Internal reflection pattern of Korea Strait shelf mud (Nakdong River subaqueous delta) off southeast Korea and implications for Holocene relative base-level change

The Korea Strait shelf mud (KSSM) (Nakdong River subaqueous delta) is the most conspicuous Holocene sedimentary feature in the inner shelf off southeast Korea. Analysis of multi-channel sparker profiles and ¹⁴C ages of sediment cores reveals that the KSSM consists of three seismic units at the depocenter (>60 m thick): (i) the thin transgressive bottom (> ca 8000 cal bp ); (ii) thick (>40 m) obliquely progradational middle ( ca 8000– ca 2600 cal bp ); and (iii) thin transgressive top ( ca 2600 cal bp –present) units. The relative base level, predicted from the internal reflection pattern of the KSSM, remained significantly deeper (up to >70 m) than global sealevel during much of the Holocene. The apparent gradual drop (∼20 m) of the relative base level during the deposition of the middle unit, followed by a rise, further suggests that base level does not conform to sealevel and is more sensitive than the relative sealevel is to the local oceanographic regime and processes.     

Detrital zircon geochronology of the Cretaceous Sindong Group,Southeast Korea: Implications for depositional age and Early Cretaceous igneous activity

The Sindong Group forms the lowermost basin‐fill of the Gyeongsang Basin, the largest Cretaceous nonmarine basin located in southeastern Korea, and comprises the Nakdong, Hasandong, and Jinju Formations with decreasing age. The depositional age of the Sindong Group has not yet been determined well and the reported age ranges from the Valanginian to Albian. Detrital zircons from the Sindong Group have been subjected to U–Pb dating using laser ablation inductively coupled plasma mass spectrometry. The Sindong Group contains noticeable amounts of detrital magmatic zircons of Cretaceous age (138–106 Ma), indicative of continuous magmatic activity prior to and during deposition of the Sindong Group. The youngest detrital zircon age of three formations becomes progressively younger stratigraphically: 118 Ma for the Nakdong Formation, 109 Ma for the Hasandong Formation, and 106 Ma for the Jinju Formation. Accordingly, the depositional age of the Sindong Group ranges from the late Aptian to late Albian, which is much younger than previously thought. Lower Cretaceous magmatic activity, which supplied detrital zircons to the Sindong Group, changed its location spatially through time; it occurred in the middle and northern source areas during the early stage, and then switched to the middle to southern source areas during the middle to late stages. This study reports first the Lower Cretaceous magmatic activity from the East Asian continental margin, which results in a narrower magmatic gap (ca 20 m.y.) than previously known.     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

Abstract

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-wavelet-convolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L₂ norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

Erosion of a high‐altitude,low‐relief area on the Korean Peninsula: implications for its development processes and evolution

The processes involved in the development of high‐altitude, low‐relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo‐surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well‐known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: (1) bedrock incision rate in the plateau (~127 m Myr^?1) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment‐wide denudation rate of the plateau (~93 m Myr^?1); (2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; (3) a discrepancy between the soil production and catchment‐wide denudation rates implies morphological disequilibrium in the plateau; (4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes; and (5) when compared with those of global paleo‐surfaces (<20 m Myr^?1), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo‐surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo‐surfaces around the world. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of the Bright Band Characteristics Measured by Micro Rain Radar （MRR） at a Mountain and a Coastal Site in South Korea

Data from a long term measurement of Micro Rain Radar (MRR) at a mountain site (Daegwallyeong,DG, one year period of 2005) and a coastal site (Haenam, HN, three years 2004–2006) in South Korea were analyzed to compare the MRR measured bright band characteristics of stratiform precipitation at the two sites. On average, the bright band was somewhat thicker and the sharpness (average gradient of reflectivity above and below the reflectivity peak) was slightly weaker at DG, compared to those values at HN. The ...     

Local Meteorological and Synoptic Characteristics of Fogs Formed over Incheon International Airport in the West Coast of Korea

Fogs observed over Incheon international airport (IIA) in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature (T) and the SST, i.e., cold sea fog if TSST = T-SST>0^oC and warm sea fog if TSST <0^oC. The numbers of coastal, cold, and warm sea fog cases are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea fogs occur mostly in summer and warm sea fogs are observed from January to May but not in November and December. On average the air gets colder by 1.6^oC during the three hours leading up to the coastal fog formation, and an additional cooling of 1.1^oC occurs during the fog. The change in the dew point temperature (T_d) is minimal except during the fog (0.6^oC). Decreases in T for the cold and warm sea fogs are relatively smaller. The average T_d is higher than SST during the cold sea fog periods but this T_d is more than 4^oC higher than that for the corresponding non-fog days, suggesting that cold sea fogs be formed by the cooling of already humid air (i.e., T_d>SST). Increases of T_d are significant during the warm sea fog periods (1.4^oC), implying that efficient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.     

Pyrosequencing reveals specific associations of bacterial clades Roseobacter and Flavobacterium with the harmful dinoflagellate Cochlodinium polykrikoides growing in culture

Harmful algal blooms of the dinoflagellate Cochlodinium polykrikoides are of worldwide environmental concern. Previous field studies have demonstrated the association of such algal blooms with free‐living bacteria (FLB) and particle‐associated bacteria (PAB). In the present study, we report evidence for bacterial association with C. polykrikoides in laboratory culture. Sampling was performed at different growth stages (lag, exponential and stationary) and pyrosequencing was used to identify taxa. As a result, the community structures of FLB and PAB were elucidated and significant differences between FLB and PAB were identified by hierarchical cluster analysis and the similarity profiles test (p = .05). The relative abundances of bacterial operational taxonomic units distinctly changed in response to the different phases of C. polykrikoides growth. The Roseobacter genus Marivita and the Flavobacterium genus Winogradskyella were dominant in the FLB and PAB associated with C. polykrikoides, respectively. The Roseobacter clade, which has also exhibited associations with C. polykrikoides blooms in field samples, may influence host cell growth through the provision of vitamins.     

Geology, tectonics, and the 2002-2003 eruption of the Semeru volcano, Indonesia: Interpreted from high-spatial resolution satellite imagery

The paper illustrates the application of high-spatial resolution satellite images in interpreting volcanic structures and eruption impacts in the Tengger-Semeru massif in east Java, Indonesia. We use high-spatial resolution images (IKONOS and SPOT 5) and aerial photos in order to analyze the structures of Semeru volcano and map the deposits. Geological and tectonic mapping is based on two DEMs and on the interpretation of aerial photos and four SPOT and IKONOS optical satellite images acquired between 1996 and 2002. We also compared two thermal Surface Kinetic Temperature ASTER images before and after the 2002-2003 eruption in order to delineate and evaluate the impacts of the pyroclastic density currents. Semeru's principal structural features are probably due to the tectonic setting of the volcano. A structural map of the Tengger-Semeru massif shows four groups of faults orientated N40, N160, N75, and N105 to N140. Conspicuous structures, such as the SE-trending horseshoe-shaped scar on Semeru's summit cone, coincide with the N160-trending faults. The direction of minor scars on the east flank parallels the first and second groups of faults. The Semeru composite cone hosts the currently active Jonggring-Seloko vent. This is located on, and buttressed against, the Mahameru edifice at the head of a large scar that may reflect a failure plane at shallow depth. Dipping 35° towards the SE, this failure plane may correspond to a weak basal layer of weathered volcaniclastic rocks of Tertiary age. We suggest that the deformation pattern of Semeru and its large scar may be induced by flank spreading over the weak basal layer of the volcano. It is therefore necessary to consider the potential for flank and summit collapse in the future. The last major eruption took place in December 2002-January 2003, and involved emplacement of block-and-ash flows. We have used the 2003 ASTER Surface Kinetic Temperature image to map the 2002-2003 pyroclastic density current deposits. We have also compared two 10 m-pixel images acquired before and after the event to describe the extent and impact of an estimated volume of 5.45 × 10⁶ m³ of block-and-ash flow deposits. An ash-rich pyroclastic surge escaped from one of the valley-confined block-and ash flows at 5 to 8 km distance from the crater and swept across the forest and tilled land on the SW side of the Bang River Valley. Downvalley, the temperature of the pyroclastic surge decreased and a mud-rich deposit coated the banks of the Bang River Valley. Thus, hazard mitigation at Semeru should combine: (1) continuous monitoring of the eruptive activity through an early-warning system, and (2) continuous remote sensing of the morphological changes in the drainage system due to the impact of frequent pyroclastic density currents and lahars.     

Spawning characteristics of <Emphasis Type="Italic">Clupea pallasii</Emphasis> in the coastal waters off Gyeongnam,Korea, during spawning season

The purpose of this study is to research the characteristics of spawning grounds of Clupea pallasii found at 1 spawning ground located in the coast of Yeongun-ri, Tongyeong, Gyeongnam, and 3 stations in Jinhae Bay. Diving observation was performed from January to June, 2014 at the coast of Yeongun-ri, and from February to June, 2016 at Jinhae Bay after total 4 stations (A: Gusan-myeon, B: Haengamdong, C: Hacheong-myeon, D: Jam-do) were constituted. During observation period, 1 spawning ground was found in Tongyeong area in January. In Jinhae Bay spawning grounds were found at 3 stations (A, B, D) out of 4 stations in February. Regarding the surrounding environment of spawning ground found at Yeongunri, Tongyeong, various kinds of seaweeds were distributed up to 1–5 m depth, and many branch type red algae were distributed. In case of Jinhae Bay, seaweeds were widely distributed from shallow water to 5 m depth. In addition, the scope that eggs were attached was considerably wide compared to Tongyeong area, and they were found at all the 3 spots, so C. pallasii is thought to use Jinhae Bay for its spawning ground widely. Eggs were attached from the surface to 3–4 m, and like Tongyeong area, eggs were attached to mostly branch type of red algae. The results of this study suggest that the spawning season of the C. pallasii in coast waters off Gyeongnam is until mid-February.     

Estimation of net ecosystem metabolism of seagrass meadows in the coastal waters of the East Sea and Black Sea using the noninvasive eddy covariance technique

We measured the community-scale metabolism of seagrass meadows in Bulgaria (Byala [BY]) and Korea (Hoopo Bay [HP]) to understand their ecosystem function in coastal waters. A noninvasive in situ eddy covariance technique was applied to estimate net O₂ flux in the seagrass meadows. From the high-quality and high-resolution time series O₂ data acquired over > 24 h, the O₂ flux driven by turbulence was extracted at 15-min intervals. The spectrum analysis of vertical flow velocity and O₂ concentration clearly showed well-developed turbulence characteristics in the inertial subrange region. The hourly averaged net O₂ fluxes per day ranged from -474 to 326 mmol O₂ m^-2 d^-1 (-19 ± 41 mmol O₂ m^-2 d^-1) at BY and from -74 to 482 mmol O₂ m^-2 d^-1 (31 ± 17 mmol O₂ m^-2 d^-1) at HP. The net O₂ production rapidly responded to photosynthetically available radiation (PAR) and showed a good relationship between production and irradiance (P-I curve). The hysteresis pattern of P-I relationships during daytime also suggested increasing heterotrophic respiration in the afternoon. With the flow velocity between 3.30 and 6.70 cm s^-1, the community metabolism during daytime and nighttime was significantly increased by 20 times and 5 times, respectively. The local hydrodynamic characteristics may be vital to determining the efficiency of community photosynthesis. The net ecosystem metabolism at BY was estimated to be -17 mmol O₂ m^-2 d^-1, which was assessed as heterotrophy. However, that at HP was 36 mmol O₂ m^-2 d^-1, which suggested an autotrophic state.