Suruga Bay Research Articles

Underwater Acoustic Communication Using Multiple-Input–Multiple-Output Doppler-Resilient Orthogonal Signal Division Multiplexing

In this paper, we propose a novel underwater acoustic (UWA) communication scheme that achieves energy and spectrum efficiency simultaneously by combining Doppler-resilient orthogonal signal division multiplexing (D-OSDM) and multiple-input-multiple-output (MIMO) signaling. We present both the transmitter processing and the receiver processing for MIMO D-OSDM. We evaluate the performance of MIMO D-OSDM in simulations with a large intersymbol interference of 25 symbols and a Doppler spread with a maximum Doppler shift of 8 Hz. In addition, the sea trial is performed in Suruga Bay, where the receiver is mounted on a barge and a research vessel with the transmitter makes round trips along a line with a speed of 4 kn. In the experiments, we obtain an intersymbol interference of 3.6-29.7 symbols and a Doppler spread of several Hertz (leading to a spread of over two to three subcarrier spacings). The simulation results suggest that MIMO D-OSDM has an advantage over normal D-OSDM, Doppler-resilient MIMO orthogonal frequency division multiplexing (MIMO D-OFDM), and classical OFDM with MIMO signaling (MIMO OFDM)-MIMO D-OSDM achieves better bit error rate performance than the benchmarks. The sea trial results also support the advantage of MIMO D-OSDM-it achieves a coded block error rate of 3.2% while normal D-OSDM and MIMO D-OFDM achieve a coded block error rate of 9.7% and 9.3%, respectively. We conclude that MIMO D-OSDM can become a viable technique that achieves reliable and effective UWA communication.

Full-Scale Experiment of Earthquake Resistant Embankment Using Flexible Container Bag

There exists many road embankments in Japan which are not earthquake resistant. For example, a road embankment collapsed at Okuradani IC in Hyogo Prefecture during the Great Hanshin-Awaji Earthquake of 1995. In 2009, a road embankment along the Tomei Expressway collapsed during an earthquake with epicenter in Suruga Bay. Road failure makes relief activity and transportation of goods difficult, causing social damage. Furthermore, recovery of damaged embankments takes much time and cost. Accordingly, it is important to conduct research on methods of construction which would help build embankments inexpensively and swiftly. Against this background, a full-scale experiment was conducted at E-Defense to confirm the validity of a method of construction that uses flexible container bag to pack soil for quick embankment recovery. Generally, flexible container bags are easy to handle, and ensure and maintain the earthquake resistance performance of embankments after the completion of recovery work, taking the longer life time of the reinforced structure into consideration. In the experiment, two kinds of reinforced structures with flexible container bags stacked differently were placed at either toe of the slope of an embankment of height 4 m, and shake tests were performed three times to compare the effectiveness of both reinforced structures. For both kinds of structures, the flexible container bags were stacked in two tiers and compressed from top and bottom using compression plates to make the structures rigid. One of the structures was one-tier type where the flexible container bags were stacked in series and the other was two-tier type where the flexible container bags were stacked along the side of the embankment. In the case with the target acceleration of sine wave of 376 Gal, crack occurred on the reinforced structure of one-tier type, but the embankment collapsed a little near the top of the slope. There was little displacement in both reinforced structures, hence, it is judged that the deformation would not impair the functionality of the road. As for the seismic performance, it can be said that the two-tier type would be slightly superior to one-tier type, however, this assumption cannot be evaluated decisively under the present circumstances. For practical use in future, form, size, workability, and economy of embankment should be examined for designing and construction which takes the specification of the structure into consideration.

Tsunamis and submarine landslides in Suruga Bay, central Japan, caused by Nankai–Suruga Trough megathrust earthquakes during the last 5000 years

Magnitude 8 megathrust earthquakes that have generated large tsunamis with wave heights of >5 m in coastal areas of southwestern Japan have occurred every 100–150 years along the Nankai–Suruga Trough, which marks the convergent boundary between the Eurasian and Philippine Sea plates. Using sedimentological, geochemical, and paleontological analyses, as well as 14C dating, we examined tsunami deposits in 12 sediment cores collected from the Hamatome lowland, Yaizu Plain, Shizuoka, which faces the Suruga Trough. Four sandy tsunami deposits (Sands 1–4) are identified in sediments deposited during the last 5000 years. Sand 1 was deposited between 805 and 405 BC, suggesting that only one tsunami left a sedimentological imprint in the Hamatome lowland lagoon during the period of ∼4000 years between 3090 and 2913 BC and the AD 1096 Eicho-Tokai earthquake. This very low frequency of tsunami inundation may suggest that this tsunami was larger than those typically associated with megathrust earthquakes. Sands 2–4 are correlated with tsunamis associated with the Eicho-Tokai, AD 1361 Shohei-Koan, and AD 1498 Meio-Tokai earthquakes, respectively. Our data indicate that a sand spit, which had previously protected the lagoon from oceanic waves, was abruptly destroyed following the AD 1096 Eicho-Tokai earthquake and did not re-form at the same location. This disappearance of the sand spit is inferred to have involved an earthquake-induced submarine landslide. The data presented in this paper, together with information obtained from historical documents, indicates that M8 megathrust earthquakes in AD 1096 and AD 1498 caused submarine landslides in the study area, resulting in coastal subsidence and damage to coastal areas additional to that caused by the tsunamis.

駿河湾における微量元素(Mn,Fe,Ni,CuおよびCd)の鉛直分布と変動

駿河湾における微量元素(Mn,Fe,Ni,CuおよびCd)の鉛直分布と変動

Improvement of communication quality using compressed sensing in underwater acoustic communication system with orthogonal signal division multiplexing

We propose the use of compressed sensing for an underwater acoustic (UWA) communication system with orthogonal signal division multiplexing (OSDM) to achieve reliable communication in UWA channels with large delay and Doppler spreads. However, OSDM does not fully exploit the characteristics of UWA channels, which have long but sparse reverberation tails. Hence, we propose an OSDM channel estimator using compressed sensing and evaluate its performance in simulations and experiments. The simulations revealed that the optimal gain determining the performance of the channel estimator depends on standard deviation of noise σ, and OSDM using compressed sensing outperforms normal OSDM. We also evaluate OSDM performance using compressed sensing in field testing in the coastal area of Suruga Bay, Japan. The experimental results suggest that compressed sensing can boost OSDM performance; the number of OSDM error blocks using compressed sensing is half that in normal OSDM. Thus, OSDM using compressed sensing provides reliable communication.

駿河湾で初記録となるミツボシカスベ（ガンギエイ目ガンギエイ科）について

駿河湾で初記録となるミツボシカスベ（ガンギエイ目ガンギエイ科）について

Areolate grouper, <i>Epinephelus</i> <i>areolatus</i> (Perciformes: Serranidae), a new host record for <i>Lernaeenicus ramosus</i> (Copepoda: Pennellidae), with comments on the known hosts and distribution records of the copepod in the Indo-West Pacific region

An ovigerous female of Lernaeenicus ramosus Kirtisinghe, 1956 was collected from an areolate grouper, Epinephelus areolatus (Forsskål, 1775), in coastal waters of Suruga Bay (western North Pacific Ocean), Shizuoka Prefecture, central Japan. This represents a new host and the easternmost distribution records for L. ramosus. Based on the literature published between 1956 and 2019, this paper tabulates the known hosts and distribution records of the species in the Indo-West Pacific region. The recent collections of L. ramosus from Japan further support a previous suggestion that the geographical distribution of the species in Japanese waters is affected by two warm currents, the Kuroshio, and its branch, the Tsushima Current.

Correction to: Paraliparis hokuto, a new snailfish (Cottoidei: Liparidae) from Suruga Bay, Japan, and a new record of the rare species Paraliparis atramentatus Gilbert and Burke 1912

In the first sentence of Introduction in the original publication, the year “1879” was included in parentheses after "Paraliparis Collett" by the typesetter mistakenly. The correct sentence should read as below:

Paraliparis hokuto, a new snailfish (Cottoidei: Liparidae) from Suruga Bay, Japan, and a new record of the rare species Paraliparis atramentatus Gilbert and Burke 1912

The new snailfish Paraliparis hokuto is described from two specimens collected between 1,432 and 1,562 m depth in the northern part of the Suruga Trough. It can be distinguished from all currently recognized congeners by the following combination of characters: 72 total vertebrae; 65 dorsal-fin rays; 60 or 61 anal-fin rays; 22 or 23 pectoral-fin rays; 6 caudal-fin rays; 3 pectoral proximal radials, all unnotched; 5 pyloric caeca, longest caecum ca. 60% of HL; teeth weak, easily bent or damaged, completely uniserial in lower jaw; paired chin pores in common pit; opercular flap present; uppermost part of pectoral-fin base horizontally level with center or lower margin of eye. A single specimen of the rare snailfish Paraliparis atramentatus Gilbert and Burke 1912, collected from 253 to 1,282 m depth on the continental slope in western Suruga Bay, and representing only the third example of the species and first record from Suruga Bay, is described and intraspecific variability in teeth tip shape noted.

Spatio-temporal variation of Prochlorococcus and phytoplankton community between Shimizu coast and Suruga bay, Northwest Pacific Ocean

A biweekly study was conducted in the surface waters of the Shimizu coast and Suruga Bay in the Northwest Pacific Ocean during January 2005 to February 2006. The diagnostic pigment fucoxanthin (Fuco), representing diatoms, and divinyl-chl a (div-chl a), representing Prochlorococcus (picophytoplankton), were highest in the near shore (type-1) water. The contribution of diatoms to the phytoplankton biomass; i.e. chlorophyll a (Chl a), was highest (∼76%) in the type-I water and lowest (∼64%) in the offshore (type-III) water. The Prochlorococcus contribution was ∼13% and ∼5% in the type-I and III water, respectively. The div-chl a concentration reached a maximum of 2.92 mg m−3 in July (summer) followed by 0.9 mg m−3 smaller peak in September, before decreasing to 0.01 mg m−3 in January (winter). Zeaxanthin, a pigment which is a biomarker for Synechococcus (picophytoplankton), peaked in May (autumn), while chlorophyll b (Chl b) and lutein, representing chlorophytes, were elevated in August (summer). In contrast, the Fuco was highest (16.3 mg m−3) in June (spring). The Prochlorococcus concentrations peaked in July and September, when the water temperature was above 20 °C. However the lowest concentrations were observed between 1 °C and 15 °C, suggesting this community experienced temperature adaptation and was highest in type-I and type-II (i.e. mid-shore) water. Results revealed that Prochlorococcus had a greater contribution of temperature adaptations than diatoms to the ecosystem in comparison of the surface area of individual to volume ratio and played a major role in the biogeochemical cycle of the region.

Geologic evidence for coseismic uplift at ~\u2009AD 400 in coastal lowland deposits on the Shimizu Plain, central Japan

Megathrust earthquakes of magnitude ~ 8 and ensuing large tsunamis occur along the Nankai and Suruga troughs, central Japan, with a recurrence interval of 90–270 years since an AD 684 Hakuho earthquake. Historical records show that the AD 1854 Ansei-Tokai earthquake caused coseismic uplift of ~ 1 m in coastal areas west of Suruga Bay, including the Shimizu Plain, east Shizuoka Prefecture. The 1361 Shohei Tokai earthquake was accompanied by coseismic uplift, but no evidence has been found to indicate uplift before the earthquake. This study examined sediment cores recovered from the coastal beach ridge in the Shimizu Plain using sedimentological and paleontological analyses and radiocarbon dating. We infer from the results that a relative sea-level fall of 1.6 m took place at AD 398–428. This coincides with archeological evidence suggesting the occurrence of a large earthquake in west Shizuoka Prefecture in AD 400. This combination of evidence indicates that the drop in sea level was caused by coseismic uplift associated with a megathrust rupture along the Suruga Trough, with a recurrence interval of ~ 500–1000 years. The results also indicate that a megathrust rupture occurred in the region from the Eastern Nankai Trough to the Suruga Trough at ca. AD 400.

Short-Term Changes in Marine Prokaryotic and Eukaryotic Microalgal Communities Exposed to the Leachate of a Seafloor Hydrothermal Sulfide

The effects of increased mining of seafloor massive sulfide deposits on marine ecosystems have not been characterized. In this study, the impact of leaching metals from a hydrothermal sulfide on photosynthetic protist and cyanobacterial communities in marine environments was investigated by amplicon analyses of small subunit rDNA (SSU rDNA) and rRNA (SSU rRNA). Seawater samples collected from the Iheya North region and Suruga Bay, Japan, were incubated with or without a leachate containing zinc, copper, cadmium, and manganese, of the actual seafloor hydrothermal sulfide from the Hakurei site in the Izena Hole region. The relative abundances of prasinophytes, diatom protists, and the cyanobacteria Synechococcus decreased substantially during incubation with leachate, indicating the vulnerability of these lineages to the leachate. Phylogenetic analysis based on the cyanobacterial phycocyanin cpcBA/rpcBA operon obtained from samples incubated with or without leachate indicated that the individual lineages of Synechococcus can determine sensitivity to heavy metals in different marine regions as well as particular clades and ecotypes.

Field testing of underwater acoustic communication using Doppler-resilient orthogonal signal division multiplexing in coastal area of Suruga Bay

Mobile underwater acoustic (UWA) communication is still challenging, since the mobile UWA channel is characterized by severe delay and Doppler spreads. In this paper, we describe a field test of Doppler-resilient orthogonal signal division multiplexing (D-OSDM)—a signal modulation technique designed to address delay and Doppler spreads efficiently. The experiment was performed in a coastal area of Suruga Bay, which has typical shallow-water sound speed profiles with delay and Doppler spreads of 5–25 ms and 1–8 Hz, respectively. The results indicated that UWA communication using D-OSDM is an effective communication tool that can provide reliable data transfer even in a mobile UWA channel with delay and Doppler spreads.

Vertical distribution of particle-associated and free-living ammonia-oxidizing archaea in Suruga Bay, a deep coastal embayment of Japan.

We analyzed the vertical distributions of ammonia-oxidizing archaea (AOA) in terms of abundance in Suruga Bay, Japan. We distinguished particle-associated (PA) from free-living (FL) assemblages. According to quantitative PCR measurements of the ammonia monooxygenase subunit A gene (amoA), most marine AOA were in an FL state. The vertical distributions of PA AOA ecotypes differed from the general trend; the Shallow Marine clade was dominant in both the surface and deep layers. Thus, although PA AOA account for a small percentage of AOA abundance, they have a community structure distinct from that of FL AOA in planktonic environments. Marine particles should be investigated further as an unexplored niche of AOA in the ocean.

A new genus for "Neocallichirus" grandis Karasawa amp; Goda, 1996, a ghost shrimp species (Decapoda: Axiidea: Callianassidae) heretofore known only by fossil materials.

A new genus of the family Callianassidae, Laticallichirus, is established for "Neocallichirus" grandis Karasawa Goda, 1996, a ghost shrimp species heretofore represented only by fossil materials from the middle to upper Pleistocene of Japan. The newly collected specimens came from two Japanese localities: Numazu, Shizuoka Prefecture (Suruga Bay) and Tosa, Kochi Prefecture (Tosa Bay), included within the known geographical range derived from fossil records. The species identification was based on the close agreement in the cheliped morphology and the known fossil distributions. The new genus is assigned to the subfamily Callichirinae Manning Felder, 1991, and compared with seven genera, Balsscallichirus Sakai, 2011, Callichirus Stimpson, 1866, Callichiropsis Sakai, 2010, Grynaminna Poore, 2000, Michaelcallianassa Sakai, 2002, Lepidophthalmus Holmes, 1904 and Podocallichirus Sakai, 1999, all characterized by the antennular peduncle being longer and stouter than the antennal peduncle. The new genus is characteristic in combination of the following characters: rostrum spiniform; maxilliped 3 devoid of exopod; ischium-merus of maxilliped 3 broadly operculiform; maxilliped 3 ischium devoid of crista dentata; major cheliped devoid of meral hook or associated lobe-like structure; tergites of the pleomeres 3-5 without conspicuous ornamentation; male pleopod 2 biramous, its endopod devoid of appendices interna and masculina; uropodal endopod suboval in shape; telson distinctly wider than long, with shallowly concave posterior margin. The genetic analysis using the mitochondrial 16S rRNA places the new genus as sister to Callichirus Stimpson, 1866, although bootstrap support for major branches is generally low. The newly collected specimens were found in burrows in soft sediments of shallow subtidal zone being accessible at low tide.

Four new deepwater Ophichthus (Anguilliformes: Ophichthidae) from Japan with a redescription of Ophichthus pallens (Richardson 1848)

In this paper, new and uncertain Japanese snake eels of the genus Ophichthus are treated. Ophichthus kusanagi, O. lupus, O. oligosteus and O. yamakawai are herein described as new species. Ophichthus kusanagi, collected from Suruga Bay of Shizuoka Prefecture, off Owase, Mie Prefecture, and Tosa Bay, Kochi Prefecture, is distinguishable from four similar congeners by having one + four supraorbital and two preopercular pores, 13 pectoral-fin rays, fewer total vertebrae (158–163), a longer tail [58–60% of total length (TL)], a small eye [7.5–9.0% of head length (HL)], an acute snout, a low knob on upper lip between nostrils, relatively slender teeth, and a pointed pectoral fin. Ophichthus lupus, collected from the East China Sea, is characterized by its numerous total vertebrae (180–182), shorter pectoral fins (20–25% HL), and the position of the dorsal-fin origin (slightly behind the pectoral-fin tip); it can be distinguished from similar species in its supraorbital and mandibular pores (one + four and six or seven), arrangements of teeth on its mandible and vomer (almost uniserial), its robust body (depth 2.6–3.1% TL), slightly larger head (7.8–8.1% TL), longer and acute snout (24% HL), longer upper jaw (45–48% HL), absence of protrusion along upper lip, and the narrow dark margin of its dorsal fin. Ophichthus oligosteus, collected from Tosa Bay of Kochi Prefecture, is characterized by its fewer preanal and total vertebrae (46 and 121). Ophichthus yamakawai, collected from Kochi Prefecture, is characterized by its large blotches along the lateral line and numerous preanal and total vertebrae (67 and 172). We refer an uncertain species, Ophichthus stenopterus Cope 1871, to the synonymy of Ophichthus pallens (Richardson 1848), a forgotten species described from China. Pisoodonophis zophistius Jordan and Snyder 1901 is recognized as valid in Ophichthus and a senior synonym of Ophichthys intermedius Regan 1905. Ophichthus habereri Franz 1910, originally described from Yokohama, central Japan, is a junior synonym of Ophichthus asakusae Jordan and Snyder 1901. Pisodonophis sangjuensis Ji and Kim 2011 is referred to Ophichthus. We currently recognize 20 species of Ophichthus from Japan. A key to the Japanese species of Ophichthus and its closely associated group Pisodonophis is provided.

New record of Parascombrops mochizukii from Suruga Bay; the northernmost record of the species

New record of <i>Parascombrops mochizukii</i> from Suruga Bay; the northernmost record of the species

PROBABILISTIC EVALUATION OF STORM SURGES IN SURUGA BAY EMPLOYING STOCHASTIC TYPHOON MODEL

Design procedure of coastal embankment in Japan compares tsunami height and storm surge height and employs higher value as a crown level. Estimation of tsunami or storm surge height is usually based on the historical maximum record or an assumed maximum value. Estimation of storm surge needs not only typhoon intensity but also its characteristics e.g. tracks and travel speed. It is difficult to estimate the probability of storm surges using only observed data since typhoon rarely attacks particular area and storm surges are seldom generated. This study proposes probabilistic evaluation procedure of storm surges employing stochastic typhoon model and applies to Suruga Bay, Japan.

Effects of slaking and degree of compaction on the mechanical properties of mudstones with varying slaking properties

An earthquake in Suruga Bay off Shizuoka Prefecture in 2009 caused an embankment near the Makinohara Service Area of the Tomei Expressway to fail. One of the causes of this failure was the slaking progression of the Neogene Period mudstone in the lower portion of the embankment.The objective of this study is to understand how the degree of slaking affects the compressive and shearing behaviors of crushed mudstone aggregates. A drying-immersion cycle test is proposed; it illuminates how the number of repeated drying and immersion cycles affects the slaking of fine-grained material. Unconfined compression, triaxial compression, and one-dimensional consolidation tests were carried out on crushed mudstone aggregate specimens created by compaction.Consequently, the unconfined compressive strength and maximum deviator stress in the triaxial compression tests on the crushed mudstone aggregates dropped as the grains became finer due to slaking even if the initial density was the same. The compressibility increased and the consolidation yield stress decreased as the grains became finer particles. The degree to which slaking had progressed affected these characteristics as well.

Regional groundwater flow system in a stratovolcano adjacent to a coastal area: a case study of Mt. Fuji and Suruga Bay, Japan

Groundwater movement through the slope area of Mt. Fuji to the coastal area of Suruga Bay (central Japan) was investigated using spatially dense geochemical data, as a case study for elucidating the groundwater flow system in a stratovolcano adjacent to the coast. Spatial distributions of the hydrogen stable isotope ratio, vanadium concentration, and water temperature in the groundwater showed anomalies at the coastal area of Suruga Bay. The anomalies were characterized as depleted isotope ratio, high vanadium concentration, and low water temperature relative to surroundings. This can be explained as a regional deep groundwater flow from the slope of Mr. Fuji to the coastal area of Suruga Bay because groundwater recharged at higher elevation has a depleted isotope ratio caused by the altitude effect and high vanadium concentration as a result of dissolution from the basaltic aquifer. These characteristics also imply a hierarchical flow system, which is incorporated into a hydrogeological model of the coastal aquifer.