• 방사성폐기물학회지
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• 제19권4호
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• pp.469-477
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• 2021

Safe storage of spent nuclear fuel in deep underground repositories necessitates an understanding of the long-term alteration of metal canisters and buffer materials. A small-scale laboratory alteration test was performed on metal (Cu or Fe) chips embedded in compacted bentonite blocks placed in anaerobic water for 1 year. Lactate, sulfate, and bacteria were separately added to the water to promote biochemical reactions in the system. The bentonite blocks immersed in the water were dismantled after 1 year, showing that their alteration was insignificant. However, the Cu chip exhibited some microscopic etch pits on its surface, wherein a slight sulfur component was detected. Overall, the Fe chip was more corroded than the Cu chip under the same conditions. The secondary phase of the Fe chip was locally found as carbonate materials, such as siderite (FeCO₃) and calcite ((Ca, Fe)CO₃). These secondary products can imply that the local carbonate occurrence on the Fe chip may be initiated and developed by an evolution (alteration) of bentonite and a diffusive provision of biogenic CO₂ gas. These laboratory scale results suggest that the actual long-term alteration of metal canisters/bentonite blocks in the engineered barrier could be possible by microbial activities.

• Ocean Science Journal
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• 제40권3호
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• pp.167-176
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• 2005

A time-series sediment trap was deployed at 1,034 m water depth in the eastern Bransfield Strait for a complete year from December 25, 1998 to December 24, 1999. About 99% of total mass flux was trapped during an austral summer, showing distinct seasonal variation. Biogenic particles (biogenic opal, particulate organic carbon, and calcium carbonate) account for about two thirds of annual total mass flux $(49.2\;g\;m^{-2})$, among which biogenic opal flux is the most dominant (42% of the total flux). A positive relationship (except January) between biogenic opal and total organic carbon fluxes suggests that these two variables were coupled, due to the surface-water production (mainly diatoms). The relatively low $\delta^{13}C$ values of settling particles result from effects on C-fixation processes at low temperature and the high $CO_2$ availability to phytoplankton. The correspondingly low $\delta^{l5}N$ values are due to intense and steady input of nitrates into surface waters, reflecting an unlikely nitrate isotope fractionation by degree of surface-water production. The $\delta^{l5}N$ and $\delta^{l3}C$ values of sinking particles increased from the beginning to the end of a presumed phytoplankton bloom, except for anomalous $\delta^{l5}N$ values. Krill and the zooplankton fecal pellets, the most important carriers of sinking particles, may have contributed gradually to the increasing $\delta^{l3}C$ values towards the unproductive period through the biomodification of the $\delta^{l3}C$ values in the food web, respiring preferentially and selectively $^{12}C$ atoms. Correspondingly, the increasing $\delta^{l5}N$ values in the intermediate-water trap are likely associated with a switch in source from diatom aggregates to some remains of zooplankton, because organic matter dominated by diatom may be more liable and prone to remineralization, leading to greater isotopic alteration. In particular, the tendency for abnormally high $\delta^{l5}N$ values in February seems to be enigmatic. A specific species dominancy during the production may be suggested as a possible and speculative reason.

• Ocean and Polar Research
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• 제44권2호
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• pp.139-145
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• 2022

Manganese nodules were recovered within the deep subseafloor sediments (118.22 mbsf) at Site U1371 during International Ocean Discovery Program (IODP) expedition 329 from the South Pacific Gyre (SPG). Because most manganese nodules exist on the seabed surface, nodules present in deep sediments are uncommon. Therefore, the growth origin of manganese nodules was identified through mineralogical and geochemical analyses. The manganese nodule was divided into the concentric layer outside the manganese region and the inner part of the phosphatized region consisting of manganese oxide minerals and carbonate fluorapatite (CFA) minerals, respectively. The two-dimensional element distribution analysis of Mn, Co, Ni, Sr and Cu, Zn with low Mn/Fe ratio confirmed that manganese nodules were formed predominantly by a hydrogenetic process and a biogenic process in certain manganese layers. As a result, the manganese nodule was continuously precipitated in SPG environments of oligotrophic open paleoocean conditions and rapidly buried with siliceous ooze sediments when the SPG changed to a eutrophic environment. It has been confirmed that manganese nodules found within deep subseafloor sediments could be used as a new proxy for the reconstruction of paleooceanographic conditions.

• 한국해양학회지:바다
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• 제13권3호
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• pp.200-209
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• 2008

2003년 7월부터 2005년 6월까지 약 24 개월 동안 북동태평양 대한민국 망간단괴 개발광구 내에 위치한 정점 KOMO(Korea Deep-Sea Environmental Study Long-Term Monitoring Station, $10^{\circ}30'N,\;131^{\circ}20'W$)에서 시계열 퇴적물 포집장치를 설치하여 물질 플럭스를 측정하였다. 약 4,960 m 수심에서 획득된 침강입자의 총질량 플럭스는 겨울(12월-2월)과 봄(3월-5월)에 높고, 여름(6월-8월)과 가을(9월-11월)에 낮은 뚜렷한 계절변동을 보였다. 생물기원 물질플럭스도 총질량 플럭스와 유사하게 뚜렷한 계절변동을 나타냈다. 특히, 겨울과 봄에 관측된 탄산염 플럭스는 여름과 가을보다 두 배가량 높게 측정되어, 다른 생물기원 구성성분들의 계절변동에 비해 가장 크게 나타났다. 심해저층에서 관측된 침강입자의 총질량 플럭스와 생물기원 물질플럭스는 표층 해양 일차 생산력의 계절변동을 반영하는 것으로 생각된다. 겨울과 봄에는 강한 바람의 영향으로 혼합층 아래로부터 영양염의 공급이 증가되어 일차생산력이 높아진 것으로 생각되며, 여름과 가을에는 바람의 약화와 강한 성층으로 인하여 영양염 공급이 약해져서 일차생산력이 감소한 것으로 판단된다. 침강입자의 총질량 플럭스와 생물기원 물질플럭스의 계절적 변동은 이전에 연구된 엘니뇨/라니냐와 같은 환경변화에 따른 물질플럭스의 변화보다 크게 나타났다. 따라서 북동태평양 적도지역에서 엘니뇨와 라니냐 같은 환경변화의 영향에 의한 해양 물질플럭스의 변화를 이해하기 위해서는 일반적인 계절적 변동을 정확하게 측정하여야 한다.

• Geomechanics and Engineering
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• 제22권2호
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• pp.173-185
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• 2020

Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

• Ocean and Polar Research
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• 제24권2호
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• pp.153-166
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• 2002

Particle fluxes were measured by using time-series sediment traps in the Bransfield Strait from December 27th, 1999 to December 26th, 2000. Total mass fluxes showed distinct seasonal variations with high fluxes in the austral summer and low fluxes in the austral winter at a 678m water depth in the eastern Bransfield Strait, while they were high only in January and fairly low in other months at a 960m water depth in the central Bransfield Strait. The reason that total mass fluxes occurred only in January at a 960m water depth in the central Bransfield Strait seems to be the strong current in the surface waters, which leads to a substantial amount of terrestrial materials and locally produced organic matter being advected away from the mooring site. Total mass fluxes were very high from January to October at a 1678m water depth in the eastern Bransfield Strait, while they were high only in January and February at a 1860m water depth in the central Bransfield Strait. The fact that total mass fluxes were higher at the deep water in the both sites than at the intermediate water depth may reflect that a substantial amount of terrestrial and organic materials are laterally transported by strong tidal current from the shallow environments to the deep basins.

• Ocean and Polar Research
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• 제42권1호
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• pp.33-47
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• 2020

The bulk and partition geochemistry was studied in two sediment cores collected from the axial valley of the north-central Fonualei Rift and Spreading Center (FRSC), Lau back-arc Basin, southwest Pacific. The sediments consist of mostly volcanic ash, although minor amounts of biogenic and other components were present in some intervals. The major element composition of bulk sediments recalculated to a carbonate-free basis was in good agreement with the magma compositions of the adjacent Tofua Arc and the FRSC, with only significant difference in Mn content. The enrichment of Mn and other associated elements (e.g. Cu, Co, Ni, and P) is attributed to hydrothermal input to the sediments, as evidenced by their significant partitioning in the non-detrital phases according to the partition geochemistry. Hydrogenetic and diagenetic inputs were assessed to be relatively insignificant. Estimated hydrothermal Mn fluxes during the Holocene ranged between 5.0 and 37.1 mg cm^-2 kyr^-1, with the higher values in younger sediments, suggesting enhanced hydrothermal activity. The hydrothermal Mn fluxes comparable to or higher than those reported from other spreading centers with strong hydrothermal activities may indicate the presence of unknown hydrothermal vent sites and/or topographic restriction on the dispersal of hydrothermal plumes in the northern part of the FRSC.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.407-409
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• 2006

Geochemical analyses carried out on samples collected from cores on and near the southern smit of Hydrate Ridge have advanced understanding by providing a clear contrast of the two major modes of marine gas hydrate occurrence. High concentrations (15%-40% of pore space) of gas hydrate occurring at shallow depths (0-40 mbsf) on and near the southern summit are fed by gas migrating from depths of as much as 2km within the accretionary prism. This gas carries a characteristic minor component of C2-C5 thermogenic hydrocarbons that enable tracing of migration pathways and may stabilize the occurrence of some structure II gas hydrate. A structure II wet gas hydrate that is stable to greater depths and temperatures than structure I methane hydrate may account for the deeper, faint second bottom simulating reflection (BSR2) that occurs on the seaward side of the ridge. The wet gas is migrating In an ash/turbidite layer that intersects the base of gas hydrate stability on the seaward side of and directly beneath the southern summit of Hydrate Ridge. The high gas saturation (>65%) of the pore space within this layer could create a two-phase (gas + solid) system that would enable free gas to move vertically upward through the gas hydrate stability zone. Away from the summit of the ridge there is no apparent influx of the gas seeping from depth and sediments are characterized by the normal sequence of early diagenetic processes involving anaerobic oxidation of sedimentary organic matter, initially linked to the reduction of sulfate and later continued by means of carbonate reduction leading to the formation of microbial methane.

• 자원환경지질
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• 제39권6호
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• pp.739-752
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• 2006

북동태평양 클라리온-클리퍼톤 균열대(Clarion-Clipperton Fracture Zone) 사이에 위치한 연구지역 퇴적물의 입도, 함수율, 입자 밀도, 전밀도, 공극비, 그리고 공극률 등 물리적 특성과 퇴적학적 변화요인을 파악하기 위하여 1999년부터 2002년까지 7회의 조사작업을 통해 연구지역 각 지점에서 다중주상시료채취기로 채취된 69개 표층퇴적물을 분석하였다. 연구지역 퇴적물은 원양성 적점토가 분포하는 북부지역(북위 16-17도), 생물기원의 규질 퇴적물이 분포하는 중부지역(북위 10-11도), 탄산질 퇴적물이 분포하는 남부지역(북위 5-6도)으로 구분되며, 퇴적물의 물리적 특성은 이들 퇴적물의 유형에 따라 뚜렷이 다른 특성을 보인다. 북부지역은 수층의 기초생산성이 낮고 육성기원 입자의 유입이 많으므로 입도는 세립질이며, 함수율이 낮은 특성을 보인다. 반면에 중부지역은 수층의 생산성이 높고 수심이 탄산염보 상심도보다 깊으므로 다공질이며 입자크기가 큰 생물기원 규질 입자의 유입이 높아 평균입도는 가장 조립질이며, 함수율이 매우 높다. 한편, 남부지역은 수심이 탄산염보상심도보다 얕으므로 수층으로부터 유입되는 탄산질 퇴적물이 용해되지 않고 지속적으로 퇴적되어 가장 낮은 함수율과 높은 밀도를 보인다. C-C지역 퇴적물의 물리적 특성과 연관된 주요 요인들은 적도부근 해역의 높은 생산성에 따른 생물기원 입자의 유입, 탄산염보상심도를 고려한 수심 수층 생산성에 비례하는 퇴적률, 대륙으로부터 바람에 의해 유입되는 육성기원 입자의 공급, 그리고 생물기원 퇴적입자의 용해 및 자생광물의 형성과 연관된 저층해수의 화학적 특성 등으로 판단할 수 있다.

• 자원환경지질
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• 제38권2호
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• pp.129-134
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• 2005

수중생물과 그 생물이 살았던 물과의 Sr 동위원소 조성은 크게 다르지 않으나, Pb 동위원소비는 Sr 동위원소와는 달리 생물과 그 생물이 살았던 물과 상이한 값을 보인다. 이 두 동위원소를 환경추적인자로 동시에 적용할 목적으로 담수에 사는 수중생물인 다슬기(Semisulcospira libertina) 껍질의 두 동위원소비를 측정하여 보았다. 하천수에 사는 다슬기 껍질의 Sr 동위원소비는 그들이 살았던 하천수의 동위원소비와는 같은 값을 보이지만, 채취지역에 따라서는 다른 값을 가진다. 하천수의 Sr 동위원소조성이 다른 것은 각 하천수의 기반암의 Sr 동위원소가 서로 다르기 때문으로 결국 하천수중의 Sr은 기반암으로부터 유래하고 다슬기 껍질의 Sr은 하천수에서 기인한 것으로 볼 수 있다. 반면에 Pb 동위원소비는 하천수와 다슬기 껍질이 서로 다른 값을 보이는 것은 하천수에 용해된 Pb이 다슬기가 흡수 가능한 Pb과는 다른 것으로 생각되며, 다슬기 껍질의 Pb 동위원소비는 강우의 Pb 동위원소비와 유사하다. 하천수에 용해된 Pb은 기반암에서 유래한 것이 아니라 토양 중에 집적된 대기기원의 Pb이 대부분인 것으로 생각된다.