Sediment dispersal and deposition due to sand mining in the coastal waters of Korea

Understanding the impact of marine sand mining operations in a complex coastal environment requires a combined observational and modeling approach. Here, we use field measurements collected during mining operations in Kyunggi Bay, Korea to develop sediment parameters and source conditions for a three-dimensional (3D) sediment transport model built on the Regional Ocean Modeling System (ROMS). The model is run with realistic forcing obtained from a 9 km meteorological model, tides, and river discharges. The resulting vertical and horizontal distributions of sediment show encouraging agreement with the field data, demonstrating markedly different dispersal patterns due largely to the differential settling of the various sand classes. The resulting depositional patterns suggest that only the coarser size classes (500 and 250 μm) particles remain close to the mined site, while finer size classes are widely dispersed. These results suggest that this new methodology of multi-size class, 3D sediment transport modeling is quite promising, and further work is ongoing to include more realistic representation of sediment resuspension processes.     

Seismological Research in Singapore

The Singapore seimic network and the seismicity of Singapore are briefly described,the four tremor events experienced by Singapore are discussed and the ground responses of different stations are compared,The tremor incident standing operation procedure is also prsented.     

Dynamic finite strip analysis of surface foundations

The finite strip method is used to study the dynamic response of surface strip foundations. This method is simple to use and versatile. The two-dimensional problem is effectively reduced to an equivalent one-dimensional problem. The choice of trigonometric series for the displacement functions results in the uncoupling of the terms of the series and a significant reduction in the semi-bandwidth of the complex set of equations, making the method well suited to small computers. Non-homogeneous soil profiles are treated as a matter of course. The finite strip solutions are shown to be in general agreement with other theoretical methods of analysis.     

Harmful Dinoflagellate Prorocentrum donghaiense Lu is Widely Distributed Along the East China Sea and Korean Coastal Area

Ocean Science Journal - There have been controversies regarding the taxonomy of Prorocentrum donghaiense, however Zhang et al. (2016) recently developed a probe with a quantitative real-time PCR...     

Variations of methane induced pyrite formation in the accretionary wedge sediments offshore southwestern Taiwan

The accretionary wedge of offshore southwestern Taiwan contains abundant deposits of gas hydrate beneath the sea floor. High concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available. To understand temporal variation of methane venting in sediments over geologic time, a 23-m-long Calypso piston core (MD05-2911) was collected on the flank of the Yung-An Ridge. Pore water sulfate, dissolved sulfide, dissolved iron, methane, sedimentary pyrite, acid volatile sulfide, reactive iron, organic carbon and nitrogen as well as carbonate δ¹³C were analyzed.Three zones with markedly different pyrite concentration were found at the study site. Unit I sediments (>20 mbsf) were characterized with a high amount of pyrite (251–380 μmol/g) and a δ¹³C-depleted carbonate, Unit II sediments (15–20 mbsf) with a low pyrite (15–43 μmol/g) and a high content of iron oxide mineral and Unit III sediments (<10 mbsf) by a present-day sulfate–methane interface (SMI) at 5 m with a high amount of pyrite (84–221 μmol/g) and a high concentration of dissolved sulfide.The oscillation records of pyrite concentrations are controlled by temporal variations of methane flux. With an abundant supply of methane to Unit I and III, anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation. No AOM signal was found in Unit II, characterized by typical organically-limited normal marine sediments with little pyrite formation. The AOM induced pyrite formation near the SMI generates a marked pyrite signature, rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment.     

Recent sediment accumulation and origin of shelf mud deposits in the Yellow and East China Seas

Modern (last 100 yr) accumulation rates of shelf mud deposits in the Yellow and East China Seas were investigated using the distribution of excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples. Compilation and merger of new and previously published data helped clarify sediment accumulation in these seas. The estimated accumulation rates, together with data of suspended sediment concentrations, provided findings on the sediment budget, origin, and transport pathway of the mud deposits. The overall accumulation distribution in the Yellow and East China Sea shelf revealed a general, cross-shelf decreasing trend along the sediment dispersal system away from the rivers, except for the South Sea (SSM) and southeastern Yellow Sea (SEYSM) mud patches found along the Korean coast. Notably, ²¹⁰Pb_ex activity profiles within the SSM and the SEYSM yielded a relatively high accumulation rate of 2-5 mm/yr, implying a sedimentation rate of 4-15 × 10⁷ tons per year in this coastal zone. Such an annual accumulation rate is about one order of magnitude greater than the total sediment discharge (6-20 × 10⁶ tons/yr) from Korean rivers, suggesting an additional offshore source. The distribution pattern of the well-defined suspended plume clearly showed the possible transport and exchange of fine-grained sediments between the ECS shelf and the coastal area of Korea, especially during winter. Such a high accumulation in Korean coastal areas is attributable to the sediments supplied from the mud deposit of the ECS (i.e., SWCIM), with origins in Chinese rivers. Therefore, the Korean coastal area may be an important sink for some of Chinese river sediments being transported from the south by the Yellow Sea Warm Current.     

Enhanced biological activity by an anticyclonic warm eddy during early spring in the East Sea (Japan Sea) detected by the geostationary ocean color satellite

The high primary production enhanced by anticyclonic eddies and hourly variation pattern in the productivity during the spring season in the East Sea were first investigated using the first Korean Geostationary Ocean Color Imager (GOCI). Even though the stratification for a seasonal spring bloom is not well developed in the water column in early April in the East Sea, a physical upward water flux movement at the periphery of the anticyclonic eddies could remain the phytoplankton in euphotic zone to sustain high chlorophyll-a concentration conditions in the Ulleung Basin. At this time, nutrients were no major controlling factor for phytoplankton growth since concentrations of major nutrients (nitrate, silicate, and phosphate) were relatively high in the observed eddy sites based on the observation data from the Korean Oceanographic Data Center (KODC). The estimated mixed layer depth (MLD) significantly shallower at the periphery supports for this mechanism. The hourly primary productivity estimation based on a Carbon-based Productivity Model (CbPM) provides a bimodal pattern along the time especially in L1 with an approximately one order magnitude difference between the lowest and highest values of productivities on 5 April, 2011. Potential possibilities for this large discrepancy in the hourly productivity and some thoughts on a short time in situ incubation method were discussed.     

Comparison of Helicity Signs in Interplanetary CMEs and Their Solar Source Regions

If all coronal mass ejections (CMEs) have flux ropes, then the CMEs should keep their helicity signs from the Sun to the Earth according to the helicity conservation principle. This study presents an attempt to answer the question from the Coordinated Data Analysis Workshop (CDAW), “Do all CMEs have flux ropes?”, by using a qualitative helicity sign comparison between interplanetary CMEs (ICMEs) and their CME source regions. For this, we select 34 CME–ICME pairs whose source active regions (ARs) have continuous SOHO/MDI magnetogram data covering more than 24 hr without data gap during the passage of the ARs near the solar disk center. The helicity signs in the ARs are determined by estimation of cumulative magnetic helicity injected through the photosphere in the entire source ARs. The helicity signs in the ICMEs are estimated by applying the cylinder model developed by Marubashi (Adv. Space. Res., 26, 55, 2000) to 16 second resolution magnetic field data from the MAG instrument onboard the ACE spacecraft. It is found that 30 out of 34 events (88 %) are helicity sign-consistent events, while four events (12 %) are sign-inconsistent. Through a detailed investigation of the source ARs of the four sign-inconsistent events, we find that those events can be explained by the local helicity sign opposite to that of the entire AR helicity (28 July 2000 ICME), incorrectly reported solar source region in the CDAW list (20 May 2005 ICME), or the helicity sign of the pre-existing coronal magnetic field (13 October 2000 and 20 November 2003 ICMEs). We conclude that the helicity signs of the ICMEs are quite consistent with those of the injected helicities in the AR regions from where the CMEs erupted.