Characteristics of Seafloor Morphology and Ferromanganese Nodule Occurrence in the Korea Deep-sea Environmental Study (KODES) Area, NE Equatorial Pacific

Seafloor morphology and ferromanganese nodule occurrence were studied using a multibeam side scan sonar (SeaBeam, 2000) and a deep-sea camera system in the Korea Deep-sea Environmental Study (KODES) area, northeast equatorial Pacific. Seafloor morphology and nodule abundance are highly variable even in this small study area. The NNE-SSW oriented hills are parallel and about 100-200 m high. Valleys are very flat-floored, while hilltops are rugged with depressions of tens of meters. Cliffs to about 100 m bound the valleys and the hills. The study area can be classified into three types based both on nodule occurrence and seafloor morphology, mostly G- and B-types and some M-type. G-type is characterized by high nodule abundance, ubiquitous bioturbation, and flat seafloor morphology, while B-type is characterized by irregular-shaped nodules, variable nodule abundance, occurrence of giant nodules and sediment lumps, rugged bottom morphology with depressions, and white calcareous surface sediments. Medium nodule abundance and a generally flat seafloor characterize M-type. G-type occurs mostly in the valley regions, while B-type is on the hilltop areas. M-type is located between the hilltop and the valley. Tectonic movement of the Pacific plate resulted in the elongated abyssal hills and cliffs. The rugged morphology on hilltops resulted from erosion and redistribution of surface siliceous sediments on hilltops by bottom currents, outcropping of underlying calcareous sediments, and dissolution of the carbonate sediments by corrosive bottom water undersaturated with CaCO 3 . Sediment eroded from the hills, which is relatively young and organic-rich, is deposited in the valleys, and diagenetic metal supply to manganese nodules in the valley area is more active than on the hills. We suggest that tectonic movement ultimately constrains morphology, surface sediment facies, bottom currents and sediment redistribution, bioturbation, thickness of the sedimentary layer, and other conditions, which are all interrelated and control nodule occurrence. The best potential area for mining in the study area is the G-type valley zones with about 3-4 km width and NNW-SSE orientation.     

Ocean bottom friction study from numerical modelling of sea surface height and SEASAT-ALT data

Tidal dissipation at the ocean floor has long been regarded as an adquated explanation to the behaviour of lunar orbit and Earth's rotation, although the actual mechanism involved is yet a fascinating research subject to date. The most common way to evaluate the dissipation is to find the rate of work done per unit surface by the current on the sea floor (Munk and Mac Donald 1960, Lambeck 1975). The success of this approach rely on the knowledge of the frictional coefficient which links the frictional force at the ocean floor, either quadratically or linearly, with the current velocity. Not only is the frictional coefficient important in this context, a variety of storm surge and tidal modelling problems also require a similar dissipation meachanism (Heaps 1969, Grace 1930, Stock 1976 etc.). The University of Manitoba, Center for Precambrian Studies Publication No. 089     

Evaluation of typhoon‐induced rainfall using nonparametric Monte Carlo simulation and locally weighted polynomial regression

Typhoons in Korea are the major causes of natural disasters in the Korean peninsula. In this study, rainfall generated by typhoons was quantitatively analysed using various statistical methods. First, the frequency analysis of rainfall induced by typhoons was carried out to calculate the design rainfall. Second, the frequency analysis of simulated rainfall derived by nonparametric Monte Carlo simulation (NMCS) was performed to evaluate the uncertainty of rainfall caused by typhoons. Third, the regression relationship between the physical characteristic factors of typhoons and rainfall was established by locally weighted polynomial regression (LWPR), and the characteristic factors of typhoons were simulated. The simulated characteristic factors were then used to estimate rainfall and to calculate the design rainfall by typhoons. Comparative analyses of design rainfalls as estimated using various statistical methods were performed. The LWPR showed good performance in terms of reproducing typhoon characteristics. Therefore, the combined NMCS and LWPR method suggested in this study can be used as a supplementary technique for assessing extreme rainfall with climate change and reflected variability. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrochemistry of groundwaters in a spa area of Korea: an implication for water quality degradation by intensive pumping

A geochemical study was carried out in a small spa area (Onyang Spa, Korea) where intensive pumping of deep thermal groundwater (1 300 000 m³ year⁻¹) is taking place. This has caused the deep fractures to lose their artesian pressure and the upper shallow fractures have been encroached by shallow, cold waters. To quantify the influence of long‐term heavy pumping on the quality of the geothermal water, groundwater sampling and chemical analysis, water‐level measurement, and well loggings were performed for the selected deep thermal wells and shallow cold wells. Chemical analysis results indicate a big contrast in water chemistry and origins between the two water types. Shallow groundwater shows a wider concentration ranges in solutes that are closely related to human activity, illustrating the water's vulnerability to contamination near the land surface. Plots of water chemistry as a function of fluoride reveal that the quality of the thermal water was greatly influenced by the shallow, cold groundwater and that intensive pumping of the deep thermal groundwater has caused the introduction of shallow groundwater into the deeper fractures. Although the deep and the shallow fractures were piezometrically separated to some extent, a mixing model based on fluoride and nitrate indicated that the cold‐water fractions in the thermal wells are up to 50%. This suggests that the thermal water is faced with water quality degradation by the downward flow of the shallow, cold water. Restriction on the total of all the pumpage permits per unit area is suggested to restore the artesian pressure of the deep thermal aquifer and to prevent cold‐water intrusion in the study area. Copyright © 2004 John Wiley & Sons, Ltd.     

Statistical Analysis of the Relationships among Coronal Holes,Corotating Interaction Regions,and Geomagnetic Storms

We have examined the relationships among coronal holes (CHs), corotating interaction regions (CIRs), and geomagnetic storms in the period 1996?–?2003. We have identified 123 CIRs with forward and reverse shock or wave features in ACE and Wind data and have linked them to coronal holes shown in National Solar Observatory/Kitt Peak (NSO/KP) daily He i 10?830 Å maps considering the Sun?–?Earth transit time of the solar wind with the observed wind speed. A sample of 107 CH?–?CIR pairs is thus identified. We have examined the magnetic polarity, location, and area of the CHs as well as their association with geomagnetic storms (Dst≤?50 nT). For all pairs, the magnetic polarity of the CHs is found to be consistent with the sunward (or earthward) direction of the interplanetary magnetic fields (IMFs), which confirms the linkage between the CHs and the CIRs in the sample. Our statistical analysis shows that (1) the mean longitude of the center of CHs is about 8°E, (2) 74% of the CHs are located between 30°S and 30°N (i.e., mostly in the equatorial regions), (3) 46% of the CIRs are associated with geomagnetic storms, (4) the area of geoeffective coronal holes is found to be larger than 0.12% of the solar hemisphere area, and (5) the maximum convective electric field E _y in the solar wind is much more highly correlated with the Dst index than any other solar or interplanetary parameter. In addition, we found that there is also a semiannual variation of CIR-associated geomagnetic storms and discovered new tendencies as follows: For negative-polarity coronal holes, the percentage (59%; 16 out of 27 events) of CIRs associated with geomagnetic storms in the first half of the year is much larger than that (25%; 6 out of 24 events) in the second half of the year and the occurrence percentage (63%; 15 out of 24 events) of CIR-associated storms in the southern hemisphere is significantly larger than that (26%; 7 out of 27 events) in the northern hemisphere. Positive-polarity coronal holes exhibit an opposite tendency.     

Geochemical dispersion patterns of As, Sb, Bi and Se associated with sulfide mineralization at Avoca, Eire

At Avoca, Eire, Kuroko-like sulfide mineralization comprising massive stratiform cupriferous pyrite, accompanied by hanging-wall galena-sphalerite mineralization and footwall stringer pyrite, is hosted by Ordovician sediments, calc-alkaline lavas and pyroclastics. The sequence has been subjected to low-grade regional metamorphism, isoclinal folding and thrusting. The surficial cover comprises nonexotic glacial drift some 2 m thick. Previous work has demonstrated that major-element lithogeochemistry reflects the wall-rock alteration associated with the mineralization, but these signatures are absent from the overlying till. There is a poor heavy metal-expression at surface of the concealed mineralization.Analysis of wall rock, basal till and surface till samples for the chalcophile pathfinder elements As, Sb, Bi and Se (by rapid techniques which involve the introduction of their volatile hydrides into an inductively coupled plasma emission spectrometer) shows that a primary zonation of these elements around the mineralization can, in part, be traced to surface. In wall rocks, Bi enrichment is associated with the massive pyrite and footwall mineralization, Sb and Se anomalies occur in the hanging wall, and an As halo extends across all three types of mineralization. At surface, Bi and As anomalies are found over the massive pyrite and footwall zones, and an Sb anomaly occurs above the hanging-wall mineralization. The development of these patterns is attributed to mainly hydromorphic dispersion.The primary and surficial dispersion patterns of the chalcophile pathfinders should prove useful in exploration for other examples of Kuroko-type mineralization. The determination of these elements in geochemical exploration can be carried out quickly and cost-effectively.     

Synrift stratigraphic geometry in a transfer zone coarse-grained delta complex, Miocene Pohang Basin, SE Korea

The Gojusan fan delta is a coarse‐grained delta complex on the western margin of the Miocene Pohang Basin, SE Korea. The deposits consist of five facies associations (FA): alluvial‐fan conglomerates (FA I), shallow‐marine mouth‐bar sandstones (FA II), fluvial and mouth‐bar conglomerates (FA III), Gilbert‐type foreset conglomerates (FA IV) and hemipelagic mudstones (FA V). Different facies associations characterize the northern, central and southern parts of the delta complex. To the north, FA IV is laterally juxtaposed with FA I or the basement, with scarp‐derived breccias along the contact. Centrally, and to the south, FA I is laterally juxtaposed with FA II, with an abrupt facies change and local inliers of basement rocks along the contact. Early alluvial fan and mouth‐bar deposits are overlain by the topset (FA III) and truncated by the foreset (FA IV) of a Gilbert‐type delta in the central part of the fan delta complex, whereas FA II passes transitionally upward into FA III in the south, with the latter extending basinward into a gently inclined shoal water delta front. Gilbert‐type and shoal‐water geometries are therefore developed in the same delta complex. The composite delta geometry is interpreted as reflecting (1) its development near an extensional transfer zone where the hangingwall relief was variable over short distances along strike, and (2) the operation of intrabasinal faults. This interpretation contrasts with previous studies that viewed the delta complex as having formed along a pull‐apart basin margin.     

The high-velocity molecular stream in W51B: a ring structure with compact H ii regions

We present ¹³ CO J  = 1 − 0 line observations of the H  ii region complex W51B located in the high-velocity (HV) stream. These observations reveal a filamentary and clumpy structure in the molecular gas. The mean local standard of rest (LSR) velocity ∼ + 65 km s⁻¹ of the molecular gas in this region is greater than the maximum velocities allowed by kinematic Galactic rotation curves. The size and mass of the molecular clouds are ∼ 48 × 17 pc² and ∼ 2.4 × 10⁵ M⊙ respectively. In a position–velocity diagram, molecular gas in the southern part comprises a redshifted ring structure with v _LSR=+ 60 to +73 km s⁻¹. The velocity gradient of this ring is ∼ 0.5 km s⁻¹ pc⁻¹, and the mass is ∼ 6.2 × 10⁴ M⊙. If we assume that the ring is expanding with a uniform velocity, the expansion velocity, radius and kinetic energy are ∼ 7 km s⁻¹, ∼ 13 pc and ∼ 3.0 × 10 ⁴⁹ erg respectively. The kinetic energy and mass spectrum of the ring could be explained by an expanding cylindrical cloud with a centrally condensed mass distribution. The locations of two compact H  ii regions, G49.0−0.3 and G48.9−0.3, coincide with the two molecular clumps in this ring. We discuss star formation, and the mechanism that produced the ring structure.     

Adaptive bang–bang control for the vibration control of structures under earthquakes

An adaptive method based on the modified bang–bang control algorithm is proposed for the vibration control of structures subjected to unexpected severe seismic loads greater than the design loads. A hydraulic‐type active mass damper was made and experiments were carried out in the laboratory using a one‐story test structure and a five‐story test structure with the active mass damper. Through numerical simulations and experiments it was confirmed that the proposed method works well to suppress the vibration of structures subjected to unexpected severe seismic loads greater than the design loads without causing any unstable situations. Copyright © 2003 John Wiley & Sons, Ltd.     

Summer monsoon rainfall patterns over South Korea and associated circulation features

Summary Seasonal summer monsoon (June through August) rainfall patterns over South Korea are classified by an objective method using data for a 40-year period (1961–2000). The rainfall patterns are represented by the percentage departures from the normal rainfall of 12 stations spread uniformly over South Korea. The statistical technique employed is the k-means (KM) clustering method. The Euclidean distance has been used as a measure of similarity between the patterns. Four dominant types are obtained by this method. Intercorrelations among the types suggest that the dominant patterns are distinct. The summer monsoon rainfall shows an increasing trend. Investigation of the physical processes associated with these patterns using NCEP/NCAR Reanalysis data clearly reveals contrasting circulation features associated with the dominant types during the summer monsoon period. In particular, contrasting circulation features are related to the position, shape and strength of the North Pacific Subtropical High. Received October 30, 2000 Revised November 12, 2001