https://repository.kopri.re.kr/handle/201206/11898 Wed, 22 Apr 2026 08:02:46 GMT 2026-04-22T08:02:46Z https://repository.kopri.re.kr/handle/201206/13982 Title: Changes in Arctic Halocline Waters Along the East Siberian Slope and in the Makarov Basin From 2007 to 2020 Authors: Bertosio, Cecilia; Provost, Christine; Athanase, Marylou; Sennechael, Nathalie; Garric, Gilles; Lellouche, Jean-Michel; Kim, Joo-Hong; Cho, Kyoung-Ho; Park, Taewook Abstract: The evolution of halocline waters in the Makarov Basin and along the East Siberian continental slope is examined by combining drifting platform observations, shipborne hydrographic data, and simulations from a global operational physical model from 2007 to 2020. From 2012 onwards, relatively shallow and cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian continental slope. Their eastward extent abruptly shifted from 155°E to 170°E in early 2012, stabilized at 170°E until the end of 2015, then gradually advanced to reach the western Chukchi Sea in 2017. Such eastward progression led to a strengthening of the associated boundary current and to the shedding of mesoscale eddies of cold Atlantic-derived waters into the lower halocline of the Makarov Basin in September 2015 and near the East Siberian continental slope in November 2017. Additionally, active mixing between upwelled Atlantic Water and shelf water formed dense warm water supplying the Makarov Basin lower halocline. The increasing contribution from Atlantic-derived waters into the lower halocline along the East Siberian continental slope and in the Makarov Basin led to a weakening of the halocline, which is characteristic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime may now extend toward the Amerasian Basin. Thu, 01 Sep 2022 00:00:00 GMT https://repository.kopri.re.kr/handle/201206/13982 2022-09-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/14068 Title: Spatial dynamics of active microeukaryotes along a latitudinal gradient: Diversity, assembly process, and co-occurrence relationships Authors: Xu, Dapeng; Kong, Hejun; Yang, Eun-Jin; Wang, Ying; Li, Xinran; Sun, Ping; Jiao, Nianzhi; Lee, Youngju; Jung, Jinyoung; Cho, Kyoung-Ho Abstract: Recent global warming is profoundly and increasingly influencing the Arctic ecosystem. Understanding how microeukaryote communities respond to changes in the Arctic Ocean is crucial for understanding their roles in the biogeochemical cycles of nutrients and elements. Between July 22 and August 19, 2016, during cruise ARA07, seawater samples were collected along a latitudinal transect extending from the East Sea of Korea to the central Arctic Ocean. Environmental RNA was extracted and the V4 hypervariable regions of the reverse tran- scribed SSU rRNA were amplified. The sequences generated by high throughput sequencing were clustered into zero-radius OTUs (ZOTUs), and the taxonomic identities of each ZOTU were assigned using SINTAX against the PR2 database. Thus, the diversity, community composition, and co-occurrence networks of size fractionated microeukaryotes were revealed. The present study found: 1) the alpha diversity of pico- and nano-sized microeukaryotes showed a latitudinal diversity gradient; 2) three distinct communities were identified, i.e., the Leg-A, Leg-B surface, and Leg-B subsurface chlorophyll a maximum (SCM) groups; 3) distinct network structure and composition were found in the three groups; and 4) water temperature was identified as the pri- mary factor driving both the alpha and beta diversities of microeukaryotes. This study conducted a compre- hensive and systematic survey of active microeukaryotes along a latitudinal gradient, elucidated the diversity, community composition, co-occurrence relationships, and community assembly processes among major micro- eukaryote assemblages, and will help shed more light on our understanding of the responses of microeukaryote communities to the changing Arctic Ocean. Thu, 01 Sep 2022 00:00:00 GMT https://repository.kopri.re.kr/handle/201206/14068 2022-09-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/14093 Title: Spatial Distributions of Riverine and Marine Dissolved Organic Carbon in the Western Arctic Ocean: Results From the 2018 Korean Expedition Authors: Jung, Jinyoung; Lee, Youngju; Cho, Kyoung-Ho; Yang, Eun Jin; Kang, Sung-Ho Abstract: Seasonal primary production and river discharge increases in the Arctic Ocean exert a significant influence on the dissolved organic carbon (DOC) cycle. To improve our knowledge of the spatial heterogeneity of DOC source and concentration in the rapidly changing Arctic Ocean, we investigated the distributions of riverine and marine DOC in the western Arctic Ocean during the summer of 2018. Although the surface bulk DOC concentration indicated no clear distinction in its distribution between the Chukchi Borderland (CBL)/northern Chukchi Sea (NCS) and East Siberian Sea (ESS)/Mendeleyev Ridge (MR) regions, the estimated riverine DOC concentration(28 ± 4.2 μM C) and its contribution (40 ± 5.7 %) in the surface layer of the CBL/NCS region were higher than those (19 ± 5.6 μM C and 26 ± 8.5 %) in the ESS/MR region, which was attributed to the accumulation of freshwater, strong stratification, and a longer residence time in the CBL/NCS region. In contrast, although marine DOC was the dominant DOC component in both the CBL/NCS and ESS/MR regions, the higher marine DOC concentration (54 ± 8.1 μM C) and its contribution (73 ± 8.2 %) in the East Siberian shelf/slope region were consistent with high bacterial abundance, which was associated with extremely high surface phytoplankton blooms sustained by nutrient supply from the deep layer, suggesting that the supply of bioavailable DOC resulted in active bacterial activities. Overall, the spatial differences in water properties between the two regions had large influences on the regional distributions of riverine and marine DOC. Fri, 01 Jul 2022 00:00:00 GMT https://repository.kopri.re.kr/handle/201206/14093 2022-07-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/14095 Title: Ecological Responses of Core Phytoplankton by Latitudinal Differences in the Arctic Ocean in Late Summer Revealed by 18S rDNA Metabarcoding Authors: Joo, Hyoung Min; Kim, Kang Eun; Park, Joon Sang; Kim, Hyun-Jung; Yang, Eun Jin; Lee, Taek-Kyun; Cho, Kyoung-Ho; Jung, Jinyoung; Lee, Youngju; Kang, Sung-Ho; Jung, Seung Won Abstract: Limited information is available regarding the phytoplankton communities in the Arctic Ocean, especially in the Chukchi Sea. We conducted research cruises in the Arctic Ocean in the late summers of 2015, 2016, 2018, and 2019, and used 18S ribosomal DNA metabarcoding to examine the dynamic changes in core phytoplankton. Environmental factors were divided into three Groups: “surface layers in low latitude”, “subsurface chlorophyll maximum layers in low latitude”, and “high latitude.” The phytoplankton community was divided into two Groups. One Group, “the phytoplankton community in lower latitudes affected by the Pacific Influx ”, comprised Dinophyta (56.33%), Bacillariophyta (22.28%), and Chlorophyta (20.77%), while the other Group, “the phytoplankton community in higher latitudes affected by the Arctic Sea ”, comprised Dinophyta (57.51%), Bacillariophyta (10.71%), and Chlorophyta (27.57%). The common phytoplankton taxa in Group of lower latitudes included 33 operational taxonomic units (OTUs) (99.04%), while the other Group included nine OTUs (98.80%). In these groups, OTUs #005 (Heterocapsa rotundata), #001 (Micromonas pusilla), and #003 (Chaetoceros gelidus) were core OTUs (>5%). These core OTUs were significantly different between the two Groups; OTU #001 and #003 were distributed at high relative abundance and rapidly increased at higher latitudes. OTU #005 showed a relatively high abundance at lower latitudes. Analysis of the indicator species revealed that 34 OTUs in lower latitudes and only one OTU (#003) in higher latitudes were observed to have a strong value of >0.8. Our results indicate that core phytoplankton taxa and community structures by latitudinal differences are highly dependent on different water masses and show their dynamic ecological responses to extreme environmental conditions. Wed, 29 Jun 2022 00:00:00 GMT https://repository.kopri.re.kr/handle/201206/14095 2022-06-29T00:00:00Z