Southern Coast Of Japan Research Articles

Habitat use and movement patterns of small (age‐0) juvenile Pacific bluefin tuna (Thunnus orientalis) relative to the Kuroshio

AbstractThe habitat use of Pacific bluefin tuna (Thunnus orientalis; PBF) in nursery waters off the southern coast of Japan was investigated using archival tags over a 3 year study period (2012–2015), and the data were used to examine the free‐ranging habitat preferences of PBF and the relationship between their horizontal movements and the path of the Kuroshio off the Pacific coast of Japan. The path of the Kuroshio fluctuated seasonally, leading to changes in water temperature that strongly influenced the habitat use of small PBF (2–3 months after hatching). Most PBF were present in coastal waters inshore of the path of the current, and their habitat use changed in response to the distance of the current from the coast. The Kuroshio typically flowed along the coast from summer to autumn, and PBF remained in the coastal waters off Kochi Prefecture during this period. In contrast, PBF quickly moved eastward in winter when the current moved away from the coast. Throughout the winter and spring, the area of habitat use extended widely from the eastern end of the southern coast of Japan (the Boso Peninsula) to the offshore Kuroshio‐Oyashio transition region. These findings suggest that the seasonal habitat use and movement behavior of juvenile PBF are influenced by the distance of the Kuroshio axis from the coast, and the ultimate drivers are likely variations in oceanographic conditions and prey availability along the southern coast of Japan.

Temporal variability of tsunami arrival detection distance revealed by virtual tsunami observation experiments using numerical simulation and 1-month HF radar observation

The combination of a high-frequency ocean surface radar and a tsunami detection method should be assessed as the onshore-offshore distribution of tsunami detection probability, because the probability will vary in accordance with the signal-to-noise ratio (SNR) and the tsunami magnitude in addition to the radar system specifications. Here, we statistically examine the tsunami detection distance based on virtual tsunami observation experiments by using signals received by a high-frequency radar in February 2014 installed on the southern coast of Japan and numerically simulated velocities induced by a Nankai Trough earthquake. In the experiments, the Doppler frequencies associated with the simulated velocities were superimposed on the receiving signals of the radar, and the radial velocities were calculated from the synthesized signals by the fast Fourier transform. Tsunami arrival was then detected based on the temporal change in the cross-correlation of the velocities, before and after tsunami arrival, between two points 3 km apart along a radar beam. We found that the possibility of tsunami detection primarily depends on the kinetic energy ratio between tsunami current and background current velocities. The monthly average detection probability is over 90% when the energy ratio exceeds 5 (offshore distance: 9 km ≤ L ≤ 36 km) and reduces to 50% when the energy ratio is approximately 1 (L = 42 km) over the shelf slope. The ratio varied with the background current physics and SNR, which was mainly affected by ocean surface wave heights and ionospheric electron density.

Archival tagging reveals swimming depth and ambient and peritoneal cavity temperature in age-0 Pacific bluefin tuna, Thunnus orientalis, off the southern coast of Japan

Although archival tags have been deployed in Thunnus since the early 1990s, few studies have placed such loggers on the small-size growth stage. In this study, Pacific bluefin tuna (PBT, Thunnus orientalis) 20–26.5 cm in fork length (FL) were fitted with archival tags and released off the southern coastal area of Japan from July to August in 2012, 2013, and 2014. Time-series data on swimming depth, ambient water temperature, and peritoneal cavity temperatures collected at 30-s intervals during 78–144 days were analyzed in 11 age-0 PBT. In August, the age-0 PBT spent 69.5 to 83.4% of their time within the mixed layer at mean temperatures between 27.6 and 28.3 °C, while previous studies reported that PBT with FL > 50 cm in the East China Sea are found most often in zones with temperatures between 14 and 19 °C. The thermal difference between the peritoneal cavity and ambient temperature was less than 1 °C for age-0 PBT in August, indicating that they were not in danger of overheating. The mean daytime swimming depths of age-0 PBT were significantly and positively correlated with the depth of the thermocline, especially from August to October. By focusing their swimming depths around the thermocline, the age-0 PBT potentially maximize the probability of encountering prey. There was a significant correlation between the mean nighttime depth and lunar illumination. The change in vertical distribution with the lunar cycle during nighttime is likely a form of predator avoidance.

Well-Integrity Evaluation for Methane-Hydrate Production in the Deepwater Nankai Trough

Summary Large accumulations of methane hydrates are known to exist in the deepwater Nankai Trough off the southern coast of Japan. Because of its enormous potential as an energy source, there is growing interest in the production of methane gas from these deposits. An offshore production test was scheduled to test the technological viability to produce the methane hydrate with a depressurization method. However, methane-hydrate production may cause large amounts of compaction and subsidence, which can damage well integrity and cause loss of zonal isolation in the overburden. This condition could provide potential leakage pathways for methane gas to the surface and endanger offshore operations. The paper presents a study in which well integrity was evaluated for a methane-hydrate-production test well in the Nankai Trough. In this study, a new work flow was proposed and applied to honor both fieldwide formation heterogeneity and near-wellbore geometry. The geomechanics properties were determined through integration of seismic inversion data, log data, and core data from the Nankai Trough. Interface elements were installed between the casing and cement and the cement and formation to evaluate the impact of cement-bond quality on the well integrity. The numerical simulation was conducted through coupling of the simulation results produced by a methane-hydrate production simulator from a third party with a 3D finite-element geomechanics simulator. The study predicted the occurrence of 2 cm of subsidence on the seafloor generated by approximately 1.5% of reservoir compaction for a production test of 20 days. Over this period, casing would yield with a plastic strain of approximately 1%. Most findings indicated a low risk in the loss of zonal isolation that is consistent with the results of the production test conducted in March 2013. This simulation evaluated potential risks related to well integrity, and provided critical information for the preparation and execution of the pioneering offshore methane-hydrate production test in the Nankai Trough.

Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 62:71-78 (2014) - DOI: https://doi.org/10.3354/cr01260 Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan Teruhisa Shimada* Graduate School of Science, Tohoku University, Aramaki Aza Aoba 6-3, Aoba-ku, Sendai, Miyagi 980-8578, Japan *Corresponding author: shimada@ocean.caos.tohoku.ac.jp ABSTRACT: Wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan in June–August is investigated using in situ measurements and reanalysis data. The coastal wave height is dominated by the persistent easterly winds induced by the developed Okhotsk high. These winds, which can induce cool summers in northern Japan, favor wave development toward the coast of northern Japan. The wave variability is enhanced along the coast of northern Tohoku by the strong local winds occurring in the lee of Cape Erimo. The results for variability of wave height along the Pacific and Okhotsk Sea coasts of northern Japan are supported by composite analysis of reanalysis wave data. When the Okhotsk high develops and the resulting easterly winds are dominant, the wave height increases near the coast of and to the east of northern Japan. Wave height also increases in the Japan Sea and along the southern coast of Japan, whereas wave height decreases in the Okhotsk Sea. These wave height variations reflect the distinct wind fields associated with the developed Okhotsk high. Trends in wave height are examined using the in situ measurements available for over 20 yr. Only the decreasing trends in the south of northern Japan in August are statistically significant. KEY WORDS: Wave climate · Okhotsk high · Northern Japan · Significant wave height · Cool summer · Yamase Full text in pdf format PreviousCite this article as: Shimada T (2014) Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan. Clim Res 62:71-78. https://doi.org/10.3354/cr01260 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 62, No. 1. Online publication date: December 02, 2014 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2014 Inter-Research.

Meteorological impacts of sea-surface temperature associated with the humid airflow from Tropical Cyclone Talas (2011)

Abstract. This paper examines meteorological impacts of sea-surface temperature (SST) in the presence of the humid airflow from Tropical Cyclone Talas (2011). To investigate the influence of the SST on the severe weather in and around Japan, sensitivity simulations were conducted using six SST data products covering a period of 7 days. The upward sea-surface latent heat flux that accumulated over the 7-day period was high around the Kuroshio during the slow passage of the tropical cyclone. Large differences were found among the individual SST products around the southern coast of Japan. The coastal warm SST anomaly of ~ 1.5 °C enhanced the surface upward latent heat fluxes (by 60 to 80%), surface southeasterly winds (by 6 to 8%), and surface water mixing ratios (by 4%) over the coastal sea area. The enhanced latent heat flux resulting from the coastal SST anomaly contributed to the further enhancement of the latent heat flux itself via a positive feedback with the amplified surface horizontal wind. The SST anomalies produced an anomaly in 7-day precipitation (ca. 40 mm) along the mountainsides and over a coastal area where the surface wind anomaly was locally large. Thus, coastal SST error is important in the atmospheric simulation of accumulated evaporation and precipitation associated with tropical cyclones making landfall.

The El Salvador and Philippines Tsunamis of August 2012: Insights from Sea Level Data Analysis and Numerical Modeling

We studied two tsunamis from 2012, one generated by the El Salvador earthquake of 27 August (Mw 7.3) and the other generated by the Philippines earthquake of 31 August (Mw 7.6), using sea level data analysis and numerical modeling. For the El Salvador tsunami, the largest wave height was observed in Baltra, Galapagos Islands (71.1 cm) located about 1,400 km away from the source. The tsunami governing periods were around 9 and 19 min. Numerical modeling indicated that most of the tsunami energy was directed towards the Galapagos Islands, explaining the relatively large wave height there. For the Philippines tsunami, the maximum wave height of 30.5 cm was observed at Kushimoto in Japan located about 2,700 km away from the source. The tsunami governing periods were around 8, 12 and 29 min. Numerical modeling showed that a significant part of the far-field tsunami energy was directed towards the southern coast of Japan. Fourier and wavelet analyses as well as numerical modeling suggested that the dominant period of the first wave at stations normal to the fault strike is related to the fault width, while the period of the first wave at stations in the direction of fault strike is representative of the fault length.

A numerical study of the Kuroshio-induced circulation in Tosa Bay, off the southern coast of Japan

We performed a numerical experiment for the circulation in Tosa Bay using a triply-nested 1/50-degree model. This study revisits the climatological features of the Kuroshio-induced circulation in Tosa Bay by comparison with previous studies based on hydrographic observations. The model well reproduces the climatological features previously reported and reveals the following new findings: long-term mean circulation in Tosa Bay is characterized by an anticlockwise circulation (AC) spreading over the bay. The AC exhibits a cold-dome structure with deep baroclinic velocity shears. The velocity shears can be accounted for mainly by geostrophic shear. In this regard, however, the gradient wind balance is maintained because an ageostrophic velocity attributed to the momentum advection is caused by the state where the AC is intensified. The primary condition for controlling the development and decay of the AC is the mesoscale onshore–offshore movement of the Kuroshio axis; the secondary condition is a high-frequency submesoscale variation such as a Kuroshio frontal wave, which can be regarded as noise for the primary condition. Sequential development and decay of the AC is frequently simulated when the Kuroshio takes a nearshore path, and the frontal waves propagate eastward and interact with coastal water in Tosa Bay. That is, the horizontal advection of relative vorticity due to the frontal wave propagation plays an important role in controlling the sequential response.

Atmospheric impact on the northwestern Pacific under a global warming scenario

Eleven climate models, one high‐resolution and ten low‐resolution, were analyzed to investigate the response of the northwestern Pacific under a global warming scenario. Application of scenario A1B of the Special Report on Emission Scenarios (SRES) weakens (intensifies) the southern (northern) part of the interior subtropical gyre both in high‐resolution and low‐resolution model. Such a dipole type change is mainly due to a basin‐scale dynamic atmosphere‐to‐ocean process. Namely, under global warming the Hadley circulation is weakened and expanded poleward. The Ferrel circulation is also displaced poleward, leading to weakening of ascending (descending) air motion and a high (low) sea level pressure anomaly in the northwestern (southeastern extratropical) North Pacific. Finally, a negative wind stress curl anomaly developed along the zero wind stress curl line of the present‐day climate to enhance the northern part of the gyre. The high‐resolution model results show greater changes in the structure of the Kuroshio and Kuroshio Extension, with strong intensification of the Kuroshio Extension front and jet, while in the low‐resolution models the changes are small. The Kuroshio between Taiwan and the southern coast of Japan is significantly intensified in the high‐resolution model results, but is slightly weakened in the ensemble of the low‐resolution models.

Influence of temperature on growth, toxicity and carbohydrate production of a Japanese Ostreopsis ovata strain, a toxic-bloom-forming dinoflagellate

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 65:261-270 (2012) - DOI: https://doi.org/10.3354/ame01555 Influence of temperature on growth, toxicity and carbohydrate production of a Japanese Ostreopsis ovata strain, a toxic-bloom-forming dinoflagellate Nayani K. Vidyarathna*, Edna Granéli School of Natural Sciences, Marine Ecology Department, Linnaeus University, Kalmar 39182, Sweden *Email: nayani.vidyarathna@lnu.se ABSTRACT: Ostreopsis ovata is a benthic dinoflagellate that produces palytoxin and its analogues. Since the end of the 1990s, toxic blooms of O. ovata have been recorded in many tropical and temperate marine waters. These blooms often kill benthic invertebrates and cause health problems for humans. We hypothesize that increases in seawater temperature might induce these blooms. A strain of O. ovata isolated from the southern coast of Japan was selected for study. O. ovata cells were exposed to 7 different temperatures from 24 to 30°C for 30 d, and growth rates were noted. The specific growth rate was found to be highest at 25°C, next highest at 24°C and lower at 26, 28, 27, 30 and 29°C, in that order. The hypothesis that increased seawater temperature causes increases in growth rate was thus not supported. The cell toxicity and carbohydrate production of O. ovata were highest at the temperature range that is optimal for cell growth. Increasesing sea surface temperature, as a result of global warming, is therefore not likely to have a substantial effect on the bloom formation and toxicity of this Japanese strain of O. ovata. KEY WORDS: Ostreopsis ovata · Benthic dinoflagellate · Palytoxin · Toxicity · Climate change · Carbohydrate production Full text in pdf format PreviousNextCite this article as: Vidyarathna NK, Granéli E (2012) Influence of temperature on growth, toxicity and carbohydrate production of a Japanese Ostreopsis ovata strain, a toxic-bloom-forming dinoflagellate. Aquat Microb Ecol 65:261-270. https://doi.org/10.3354/ame01555 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 65, No. 3. Online publication date: March 02, 2012 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2012 Inter-Research.

Low-Level Easterly Winds Blowing through the Tsugaru Strait, Japan. Part I: Case Study and Statistical Characteristics Based on Observations

Abstract This study has investigated structures and diurnal variations of the easterly surface winds blowing throughout the east–west passage comprising the Tsugaru Strait, Mutsu Bay, and circumjacent terrestrial gaps in northern Japan during the summer months. Based on observational and reanalysis data, a representative case study in June 2003 and supplemental statistical analyses are presented. The cool easterly winds accompanied by clouds and fog are blocked by the central mountain range. This condition increases an along-strait sea level pressure (SLP) gradient, which induces strong winds in the west of the strait. The along-strait SLP gradient is enhanced by the developed Okhotsk high and by low pressure systems passing along the southern coast of Japan or over the Japan Sea. Stronger (weaker) and easterly (east-northeasterly) winds are observed during the nighttime (daytime), corresponding to the cool air intrusion from the east (retreat from west). Differences in SLP observed at meteorological observation stations on the east and west can be a good indicator of wind speed in the west of the strait. Meanwhile, the winds over the land also show diurnal variations specific to the times of the prevailing cool easterly winds. The easterly winds over the land are stronger and more divergent across the strait during the daytime than nighttime. This indicates the possibility that the diurnal wind variations are thermally induced. Reduction of diurnal air temperature changes in the east increases east–west thermal contrast. Additionally, the cool air over the strait and the bay can enhance land–sea thermal contrast across the coast.

An underwater photograph of Sphyraena iburiensis (Perciformes: Sphyraenidae) from the Red Sea: first record outside Japanese waters

Sphyraena iburiensis, a small-sized barracuda (family Sphyraenidae) recently described by Doiuchi and Nakabo (2005), belongs to the S. obtusata group sensu Doiuchi and Nakabo (2005), characterized by two gill rakers on the first gill arch. The original description of S. iburiensis was based on the holotype and paratypes collected from Iburi, Kochi Prefecture, with additional paratypes from Kushimoto, Wakayama Pref. and Kawana, Shizuoka Pref., all located on the Pacific coast of southern Japan. Subsequently, a specimen of S. iburiensis was reported from Fukaura, Ehime Pref., Japan by Takagi et al. (2010), although additional records based on underwater photographs include Taketomi Island, Ryukyu Islands, Japan (KPM-NR 12009, taken by J. Nakamoto) and Hachijo Island, Izu Islands, Japan (KPM-NR 91935–91937, taken by S. Kato); the photographs are deposited at the Image Database of Fishes, Kanagawa Prefectural Museum of Natural History (http://research.kahaku.go.jp/zoology/ photoDB/). To date, therefore, S. iburiensis has been considered endemic to Japanese waters, although Sphyraena obtusata and Sphyraena pinguis, also members of the S. obtusata group, are both widely known from the IndoWest Pacific (Doiuchi and Nakabo 2005). In 10 October 2008, an underwater photograph of S. iburiensis (Fig. 1) was taken at Shams Alam reef, Wadi Gimal area, Red Sea coast of Egypt (24 4101800N, 35 0500800E), by the second author (S. B.). This record is the first of S. iburiensis outside Japanese waters; the fishes pictured agree well with the diagnostic characters of the S. obtusata group given by Doiuchi and Nakabo (2005), viz. pored lateral-line scales ca. 81–84; scales below lateral line ca. 10 , orbit diameter ca. 5.5% in standard length, posterior tip of maxilla not reaching anterior margin of eye, anterior tip of lower jaw without a pointed fleshy knob, origin of first dorsal fin well behind that of pelvic fin, and body with two longitudinal stripes on the lateral surface. Among the S. obtusata group, S. iburiensis differs from S. pinguis as follows: two longitudinal stripes, lower stripe running through upper part of pectoral-fin base (a single stripe running above pectoral-fin base in S. pinguis) (Doiuchi and Nakabo 2005). Sphyraena iburiensis differs from S. obtusata in having both longitudinal stripes distinct (somewhat indistinct in S. obtusata), the lower stripe extending to the caudal-fin base just below the lateral line (lower stripe joining lateral line midway between end of second dorsal-fin base and caudal-fin base, extending to middle of caudal-fin base in the latter), in addition to 10 – 11 scales below the lateral line (8 –9 in S. obtusata) (Doiuchi and Nakabo 2005). The individuals in Fig. 1 agree closely with the original description of these characters. Shams Alam reef is a large, semi-enclosed lagoon characterized by sandy areas, seagrass beds, isolated coral reefs and fringing reefs. The pictured individuals were observed at a depth of between 1 and 2 m (over about 3 m). Approximately 20 individuals with total lengths of R. Doiuchi (&) Fisheries Experimental Station, Wakayama Research Center of Agriculture, Forestry, and Fisheries, 1557-20 Kushimoto, Higashimuro-gun, Wakayama 649-3503, Japan e-mail: doiuchi_r0001@pref.wakayama.lg.jp

Stable volume and heat transports of the North Pacific subtropical gyre revealed by identifying the Kuroshio in synoptic hydrography south of Japan

We conducted synoptic hydrographic surveys three times under distinctly different conditions of the Kuroshio in the region off the southern coast of Japan; the large‐meander (October 2004) and non‐large‐meander (September 2005 and September 2006) states. As a result of the water mass analysis, we could separate the volume and heat transports of the North Pacific subtropical gyre from the local recirculation gyre and mesoscale eddies. Despite the different flow conditions of the Kuroshio, the volume transport and the volume transport‐averaged temperature of the subtropical gyre fluctuate within the ranges of 23.3–29.0 × 106 m3 s−1 and 17.3–17.6°C, respectively, which are quite stable with respect to those for the Kuroshio south of Japan estimated in the past studies. Taking into account the decrease in the volume transport‐averaged temperature in the North Pacific interior region, the net heat transport of the subtropical gyre across the latitude of 30°N was estimated to be between 0.19 and 0.22 × 1015 W.

A hybrid specimen between two Pseudolabrus species from the southern coast of Japan.

A hybrid specimen between two Pseudolabrus species from the southern coast of Japan.

Tsunami waveform inversion including dispersive waves: the 2004 earthquake off Kii Peninsula, Japan

Long waves are often assumed to model tsunamis, but the wavelength of the initial water height distribution produced by a large submarine earthquake, particularly in the direction perpendicular to the fault strike, is sometimes not much greater than the water depth. The resulting tsunami may have a dispersive character that cannot be simulated based on a conventional long‐wave approximation. The 2004 earthquake off Kii Peninsula (M 7.4) on the southern coast of Japan indeed produced a dispersive tsunami that was recorded at two stations located off Shikoku. For the foreshock (M 7.1), on the contrary, a dominant dispersive tsunami was not recognized at these stations. Because dispersive waves show strong directional dependence with respect to the fault strike, the above difference indicates that the strikes of the main shock and the foreshock were different. We conducted a tsunami waveform inversion analysis based on the dispersive tsunami equations to estimate the initial water height distribution of the main shock. The estimated initial water height distribution overlapped with the aftershock region, suggesting that the fault strike was perpendicular to the trough axis, and the total displaced water volume was 1.7–2.0 × 109 m3. When we used the conventional long‐wave approximation, the estimated initial water height distribution extended considerably from the aftershock area, because artificial sources were needed outside the aftershock area to reproduce the observed dispersive waves.

Structural architecture and active deformation of the Nankai Accretionary Prism, Japan: Submersible survey results from the Tenryu Submarine Canyon

Two research cruises that deployed submersible surveys were undertaken along the Tenryu Submarine Canyon to directly observe the structural architecture of the eastern Nankai Accretionary Prism off the coast of southern Japan. The surveys have demonstrated that the accreted sediments are strongly deformed turbidite sequences that occur in repeated thrust-anticline structures. From the leading edge of the prism near the trench toward the arc, the following deformation zones have been identified within the prism: Frontal Thrust zone, Prism Toe zone, Imbricate Thrust zone, and Tokai Thrust zone (or out-of-sequence thrust or OOST zone). The Frontal Thrust zone is characterized by debris deposits within the hanging wall that have an age of 0–0.43 Ma, as determined from radiolarian biostratigraphy. The Prism Toe zone is characterized by unconsolidated turbidite sequences that are 1.98–3.4 Ma; these sequences are cut by normal and thrust faults. The Imbricate Thrust zone includes consolidated muddy layers and unconsolidated sandy layers that contain numerous fracture cleavages. The OOST zone consists of highly deformed consolidated sediments, ranging in age from 0.18 to 1.03 Ma. From the Prism Toe zone to the Imbricate Thrust zone, the uniaxial compressive strength increases gradually from 0.5–3.0 to 1.0–6.0 MPa, while the anisotropy of magnetic susceptibility changes from oblate to prolate shapes, and porosity decreases from 40%–50% to 30%–50%. These data indicate that the eastern Nankai Accretionary Prism appears to have been deformed toward the Imbricate Thrust zone just south of the OOST. Stable isotope analyses of calcite veins and calcite cement of the sandstone samples from the Tokai Thrust zone have shown that fluid temperatures for calcite precipitation were 24–63 °C in the OOST zone. The occurrence of highly deformed and consolidated rocks within the Nankai Accretionary Prism likely resulted from tectonic transportation of deeply buried rocks along major out-of-sequence thrust faults, such as the Tokai OOST. We infer therefore that out-of-sequence thrust faults play a major role in transporting deeply buried, deformed rocks in accretionary prisms to the shallower depths and even to the seafloor during ongoing subduction.

Transport of oceanic nitrate from the continental shelf to the coastal basin in relation to the path of the Kuroshio

Hydrographic and biogeochemical observations were conducted along the longitudinal section from Ise Bay to the continental margin (southern coast of Japan) to investigate changes according to the Kuroshio path variations during the summer. The strength of the uplift of the cold deep water was influenced by the surface intrusion of the Kuroshio water to the shelf region. When the intrusion of the Kuroshio surface water to the shelf region was weak in 2006, the cold and NO 3 −-rich shelf water intruded into the bottom layer in the bay from the shelf. This bottom intrusion was intensified by the large river discharge. The nitrogen isotope ratio (δ 15N) of NO 3 − (4–5‰) in the bottom bay water was same as that in the deeper NO 3 − over the shelf, indicating the supply of new nitrogen to the bay. The warm and NO 3 −-poor shelf water intruded into the middle layer via the mixing region at the bay mouth when the Kuroshio water distributed in the coastal areas off Ise Bay in 2005. The regenerated NO 3 − with isotopically light nitrogen (δ 15N=−1‰) was supplied from the shelf to the bay. This NO 3 − is regenerated by the nitrification in the upper layer over the shelf. The contribution rate of regenerated NO 3 − over the shelf to the total NO 3 − in the subsurface chlorophyll maximum layer in the bay was estimated at ∼56% by a two-source mixing model coupled with the Rayleigh equation.

Halogenated Bipyrroles and Methoxylated Tetrabromodiphenyl Ethers in Tiger Shark (Galeocerdo cuvier) from the Southern Coast of Japan

Naturally produced halogenated bipyrroles (HBPs) and methoxylated tetraBDEs (MeO-tetraBDEs) are lipophilic and persistent, and therefore may bioaccumulate with higher trophic levels. In this study, the livers of tiger shark (Galeocerdo cuvier) collected from the southern coast of Japan were investigated for size-related bioaccumulation of natural HBPs and MeO-tetraBDEs in comparison with anthropogenic PCBs and PBDEs. Heptachloro-1'-methyl-1,2'-bipyrrole (Cl7-MBP) and hexahalogenated 1,1'-dimethyl-2,2'-bipyrrole (Br4Cl2-DBP) were present at similar concentration ranges (4-4400 ng/g lipid) in the liver and increased with increasing body length. Two MeO-tetraBDEs, 6-methoxy-2,2',4,4'-tetrabromodiphenyl ether(6-MeO-BDE47), and 2'-methoxy-2,3',4,5'-tetrabromodiphenyl ether (2'-MeO-BDE68) were present at 4- to 6-fold higher concentrations (88 and 58 ng/g lipid, respectively) than BDE-47. In mature tiger sharks, 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl (2,2'-diMeO-BB80) was present at a median concentration of 330 ng/g lipid. Concentrations of 6-MeO-BDE47 were positively correlated to body length (P < 0.01), but no such correlation was observed for 2'-MeO-BDE68 and 2,2'-diMeO-BB80. The concentration ratios (patterns) of PBDE-like natural products in tiger sharks were largely different from that found in other species, such as the bull shark (Carcharhinus leucas), the silvertip shark (Carcharhinus albimarginatus), and the sandbar shark (Carcharhinus plumbeus). The present study suggests thatthe concentrations of natural HBPs in the liver are size (age)-dependent whereas MeO-tetraBDEs have species-specific biomagnification potentials.

Spatial variability of snow water equivalent in a mountainous area of the Japanese Central Alps

The temporal and spatial variability of the snow water equivalent (SWE) content of the snowpack on an east‐west ridge in the vicinity of the timberline altitude in the Japanese Central Alps was examined using snow weights obtained from snow surveys, as well as the chemical stratigraphy in the snow layers, from 22 February 2006 until 18 April 2006. Snow erosion was observed at elevations above 2700 m on the west ridge and at elevations above 2650 m on the east ridge. The SWE below 2600 m on the east ridge was significantly greater than that on the west ridge for the same period and elevation. Further, on the east ridge, 49–55% of the SWE at the 2500‐m site and 30–52% of the SWE at the 2200‐m site could be explained by snow transport from the alpine area. The SWE at the 2500 and 2200‐m sites on the east ridge experienced variations that were 1.7–1.9 times and 1.2–1.3 times those at the 2500 and 2200‐m sites on the west ridge, respectively. We infer that the ratio of the SWE on the east ridge to that on the west ridge varies within a constant range throughout a single snow season. The SWE on the west ridge below 2680 m exhibited a good correlation with elevation. Altitudinal distribution of the SWE increased markedly at the upper part of the west ridge (below the timberline) within a time series set of data. The major reason for this fact is a change in the source of the precipitation from the Asian winter monsoon to low pressure passing along the southern coast of Japan. The main wind direction, the existence of the forest area, and the difference in the pressure patterns strongly influence the formation of SWE in the mountainous areas in the vicinity of timberline.

Growth and annual production of the brown alga Laminaria religiosa introduced into the Uwa Sea in southern Japan

SUMMARY Recently, aquaculture of Laminaria japonica has expanded to the southern coast of Japan and to China along the East China Sea. The southerly distribution of L. religiosa, compared to that of L. japonica, indicated that the aquaculture of L. religiosa along the southern coasts of Japan might be feasible. Thus, we examined the growth, biomass and productivity of L. religiosa cultivated in the Uwa Sea, in southwestern Japan over a period of two years. The seawater temperature ranged from 12.9 to 27.4°C in 2003/2004 and from 12.2 to 28.3°C in 2004/2005. In 2003/2004, the maximum mean density, maximum mean length, and maximum mean wet weight of L. religiosa was 7.8 ± 5.0 ind. m−1 (mean ± SD), 14.8 ± 4.6 cm, and 1.2 ± 0.8 g wet wt., respectively. In 2004/2005, no germination was confirmed through the study period. The maximum biomass and annual production in 2003/2004 were estimated to be 6.9 ± 5.2 g wet wt. m−1 and 8.9 g wet wt. m−1 year−1, respectively. The present study revealed that L. religiosa cultivated in the Uwa Sea were much smaller compared with those of Hokkaido Island, where the alga is naturally found. For the growth of L. religiosa, a relatively long period of seawater temperatures below 13.5°C is required. In the study area, seawater temperatures were below 13.5°C only 11 days in 2003, and 12 days in 2004. As a result, it is thought that expanding the cultivation of L. religiosa to southern areas including the Uwa Sea will be difficult.