Circulation and currents in the southwestern East/Japan Sea: Overview and review

A review is made of circulation and currents in the southwestern East/Japan Sea (the Ulleung Basin), and the Korea/Tsushima Strait which is a unique conduit for surface inflow into the Ulleung Basin. The review particularly concentrates on describing some preliminary results from recent extensive measurements made after 1996. Mean flow patterns are different in the upstream and downstream regions of the Korea/Tsushima Strait. A high velocity core occurs in the mid-section in the upstream region, and splits into two cores hugging the coasts of Korea and Japan, the downstream region, after passing around Tsushima Island located in the middle of the strait. Four-year mean transport into the East/Japan Sea through the Korea/Tsushima Strait based on submarine cable data calibrated by direct observations is 2.4 Sv (1 Sv = 10⁶ m³ s⁻¹). A wide range of variability occurs for the subtidal transport variation from subinertial (2–10 days) to interannual scales. While the subinertial variability is shown to arise from the atmospheric pressure disturbances, the longer period variation has been poorly understood.Mean upper circulation of the Ulleung Basin is characterized by the northward flowing East Korean Warm Current along the east coast of Korea and its meander eastward after the separation from the coast, the Offshore Branch along the coast of Japan, and the anticyclonic Ulleung Warm Eddy that forms from a meander of the East Korean Warm Current. Continuous acoustic travel-time measurements between June 1999 and June 2001 suggest five quasi-stable upper circulation patterns that persist for about 3–5 months with transitions between successive patterns occurring in a few months or days. Disappearance of the East Korean Warm Current is triggered by merging the Dok Cold Eddy, originating from the pinching-off of the meander trough, with the coastal cold water carried Southward by the North Korean Cold Current. The Ulleung Warm Eddy persisted for about 20 months in the middle of the Ulleung Basin with changes in its position and spatial scale associated with strengthening and weakening of the transport through the Korea/Tsushima Strait. The variability of upper circulation is partly related to the transport variation through the Korea/Tsushima Strait. Movements of the coastal cold water and the instability of the polar front also appear to be important factors affecting the variability.Deep circulation in the Ulleung Basin is primarily cyclonic and commonly consists of one or more cyclonic cells, and an anticyclonic cell centered near Ulleung Island. The cyclonic circulation is conjectured to be driven by a net inflow through the Ulleung Interplain Gap, which serves as a conduit for the exchange of deep waters between the Japan Basin in the northern East Sea and the Ulleung Basin. Deep currents are characterized by a short correlation scale and the predominance of mesoscale variability with periods of 20–40 days. Seasonality of deep currents is indistinct, and the coupling of upper and deep circulation has not been clarified yet.     

Testate amoeba analysis of lake sediments: impact of filter size and total count on estimates of density,species richness and assemblage structure

Testate amoebae are informative about palaeoecological conditions, but the methods generally used for their analyses in lake sediments differ from those used for their analyses in peats, making comparisons difficult. This study examines how filter mesh size and total number of individuals counted affect species richness, Shannon diversity, equitability, density and assemblage structure. We analysed the complete testate amoeba contents of six sediment samples from Lake Lautrey, France. The abundance of testate amoebae was high (1,403–10,870 shells cm⁻³), and species smaller than 63 μm in both length and width represented up to 89% of total abundance and 43% of species richness. A simulation showed that using 47- or 63-μm mesh-size filters reduced inter-sample differences and changed the patterns of abundance, species richness and assemblage structure, causing loss of information and leading to potential erroneous palaeoecological interpretation. Rarefaction analyses suggest that although 170 shells are sufficient to assess the general structure of assemblages, such small sample sizes can underestimate species richness by overlooking taxa with relative abundances <4%. Total counts of 400 shells yield better estimates of assemblage structure and recover at least 50% of total species richness, although species with absolute frequencies below 2% may still be missed. Higher counts are required to obtain reliable estimates of species richness and assemblage structure in samples that have high testate amoeba densities but are dominated by a few small taxa. Further studies should determine the bioindicator value and functional roles of small and/or rare species in lakes and thus to what extent overlooking them affects palaeoecological interpretations.     

Variable stars in the field of open cluster NGC 6819

We report on the discovery of 25 variable stars plus 13 suspected variables found in the field of the open cluster NGC 6819. The stars were identified from time-series photometric data obtained on the Isaac Newton Telescope, La Palma, during two observing runs covering the 19 nights between 1999 June  22–30  and 1999 July  22–31  . The variables found include 12 eclipsing binaries with an additional three suspected, nine BY Draconis systems, plus four variables of other types, including one star believed to be a Cepheid. Three of the 15 eclipsing binaries are believed to be cluster members. Details of a further 10 suspected variable stars are also included.     

INSTITUTIONAL OBSTACLES TO SUSTAINABLE DEVELOPMENT IN BALI, INDONESIA

Developing and implementing sustainable development strategies involve overcoming many obstacles. The experience in Bali, Indonesia, illustrates some key institutional challenges which most countries must handle to achieve sustainable development, such as realising cross-sectoral integration, combining top-down and bottom-up planning, and creating credibility for a new policy initiative. Indonesia in general and Bali in particular has, in theory, considerable capability to implement sustainable development. However, as in most countries, effective practice does not always follow from theoretical potential. Strengths and weaknesses related to institutional challenges are identified and assessed, and their general implications are considered. Some key implications are the need to develop sustainable development strategies which reflect the conditions and needs specific to the targetted region, and to address different national and regional perspectives.     

Sea-surface topography around Australia

The sea-surface topographys, as represented by the separation between the ocean surface and a level surface, is viewed as a problem involving and concerning both geodesy and physical oceanography. The determination of this topography bygeodetic levelling processes, in conjunction with tide-gauge observation, is examined. Sources of error, difficulties, estimates of accuracies, and actual results are mainly related to the third-order Australian levelling net, which has indicated a sea-surface topography variation, with position, of 2 m, with a standard deviation estimated to be about 30 cm. The expectedoceanographic influences on the sea-level are described, the individual contributing factors being discussed separately. Around Australia, differences in water density can account for an estimated 60 cm of the above mentioned 200 cm sea-level variation, while the airpressure effect appears to account for another 10 cm only. The wind influence undoubtedly also contributes to the sea-surface topography but it is presently virtually impossible to provide a suitable figure. Some discussion is given to the apparent differences between the results from these separate sources, for this continent.     

Diamond genesis — A synthesis of opposing views

Estimates of the pressure and temperature in the region of kimberlite magma generation are compatible with the formation of diamond in its own thermodynamic stability field as deduced from high pressure experimental synthesis of diamond. However, if diamond growth is allowed only within its stability field, preservation during ascent of kimberlite magma and many properties of diamond distribution in kimberlite pipes as well as some of the geochemical properties of diamond are very difficult to explain. Metastable diamond growth in the laboratory is well established and its occurrence in natural systems is proposed. A theory of genesis with synthesis of diamond seed nucleii in kimberlite magma at depth in the mantle and with continued metastable growth during ascent and in kimberlite magma pools at the base of the crust is proposed. Eruption of kimberlite pipes to the surface terminates diamond growth.

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Résumé Les estimations de la pression et de la température dans la région de formation du magma kimberlitique sont compatibles avec la formation du diamant dans son propre domaine de stabilité thermodynamique comme déduit des données obtenues par la synthèse du diamant à haute pression. Néanmoins, en admettant la croissance du diamant seulement dans son propre domaine de stabilité, il est très difficile d'expliquer sa preservation pendant l'ascension du magma kimberlitique, beaucoup de ses caractéristiques de répartition dans les pipes kimberlitiques ainsi que certaines propriétés géochimiques. L'évolution du diamant métastable en laboratoire est bien connue et nous suggérons donc l'existence de cet état dans les systèmes naturels. On propose une théorie envisageant la formation du diamant en partant d'une synthèse de noyaux de germes de diamant dans le magma kimberlitique à profondeur dans le manteau suivie d'une évolution métastable continuelle pendant l'ascension de ce magma kimberlitique et dans les chambres magmatiques à la base de la croûte terrestre. L'éruption des pipes kimberlitiques à la surface termine la croissance du diamant.