Holocene salinity fluctuations of the East Korean lagoon related to sea level and precipitation changes

Detailed diatom records within core sediments from Maeho Lagoon along the Eastern coast of South Korea revealed that the ecological dynamics of the lagoon during the Holocene were associated with relative sea level and regional precipitation. Accelerator mass spectrometry (AMS) ¹⁴C dating indicates that sediment accumulation began prior to 8300 cal. year BP, and that the lagoon formed around 8000 cal. year BP. The salinity level of the lagoon increased until 5000 cal. year BP, and then decreased. Long‐term trends in salinity were dependent upon changes in sea level: periods of high salinity in the lagoon were generally coincident with periods of high sea levels along the east coasts of Korea and Japan. On the other hand, multicentennial‐scale fluctuations in diatom assemblages and magnetic susceptibility (MS) suggest that a 400 year fluctuation in salinity was regulated by changes in precipitation in the area of this lagoon. Changes in the westerly jet stream, controlled by variation in solar irradiance, had an important influence on precipitation volume in South Korea, suggesting that the patterns of the westerly jet stream fluctuate on a 400 year cycle.     

Ground-based observations and simulation of ionospheric VLF source in experiments on modification of the polar ionosphere

The phase velocities of TE and TEM waves at frequencies of 1017 and 3017 Hz, as well as the effect of precipitations during auroras on the velocities, are estimated in the Earth–ionosphere waveguide on the basis of observations of electromagnetic fields of an ionospheric source in experiments on modification of the lower ionosphere by a modulated high-power short-wave signals performed by the Arctic and Antarctic Research Institute (AARI) at the EISCAT/Heating test bench in October 2016. Probable electron density profiles in the plane-stratified ionosphere are retrieved from the numerical solution of a wave equation, which are used for the calculation of the phase velocities close to measured ones.     

Influence of frequency‐dependent soil–structure interaction on the fragility of R/C bridges

Bridge performance under earthquake loading can be significantly influenced by the interaction between the structure and the supporting soil. Even though the frequency dependence of the interaction mentioned in this study has long been documented, the simplifying assumption that the dynamic stiffness is dominated by the mean or predominant excitation frequency is still commonly made, primarily as a result of the associated numerical difficulties when the analysis has to be performed in the time domain. This study makes use of the advanced lumped parameter models recently developed 1 in order to quantify the impact of the assumption on the predicted fragility of bridges mentioned in this study. This is achieved by comparing the predicted vulnerability for the case of a reference, well studied, actual bridge using both conventional, frequency‐independent, Kelvin–Voigt models and the aforementioned lumped parameter formulation. Analysis results demonstrate that the more refined consideration of frequency dependence of soil–structure interaction at the piers and the abutments of a bridge not only leads to different probabilities of failure for given intensity measures but also leads to different hierarchy and distribution of damage within the structure for the same set of earthquake ground motions even if the overall probability of exceeding a given damage state is the same. The paper concludes with the comparative assessment of the effect for different soil conditions, foundation configurations, and ground motion characteristics mentioned in this study along with the relevant analysis and design recommendations. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of benthic macroinvertebrates sediment index(BSI) for bioassessment of freshwater sediment

Sediment quality has been evaluated in a variety of ways since the early 1990s in studies from Europe. In South Korea, most studies have used an indicator value for benthic macroinvertebrates based on water quality, not sediment quality. To date, few studies have examined the biological integrity of benthic macroinvertebrate communities in South Korea. In the current study, the tolerance valency and value in samples and the indicator weight values were measured for 43 benthic macroinvertebrate taxa from 73 sampling units in South Korea from 2014 to 2016. Total organic carbon, the amount of heavy metals, and total ammonia nitrogen were analyzed. The average grade for each pollutant was used as the sediment quality index. A benthic macroinvertebrates sediment index was developed for bioassessment of freshwater sediment. The benthic macroinvertebrates sediment index, which is based on the relative frequency of occurrence of macroinvertebrates, was highly correlated with pollution levels in the sediment. This index can be used in the field to assess the contamination of freshwater sediment. As the sample size was small in the current study and there were taxonomic limitations of Chironomidae larvae, further research is needed to improve the reliability of the benthic macroinvertebrates sediment index.     

Stipe Length as an Indicator of Reproductive Maturity in the Kelp <Emphasis Type="Italic">Ecklonia cava</Emphasis>

We conducted testing to determine whether stipe length is a useful indicator of reproductive maturity in the kelp Ecklonia cava, a species that plays a pivotal role in ecosystem functioning and services in subtidal areas. Approximately 100 sporophytes with stipes of various lengths were collected during the fertile period (July–November, 2013). We investigated the relationships between stipe length and other morphological characteristics to determine whether stipe length could indicate the age of reproductive maturity. Primary blade length, longest blade length, thallus height, and total length showed significant relationships with stipe length. The length of the primary and longest blades gradually declined as stipe length increased above 125 mm. Zoosporangial sori were found on the blades of more than 70% of individuals with stipes longer than 125 mm, but on only 8% of individuals with stipes less than 125 mm long. Stipe length therefore seems to be an acceptable proxy for reproductive maturity. Another factor to consider, however, is that all specimens with zoosporangial sori, regardless of stipe length, had a dry weight of 80 g or more; thus, individual biomass may also be an important parameter influencing the initiation of reproduction.     

The distribution and characteristics of the igneous complexes in the northern East China Sea Shelf Basin and their implications for hydrocarbon potential

This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. Various igneous features such as sills, volcanic edifices and stocks were identified by the geophysical exploration. The sills are most common, and are observed at more than 90 locations. Most mapped sills in the study area are characterized by high-amplitude continuous reflections with distinct terminations. Saucer- and cup-shaped sills are observed locally. The stocks are discordant (nearly vertical) igneous bodies and they are characterized by seismic transparency, with upturned host rocks and uplifted overburden. The volcanic edifices and/or necks consist of irregular mounds and peaks and are characterized by strong positive top reflections with chaotic internal facies. The oldest igneous activity in the northern East China Sea Shelf Basin is Early Cretaceous (123.3 ± 3.7). This igneous activity coincides with those observed in eastern China which has been related mainly to the subduction of the Pacific Plate beneath Eurasia Plate. The Miocene igneous activity is well constrained based on seismic stratigraphic relationships within the folded stratigraphy, age dating, and the occurrence of igneous sills. The timing of this intrusion is coincident with the intensive igneous activity as previously suggested for the eastern China. Igneous rocks can produce hydrocarbon traps, reservoirs and they can act as a seal, and therefore are of great importance in petroleum study.     

Photometric Survey of Galactic Open Clusters

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Gradual downslope change in high-resolution acoustic characters and geometry of large-scale submarine debris lobes in Ulleung Basin, East Sea (Sea of Japan), Korea

A detailed analysis of high-resolution seismic data (Chirp, 2–7 kHz) in the Ulleung Basin reveals spatial variation in echo characteristics and geometry of large-scale debris lobes. In the proximal part, the debris lobes are dominated by hummocky surface echoes and gradually transitional downslope to seafloor-tangent hyperbolic and smooth prolonged bottom echoes, reflecting progressive decrease in size, spacing, and relief of surface forms. The strongly convex-upward upper surface with steep blunt margins in the proximal part is gradually transitional downslope to slightly convex- upward or nearly flat form with less blunt margins. The gradual downslope decrease in both scale and spacing of surface forms and convexity of upper surface within each debris lobe is suggestive of progressive dilution in flow concentration within a debris flow, probably due to mixing of ambient water and removal of suspended sediment by deposition during downslope movement. Received: 3 February 1999 / Revision received: 27 April 1999     

A Review on the Macromolecular Compositions of Phytoplankton and the Implications for Aquatic Biogeochemistry

Ocean Science Journal - Biochemical composition of phytoplankton is a key indicator of the physiological and nutritional status of phytoplankton. A balanced biochemical pattern represents a healthy...     

Drained and undrained pullout capacity of a stiff inclusion in a saturated poroelastic matrix

Shear‐lag analysis is used to obtain closed‐form solutions for the problem of a stiff inclusion embedded in a poroelastic soil matrix. The following assumptions are made: the soil matrix and the inclusion are elastic; plane strain conditions apply; and shear stresses at the soil‐inclusion interface follow Coulomb's friction law. Two solutions are obtained, the first one for drained conditions where no excess pore pressures are generated, and the second one for undrained conditions where excess pore pressures are produced and the soil does not change volume during pullout. The solutions are verified by comparing analytical predictions with numerical results obtained using a finite element method. Predictions from the analytical solutions are also compared with results from experiments conducted in a large‐scale pullout box. Both comparisons show good agreement. The analytical solution shows that the pullout capacity in drained and undrained conditions is overall independent of the relative stiffness of the soil and the inclusion. The most important factor controlling the pullout capacity is the coefficient of friction between the soil and the inclusion. Both drained and undrained pullout capacities increase with the coefficient of friction; although the drained capacity shows a proportional increase, it is not so for the undrained capacity. The ratio of undrained to drained pullout capacity is about 0.9 for friction coefficients smaller than 0.2, but can be as small as 0.6 for a coefficient of friction of 1.0. Copyright © 2006 John Wiley & Sons, Ltd.