Korea Deep Ocean Study Research Articles

Fine-scale Microbial Communities Associated with Manganese Nodules in Deep-sea Sediment of the Korea Deep Ocean Study Area in the Northeast Equatorial Pacific

Despite its potential significance for industrial utilization, any activities associated with the mining of manganese (Mn) nodules might have substantial impacts on benthic ecosystems. Because microorganisms respond quickly to changing environmental conditions, a study of microbial communities provides a relevant proxy to assess possible changes in benthic ecosystems associated with mining activities. We investigated fine-scale microbial community composition and diversity inside and on the surface of Mn nodules and in nearby deep-sea sediments in the Korea Deep Ocean Study (KODOS) area located in the Clarion-Clipperton Fracture Zone (CCFZ) of the northeast equatorial Pacific. Although microbial cell density was lower within nodules (3.21 × 106 cells g-1) than in sediment (2.14 × 108 cells g-1), nodules provided a unique habitat for microorganisms. Manganese-oxidizing bacteria including Hyphomicrobium and Aurantimonas in Alphaproteobacteria and Marinobacter in Gammaproteobacteria were abundant in nodules, which implied that these bacteria play a significant role in nodule formation. In contrast, Idiomarina in Gammaproteobacteria and Erythrobacter and Sulfitobacter in Alphaproteobacteria were abundant in sediments. Meanwhile, Thaumarchaeota, a phylum that consists of ammonia-oxidizing chemolithoautotrophs, were the predominant archaeal group both in nodules and sediment. Overall, microbial communities in Mn nodules were unique compared to those observed in sediments. Furthermore, the phylogenetic composition of microorganisms in the KODOS area was distinguishable from that in the nodule provinces claimed by China and Germany in the CCFZ and nodule fields in the central South Pacific Gyre, respectively.

Rock Magnetic Approaches Used on Deep-sea Sediments in the Northeastern Equatorial Pacific

Rock magnetic properties of unconsolidated sediments from the Korea Deep Ocean Study area of the northeastern equatorial Pacific were analyzed to trace the time-dependent variations of sedimentary environments. For upper Pleistocene sediments, light-brown sediments predominate, whereas the lower sediments deposited in the late Pliocene are dark brown. Rock magnetic properties also clearly differ among the two distinct color environments. Values of anhysteretic remanent magnetization and low-field magnetic susceptibility are highly responsive to changes in the color of the sediment. For example, comparatively low values denote a dominance of coarse-grained magnetic minerals as observed in the lower dark-brown layers. With respect to the content of magnetic minerals, coarse magnetic grains are highly concentrated in the darker-colored sediment layers. However, both the magnetic mineral dependent parameter (S ratio) and results of the scanning electron microscope observation indicate that magnetic mineral changes did not occur along the core depth, which means that there was no apparent source change. Without distinctive source changes, the variations in the rock magnetic properties likely reflect a process by which the magnetic grains were primarily transported by enhanced wind and bottom currents and affected by diagenetic dissolution as a function of both the time from burial and the extremely low sedimentation rates after deposition.

Three new species of the deep-sea genus ColletteaLang, 1973 (Tanaidacea; Colletteidae) in the eastern central Pacific

Three new species of ColletteaLang, 1973 are described from the Korea Deep Ocean Study (KODOS) area of the eastern central Pacific based on collections made at a depth of approximately 5000 m by R/V Onnuri. This study is a component of environmental impact research for manganese nodule mining in the Clarion-Clipperton Fracture Zone (CCFZ). Only one species of the genus Colletteahas previously been described from the CCFZ. This situation may result from similar morphologies among related species, a lack of samples, and the frequent poor quality of specimens which results from sampling difficulties. This paper describes three new Colletteaspecies from the KODOS area. These species vary in the characteristics of the cheliped propodus: in C. asperaand C. prominentia, this structure shows bark-like ornamentation on its outer surface. Additionally, the cephalothorax bears fine setules along the mid-lateral margins ( C. eminulaand C. aspera), and the cheliped fixed finger shows protrusions along the proximal incisive margin ( C. eminula). These characteristics have not yet been found in other species of the genus. In this study, full descriptions of new species of Colletteaand the key characters of genus are provided, and the comparison of these characteristics with those of closely related species is given.

Description of two new species of Neotanais Beddard, 1886 (Crustacea, Tanaidacea) from KODOS area.

Two new species of Neotanais Beddard, 1886 are described from the Korea Deep Ocean Study (KODOS) area in the Clarion-Clipperton Fracture Zone, based on the collections performed on board R/V Onnuri from a depth of 5180 m. Neotanais triqueturus n. sp. is similar to the 'pfaffi group' characterized by pereonites with a swollen distolateral margin, pleonites with mid-ventral spurs and tapered lateral margins but can be differentiated by a longer cephalothorax (length: width 1.6: 1), a cheliped with a large protrusion on the mid-dorsal margin of the fixed finger, and the presence of a ventral process on the cheliped carpus. Neotanais brevis n. sp. has the characteristics of the 'micromopher' group, with pleonites narrower than pereon, a cheliped carpus without a ventral process, and a uropod endopod with nine articles but can be differentiated by a combination of the pleonites without mid-ventral spurs, a relatively longer pleotelson (length: width 1: 1.5 vs. 1: 2), a uropod basis with one seta on each of the ventral and dorsal margins, and the cheliped fixed finger with proximal denticles. In this study, in order to prove N. triqueturus and N. brevis were new species, full descriptions and a comparison with the closely related species are given. In addition, comprehensive comparisons with the species of Neotanais from the east-central Pacific are tabulated and discussed.

북동태평양 KODOS 해역 심해 해저특성에 따른 초대형저서동물 분포

In August, 2013, we collected epifaunal megabenthos using a deep sea camera (DSC) around a benthic impact study (BIS) site. This was located in the KR5 block of the Korea Deep Ocean Study (KODOS) area in the Northeastern Pacific. The DSC was positioned at 6.8 ± 2.9 m (SD) from the sea bottom and was operated from a position at 131°56.85 - 131°55.02W for 2.3 h at a speed of 1-2 knot. The geographical features of the study area consisted of two structures; a trough in the middle and hills at the east and west sides. Sediment conditions were consistent within six blocks and were affected by slope and polymetallic nodule deposits. We analyzed 226 megafaunal species. Sipunculida comprised the highest percentage of individuals (39%), and the dominant epifaunal megabenthos were Hormathiidae sp., Primnoidae sp., Hexactinellida sp., Hyphalaster inermis, Freyella benthophila, Paelopatides confundens, Psychropotes longicauda, and Peniagone leander. More than 80% of the total density of megafauna occurred on sea plain (D- and E-blocks). We found two distinct groups in the community, one located on sea plains and the other along both sides of the sea slop. Our results suggest that geographical features such as slope and polymetalic nodule deposits are important in controlling the distribution of the epifaunal megabenthos around the KODOS area.

Two new species of the deep-sea genus Neotanais Beddard, 1886 (Tanaidacea: Neotanaididae) from the eastern central Pacific

We describe two new species of deep-water neotanaids collected from the Korea Deep Ocean Study (KODOS) Area in the eastern central Pacific. Neotanais pacificus is distinguished from other species of Neotanais by the following morphological combination: in the female: 1) pereiomere 5 is the longest of the pereiomeres, 2) distal claw of the cheliped fixed finger bulges outward, and the cutting edge descends steeply, 3) the uropod exopod is much longer than first endopodal article, 4) the setal row of the left mandible has bi-serrated setae and plumose seta, 5) the maxilliped endite bears three bipinnate spiniform setae on the inner posterior margin and medially expanded plumose seta on the distal margin, and 6) the propodi of pereipods 1 to 3 bear thick bi-pinnate spiniform setae. The female of N. capillus distinctly differs from other species of Neotanais by the following morphological combination: 1) pereiomeres 4 and 5 are longer than wide, 2) the pleomeres are without midventral spurs, 3) the pleotelson bears fine setules along the distal margin, 4) the maxilliped endite has a very long plumose seta on the distal outer corner and two bipinnate spiniform setae on inner posterior margin, 5) the propodi of pereiopods 1 to 6 have thick bipinnate spiniform setae, and 6) the uropod is shorter than the pleon. In this study, distinct morphological characters differentiating the N. pacificus and N. capillus from other species of Neotanais are given on the basis of detailed descriptions.

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.

Metal-bearing molten sulfur collected from a submarine volcano: Implications for vapor transport of metals in seafloor hydrothermal systems

Gray, metal-bearing molten sulfur was collected from the central volcanic cone of an active off-axis caldera (MTJ-1) in the northeastern Lau Basin, southwestern Pacific Ocean, during an expedition for hydrothermal vents undertaken by the Korea Deep Ocean Study (KODOS) program in 2006. The molten sulfur enveloped the frame and chain bag of the dredge at a depth of ∼1700 m. Microscopically, the sulfur matrix contains numerous covellite (CuS) inclusions of various sizes and irregular shapes, indicating their formation via volcanic sublimation. The molten sulfur is enriched in elements commonly associated with magmatic input, including Cu, As, Au, Bi, Te, and Sb. The low sulfur isotope composition of the sulfur (δ 34 S = −7.5‰ to −8.2‰) indicates an origin via the magmatic degassing of SO 2 and disproportionation. The present results represent field-scale evidence for metal transport via sulfur-rich volcanic degassing in submarine massive sulfide deposits. The molten sulfur deposit plays an important role in enhancing the efficiency of the transfer of magmatic fluid to the hydrothermal system.

북동태평양 KODOS 해역의 유기탄소 및 겉보기산소량 특성

The samples for organic carbon analysis were collected between <TEX>$5^{\circ}\;and\;17^{\circ}N$</TEX> along <TEX>$131.5^{\circ}W$</TEX> in the northeast Pacific KODOS (Korea Deep Ocean Study) area. The mean concentration of total organic carbon (TOC) in the surface mixed layer <TEX>$({\sim}50 m)$</TEX> was <TEX>$100.13{\pm}2.05{\mu}M-C$</TEX>, while the mean concentration of TOC in the lower 500m of the water column was <TEX>$50.19{\pm}4.23{\mu}M-C$</TEX>. A strong linear regression between TOC and temperature <TEX>$(r^2=0.70)$</TEX> 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 <TEX>$30{\sim}50m$</TEX> and DOC consumption occurred in the depth range of <TEX>$50{\sim}200m$</TEX>. 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 <TEX>$10.9{\sim}30.1%$</TEX> (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.

Distribution and structure of heterotrophic protist communities in the northeast equatorial Pacific Ocean

The distribution and structure of heterotrophic protist communities and size-fractionated chlorophyll a were studied during the Korea Deep Ocean Study 98 (KODOS 98) research expedition (July 1998) in the northeast equatorial Pacific Ocean (5–11°N). Areas of convergence and divergence formed at the boundaries of the South Equatorial Current (SEC), North Equatorial Current (NEC), and North Equatorial Counter Current (NECC) during the expedition. Water column physicochemical characteristics significantly influenced the size structure of heterotrophic protist communities. Intense vertical mixing and high nutrient and chlorophyll a concentrations characterized SEC and NECC areas, which were affected by converging and diverging water masses, respectively. Nanophytoplankton dominated in SEC and NECC areas; both areas also had relatively high heterotrophic protist biomasses (average 743 µg C m−2). NEC areas were characterized by a stratified vertical structure, low nutrient and chlorophyll a concentrations, and picophytoplankton dominance. The heterotrophic protist biomass in NEC areas averaged 414 µg C m−2; nanoprotists ( 20 µm size classes in both water columns. The biomass of heterotrophic protists significantly correlated with the net-, nano-, and picophytoplankton biomass in SEC/NECC areas and with the nano- and picophytoplankton biomass in NEC areas. Heterotrophic protists and phytoplankton also showed strong positive correlation in the study area. The size structure of the phytoplankton biomass coincided with that of heterotrophic protists; the heterotrophic protist biomass positively correlated with the protists’ prey source. These relationships suggest that the community structure of heterotrophic protists and the microbial food web depended on size classes within the phytoplankton biomass. Microzooplankton grazing and phytoplankton growth rates were higher in SEC/NECC areas than in NEC areas. In contrast, the potential primary production grazed by microzooplankton was relatively high in NEC areas (127.3%) compared with SEC/NECC areas (94.6%). Our results indicate that the relative importance and size structure of heterotrophic protists might vary according to two distinct water column structures.

동태평양 KODOS 탐사해역에서의 물리해양환경 및 저층해류 특성

Hyrdography and deep currents were measured from 1997 to 1999 to investigate deep-sea environments in the KODOS (Korea Deep Ocean Study) area of the northeastern tropical Pacific. KODOS area is located meridionally from the North Equatorial Current to the boundary between the North Equatorial Current and the Equatorial Counter Current. Strong thermocline exists between 10 m and 120 m depths at the study area. Since that strong thermocline does hardly allow vertical mixing between surface and lower layer waters, vertical distributions of temperature, salinity, dissolved oxygen and nutrients drastically change near the thermocline. Salinity-minimum layer, which indicate the North Pacific Intermediate Water (NPIW) and the Antartic Intermediate Water (AAIW), vertically occupies vertically at the depths from 500 m down to 1400 m. The NPIW and the AAIW horizontally occur to the north and to the south of <TEX>$7^{\circ}N$</TEX>, respectively. The near-bottom water shows the physical characteristics of <TEX>$1.05^{\circ}C$</TEX> and 34.70 psu at the depths of 10 m to 110 m above the bottom (approximately 4000-5000 m), which was originated from the Antarctic Circumpolar Water. It flows northeastwards for 2 to 4 months at the study area, and its mean velocity was 3.1-3.7 cm/s. Meanwhile, reverse (southwestward) currents appear for about 15 days with the average of 1.0-6.1 cm/s every 1 to 6 months. Dominant direction of the bottom currents obtained from the data for more than 6 months is northeastward with the average speeds of 1.7-2.1 cm/s. Therefore, it seems that deep waters from the Antarctica flow northwards passing through the KODOS area in the northeastern tropical Pacific.

자유낙하식 시료채취기(free-fall grab)의 개량에 따른 회수율 향상 검토

Deep-sea Resources Research Center (DRRC) has been using a free-fall grab (FFG) for the resource evaluation of polymetallic nodules in the KODOS (Korea Deep Ocean Study) area, NE Pacific, since 1992. A FFG model (Model 4200, Benthos) adapting one glass buoy system (diameter 17 inch, net buoyance 25.4 kg) has been used until 1993. Since then, DRRC has carried out a study to increase the recovery rate of FFG and it was found that a revised system adapting an additional buoy (diameter 10 inch, net buoyance 4.5 kg) gives improved results. The nodule sampling tests were performed using two different models for the same study area and the resulting recovery rates were compared. The result shows no distinct difference in recovery time between two models, but average recovery rate of the revised model was increased to 99.44% from 96.06% of the original model.

Flow cytometer를 이용한 열대 동태평양의 독립영양 극미소 플랑크톤 연구

The effects of environmental forcing on autotrophic picoplankton distributional patterns were investigated for convergence (5 o N), divergence (9 o N-10 o 30'N) and oligotrophic (17 o N) sites in the tropical eastern Pacific during 2001 and 2003 KODOS (Korea Deep Ocean Study) cruises. The distributions of picoplankton populations - Prochlorococcus, Synechococcus and picoeukaryotes algae - were determined by flow cytometric analyses. Latitudinal variations in abundance maxima, vertical profiles, integrated abundance (0-150 m), and estimated carbon biomass were contrasted for each site according to three hydrological conditions. Prochlorococcus showed consistently high abundance in the surface mixed layers of all sites at 1×1 0 5 ~3 × 10 5 cells ml −1 and showed declining abundance below these layers. However, these decreasing rates were not particularly sharp showing considerably high abundance at 1 × 10 4 cells ml −1 or higher even at 100 m depth. Vertical profiles of Synechococcus and picoeukaryotes were generally parallel to each other in all sites. A clear abundance maximum was observed at divergence site at or slightly above the pycnocline depth. Higher abundance was observed at the surface mixed layer for convergence site but a sharp decrease was observed below the pycnocline. However, there was no significant abundance fluctuation with depth at more oligotrophic site (17 o N). Integrated cell abundance of Prochlorococcus was high in the oligotrophic site at 2.17 × 10 13 cells m −2 , and low in the convergence site at 0.88 × 10 13 cells m −2 . However, opposite pattern was observed for Synechococcus and picoeukaryotes where relatively high integrated cell abundance was shown in the convergence site. Estimated carbon biomass of Prochlorococcus contributed 30.4-80.3% of total autotrophic picoplankton carbon showing the highest contribution in the oligotrophic site and the lowest contribution in the convergence site. Synechococcus contribution of total autotrophic picoplantkon carbon biomass was lower than 5.8% for most of sites except the convergence site where Synechococcus contributed 23.2% of picoplankton carbon biomass. Carbon biomass of picoeukaryotes was 18.8-46.4% showing the highest carbon biomass at the convergence site. Overall, Prochlorococcus showed higher cell abundance and carbon biomass and exhibited different reaction to hydrological conditions when compare with the other two major autotrophic picoplankton groups.

북동 태평양수역에서 위도에 따른 부유 원생동물의 분포

As a part of Korea Deep Ocean Study program, we investigated the distribution of planktonic protists in the upper 200 m of the northeast Pacific from <TEX>$5^{\circ}N$</TEX> to <TEX>$17^{\circ}N$</TEX>, along <TEX>$131^{\circ}30'W$</TEX>. Area of divergence was formed at <TEX>$9^{\circ}N$</TEX> which is boundaries of the north equatorial counter current (NECC) and the north equatorial current (NEC) during this cruise. Chlorophyll-a concentration was higher in NECC than in NEC area. Pico chl-a(<<TEX>$2\;{\mu}m$</TEX>) to total chl-a accounted for average 89% in the study area. The contribution of pico chl-a to total chl-a was relatively high in NEC area than in NECC area. Biomass of planktonic protists, ranging from 635.3 to <TEX>$1077.3\;mgC\;m^{-2}$</TEX>(average <TEX>$810\;mgC\;m^{-2}$</TEX>), was most enhanced in NECC area and showed distinct latitudinal variation. Biomass of HNF ranged from 88.7 to <TEX>$208.3\;mgC\;m^{-2}$</TEX> and comprised 15% of planktonic protists. Biomass of ciliates ranged from 123.6 to <TEX>$393.0\;mgC\;m^{-2}$</TEX> and comprised 25% of planktonic protists. Biomass of HDF ranged from 407.2 to <TEX>$607.8\;mgC\;m^{-2}$</TEX> and comprised 60% of planktonic protists. HDF was the most dominant component in both NECC and NEC areas. Nano-protist biomass accounted for more than 50% of total protists in the both areas. The contribution of nanoprotist to total protists biomass was relatively higher in NEC area than in NECC. The biomass of planktonic protists was significantly correlated with phytoplankton biomass in this study area. The size structure of phytoplankton biomass coincided with that of planktonic protists. This suggested that the structure of the planktonic protists community and the microbial food web were dependent on the size structure of the phytoplankton biomass. However, biomass and size structure of planktonic protist communities might be significantly influenced by physical characteristics of the water column and food concentration in this study area.

Paleomagnetic results from deep-sea sediment of the Korea Deep Ocean Study (KODOS) area (northern equatorial Pacific) and their paleodepositional implications

Paleomagnetic properties of sediment cores were examined to reconstruct paleodepositional conditions in the Korea Deep Ocean Study (KODOS) area, located in the northeastern equatorial Pacific. The studied KODOS sediments have a stable remanent magnetization with both normal and reversed polarities, which are well correlated with the geomagnetic polarity timescale for the late Pliocene and Pleistocene. Average sedimentation rates are 1.56 and 0.88 mm/kiloyear for the Pleistocene and late Pliocene, respectively. Clay mineralogy and scanning electron microscope analyses of the sediments indicate that terrestrial material was transported to the deep-sea floor during these times. The variations of sedimentation rates with age may be explained by the onset of the northern hemisphere glaciation and subsequent climatic deterioration during the Pliocene and Pleistocene. For the Pleistocene, an increasing sedimentation rate implies that input of terrestrial materials was high, and also a high input of biogenic materials was detected as a result of increased primary production in the surface water. The down-core variations in paleomagnetic and rock-magnetic properties of the KODOS sediments were affected by dissolution processes in an oxic depositional regime. As shown by magnetic intensity and hysteresis parameters, the high natural remanent magnetization (NRM) stability in the upper, yellowish brown layers indicates that the magnetic carrier was in pseudo-single domain states. In the lower, dark brown sediments, only coarse magnetic grains survived dissolution and the NRM was carried by more abundant, multi-domain grains of low magnetic stability. The down-core variation of magnetic properties suggests that the KODOS sediments were subjected to dissolution processes resulting in a loss of the more stable components of the magnetic fraction with increasing core depth.

Sedimentary fabric on deep-sea sediments from KODOS area in the eastern Pacific

An anisotropy of magnetic susceptibility (AMS) study on three sediment cores taken from the Korea Deep Ocean Study (KODOS) area in eastern Pacific was carried out to understand the relationship between magnetic fabric patterns and paleo-depositional conditions of deep-sea sediments. Most AMS measurements reveal normal sedimentary fabric patterns indicating a stable sedimentation mode. However, some intervals show deformed AMS patterns (magnetic lineation), and this anomalous fabric is mainly observed at the boundary where sediment color changes. The abrupt change of AMS parameters at this boundary provides evidence that the linear fabric was induced by input of intensified bottom currents. Based on the trend of microfossil occurrences, it is interpreted that the discontinuous color boundary was formed by hiatus between Tertiary and Quaternary age. The change of magnetic fabric at the topmost color boundary coincides with the time of prevailed antarctic bottom water (AABW) activity. In this study, the AMS properties are shown to be useful tools for making inferences concerning the paleoenvironment of abyssal basins.

Potential environmental impact of deep seabed manganese nodule mining on the synechococcus (cyanobacteria) in the northeast equatorial pacific: Effect of bottom water‐sediment slurry

Synechococcus (photoautotrophic cyanobacteria) are among the major primary producers in the oligotrophic open ocean. Potential environmental impacts of bottom water and sediment intrusion on the Synechococcus population in the surface water column of the northeast equatorial Pacific were investigated during the KODOS (Korea Deep Ocean Study) 95–2 cruise. The growth of Synechococcus was limited primarily by Fe deficit and secondarily by nitrogenous nutrients. Since bottom water and sediment are abundant in both inorganic nutrients and trace metab, the addition of bottom water‐sediment slurry to surface water samples stimulated the growth of Synechococcus. Our results together with other experimental estimation suggest that certain impacts could occur on the photoautotrophic plankton biomass in the water column by the surface discharge of bottom water and sediment during large‐scale and long‐term commercial mining of Mn nodules. More quantitative estimation for those environmental aspects in the water column is necessary for the construction of environmentally affiliated mining systems in the future.

Geochemistry of rare earth elements in two-color core sediments from the Korea Deep Ocean Study (KODOS)-90 site, NE equatorial Pacific.

Major factors controlling the variation of rare earth element (REE) contents in deep-sea sediments were identified using box-core sediments from the Korea Deep Ocean Study (KODOS)-90 site in the western part between the Clarion-Clipperton fracture zones, northeast equatorial Pacific. Four of ten core columns can be divided into two layers by a sharp color boundary; an upper pale brown layer (Unit A) and a lower dark brown layer (Unit B). Trivalent REEs (3 + REEs) as well as micronodules, smectite, smectite aggregate, and fish remains (spicules and spines) are highly enriched in Unit B compared to Unit A. 3 + REEs in micronodule, smectite, and smectite aggregate are not significantly concentrated compared to those in bulk Unit B sediments. 3 + REE contents in coarse-grained fish remains (>25 μm), which is likely biogenic apatite, are about seven and two times higher, respectively, than the contents in Units A and B. Contents of fish remains in bulk Unit B sediments, however, are too low to explain the enrichment of 3 + REEs in Unit B. Based on the results of phosphorus speciation and linear relationships in two pair diagrams (La contents vs. total inorganic phosphorus and 1/(Ce/Ce∗) vs. total inorganic phosphorous), it can be inferred that 3 + REEs are dominantly enriched in apatite in fine sediments (<25 μm) with strong negative Ce anomaly and convex-type distribution pattern of REEs normalized with NASC. It is suggested that apatite grains, supplied abundantly from surface water during the time of Unit B formation with high paleo-productivity, had incorporated and concentrated 3 + REEs.

Geochemical and mineralogical characteristics in two-color core sediments from the Korea Deep Ocean Study (KODOS) area, northeast equatorial Pacific

At sites 89 and 90 of the Korea Deep Ocean Study (KODOS), located in the western part of the area between the Clarion and Clipperton fracture zones, the topmost sediment column can be divided into two layers by a sharp color boundary: an upper pale brown layer (Unit A) and a lower dark brown layer (Unit B). Geochemical and mineralogical properties in Units A and B are clearly different across the color boundary, which can be interpreted to be a hiatus with an age gap of at least 3 Ma. The large gap in sediment ages results in an overall difference in sediment properties between Units A and B. That is, older Unit B sediment is higher in smectite contents, more severe in fossil dissolution, and lower in POC contents, commonly due to prolonged diagenesis. Disappearance of the coarse mode (50–60 μm) of the size distribution in Unit B is a result of prolonged dissolution of siliceous fossils. However, other phenomena occurring just below the color boundary (the most severe dissolution of fossils, the most frequent occurrence of coarse-grained micronodules and smectite aggregates, maximum value of metals (Mn, Cu, Ni), and increased water contents) can be explained by the active stirring of bottom sediments by intensified paleo-bottom currents present during the hiatus. That is, turbulence as well as winnowing action caused by the paleo-currents had, respectively, accelerated the dissolution of siliceous fossils and the concentration of coarse grains at the hiatus. In addition, micronodule formation was promoted by the efficient formation of oxygen-depleted micro-environments around in-situ fauna remains, which were buried efficiently by increased reworking and resedimentation of bottom sediments by the paleo-current activity. Meanwhile, increases in metal and water contents just below the color boundary are the results of the concentration of micronodules enriched in metals and probable formation of ‘woodpile’ fabric by abundant spicules and spines, respectively. Active stirring of bottom sediments by the intensified paleo-bottom currents as well as the large gap in sediment age between Units A and B are mostly responsible for the vertical variations of geochemical and mineralogical properties in two-color core sediments.

Sedimentary processes and manganese nodule formation in the Korea Deep Ocean Study (KODOS) area, western part of Clarion-Clipperton fracture zones, northeast equatorial Pacific

In the southern part of the Korea Deep Ocean Study (KODOS) area, the western part of the Clarion-Clipperton fracture zones, abundant nodules occur in the Oligocene to Miocene radiolarian-bearing smectitic clay. The nodules are generally concentrated in patchy pavements (more than 5 kg/m2) on the hilly seafloor with sediment waves. They are either rare or abundant on the seamounts and are generally rare in the abyssal plain. The nodules can be classified into three types based on distinct surface texture. The S-type nodules occur in intensely bioturbated sediment of the abyssal hill and seamount areas. In the abyssal plain, the R-type nodules are dominant, embedded within the topmost Quaternary sediment layer. In the southeastern part where Pliocene sediment occurs, they are in an incipient stage of growth. The S-type nodules are rich in Fe and Co in columnar structures of δ-MnO2, whereas the R-types contain abundant Mn, Ni, Cu, and Zn in dendritic and massive 10Å-manganate layers. The T-type nodules occur together with either the R- or S-type, showing intermediate composition. Regardless of the type and shape, the bottoms of nodules contain more abundant Mn, Ni, Cu, Zn, and 10Å-manganate than the tops. As the MnFe ratio increases in the nodules, the abundance of Ni, Cu, and Zn increases up to a constant value (about 11% of Mn) southward. In the underlying sediment, however, it decreases northward. Manganese and these minor metals are concentrated in the lowermost Tertiary sediment as much as 2 to 3 times than those in the topmost sediment layer which is intensely bioturbated. Iron and Co are relatively uniform downcore. Manganese, Ni, and Cu are abundant in micronodules, whereas Fe is concentrated in smectite.Redistributional processes of bottom currents seem to be most responsible for the (re)generation and concentration of nodules in patchy pavements, by excavating buried nodules. These processes result in an inverse relation of nodule abundance to the thickness of uppermost sedimentary layer which comprises the radiolarian ooze of Clipperton Formation. In the seamount areas, sediment slumping has also contributed to the concentration of nodules. The fragmentation of old nodules also enhances the nodule (re)generation. Activities of benthic animals cause the nodules to be lifted upward onto the seafloor mostly during the quiescent periods of bottom currents. The growth of nodules by resedimentation processes results in the large discrepancy in composition not only between the types but also the tops and bottoms, controlled by the burial rates of nodules within the topmost sediment layer where the diagenesis takes place. Diagenetic growth of nodules occurs by utilizing Mn and minor metals remobilized from micronodules during biomixing and decomposition of organic materials within Tertiary sediment. Nodule growth is more active southward toward the equator. Latitudinal variations of nodule size, distribution, abundance, and composition result from the change in surface water productivity and the timing of nodule nucleation as the Pacific plate migrates northwestward.