Gallium content in seaweeds

Analyses of gallium content were made by the fluorometric method on 57 samples of seaweeds which were composed of 30 species. As the result of it, the gallium content was found ranging from 0.02 to 0.64g g^–1 and the average was 0.14g g^–1 in the dried seaweeds.Generally, the gallium content in seaweeds had a close relationship to the aluminium and iron contents. The average weight ratio of Ga/Al was 3.8×10^–4 and one of Ga/Fe was 4.0×10^–4. The average Ga/Al weight ratio (3.8×10^–4) was very similar to that reported for shallow-water deposits (2.1×10^–4), but was definitely lower than that in sea water (1.5×10^–2).     

Contents of strontinm-90 and ruthenium-106 in beach and shallow water deposits of noto peninsula

⁹⁰Sr,¹⁰⁶Ru, natural strontium and major elements were studied in 12 samples of beach deposits from Togi, Fukuura and Shiga, and in 26 samples of shallow water sediments from sea off Fukuura, Noto Peninsula, Ishikawa Pref., Japan.The average contents of natural strontium and⁹⁰Sr in the beach deposits were 488 ppm ranging from 247 to 1,550 ppm and 45±9 pCi kg^–1-dry mud ranging from 18 to 72 pCi kg^–1-dry mud, respectively. While the average contents of natural strontium,⁹⁰Sr and¹⁰⁶Ru in the sediments were 234 ppm ranging from 136 to 415 ppm, 22±6 pCi kg^–1-dry sand ranging from 7 to 48 pCi kg^–1-dry sand and 0.6 ±0.2 nCi kg^–1-dry ranging from 0.3 to 1.2 nCi kg^–1-dry, respectively.The average contents of each natural strontium and⁹⁰Sr in the beach deposits were about two times higher than those in the shallow water sediments. But no obvious relation of natural strontium to⁹⁰Sr was found in all the samples. The enrichment of⁹⁰Sr and¹⁰⁸Ru in the beach deposits or tthe sediments were as high as 150320 and of 2,0003,000 compared with average contents of⁹⁰Sr and¹⁰⁶Ru in a liter of surface water from the Japan Sea. It is to be noticed that the average¹⁰⁶Ru to⁹⁰Sr ratio of 27 for the shallow water sediments is much higher than the average of 1.0 for surface sea water of the Japan Sea.As to major elements of the samples, the beach deposits are rich in silicon (Av. 70.89 ±0.92% SiO₂), but poor in iron (Av. 2.99±0.32% Fe₂O₃). Whereas the shallow water sediments are poor in silicon (Av. 52.96±10.33% SiO₂) and rich in iron (Av. 5.50±1.90% Fe₂O₃), calcium (Av. 9.64±9.22% CaO) and magnesium (Av. 2.83±1.58% MgO).     

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.     

Study on heterogeneous distribution of plankters at oceanic fronts

In this paper, I review my study on heterogeneous distribution of plankters at oceanic fronts, taking advantage of an opportunity awarded the Okada Prize 1989 of the Oceanographical Society of Japan. The main focus is on the formation and retention mechanisms of phytoplankton peak abundance at the Kuroshio Front, and the events observed at other oceanic fronts, such as the Oyashio Front, the Antarctic Polar Front and the Subtropical Convergence in the southern hemisphere are compared to those found at the Kuroshio Front.Phytoplankton standing stock was hign in the inner cold belt of the Kuroshio Front. Since the inner cold belt form from water masses entrained into the front from coastal and/or the Oyashio areas, one of the characteristics of the phytoplankton community is high contribution of microplankton fraction. Rising of isopleths of temperature and nutrient saltsetc. at the front suggested that upwelling event occurred along the front. Incubation experiments with nutrient addition showed it would flourish the entrained species but oceanic ones when upwelling occurred at the front.Zooplankton was strongly aggregated at the Kuroshio Warm-Core Ring Front, and the peak of abundance was spatially separated in each individual. I thought that biological processes, such as motility and prey-predator interaction, play an important role to control the aggregated patterns.Since the cabbeling event is expected at the Oyashio Front where the relatively cold and low-salinity Oyashio water faces the relatively warm and saline water of the perturbed area, it appears that the phytoplankton species having larger density than that of sea water sink down there. The mixture of sea waters on both sides of the front, however, may accelerate their growth by supply of some deficient element (s).I consider that raise of temperature is the most plausible factor to make phytoplankton peak abundance at the Polar Front. Experiments on board showed that raising temperature activates photosynthesis of antarctic phytoplankton. Phytoplankton standing stock and productivity were also high at the Subtropical Convergence.The primary object of this study is the biological role of oceanic fronts for fish ecology. I consider that concentrated phyto- and zooplankton communities at oceanic fronts support the energy of migrating fishes, and also support the survival of juvenile fishes just after hatching which are transported from coastal areas.     

Vanishing Island States and sovereignty

Sea level rise could bring about an event that has not previously been seen in modern history, that of the physical disappearance of some low-lying Island States. The objective of this paper is to examine what are the likely scenarios for some of these islands in the course of the next century, and analyse for each scenario if these Island States could continue to claim an Exclusive Economic Zone or not. Also, it will analyse the possibility that Island States could continue having some sort of status analogous to statehood even if it was to lose all territory. Finally, the idea of a “government-in-exile” will be discussed, where the State could retain its identity waiting for a future re-emergence of the island.     

Impacts of the Nakhodka heavy-oil spill on an intertidal ecosystem: an approach to impact evaluation using geographical information system

A major heavy-oil spill from the Russian tanker Nakhodka occurred in the Sea of Japan on 2 January 1997. We investigated the impacts of this spill on a rocky intertidal ecosystem along the southern coast of the Sea of Japan. We selected Imago-Ura Cove as our study site to observe temporal changes along the oiled shore, because minimal cleaning effort was made in this area. Field surveys were conducted every autumn and spring from 1997 to 2000. We measured coverage by macroalgae in 1 x 1-m(2) quadrats and counted the animals in 5 x 5-m(2) quadrats along the intertidal zone. Changes in the ecosystem caused by the oil spill were analyzed by applying a geographical information system (GIS) to the Sea of Japan for the first time. The GIS showed that following the accident there were heavily oiled areas in sheltered regions, but these decreased over the three years. It also showed that coverage by macroalgae and the number of animals increased, although some species of algae with microscopic sporophyte generations, and some populations of perennial shellfish, remained stable or decreased during the study period. GIS was able to trace temporal changes in intertidal communities resulting from the impacts of heavy oil on flora and fauna at a spatial scale of 10-100 m. GIS is thus a practical tool for visualizing, analyzing, and monitoring changes in an ecosystem polluted by oil, taking into account topographic differences along the coastline.     

Distribution and photo-physiological condition of phytoplankton in the tropical and subtropical North Pacific

To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F _m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F _v/F _m) and effective absorption cross-section of photosystem II (σ_PSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F _v/F _m [Z(F _v/F _{m max})] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F _v/F _m at the Z(F _v/F _{m max}) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.     

Seabed shear modulus profile inversion using surface gravity (water) wave-induced bottom motion

Summary. The motion of a layered seabed induced by propagating gravity water waves is modelled by the coupling matrix for a massless incompressible elastic bed according to Yamamoto. An amplitude inversion scheme is developed to extract the bottom shear modulus profile from the motion of the seabed at a point on the bed surface using the linear inverse theory combined with the Yamamoto theory of wave-seabed interaction. Numerical tests using synthetic data without noise confirmed that the inversion is unique and consistent. The inversion technique is applied to a set of field data from the Mississippi River Delta. A good agreement is obtained between the inverted profile and the direct measurements.