Stokes' expansion of internal deep water waves to the fifth order

Stokes' expansion is applied to the internal waves of finite amplitude, which propagate on the interface between two layers of infinite thickness. Stream function, wave profile, phase velocity and mass transport velocity are given in the fifth order approximation. It is shown that (a) phase velocity increases with increase of wave steepness, (b) mass transport appears in the direction of the wave propagation in both layers as in the case of the surface waves, and (c) when the density difference is very small, the wave profile is flattened not only at the troughs but also at the crests.     

Observation of edge waves trapped on the continental shelf in the vicinity of Makurazaki Harbor, Kyushu, Japan

Sea-bottom pressure gauges were used to measure sea levels at two points on the shelf off the southern coast of Satsuma Peninsula, Kyushu, Japan. Spectral analysis of the observed records and the tide-gauge record of Makurazaki Harbor revealed several predominant common peaks. At the same time, the eigenmodes for the trapped waves on the shelf and inside Makurazaki Bay were obtained numerically using a two-dimensional model, and the periods and the spatial distribution of amplitudes of the proper modes were obtained. A comparison of the calculated modes with the periods and phase patterns of the observed peaks clarified that peaks with periods of 19.5, 16, 13.3, and 12.2 minutes in the shelf region were the modes of standing-edge waves, and the peak with the period of 16 minutes in Makurazaki Harbor was the fundamental mode of the harbor. Among the modes of standing-edge waves, the mode of the period 16 minutes on the shelf had nearly the same period as that of the fundamental mode of Makurazaki Harbor. An analysis of changes of spectral densities of these two modes confirmed that the fundamental mode of the Makurazaki Harbor was induced by this standing-wave mode.     

Influence of Source/Sink Distributions on Flux–Gradient Relationships in the Roughness Sublayer Over an Open Forest Canopy Under Unstable Conditions

The flux–gradient relationships in the unstable roughness sublayer (RSL) over an open canopy of black spruce forest were examined using long-term observations from an instrumented tower. The observed gradients normalised with the surface fluxes and height above the zero-plane displacement showed differences from a universal function established in the surface layer. The magnitude of differences was not constant throughout the year even at the same observation height. Also the magnitude of the differences was different for each scalar, and scalar similarity in the context of the flux–gradient relationship did not always hold. The variation of the differences was explained by the relative contribution of overstorey vegetation to the total flux from the entire ecosystem. This suggests that a mismatch of the vertical source/sink distributions between scalars leads to a different strength of the near-field dispersion effect for each scalar, and this resulted in inequality of eddy diffusivity among scalars in the RSL. An empirical method that predicts the magnitude of differences is proposed. With this method, it is possible to estimate the eddy diffusivity of scalars provided that the relative contribution of overstorey vegetation to the total flux from the ecosystem is known. Also this method can be used to estimate the eddy diffusivity for scalars whose primary sources are at ground level, such as methane and nitrous oxide.     

Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources

Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001.     

230Th/234U and 14C dating of a lowstand coral reef beneath the insular shelf off Irabu Island, Ryukyus, southwestern Japan

Abstract   High-resolution seismic reflection profiles delineated the distribution of mound-shaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral–algal boundstone suggesting a small-scaled coral reef. High-precision α-spectrometric ²³⁰Th/²³⁴U dating coupled with calibrated accelerator mass spectrometric ¹⁴C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3–2. The existence of low-Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific.     

Fluvial to bay sequence stratigraphy and seismic facies of the Cretaceous to Paleogene successions in the MITI Sanriku‐oki well and the vicinities,the Sanriku‐oki forearc basin,northeast Japan

This paper describes the significant depositional setting information derived from well and seismic survey data for the Upper Cretaceous to Lower Eocene forearc basin sediments in the central part of the Sanriku‐oki basin, which is regarded as a key area for elucidating the plate tectonic history of the Northeast Japan Arc. According to the results of well facies analysis utilizing cores, well logs and borehole images, the major depositional environments were of braided and meandering fluvial environments with sporadically intercalated marine incursion beds. Seismic facies, reflection terminations and isopach information provide the actual spatial distributions of fluvial channel zones flowing in a north–south trending direction. The transgression and regression cycles indicate that the Upper Cretaceous to Lower Eocene successions can be divided into thirteen depositional sequences (Sequences SrCr‐0 to SrCr‐5, and SrPg‐1 to SrPg‐7). These depositional sequences demonstrate three types of stacking patterns: Types A to C, each of which shows a succession mainly comprising a meandering fluvial system, a braided fluvial system with minor meandering aspects in the upper part, and major marine incursion beds in the middle part, respectively, although all show an overall transgressive to regressive succession. The Type C marine incursion beds characteristically comprise bay center and tidal‐dominated bay margin facies. Basin‐transecting long seismic sections demonstrate a roll up structure on the trench slope break (TSB) side of the basin. These facts suggest that during the Cretaceous to Eocene periods, the studied fluvial‐dominated forearc basin was sheltered by the uplifted TSB. The selective occurrences of the Type C sequences suggest that when a longer‐scale transgression occurred, especially in Santonian and early Campanian periods, a large bay basin was developed, creating accommodation space, which induced the deposition of the Cretaceous Kuji Group along the arc‐side basin margin.     

Petrochemistry of Late Miocene to Quaternary Igneous Rocks and Metallogenesis in Southwest Hokkaido, Japan

Abstract: Southwest Hokkaido is largely covered by Late Miocene to Quaternary igneous rocks, and has a large number of gold veins and base-metal veins of the same age. Investigation of the silica-normalized concentration of elements has revealed regional petrochemical zoning; large ion lithophile elements (LILE) and K₂O/(Na₂O+K₂O) of the rocks increase toward Japan Sea, whereas total FeO, CaO, and ⁸⁷Sr/⁸⁶Sr decrease. Mapped concentration isoplethes of these elements are not ideally parallel to the volcanic front, but protrude to the west at Funka Bay, and to the northwest at Matsumae Peninsula. Isoplethes of ⁸⁷Sr/⁸⁶Sr show similar patterns and two more northwestward protrusions in the northeast (Jozankei block) of southwest Hokkaido. Contrary to the general petrochemical trend, both high– and low-LILE volcanic rocks occur in the Jozankei block. The ore deposits are distributed in four metallogenic zones; manganese–base–metal zone on the Japan Sea side, pyrite-limonite zone mainly along the volcanic front, gold zone in the middle, and two units of gold–base–metal zone. The northern unit of this zone is in the Jozankei block, and seems a part of the gold zone overlapped by the manganese–base–metal zone. Thus, as a rule, pyrite–limonite, gold, and base-metal deposits accompany low–, intermediate–, and high-LILE igneous rocks, respectively. Individual deposits and volcanic rocks make chains oblique to the zones and the volcanic front. The majority of the ore deposits are distributed along ridges of Bouguer anomalies overlapped by the volcanic chains, which apparently control the patterns of the petrochemical isoplethes. This is typical for two volcanic chains to the north and south of Funka Bay, where the petrochemical isoplethes protrude to the west. This indicates that both the igneous activity and the mineralization have been under the control of tectonic fractures at the roots of the volcanic chains. The geological, petrochemical and metallogenic data support the idea that the chemical characteristics of the deposits are correlated mainly with the chemistry of the associated magmas, and partly with that of the host rocks.     

全球重要农业文化遗产静冈传统茶草综合系统:价值、保护与行动（英文）

日本静冈的传统茶草综合系统是当地政府申请的日本第一个全球重要农业遗产系统(GIAHS)。本文介绍了当初发现该系统的背景、为申报GIAHS所采取的措施以及被列入全球重要农业文化遗产名录后,静冈茶草系统当前的作用和面临的新情况。自2013年入选全球重要农业遗产系统,目前日本的半天然草原大幅减少,但在静冈的茶草系统里发现了独特的半天然草原,茶园里生物多样性非常丰富。这些茶草系统和采用的传统耕作方法被称为"Chagusaba"。然而,GIAHS的申请过程并不容易,因为许多当地农民不了解他们传统耕作方法和GIAHS品牌的价值。在Chagusaba入选GIAHS名单之后,我们的主要工作是相关的品牌推广,努力使传统农业生产出高品质的茶叶。随着日本农业节省劳动力技术的进步,劳动力成本降低,优质茶叶的价格也有所下降,因此,执行低效传统耕作方式的农民数量越来越少。有必要正确地重新认识传统农业方法种植的茶叶的价值,并在价格上得以体现。静冈县当地政府目前正致力于实施认证体系,包括利用GPS进行科学评估,以及引入生物多样性指标等等。