Late quaternary paleoceanographic changes in the northeastern Ulleung Basin, East Sea, inferred from variations in biogenic components

Two piston cores (DD09-ST21, DD09-ST39B) from the northeastern Ulleung Basin in the East Sea were obtained to investigate variations in the biogenic components (calcium carbonate, organic carbon) and biogeochemical processes (δ¹³C and δ¹⁵N). The two cores had distinctive characteristics in terms of surface production, preservation and dissolution capacity of carbonate, and redox conditions of bottom-water. Core DD09-ST21 was characterized by an oxygen-depleted condition from 15 ka (MIS 2) to 60 ka (MIS 3). Core DD09-ST39B, on the other hand, showed oxic bottom-water conditions, possibly due to shallow water depth. These two cores with different redox condition showed opposite trends in terms of CaCO₃, TOC, and C₃₇ alkenone concentrations. CaCO₃ and C₃₇ concentrations were higher during the LGM in DD09-ST21 while lower contents were observed in DD09-ST39B in the same period. Moreover, consistently low TOC in DD09-ST39B and higher fluctuation of organic matters in DD09-ST21 may suggest difference in primary productivity, preservation capacity, or a potential dissolution effect. During the Holocene, the surface productivity of both cores increased, probably due to renewed ventilation and vertical mixing in the East Sea. Therefore, this study suggests spatial variation in production and preservation of biogenic components in the two cores since last 50 ka for DD09-ST39B and 80 ka for DD09-ST21 due to difference in environmental conditions such as water depth, bottom-water conditions, surface productivity and preservation.     

Three-dimensional imaging of subsurface structures using resistivity data

We have developed a three-dimensional inverse scheme for carrying out DC resistivity surveys, incorporating complicated topography as well as arbitrary electrode arrays. The algorithm is based on the finite-element approximation to the forward problem, so that the effect of topographic variation on the resistivity data is effectively evaluated and incorporated in the inversion. Furthermore, we have enhanced the resolving power of the inversion using the active constraint balancing method. Numerical verifications show that a correct earth image can be derived even when complicated topographic variation exists. By inverting the real field data acquired at a site for an underground sewage disposal plant, we obtained a reasonable image of the subsurface structures, which correlates well with the surface geology and drill log data.     

Prediction of Typhoon Tracks Using Dynamic Linear Models

This paper presents a study on the statistical forecasts of typhoon tracks. Numerical models have their own systematic errors, like a bias. In order to improve the accuracy of track forecasting, a statistical model called DLM (dynamic linear model) is applied to remove the systematic error. In the analysis of typhoons occurring over the western North Pacific in 1997 and 2000, DLM is useful as an adaptive model for the prediction of typhoon tracks.     

Operational Implementation of the ATOVS Processing Procedure in KMA and Its Validation

The Korea Meteorological Administration (KMA) has processed the data from the advanced TOVS(ATOVS) onboard NOAA-16 satellite since May 2001. The operational production utilizes the AAPP(ATOVS and AVHRR Processing Package) of EUMETSAT and IAPP (International ATOVS ProcessingPackage) of the University of Wisconsin. For the initial guess profiles, the predicted fields (usually 6 to 12hour forecasted fields) from the global aviation model of NOAA/NCEP are used. The average number ofprofiles retrieved from the ATOVS data is about 1,300 for each morning and afternoon orbit at about 18 and06 UTC, respectively. The retrieved temperature and dew point temperatures are provided to forecastersin real time and used for initialization of prediction models. With the advanced microwave sensor (AMSU;Advanced Microwave Sounding Unit), accuracy of the ATOVS products is expected to be better than thatof the TOVS products, especially in cloudy conditions. Indeed, the preliminary results from a validationstudy with the collocated radiosonde data during a 8-month period, from May to December 2001, for theEast Asia region show an improved accuracy of the ATOVS products for cloudy skies versus the TOVS,especially for higher altitudes. The RMS (Root Mean Square) difference between the ATOVS productsand radiosonde data is about 1.3℃ for both clear and cloudy conditions, except for near the ground and athigher altitudes, at around 200 hPa. There is no significant temporal variation of the error statistics at allpressure levels. In case of the water vapor mixing ratio, the largest difference is shown at lower altitudes,while the accuracy is much better for the clear sky cases than the cloudy sky cases. The bias and RMSEat lower altitudes is about 0.557 g kg-1 and 2.5 g kg-1 and decrease significantly with increasing altitude.     

Delineating the northern part of the Socotra Basin, offshore Korea, using marine magnetics

A marine magnetic survey was carried out in and around the northern part of Socotra Basin, offshore Korea (31°42′32″–32°46′29″N and 123°56′26″–125°49′16″E), in order to better delineate its northern and eastern boundaries. Analyses of the observed magnetic field and estimation of the basement depth were used to assess these boundaries. The power spectrum and the three-dimensional analytical signal methods were used for depth estimation and to reconstruct basement configuration. Estimated depths resulting from the power spectrum method range from 1.5 to 6.0 km for deep sources (basement troughs), and from 0.3 to 1.7 km for shallower sources (basement peaks). An isopach map shows that the sedimentary sequence varies from 1.4 to 6.0 km in thickness. Estimated depths from the analytic signal method fluctuate in the range 1.2–6 km. The results of the observed field analysis and depth estimation indicate good agreement with the formerly proposed eastern boundary but disagreement with the northern boundary. The findings suggest either an extension of the Socotra Basin or the existence of other sub-basins possibly interconnected with the study area.     

Host rock geology and geochemistry of the Zona uranium occurrence, Peta Gulf Syncline (Upper Benue Trough), northeast Nigeria

The Peta Gulf Syncline (Upper Benue Trough, northeast Nigeria) is a fault-bounded pull-apart sub-basin. The boundary faults are mainly northeast-southwest-trending en echelon strike-slip faults, truncated along their lengths by normal and tear faults with stepovers. The eastern marginal faults underwent rotation during sedimentation, whereas the steeply dipping western marginal faults were inactive.The Peta Gulf Sub-basin is filled by the Bima Sandstone Formation (Lower Cretaceous) which has three siliciclastic members: (i) B₁: medial fan coarse-grained to microconglomeratic sandstones; (ii) B₂: full fluvial medium-grained sandstones with minimal fines; and (iii) B₃: lacustrine and flood basin deposits comprising alternating fine-grained sandstones and siltstones/claystones. Sediment supply was from east to west and facies changes show a general fining in this direction. B₃ offers the most favourable environment/lithology for U concentration.The only significant U occurrence in the Peta Gulf Syncline is the Zona U anomaly, which occurs within transitional B₂-B₃ brecciated sandstones with wall rock alterations zones. The mineralised zone has elevated SiO₂, Fe, As, Ba and W levels but is depleted in the alkalis, Zr, Rb and Sr. This chemical zonation supports the epigenetic orgin of this anomaly.     

Molecular diversity of phytoplankton in the East China Sea around Jeju Island (Korea), unraveled by pyrosequencing

The East China Sea (ECS) around Jeju Island lies in a transitional region between the temperate and subtropical zones and is influenced by the Kuroshio Current. Hence, this area has been considered an important monitoring site for oceanic ecosystem changes. Herein, we assessed the community structure and diversity of the phytoplankton in the ECS around Jeju Island using small subunit ribosomal RNA pyrosequencing. We analyzed eight samples collected from the surface and at 30 m- and/or 50-m depths from two neritic and oceanic stations each from 24–30 April 2011. Comparisons of 15,498 pyrosequences identified 172 phylotypes of phytoplankton, excluding cyanobacteria, from the four surface stations. These pyrosequences were represented by dinoflagellates (29 %), stramenopiles (31 %), and chlorophytes (>39 %), with minor contributions from cryptophytes, haptophytes, and Telonemia. Phylotypes retrieved at 30- and 50-m depths were very similar to the surface samples. However, phylotype diversity and community structure varied considerably with the stations. Dominant phylotypes included Karlodinium veneficum, Ostreococcus tauri, Skeletonema marinoi, and Thalassiosira curviseriata, and many of the detected phylotypes include new records for the present study area. This study provides a valuable phylotype reference for future phytoplankton community structure and diversity studies with regard to marine environmental changes.     

Prospects of using Bayesian model averaging for the calibration of one-month forecasts of surface air temperature over South Korea

In this study, we investigated the prospect of calibrating probabilistic forecasts of surface air temperature (SAT) over South Korea by using Bayesian model averaging (BMA). We used 63 months of simulation results from four regional climate models (RCMs) with two boundary conditions (NCEP-DOE and ERA-interim) over the CORDEX East Asia. Rank histograms and residual quantile-quantile (R-Q-Q) plots showed that the simulation skills of the RCMs differ according to season and geographic location, but the RCMs show a systematic cold bias irrespective of season and geographic location. As a result, the BMA weights are clearly dependent on geographic location, season, and correlations among the models. The one-month equal weighted ensemble (EWE) outputs for the 59 stations over South Korea were calibrated using the BMA method for 48 monthly time periods based on BMA weights obtained from the previous 15 months of training data. The predictive density function was calibrated using BMA and the individual forecasts were weighted according to their performance. The raw ensemble forecasts were assessed using the flatness of the rank histogram and the R-Q-Q plot. The results showed that BMA improves the calibration of the EWE and the other weighted ensemble forecasts irrespective of season, simulation skill of the RCM, and geographic location. In addition, deterministic-style BMA forecasts usually perform better than the deterministic forecast of the single best member.