-a concentration in the surface mixed layer. Nighttime satellite visible images showed a number of fishing vessels in the lee region of the Tsushima Islands, implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the Tsushima Straits.