https://repository.kopri.re.kr/handle/201206/15717 2026-04-07T16:03:30Z https://repository.kopri.re.kr/handle/201206/16466 Title: Genesis of shallow-water manganese nodules with uniquely high Mn/Fe ratios Authors: Koo Hyo Jin; Cho Hyen Goo; Jin, Young Keun; Lee Dong-Hun; Kim Ji-Hoon; Rhee, Tae Siek; Hong, Jong Kuk; Lee Sung Keun Abstract: While manganese (Mn) nodules are authigenic metal concretions that form predominantly on deep-sea seafloor, they have also been found along shallow seafloors. The formation environments of these nodules - deep sea vs. shallow water - often result in distinct chemical and morphological characteristics. As Mn is one of the essential components of energy-storing technologies, assessing the proper estimation of Mn and metal contents in both deep-and shallow-water Mn nodules is critical. It has been found that the Mn content of shallow-water nodules is often lower than that from deep-sea environments. Here, we report the discovery of shallow-water Mn nodules with exceptionally high Mn/Fe ratios on the continental slope of the East Siberian Sea, Arctic Ocean. Despite their shallow-water origin, Mn nodules show morphological and chemical characteristics that are typically unique to deep-sea nodules. These distinctive features, including exceptionally high Mn/Fe ratios, may reflect suboxic diagenesis and the preferential remobilization and re-precipitation of Mn from the adjacent continental shelf. The formation of high Mn/Fe nodules may reflect unique ocean circulation patterns that provided oxygenated bottom waters to the study area. Particularly, Pacific Water entering through the Bering Strait, which overlaps with the nodule formation depth (160-240 m) and is enriched in dissolved oxygen, could facilitate Mn-rich nodule growth under suboxic diagenetic conditions since the Holocene. Shallow-water Mn nodules with uniquely high Mn/Fe ratios may offer a novel paleo-environmental proxy for reconstructing paleohydrology and biogeochemical evolutions in shallow marine environments. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 2025-12-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/16089 Title: Subsurface Methane Accumulation in the Beaufort Sea Driven by Pelagic Processes: A Mechanistic Modeling Approach Authors: Kwon, Young Shin; Rhee, Tae Siek Abstract: Observed subsurface methane (CH4) maxima in the Arctic Ocean challenge traditional benthic-centered models. Here, we integrate a water-column CH4 module into a coupled biogeochemical model to investigate methane cycling at contrasting coastal and offshore sites in the Beaufort Sea. Baseline simulations underestimated observed subsurface CH4 peaks, but introducing additional source terms―including lateral transport, zooplankton fecal methanogenesis, organic carbon decomposition, and methylphosphonate breakdown―substantially improved model performance. Results reveal that distinct processes control CH4 accumulation across regions: both lateral transport and biological production (via zooplankton) contribute to shelf CH4 dynamics, with physical transport emerging as the dominant process, while zooplankton fecal pellet production and bacterial activity govern offshore CH4 accumulation. Seasonal variability is tightly linked to primary production, stratification, and vertical mixing. Our findings underscore the critical role of non-benthic CH4 sources in shaping Arctic methane distributions, with implications for projecting CH4 fluxes under future climate change. 2025-09-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/16124 Title: Comparative assessment of preservation methods for major nutrients in polar seawater Authors: Kim, Mi Seon; Choi, Man Sik; Rhee, Tae Siek Abstract: Major nutrients-nitrate, phosphate, and silicate-are fundamental building blocks of marine biomass. To understand the flow of material and energy in the ecosystem, it is essential to accurately quantify nutrients concentrations. When shipboard analysis is not possible, seawater samples must be preserved without altering their contents. In this study, we investigated a range of commonly used preservation methods, including filtration, chemical poisoning with HgCl2, and freezing at -20 degrees C or - 80 degrees C without pre-treatment, all aimed at minimizing biological activities. We also evaluated the effects of sample storage periods and thawing periods required before analysis in freezing treatments to determine their impact on nutrients contents. Using four different statistical methods, we assessed a total of 19 experiments to identify the most effective preservation method. Comparison between filtered and untreated seawater samples showed no detectable effect on the preservation by filtration. Deviations from shipboard measurement were detected in samples stored in a freezer, even at -80 degrees C. On the other hand, the nutrient content in the poisoned samples remained virtually intact. The deficiency in nutrient content observed during prolonged freezing and thawing or storage in a refrigerator at 4 degrees C, compared to shipboard measurements, aligns with the Redfield relationship reported in the Arctic Ocean, suggesting that biological activities occurred either within brine channels during freezing, during refrigerated storage, or both, likely due to viable cold-adapted microbes. Although our findings are based on polar seawater samples, potential biological activities during storage and post-treatment should be carefully examined in the other oceanic regions. 2025-07-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/16590 Title: Comparative assessment of preservation methods for major nutrients in polar seawater Authors: Kim, Mi Seon; Choi, Man Sik; Rhee, Tae Siek Abstract: Major nutrients―nitrate, phosphate, and silicate―are fundamental building blocks of marine biomass. To understand the flow of material and energy in the ecosystem, it is essential to accurately quantify nutrients concentrations. When shipboard analysis is not possible, seawater samples must be preserved without altering their contents. In this study, we investigated a range of commonly used preservation methods, including filtration, chemical poisoning with HgCl2, and freezing at -20°C or -80°C without pre-treatment, all aimed at minimizing biological activities. We also evaluated the effects of sample storage periods and thawing periods required before analysis in freezing treatments to determine their impact on nutrients contents. Using four different statistical methods, we assessed a total of 19 experiments to identify the most effective preservation method. Comparison between filtered and untreated seawater samples showed no detectable effect on the preservation by filtration. Deviations from shipboard measurement were detected in samples stored in a freezer, even at -80°C. On the other hand, the nutrient content in the poisoned samples remained virtually intact. The deficiency in nutrient content observed during prolonged freezing and thawing or storage in a refrigerator at 4°C, compared to shipboard measurements, aligns with the Redfield relationship reported in the Arctic Ocean, suggesting that biological activities occurred either within brine channels during freezing, during refrigerated storage, or both, likely due to viable cold-adapted microbes. Although our findings are based on polar seawater samples, potential biological activities during storage and post-treatment should be carefully examined in the other oceanic regions. 2025-07-01T00:00:00Z