Evidence for sediment recirculation on an ebb-tidal delta of the East Frisian barrier-island system, southern North Sea

The Otzum ebb-tidal delta, located between Langeoog and Spiekeroog islands along the East Frisian barrier-island coast, southern North Sea, was investigated with respect to its morphological evolution, sediment distribution patterns and internal sedimentary structures. Bathymetric charts reveal that, over the last 50 years, the size of the Otzum ebb-tidal delta has slightly shrunk, while sediment has accreted on the ebb-delta lobe to the east of the main inlet channel (west of Spiekeroog). Swash bars superimposed on the eastern ebb-tidal shoal (Robben Plate) have migrated south or south-eastwards, i.e. towards the inlet throat. The main ebb-delta body is composed of fine quartz sand, whereas the superimposed swash bars and the inlet channel bed consist of medium-grained quartz sand containing high proportions of coarser bioclastic material. Internal sedimentary structures in short box-cores (up to 30 cm long) are dominated by flood-oriented cross-beds. Longer vibro-cores (up to 1.5 m long) show that, at depth, the sediment is dominated by storm-generated parallel (upper plane bed) laminations with intercalated shell layers and dune cross-bedding. The cross-bedded sands in both box-cores and vibro-cores from the ebb-delta shoal predominantly dip towards the south or southeast, indicating transport towards the inlet throat by the flood current. The observations demonstrate that, contrary to previous contentions, the sediments of the highly mobile swash bars do not bypass the inlet but are instead being continually recirculated by the combined action of tidal currents and waves. In this model, the cycle begins with both fine and medium sands, including shell hash, being transported seawards in the main ebb channel until they reach the shallow ebb-delta front. From here, the sediment is pushed onto the eastern ebb-delta shoal by the flood current assisted by waves, becoming strongly size-sorted in the process. The medium sands together with the shell hash are formed into swash bars which migrate along arcuate paths over a base of fine sand back to the main ebb channel located south of the ebb delta. By the same token, the fine sand between the swash bars is transported south-eastwards by the flood current in the form of small dunes until it cascades into the large flood channel located to the west of Spiekeroog. From here, the fine sand is fed back into the main ebb channel, thus completing the cycle. No evidence was found on the ebb delta for alongshore sediment bypassing.     

Is the Parker Instability a Viable Mechanism for the Formation of Giant Molecular Clouds?

The stratified interstellar medium has been known to be subject to the Parker instability, and the instability has been considered as a plausible mechanism for the formation of giant molecular clouds (GMCs). By presenting our recent efforts to understand the instability through linear analyses and numerical simulations, we raise a negative point of view that the Parker instability alone could not form GMCs.     

Quaternary glacial history of the Central Karakoram

The Quaternary glacial history of the world's highest mountains, the Central Karakoram, is examined for the first time using geomorphic mapping of landforms and sediments, and ¹⁰Be terrestrial cosmogenic nuclide surface exposure dating of boulders on the moraines and glacially eroded surfaces. Four glacial stages are defined: the Bunthang glacial stage (>0.7 Ma); the Skardu glacial stage (marine Oxygen Isotope Stage [MIS] 6 or older); the Mungo glacial stage (MIS 2); and the Askole glacial stage (Holocene). Glaciers advanced several times during each glacial stage. These advances are not well defined for the oldest glacial stages, but during the Mungo and Askole glacial stages glacial advances likely occurred at 16, 11–13, 5 and 0.8 ka. The extent of glaciation in this region became increasingly more restricted over time. In the Braldu and Shigar valleys, glaciers advanced >150 km during the Bunthang and Skardu glacial stages, while glaciers advanced >80 km beyond their present positions during the Mungo glacial stage. In contrast, glaciers advanced a few kilometers from present ice margins during the Askole glacial stage. Glacier in this region likely respond in a complex fashion to the same forcing that causes changes in Northern Hemisphere oceans and ice sheets, teleconnected via the mid-latitude westerlies, and also to changes in monsoonal intensity.     

Permo-Triassic high-pressure metamorphism in the central western Korean Peninsula,and its link to Paleo-Tethyan Ocean closure: Key issues revisited

Permo-Triassic high-pressure(HP) mafic granulites, together with the Bibong retrogressed eclogite,preserved along the central western Korean Peninsula provide important insights into the Late Permian to Triassic collisional orogeny in northeast Asia. The metamorphic pressureetemperatureetime(P-T-t)paths of these rocks, however, remain poorly constrained and even overestimated, owing to outdated geothermobarometers and inaccurate isopleth techniques. Here we evaluate the metamorphic Pe T conditions of Triassic HP mafic granulites including those in Baekdong, Sinri and Daepan and the Bibong Triassic retrogressed eclogite in the Hongseong area, and the Permo-Triassic Samgot mafic granulite in the Imjingang Belt of the central western Korean Peninsula through the application of modern phase equilibria techniques. The Baekdong and Samgot mafic granulites and the Bibong retrogressed eclogite yield a range of 12.0 -16.0 kbar and 800 -900℃, representing HP granulite facies conditions. The Sinri and Daepan granulites from the Hongseong area show relatively lower grade metamorphic conditions between HP granulite and normal granulite facies, and are characterized by sub-isothermal decompression during exhumation. The similarities in the metamorphic ages and the post-collisional igneous activity from the central western Korean Peninsula indicate that the Triassic ages represent the retrograde stage of the metamorphic Pe T paths. In contrast, the Late Permian metamorphic ages, which are older than protolith ages of the post-collisional igneous rocks, correspond to the possible prograde stage of metamorphism. The P-T-t paths presented in this paper, together with the metamorphic ages and post-orogenic igneous events reported from these areas suggest trace of the subduction, accretion and exhumation history, and indicate a tectonic linkage among the northeast Asian continents during the Paleo-Tethyan Ocean closure.     

Tidal Influences on Biotic and Abiotic Factors in the Seomjin River Estuary and Gwangyang Bay,Korea

To assess changes in abiotic and biotic factors between flood and ebb tides, we investigated the seasonal phytoplankton dynamics and environmental conditions along a salinity gradient at 14 stations in the Seomjin River estuary (SRE), Korea, and conducted bioassays to investigate the effect of nutrient addition (+N, +P, and +NP) on phytoplankton growth. Saltwater intrusion upstream was greatly dependent on the amount of freshwater discharge resulting from seasonal rainfall. There was a strong negative correlation between salinity and the nitrate+nitrite concentration (p?<?0.001), and between salinity and the silicate concentration (p?<?0.001), but no clear correlation between salinity and the ammonium concentration, or salinity and the phosphate concentration (p?>?0.01). This indicates that the N and Si loading increased as a result of freshwater input. The algal bioassays showed that high phytoplankton growth rates were usually recorded in response to the +NP treatment, but in the saltwater zone, the phytoplankton community also responded rapidly to the +N treatment, and to the +P treatment in the freshwater zone. The range of nutrient limitation depended on freshwater discharge. The seasonal and horizontal distribution of phytoplankton communities changed along the salinity gradient. The significant differences in abiotic factors between flood and ebb tides play important roles in controlling the biotic factors, including the occurrence of aquatic organisms including microalgae.     

Evaluation of drought and flood risks in a multipurpose dam under climate change: a case study of Chungju Dam in Korea

The purpose of this study was to evaluate the effects of climate change on the drought and flood risks of a multipurpose dam. To achieve this, A2 climate change scenarios of RegCM3 were collected about Chungju Dam in Korea. To analyze drought risks, weather data obtained by the statistical downscaling method were entered to produce runoff series by runoff modeling and water balance was analyzed based on water use scenarios to review changes in the storage volume under climate change. To analyze flood risks, changes in water levels of the dam in future flood seasons were reviewed based on the current dam operation method. The results of the review indicated that both the drought and the flood risks of the dam would increase in the future. The reason was considered to be the movement of the flood season’s runoff characteristics from July and August to August and September because of climate change. Therefore, for climate change adaptation planning, not only quantitative changes in hydrologic values but also changes in temporal characteristics should be considered and given importance.     

Entropic force and its cosmological implications

We investigate a possibility of realizing the entropic force into the cosmology. A main issue is how the holographic screen is implemented in the Newtonian cosmology. Contrary to the relativistic realization of Friedmann equations, we do not clarify the connection between Newtonian cosmology and entropic force because there is no way of implementing the holographic screen in the Newtonian cosmology.     

Tectonometamorphic evolution of the Permo-Triassic Songrim (Indosinian) orogeny: evidence from the late Paleozoic Pyeongan Supergroup in the northeastern Taebaeksan Basin,South Korea

The deformed and metamorphosed middle Pennsylvanian to Early Triassic (?) rocks of the Pyeongan Supergroup, occurring in northeastern flank of the Paleozoic Taebaeksan Basin, east central South Korea, record the impact of the Late Permian–Triassic Songrim (Indosinian) collisional orogeny in the eastern Eurasia margin. Analysis of meso- and microstructures and their relationship with porphyroblast growth has revealed that these metasedimentary rocks were affected by four deformation events (D₁–D₄). During the polyphase deformations, successive foliations with alternately steep (S₁ and S₃) and flat-lying (S₂ and S₄) orientations were produced with growth of chloritoid, andalusite and kyanite porphyroblasts during D₁ and D₂, and growth of garnet, staurolite and andalusite porphyroblasts during D₃ and D₄. SHRIMP U–Pb detrital zircon ages (330–310 Ma) from metapelites in the oldest unit of the Pyeongan Supergroup in the study area, combined with the previous data on sandstone compositions, indicate magmatic activity that was contemporaneous with the initial deposition of the Pyeongan Supergroup. This also suggests that the Pyeongan Supergroup was deposited in an arc-related foreland basin at an active continental margin during the Late Carboniferous and Permian time. Two contractional deformation events (D₁ and D₃) and two events related to gravitational flattening (D₂ and D₄), along with Barrovian-type medium-pressure regional metamorphism, may have resulted from the Late Permian–Triassic Songrim orogeny, related to collision between the North and South China blocks and/or collision between the Eastern Eurasia margin and the proto-Japan terrane.     

Development and application of a novel miniature in situ microprofiler (NAFRI BelpI)

We have developed a novel miniature in situ microprofiler (NAFRI BelpI) for coastal and deep-sea studies. The BelpI can carry up to three oxygen microsensors, and it allows for simultaneous replicate measurements in a relatively small area. All functions can be controlled and programmed via a small magnetic bar and three reed switches; this feature facilitates the initial setup both onboard and underwater. The large LCD window shows basic information such as the movement intervals of the linear stage, number of replicate measurements, waiting time between measurements, and the pA from the microsensors. From high-resolution vertical profiles of oxygen in coastal sediment measured using the microsensors, the diffusivity boundary layer thicknesses was determined to be in the range 0.30–0.35 mm. In addition, the time-series measurement of oxygen profiles in permeable sandy sediment showed advective transport of oxygen into pore water by tidal agitation. Two examples of in situ measurement using a BelpI suggest that it can be widely applied to the study of the sediment-water interface.     

Geological consequences of the Saemangeum Dyke, mid-west coast of korea: A review

The Saemangeum Dyke is located in an estuarine setting, regulated in a complicated manner by a macrotidal regime, rivers, and winter monsoon. Accordingly, the constructed dyke resulted in a variety of artificial changes in geological characteristics in the estuary and its vicinity. To investigate those dyke-induced changes, the KORDI (Korea Ocean Research and Development Institute) performed sedimentological and sediment-dynamical observations from 2002 to 2010. On the basis of the KORDI results, the major geological changes and associated dynamical processes are reviewed. Five phenomena, among others, are focused on: depositional-channel creation; gap-related erosion; forced movements of surface sands; tidal-flat growth inside the dyke; and blanketing of mud over the sandy seafloor. These phenomena were unforeseen before the dyke construction, and reflect that the dyke could cause both erosion and deposition on an estuarine scale. The investigations conclude that the sediments in the dyke-influenced region were derived from the two rivers, Mangyeong and Dongjin, of the estuary. This is completely contrary to the offshore origin proposed before the dyke construction. As a result, the review supports the proposal that a thorough geological investigation and rational forecast is necessary prior to dyke construction to avoid economic loss and a fractious environmental debate.