Complex vertical migration of larvae of the ghost shrimp, Nihonotrypaea harmandi, in inner shelf waters of western Kyushu,Japan

The position of meroplanktonic larvae in the water column with depth-dependent current velocities determines horizontal transport trajectories. For those larvae occurring in inner shelf waters, little is known about how combined diel and tidally-synchronized vertical migration patterns shift ontogenetically. The vertical migration of larvae of Nihonotrypaea harmandi (Decapoda: Thalassinidea: Callianassidae) was investigated in mesotidal, inner shelf waters of western Kyushu, Japan in July–August 2006. The larval sampling at seven depth layers down to 60 m was conducted every 3 h for 36 h in a 68.5-m deep area 10 km off a major coastal adult habitat. Within a 61–65-m deep area 5–7.5 km off the adult habitat, water temperature, salinity, chlorophyll a concentration, and photon flux density were measured, and water currents there were characterized from harmonic analysis of current meter data collected in 2008. The water column was stratified, with pycnocline, chlorophyll a concentration maximum, and 2% of photon flux density at 2 m, recorded at around 22–24 m. The stratified residual currents were detected in their north component, directed offshore and onshore in the upper and lower mixed layers, respectively. More than 87% of larvae occurred between 20 m and 60 m, producing a net onshore transport of approximately 1.3 km d⁻¹. At the sunset flooding tide, all zoeal-stage larvae ascended, which could further promote retention (1.4-km potential onshore transport in 3 h). The actual onshore transport of larvae was detected by observing their occurrence pattern in a shallow embayment area with the adult habitat for 24 h in October 1994. However, ontogenetic differences in the vertical migration pattern in inner shelf waters were also apparent, with the maximum mean positions of zoeae deepening with increasing stages. Zoeae I and II performed a reverse diel migration, with their minimum and maximum depths being reached around noon and midnight, respectively. Zoeae IV and V descended continuously. Zoeae III had behaviors that were intermediate to those of the earlier- and later-stage zoeae. Postlarvae underwent a normal diel migration (nocturnal ascent) regardless of tides, with the deepest position (below 60 m and/or on the bottom) during the day. These findings give a new perspective towards how complex vertical migration patterns in meroplanktonic larvae enable their retention in inner shelf waters before the final entry of postlarvae into their natal populations.     

Late Mesozoic and Cenozoic rifting and its dynamic setting in Eastern China and adjacent areas

During the Late Mesozoic and Cenozoic, extension was widespread in Eastern China and adjacent areas. The first rifting stage spanned in the Late Jurassic–Early Cretaceous times and covered an area of more than 2 million km² of NE Asia from the Lake Baikal to the Sikhot-Alin in EW direction and from the Mongol–Okhotsk fold belt to North China in NS direction. This rifting was characterized by intracontinental rifts, volcanic eruptions and transform extension along large-scale strike–slip faults. Based on the magmatic activity, filling sequence of basins, tectonic framework and subsidence analysis of basins, the evolution of this area can be divided into three main developmental phases. The first phase, calc-alkaline volcanics erupted intensely along NNE-trending faults, forming Daxing'anling volcanic belt, NE China. The second phase, Basin and Range type fault basin system bearing coal and oil developed in NE Asia. During the third phase, which was marked by the change from synrifting to thermal subsidence, very thick postrift deposits developed in the Songliao basin (the largest oil basin in NE China).Following uplift and denudation, caused by compressional tectonism in the near end of Cretaceous, a Paleogene rifting stage produced widespread continental rift systems and continental margin basins in Eastern China. These rifted basins were usually filled with several kilometers of alluvial and lacustrine deposits and contain a large amount of fossil fuel resources. Integrated research in most of these rifting basins has shown that the basins are characterized by rapid subsidence, relative high paleo-geothermal history and thinned crust. It is now accepted that the formation of most of these basins was related to a lithospheric extensional regime or dextral transtensional regime. During Neogene time, early Tertiary basins in Eastern China entered a postrifting phase, forming regional downwarping. Basin fills formed in a thermal subsidence period onlapped the fault basin margins and were deposited in a broad downwarped lacustrine depression. At the same time, within plate rifting of the Lake Baikal and Shanxi graben climaxed and spreading of the Japan Sea and South China Sea occurred. Quaternary rifting was marked by basalt eruption and accelerated subsidence in the area of Tertiary rifting. The Okinawa Trough is an active rift involving back-arc extension.Continental rifting and marginal sea opening were clearly developed in various kind of tectonic settings. Three rifting styles, intracontinental rifting within fold belt, intracontinental rifting within craton and continental marginal rifting and spreading, are distinguished on the basis of nature of the basin basement, tectonic location of rifting and relations to large strike–slip faults.Changes of convergence rates of India–Eurasia and Pacific–Eurasia may have caused NW–SE-trending extensional stress field dominating the rifting. Asthenospheric upwelling may have well assisted the rifting process. In this paper, a combination model of interactions between plates and deep process of lithosphere has been proposed to explain the rifting process in East China and adjacent areas.The research on the Late Mesozoic and Cenozoic extensional tectonics of East China and adjacent areas is important because of its utility as an indicator of the dynamic setting and deformational mechanisms involved in stretching Lithosphere. The research also benefits the exploration and development of mineral and energy resources in this area.     

Stability considerations of an anchor dragged in noncohesive sea bed

The maximum holding power and the stability of stockless anchors dragged in non-cohesive media are considered. Forces and moments acting on each structural element of the anchor, such as flukes, shank and stabilizing fins, were investigated experimentally, and the results are given in formulae.The maximum holding power of an anchor depends upon its configuration in the sea bed. Considering force resultants and moments acting on all the structural elements, equilibrium equations are formulated and the configuration of a dragged anchor and its maximum holding power can be determined by solving these equations. If its equilibrium configuration cannot be determined under the surface of the sea bed, the dragged anchor will turn over as soon as the flukes come out of the bed. This instability will be called lifting-up.Instability phenomena caused by turning around the shank are analysed by considering the resulting moments acting on the anchor in a disturbed condition from the equilibrium configuration. From the results, stability conditions for lifting-up and turning are proposed for the anchor dragged in noncohesive media, and an anchor of absolute-roll-stability is realized by attaching a pair of proper stabilizing fins.     

New detection method for XBT depth error and relationship between the depth error and coefficients in the depth-time equation

New CTD-XBT (T-7 probe) comparison data are analyzed, which provide additional evidence of XBT depth error and support previous results (Hanawa and Yoritaka, 1987; Hanawa and Yoshikawa, 1991). The depth difference between the corrected and uncorrected data is about 26 m at 750 m. In the present study, new data processing procedures by which the depth errors are automatically detected, are developed and adopted. In the new method, first, temperature gradients (TG) of XBT and CTD profiles are calculated. Then, 20 m segment of the XBT-TG profile which should fit to the CTD-TG profile of 20 m segment to be referred to is searched in the XBT-TG profile. Actually, this is achieved by shifting the XBT-TG profile of 20 m segment so as to minimize the area surrounded by both TG profiles. The shifted depth of XBT-TG profile for CTD-TG profile can be regarded as the XBT depth error. This processing is repeated at intervals of 5 m from 10 m to 790 m of CTD-TG profile. The relationship between the scatter of the quadratic depth-time equation coefficients and the depth error is also discussed. It is shown that when the two coefficients have a certain relationship, the depth differences between the plural depth-time equations are small, even if the two coefficients of those equations have apparently very different values.This paper was presented and discussed in the Ad Hoc Meeting of the IGOSS Task Team on Quality Control for Automated System, held in Marion, Massachusetts,U.S.A. in June 3–6, 1991.     

Low-frequency variations of the Eastern Subtropical Front in the North Pacific in an eddy-resolving ocean general circulation model: roles of central mode water in the formation and maintenance

Temporal variations (1960–2005) of the Eastern Subtropical Front (ESTF) in the North Pacific are investigated using historical-run output data of the eddy-resolving Meteorological Research Institute Community Ocean Model, forced by atmospheric reanalysis dataset. Simulated ESTF is distributed in a region of zonal band of 24°N–30°N east of the International Date Line, and is located at the southern boundary of the central mode water (CMW) north of the front. The ESTF intensity clearly shows an interdecadal variation with a timescale of about 20?years. This variation is associated with that in the potential vorticity of CMW, which originates in the CMW formation region farther north about 3?years earlier due to changes in the surface wind forcing.     

Contamination by organochlorine pesticides from rivers

The contamination of organochlorine pesticides (OCPs) from the selected rivers in Okinawa Island was investigated to estimate the current status of pollution in water, plants and surface sediments in these rivers. The Aja River, Asato River, Houtoku River, Kokuba River and Okukubi River were selected for this study. The concentration of the total pesticides were in the range of 0.94-231.8 ng/L in river water, 0.006–191.6 ng/L dry weight in river sediments and 0.001–55.8 ng/L dry weight in plants. Among the OCPs, ΣHCB of α-BHC,β-BHC and Aldrin were the common detected compounds in river water. The α-BHC, Aldrin and Dieldrin were the most frequent detected compounds in river sediments and α-BHC and Dieldrin were the common OCPs detected in plants. Aldrin, Dieldrin and ΣHCB were in abundance. Various contamination patterns between the selected river water, sediments and plants were observed. Aja River, Asato River and Houtoku River were contaminated with α,β,δ,γ- BHC, Aldrin and Dieldrin (water and sediments) whereas the main OCPs in Kokuba River and Okukubi River were Dieldrin (plants) The OCPs levels in all rivers were generally below guideline values in Japan, but some sites displayed levels which exceeded the EC and WHO Standards for Aldrin, Dieldrin and α,β-BHC.     

High-resolution seismic stratigraphy of the Yamato Basin, Japan Sea and its geological application

Abstract High-resolution seismic stratigraphy of the Yamato Basin, Japan Sea, was successfully established using core-log-seismic data integration. The construction of synthetic seismograms by the combination of physical properties and well-log data from the Ocean Drilling Program (ODP) Site 797 was the key to accomplishing the high-resolution seismic stratigraphy. To achieve resolution comparable with well-log data and core lithology, single channel seismic reflection data taken from ODP underway geophysics were reprocessed, and then carefully compared with synthetic seismogram, core and well log profiles to identify seismic units. Ten seismic stratigraphic units were identified at the site, and seismic stratigraphic interpretation was successfully extended from the site to the nearby area along the Yamato Basin margin. The opal-A/opal-CT (biogenic silica/metastable diagenetic silica) boundary has different appearances at places from strong to weak, and mostly discontinuous. One of the significant results achieved from this study is clear distinction of the opal-A/CT boundary from a very strong reflector, which appears at 22 m below the opal-A/CT boundary. Through well-log and physical properties characterization of the different units, resistivity was found to be the best indicator of diatom content and with gamma-ray it also is an indicator of chert layers in the opal-CT zone. Velocity is not greatly effected by diatom ooze in the opal-A zone, however, it shows strong peaks and has an indirect relationship with gamma-ray in the opal-CT zone. Finally, successful correlation of Gamma-ray Attenuation Porosity Evaluator density and resistivity peaks with strong seismic reflectors from upper and lower stratified layers may provide new information on the late Neogene paleoceanography of the Japan Sea in high-resolution scale.