• Ocean and Polar Research
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• v.36 no.4
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• pp.395-405
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• 2014

A 570 cm-long sediment core was retrieved at $9^{\circ}57^{\prime}N$ and $131^{\circ}42^{\prime}W$ in 5,080 m water depth from the northeast equatorial Pacific and its stratigraphy was established with $^{10}Be/^9Be$ and paleomagnetic measurements. Successive AF demagnetization reveals eight geomagnetic field reversals. In the reference geologic time scale, the eight reversal events correspond to an age of about 4.5 Ma. However, $^{10}Be/^9Be$-based age yields 9.5 Ma at a depth of 372 cm. Such a large discrepancy in determined ages is attributed to an extremely low sedimentation rate, 0.4 mm/kyr on average, of the study core and resultant loss or smoothing of geomagnetic fields. The composite age model reveals a wide range in the sedimentation rate - varying from 0.1 to 2.4 mm/kyr. However, the sedimentation rate shows systematic variation depending on sedimentary facies (Unit II and III), which suggests that each lithologic unit has a unique provenance and transport mechanism. At depths of 110-80 cm with a sedimentation rate of about 0.1 mm/kyr, ancient geomagnetic field reversal events of at least a 1.8 Myr time span have not been recorded, which indicates the probable existence of a hiatus in the interval. Such a sedimentary hiatus is observed widely in the deep-sea sediments of the NE equatorial Pacific.

• Ocean and Polar Research
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• v.36 no.4
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• pp.373-381
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• 2014

Korea contract Mn-nodule field in the NE equatorial Pacific is composed of seven sectors with average water depths of 4,513-5,025 m. Of the various factors controlling the properties of Mn-nodule, it seems that water depth is likely connected to the chemical composition and occurrence of nodules. To test whether such an assumption held in each sector, we reviewed previous research data accumulated since 1994 for one of the northern sectors (hereafter KR1) where there are stark contrasts in water depth. High-resolution seabed mapping clearly separates a northern part (KR1N) from a deeper southern part (KR1S), cutting across in the middle of the KR1. In addition, significant volcanic activities forming numerous seamounts are distinctive especially in KR1N. In terms of nodule occurrence, manganese nodules in KR1S are comparatively larger (2-4 cm) with a discoidal shape, while those in KR1N are generally small (<2 cm) with poly-lobate and irregular shapes. Nodules in KR1N also have lower Co, Cu, Mn and Ni, and higher Fe contents. The spatial separation in nodule characteristics might be caused by volcanic activities in KR1N rather than water depth contrast. During the formation of the seamounts in KR1N, rock fragments and volcanic ashes as new nuclei of the nodules would have been continuously generated. As a result, the nodules could not grow larger than 2 cm and display the shapes of a newbie (i.e., irregular and poly-lobate shapes). Moreover, significant Fe supply from volcanic activities probably decreases the Mn/Fe ratio, which may lead to the KR1 nodules being misinterpreted as a hydrogenic in origin compared to other sectors where a high Mn/Fe ratio is present.

• Ocean and Polar Research
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• v.36 no.4
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• pp.367-371
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• 2014

In early 1990s, the Korean government has launched a deep-sea research program to secure the stable long-term supply of strategic metallic minerals including Cr, Cu and Ni. Through the pioneering surveys, Korea registered $150,000km^2$ of Mn-nodule field in the Clarion-Clipperton area, the NE equatorial Pacific to the international sea-bed authority (ISA) in 1994. Following the ISA exploration code, the final exclusive exploration area of $75,000km^2$ was assigned in 2002, based on results of eight-year researches of chemico-physical properties of nodules, bottom profiles and sediment properties. Since that time, environmental studies, mining technical developments including robot miner and lifting system and establishment of smelting systems were accompanied with the detailed geophysical studies to decipher the priori mining area until 2009. Major points of the recent Korea Mn-nodule program are deployed on a commercial scale until 2015. In order to meet the goals, we developed a 1/5 scaled robot miner compared to commercial one in 2012 and performed a mining test at the water depth of 1,370 m in 2013. In addition, detailed 25,000 scaled mining maps in the priori area, which can provide operation roots of the miner, will be prepared and an environmental-friendly mining strategy will be pursued based on the environmental impact test and environmental monitoring.

• Ocean and Polar Research
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• v.25 no.3
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• pp.257-267
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• 2003

Deep-sea bottom photographs acquired in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific were analyzed to reveal the controlling processes for the spatial variation of manganese nodule. The results show that regional-scale occurrence variations of manganese nodule are mainly controlled by primary productivity of surface water, sedimentation rate, and water depth (or carbonate compensation depth). As a result, the diagenetic accretion on nodules increases toward southwest while hydrogenetic accretion increases toward northeast. Considering the northwestward movement of Pacific Plate, this regional-scale variation of manganese nodule occurrence seems to be affected by oceanic environment during the active growth period (Oligocene-Miocene) of Pacific Plate.

• Ocean and Polar Research
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• v.27 no.1
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• pp.1-13
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• 2005

The samples for organic carbon analysis were collected between $5^{\circ}\;and\;17^{\circ}N$ along $131.5^{\circ}W$ in the northeast Pacific KODOS (Korea Deep Ocean Study) area. The mean concentration of total organic carbon (TOC) in the surface mixed layer $({\sim}50 m)$ was $100.13{\pm}2.05{\mu}M-C$, while the mean concentration of TOC in the lower 500m of the water column was $50.19{\pm}4.23{\mu}M-C$. A strong linear regression between TOC and temperature $(r^2=0.70)$ showed that TOC distribution was controlled by physical process. Results from the linear regression between chlorophyll-a and TOC, and between chlorophyll-a and particulate organic carbon (POC), decreasing of dissolved organic carbon (DOC) in the surface layer caused by non-biological photo-oxidation process. Below the surface layer, biological production and consumption occurred. DOC accumulation dominated in the depth range of $30{\sim}50m$ and DOC consumption occurred in the depth range of $50{\sim}200m$. TOC was inversely correlated with apparent oxygen utilization (AOU) and TOC/AOU molar ratios ranged from -0.077 to -0.21. These ratios indicated that TOC oxidation was responsible fur $10.9{\sim}30.1%$ (mean 20.2%) of oxygen consumption in the NE Pacific KODOS area. In the euphotic zone, distributions of dissolved and particulate organic matter were controlled by photo-chemical, chemical, biological and physical processes.

• Ocean and Polar Research
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• v.25 no.2
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• pp.133-145
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• 2003

Deep-sea surface sediments were collected using a multiple corer at 20 stations of Clarion-Clipperton fracture zone in the northeast equatorial Pacific to understand latitudinal and longitudinal variations of geotechnical properties. There was a distinct latitudinal variation of geotechnical properties in the study area. The northern sediments showed finer grain size, lower water content and porosity, higher bulk density and specific grain density, lower liquid limits and plastic limits than their southern counterparts. The northern sediments are classified into inorganic clays of low plasticity (fat clays) on plasticity charts and normal to active clay on activity chart, whereas, the southern sediments are classified into fine-grained, highly-plastic, inorganic and biogenic silt or organic clays on plasticity chart and normal to very active clay on activity chart. When shear strength are considered, the northern sediments were found to be in unconsolidated states, while the southern ones to be normal to over-consolidated states. These latitudinal variations in sediment characteristics are likely caused by differences in productivity of surface water that controls sediment compositions, sedimentation rates, and grain solubility.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.390-399
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• 1999

Siliceous and calcareous deep-sea core sediments were collected by a multiple corer from the KODOS (Korea Deep Ocean Study) area, northeast equatorial Pacific, to compare vane shear strengths measured by two different apparatuses and in different places of on-board and on-land laboratories. The apparatuses were 1) a hand-held vane with four blades of $2.0{\times}2.0$ cm, and 2) a motorized shear vane system with four blades of $1.0{\times}0.88$ attached on a rotational viscometer. Depth profiles of shear strengths of core samples determined by the apparatuses do not show any consistent difference. Also, there is no consistent difference between shear strength values measured on-board and on-land laboratories after storing the core samples for three months in a cold room by a motorized shear vane system. However, there are considerable differences between depth profiles of shear strengths measured at four different points (holes) of a core sample. Moreover, significant differences among the profiles of different tube samples from a multiple corer within a sampling station were observed. Heterogeneity in physical properties of each depth and sediment column, possibly due to bioturbation and bottom current flows, is likely responsible for the differences in the geotechnical properties.

• Journal of the Korean Geophysical Society
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• v.9 no.4
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• pp.311-320
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• 2006

Digital filters designed using wavelet theory are applied to bathymetry data acquired from KR5 area of Korea Deepsea Mining Area. The filters used in this study are the linear B-spline wavelet filter and derivative of a Cubic B-spline filter. With proper tuning of the digital filters, we can identify the location and orientation of the abyssal hill and abyssal trough in bathymetry. These features obtained from the digital filters are well correlated with bathymetric image. This quantitative information, which can be used to understand the underlying geophysical processes, can be further processed to obtain the spacing, orientation and distribution of the abyssal hill. This wavelet analysis of bathymetry provides good data to select the mining site.

• Economic and Environmental Geology
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• v.45 no.5
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• pp.477-486
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• 2012

High-resolution bathymetry and physico-chemical properties of manganese nodules were explored to identify the relationship between morphological features and nodule occurrences in the KR1, one of the Korean contract nodule fields located in the NE Pacific. The high-resolution seabed mapping showed that the southwestern sector of the KR1 (KR1-1) was relatively deeper than the northeastern sector (KR1-2) which is occupied by small-scale seamounts. In terms of nodule occurrence, manganese nodules in the KR1-1 were comparatively larger (2-4 cm) with rough surface (t-type) and discoidal shapes (D-type), while those in the KR1-2 were generally small (<2 cm) with smooth surface (s-type) and irregular shapes (I-type). In addition, the nodules in the KR1-1 had higher contents of Cu, Mn and Ni. Such connections of water depths to nodule appearances and metal contents are commonly observed in the Pacific nodule fields. On the other hand, the nodules in the KR1-2 tend to be controled by morphological features. The seamounts in the KR1-2 might continuously provide rock fragments as new nuclei of manganese nodules. As a result, the nodules could not grow over than 2 cm and showed the shapes of a newbie (i.e., smooth surface and irregular shapes). As a result, our observations indicate that occurrence features of manganese nodules could be subjected to water depths and seabed morphology simultaneously.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.323-337
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• 1999

Seafloor morphology and manganese nodule occurrence were studied in the Korea Deep-sea Environmental Study (KODES) area, northeast equatorial Pacific, to understand their relationship. Study area is composed of three elongated valleys and hills with about 100~200 m height along NNE-SSW direction. Valley region is generally flat. However, hill region is very rugged with big cliffs of about 100m height and small depressions of several tens of meters depth. Tectonic movement along the Clarion-Clipperton fracture zone, consequent formation of elongated abyssal hills and Valleys, erosion of siliceous bottom sediments by bottom currents, and dissolution of carbonate sediments on the abyssal hills below CCD result in the rugged morphology. Manganese nodule occurrence is closely related to the morphology of the study area; mostly rounded-shaped manganese nodules with about 5 cm diameter are abundant on the flat valley region, whereas irregular shaped nodules (or manganese crust) with less than 5 cm to about 1 m diameter occur on the hill. These results supports the previous reports that nodule abundance, composition, and morphology are variable both on regional and local small scales on the seafloor even within some abundant nodule provinces depending on oceanographic characteristics such as bathymetric features, surface sediment type, sediment thickness, and so on. We suggest that such oceanographic characteristics affect interrelatedly on the formation of manganese nodules, and tectonic movement of the Pacific plate ultimately constrain the nodule occurrence. A potential mining place in the KODES area seems to be the valley region, which is elongated to the NNW-SSE direction with 3-4 km width.