Hyun-Bok Lee

Relationship between polymetallic nodule genesis and sediment distribution in the KODOS (Korea Deep Ocean Study) Area, Northeastern Pacific

Polymetallic nodule and sediment characteristics were investigated for two blocks (KR2 and KR5) in the Korea Deep Ocean Study (KODOS) area in order to better understand nodule distribution and the potential effects of sediments on nodule genesis. The northern block (KR2) is dominated by hydrogenetic nodules, whereas the southern block (KR5) is dominated by diagenetic nodules. Sediments in the study area are assigned to three major lithologic units which are distinctive in color and texture. The northern block is characterized by a thick, metalpoor Unit 1 sediment, which is thin in the southern block, where metal-rich Units 2b and 3 occur close to the surface. The distribution of different nodule genetic types in the northern and southern blocks can be attributed to topographic variations (topographic high near seamounts in KR2 and abyssal plain in KR5) and different sedimentation rates (0.1 and 0.32 mm/kyr in blocks KR2 and KR5, respectively). The southern block has a geologic setting more conducive to diagenetic nodule formation, such as flat topography and sediment composition. Nodule distribution in the studied blocks might also be explained by the distribution of the sediment units of different metal contents. The northern block, in which Unit 1 is thicker, has more abundant hydrogenetic nodules, possibly because Unit 1 prevents metals that are remobilized from the underlying sediments from reaching the seabed where the nodules are forming.

Regional Variability of Manganese Nodule Facies in the KR1 Area in KODOS Area, Northeastern Equatorial Pacific

Research Vessel Building Unit, KIOST Ansan, P. O. Box 29, Seoul 425-600, KoreaHigh-resolution bathymetry and physico-chemical properties of manganese nodules were explored to identify therelationship between morphological features and nodule occurrences in the KR1, one of the Korean contract nodulefields located in the NE Pacific. The high-resolution seabed mapping showed that the southwestern sector of theKR1 (KR1-1) was relatively deeper than the northeastern sector (KR1-2) which is occupied by small-scale sea-mounts. In terms of nodule occurrence, manganese nodules in the KR1-1 were comparatively larger (2-4 cm) withrough surface (t-type) and discoidal shapes (D-type), while those in the KR1-2 were generally small (<2 cm) withsmooth surface (s-type) and irregular shapes (I-type). In addition, the nodules in the KR1-1 had higher contents ofCu, Mn and Ni. Such connections of water depths to nodule appearances and metal contents are commonlyobserved in the Pacific nodule fields. On the other hand, the nodules in the KR1-2 tend to be controled by morpho-logical features. The seamounts in the KR1-2 might continuously provide rock fragments as new nuclei of manga-nese 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 manganesenodules could be subjected to water depths and seabed morphology simultaneously.

Evaluation of Correction Parameter for the Free-fall Grab Based Mn Nodule Abundance in the Southern Sector of the KODOS

Quantitative estimate of manganese nodules based on the operation of a free fall grab (FFG) needs to be corrected because of its less retrieval ability. Previously, the correction parameter of the nodule abundance collected by FFG was calculated based on the image analysis of the photos of bottom sediment in the northern sector of the nodule exploration area of Korea in the NE equatorial Pacific. However, nodules in the southern sector are commonly covered by sediment, which may prevent the use of the correction parameter estimated by photographic techniques. In this study, we attempted dual nodule sampling at the same location by different equipments (i.e. box corer (BC) and FFG) to examine the previous correction parameter of nodule abundance for FFG operation. During the exploration cruises in 2007 to 2009, Mn-nodules were collected from 40 stations both by BC and FFG in the southern sector. The correlation analysis between BC and FFG operations revealed that the BC collected nodules 1.43 times larger than FFG. Our result suggests that the correction parameter of 1.43 can be applied for collection of FFG data to estimate Mn-nodule distribution in the southern sector. The obtained parameter is similar to the previous parameter (1.42~1.45) calculated by the image analysis method, indicating an usefulness of new correction parameter suggested by this study.

Chemical Speciations of Elements in the Fe-Mn Crusts by Sequential Extraction

Abstract : Sequential extraction was carried out on twenty two subsamples of three ferromanganese crustsfrom three seamounts (Lemkein, Lomilik, and Litakpooki) near the Marshall Islands in the western Pacific.The extraction was designed to fractionate Fe-Mn crust forming elements into four defined groups: (1)exchangeable and carbornate, (2) Mn-oxide, (3) Fe-oxyhydroxide, and (4) residual fraction. X-raydiffraction result shows that target material were well removed by each extraction step except for CFA inphosphatized crusts generation. According to chemical analysis of each leachate, most of elements in theFe-Mn crusts are bound with two major phases. Mn, Ba, Co, Ni, Zn, (Fe, Sr, Cu, and V) are stronglybounded with Mn-oxide (δ-MnO 2 ) phase, whereas Fe, Ti, Zr, Mo, Pb, Al, Cu, (V, P, and Zn) show chemicalaffinity with Fe-oxyhydroxide phase. This result indicates that significant amount of Al, Ti, and Zr can notbe explained by detrital origin. Ca, Mg, K, and Sr mainly occur as exchangeable elements and/or carbonatephase. Outermost layer 1 and innner layer 2 which are both young crusts generations are similar in chemicalspeciations of elements. However, some of Fe-oxyhydroxide bounded elements (Pb, Y, Mo, Ba, Al, and V)in phosphatized innermost layer 3 are released during phosphatization and incorporated into phosphate (Pb,Y, Mo, and Ba) or Mn-oxide phase (Al and V). Our sequential extraction results reveal that chemicalspeciations of elements in the hydrogenetic crusts are more or less different from interelemental relationshipcalculated by statistical method based on bulk chemistry.Key words : (sequential extraction), (Fe-Mn crusts), (phosphatization), (hydrogenetic elements)

Variability in Particle Mixing Rates in Sediments with Polymetallic Nodules in the Equatorial Eastern Pacific as Determined from Measurements of Excess 210 Pb

Radionuclide activities of 210Pb and 226Ra were measured to determine bioturbation coefficients (Db) in seven sediment cores from the Korean licensed block for polymetallic nodules in the Clarion–Clipperton Fracture Zone. Variability in Db is considered in the context of the sedimentological, geochemical, and geotechnical properties of the sediments. Db values in the studied cores were estimated using a steady-state diffusion model and varied over a wide range from 1.1 to 293 cm2/yr with corresponding mixing depths (L) of 26 to 144 cm. When excepting for spurious results obtained from cores where diffusive mixing does not apply, Db values range from 1.1 to 9.0 cm2/yr with corresponding mixing depths (L) of 26 to 63 cm. Such wide variability in Db and L values is exceptional in sites with water depths of ∼5000 m and is attributed in this study to an uneven distribution of sediment layers with different shear strengths and total organic carbon (TOC) contents, caused by erosion events. The studied cores can be grouped into two categories based on lithologic associations: layers with high maximum shear strength (MSS) and low TOC content, showing a narrow range of Db values (1.1–9.0 cm2/yr); and layers with low MSS and high TOC content, yielding much higher Db values of over 30 cm2/yr. The distribution of different lithologies, and the resultant spatial variability in MSS and labile organic matter content, controls the presence and maximum burrowing depth of infauna by affecting their mobility and the availability of food. This study provides a unique case showing that shear strength, which relates to the degree of sediment consolidation, might be an important factor in controlling rates of bioturbation and sediment mixing depths.

Geophysical and Sedimentological Characteristics of Lomilik Seamount, West Pacific

Lomilik Seamount in the west Pacific was seismically surveyed and photographed to illuminate the bottom topography, the condition of manganese crust, and the characteristics of sedimentary environment. Lomilik Seamount has a NW-SE elongated bottom topography with steep slopes in the NESW direction part. Even though the steep slopes of the seamount are devoid of deposits, the summit area and gentle slope of the seamount are covered with thick deposits. The seismic data indicate that Lomilik Seamount is a flat-topped and step-faulted guyot of volcanic origin. Deep-sea camera photographs show that much of the seafloor is rippled in symmetrical and asymmetrical patterns. The traces of biological activity were distinct on gentle seafloor suggesting the low-energy bottom conditions. Some photographs also show outcrops encrusted with manganese crusts. Sedimentary environments in the Lomilik Seamount appear have been governed by regional morphology and strong bottom current.