https://repository.kopri.re.kr/handle/201206/11899 2026-04-05T19:31:00Z https://repository.kopri.re.kr/handle/201206/16410 Title: Holocene paleoenvironmental change based on diatom records from the continental shelf of the Chukchi Sea in the Arctic Ocean Authors: Bak Young-Suk; Nam, Seung-il Abstract: Diatom assemblages from ARA2B-1A taken in the Chukchi Sea shelf were analyzed to reconstruct paleoenvironmental changes during the last 10 ka BP. The main factors controlling the distribution of diatom in the Chukchi Sea are the relatively warm and nutrient-rich Pacific water inflow after the opening of the Bering Strait. Based on the selected diatoms, three diatom assemblage zones are identified. The diatom assemblage zone I shows a rare or very low abundance, which corresponds to the early Holocene (10-8 ka BP). The diatom assemblage zone II corresponds to the mid-to-late Holocene (8-2 ka BP). It is a seasonal sea-ice environment with relatively abundant diatom valves and Chaetoceors resting spores, as well as sea-ice species, cold-water species, coastal species, and upwelling species. The diatom assemblage zone III corresponds to the late Holocene (2-0 ka BP), and the the sea-ice species generally decreased compared to zone II, while the coastal species Paralia sulcata occurred abundantly. In particular, the Thalassiosira antarctica, a cold-water species, increased distinctly during this time interval. After similar to 2 ka BP, T. antarctica rapidly increased while sea-ice species rarely appeared, indicating limited open-marine environments. In particular, after 1 ka BP, T. antarctica decreased while the sea-ice species increased, suggesting that the sea-ice increased again before the recent global warming of the Arctic, the late Holocene. 2024-01-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/13761 Title: Impact of High Methane Flux on the Properties of Pore Fluid and Methane-Derived Authigenic Carbonate in the ARAON Mounds, Chukchi Sea Authors: Kim, Ji-Hoon; Park, Myong-Ho; Lee, Dong-Hun; Minami, Hirotsugu; Jin, Young-Keun; Hachikubo, Akihiro; Hur, Jin; Ryu, Jong-Sik; Kang, Moo-Hee; Jang, Kwangchul; Kida, Masato; Seo, Yongwon; Chen, Meilian; Hong, Jong Kuk; Song, Yungoo; Park, Sanghee Abstract: We investigated the pore fluid and methane-derived authigenic carbonate (MDAC) chemistry from the ARAON Mounds in the Chukchi Sea to reveal how methane (CH4) seepage impacts their compositional and isotopic properties. During the ARA07C and ARA09C Expeditions, many in situ gas hydrates (GHs) and MDACs were found near the seafloor. The fluid chemistry has been considerably modified in association with the high CH4 flux and its related byproducts (GHs and MDACs). Compared to Site ARA09C-St 08 (reference site), which displays a linear SO4 2- downcore profile, the other sites (e.g., ARA07C-St 13, ARA07C-St 14, ARA09C-St 04, ARA09C-St 07, and ARA09C-St 12) that are found byproducts exhibit concave-up and/or kink type SO4 2- profiles. The physical properties and fluid pathways in sediment columns have been altered by these byproducts, which prevents the steady state condition of the dissolved species through them. Consequently, chemical zones are separated between bearing and nonbearing byproducts intervals under non-steady state condition from the seafloor to the sulfate-methane transition (SMT). GH dissociation also significantly impacts pore fluid properties (e.g., low Cl- , enriched δD and δ18O). The upward CH4 with depleted δ13C from the thermogenic origin affects the chemical signatures of MDACs. The enriched δ18O fluid from GH dissociation also influences the properties of MDACs. Thus, in the ARAON Mounds, the chemistry of the fluid and MDAC has significantly changed, most likely responding to the CH4 flux and GH dissociation through geological time. Overall, our findings will improve the understanding and prediction of the pore fluid and MDAC chemistry in the Arctic Ocean related to CH4 seepage by global climate change. 2022-07-13T00:00:00Z https://repository.kopri.re.kr/handle/201206/13904 Title: Complete genome sequence of Rhodoferax sp. PAMC 29310 from a marine sediment of the East Siberian Sea Authors: Lee, Yung Mi; Park, Yerin; Kim, Heesoo; Shin, Seung Chul Abstract: Rhodoferax sp. PAMC 29310 was isolated from a surface marine sediment of the East Siberian Sea, Arctic. Wholegenome sequencing of the strain Rhodoferax sp. PAMC 29310 was achieved using PacBio RS II and Illumina platform. The resulting complete genome comprised of 4,593,249 base pairs (G + C content of 58.0%) with a single chromosome, 4546 protein-coding genes, 57 tRNAs and 6 rRNA operons. A complete set of genes encoding the enzymes of glycolysis and citric acid cycle were identified. No genes encoding ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and nitrogenase reductase (nif) were present indicating that strain PAMC 29310 is not capable of fixing of carbon and nitrogen. PAMC 29310 genome contains genes for dissimilatory and assimilatory nitrate reduction. Gene encoding choline dehydrogenase enzyme which functions at the first step in the synthesis of betaine, one of the most effective osmoprotectants, was detected. In particular, among the genomes of the genus Rhodoferax strains, gene encoding nitrite reductase (nirK), which reduces nitrite to nitric oxide and tetA gene encoding tetracycline resistance protein involved in the resistance to tetracycline were identified only in the genome of Rhodoferax sp. PAMC 29310. As the first genome from the strain which was isolated from marine sediment in the genus Rhodoferax, investigation of physiological characteristics based on the complete genome sequences will help understand the adaptation of Rhodoferax sp. PAMC 29310 in the marine sediment. 2022-04-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/13762 Title: Assessing the impact of freshwater discharge on the fluid chemistry in the Svalbard fjords Authors: Kim, Ji-Hoon; Ryu, Jong-Sik; Hong, Wei-Li; Jang, Kwangchul; Joo, Young Ji; Lemarchand, Damien; Hur, Jin; Park, Myong-Ho; Chen, Meilian; Kang, Moo-Hee; Park, Sanghee; Nam, Seung-il; Lee, Yun Kyung Abstract: Changes in the cryosphere extent (e.g., glacier, ice sheet, permafrost, and snow) have been speculated to impact (bio) geochemical interactions and element budgets of seawater and pore fluids in Arctic regions. However, this process has rarely been documented in Arctic fjords, which leads to a poor systematic understanding of land-ocean interactions in such a warming-susceptible region. Here, we present the chemical and isotopic (δ18O, δD, δ11B, and 87Sr/86Sr) compositions of seawater and pore fluids from five fjords in the Svalbard archipelago. Compared to bottom seawater, the low Cl- concentrations and depleted water isotopic signatures (δ18O and δD) of surface seawater and pore fluids delineate freshwater discharge originating from precipitation and/or meltwater of the cryosphere (i.e., glacier, snow, and permafrost). In contrast, the high Cl- concentrations with light water isotopic values in pore fluids from Dicksonfjorden indicate a brine probably resulted from submarine permafrost formation during the late Holocene, a timing supported by the numerical simulation of dissolved Cl- concentration. The freshwater is influenced by the local diagenetic processes such as ion exchanges indicated by δ11B signatures as well as interactions with bedrock during fluid migration inferred from pore fluid 87Sr/86Sr ratios. The interactions with bedrock significantly alter the hydrogeochemical properties of pore fluids in each fjord, yielding spatiotemporal variations. Consequently, land-ocean interactions in combination with the hydrosphere-cryosphere-lithosphere are critical factors for understanding and predicting the hydrology and elemental cycling during global climate change periods in the past, present, and future of the Svalbard archipelago. 2022-02-19T00:00:00Z