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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. The Arctic Ocean is experiencing rapid environmental changes due to accelerated warming, a decline in sea ice coverage, and an increase in river discharge from Arctic rivers. However, it is not clear how these environmental changes affect the Arctic carbon cycle, particularly the quality and quantity of dissolved organic carbon (DOC). In this study, we used physical, chemical, and biological hydrographic datasets obtained from the western Arctic Ocean during the summer of 2018 and distinguished riverine and marine DOC from bulk DOC to clearly understand their distributions and utilization. The spatial distributions of riverine and marine DOC showed clear distinctions in their distributions between the Chukchi Borderland (CBL)/northern Chukchi Sea (NCS) and East Siberian Sea (ESS)/Mendeleyev Ridge (MR) regions. The high riverine DOC concentration in the CBL/NCS region was associated with the regional characteristics, including the accumulation of freshwater, strong stratification, and a longer residence time. On the other hand, anomalously high primary production was observed in the ESS/MR region, resulting in the large contribution of marine DOC. Our results highlight that the regional characteristics of water properties in the study region exerted significant influences on the spatial distributions of riverine and marine DOC. Riverine and marine dissolved organic carbon (DOC) were distinguished using hydrographic datasets obtained from the western Arctic OceanSpatial distribution of riverine DOC showed higher abundance in the Chukchi Borderland and the northern Chukchi SeaAnomalously high primary production by the upwelling event enhanced marine DOC production in the East Siberian shelf/slope region Riverine and marine dissolved organic carbon (DOC) were distinguished using hydrographic datasets obtained from the western Arctic Ocean Spatial distribution of riverine DOC showed higher abundance in the Chukchi Borderland and the northern Chukchi Sea Anomalously high primary production by the upwelling event enhanced marine DOC production in the East Siberian shelf/slope region

Mesozooplankton play a crucial role as primary or secondary consumers in Arctic ecosystems and are sensitive indicators of environmental changes. This research is the first comprehensive Arctic zooplankton study covering the area ranging from the southern Chukchi Sea (SCS) and the northern Chukchi Sea (NCS) to the East Siberian Sea (ESS). Mesozooplankton samples were collected at 151 stations in the western Arctic Ocean each August from 2016 to 2020. The mesozooplankton abundance of the study area ranged from 9 to 6,172 ind. m−3, and the predominant group was copepods at 7–3,866 ind. m−3, of which Pseudocalanusspp. and Calanus glacialiswere the most abundant copepods. In the SCS, small copepods and meroplankton, such as Pseudocalanusspp., Cirripedia larvae, Echinodermata larvae, and Centropages abdominaliswere the predominant taxa. Especiallyin 2019, C. abdominalisdominated over meroplankton when water temperatures were high (maximum 12.5°C; sea surface temperature, SST). In the NCS and ESS, C. glacialis, Pseudocalanusspp., Metridia longa, Oithona similis, Parasagitta elegans, and Calanus hyperboreuswere abundant. The distributions and structures of mesozooplankton communities indicated variability over large spatial scales in the western Arctic waters because of variations in multiple factors, such as water temperature, salinity, and sea ice; however, geographical effects cannot be ignored even during alterations in the physical properties. Our results suggest that these variable patterns of mesozooplankton communities fluctuate horizontally from south to north as warming progresses on a regional bathymetric basis, and can be used to infer the fate of mesozooplankton communities in the study area. Zooplankton play a crucial role as consumers in Arctic ecosystems and are sensitive indicators of environmental changes. This research is the first comprehensive Arctic zooplankton study from the southern Chukchi Sea to East Siberian Sea. Here, we evaluated zooplankton community studies in the western Arctic Ocean from 2016 to 2020. The most dominant zooplankton group was copepods, among which Pseudocalanusspp. and Calanus glacialiswere the most abundant copepods. In the SCS, small copepods and meroplankton, such as Pseudocalanusspp., Cirripedia larvae, Echinodermata larvae, and Centropages abdominaliswere the predominant taxa. Especiallyin 2019, C. abdominalisdominated over meroplankton when water temperatures were high (maximum 12.5°C, sea surface temperature). In the northern Chukchi Sea and East Siberian Sea, C. glacialis, Pseudocalanusspp., Metridia longa, Oithona similis, Parasagitta elegans, and Calanus hyperboreuswere abundant. The distributions and structures of mesozooplankton communities indicated variability over large spatial scales in the western Arctic waters because of variations in multiple factors, such as water temperature, salinity, and sea ice; however, geographical effects cannot be ignored even during alterations in the physical properties. Future zooplankton communities in this area are expected to fluctuate horizontally from south to north due to changes in various factors depending on regional depth variation. This is the first comprehensive Arctic zooplankton study from the Chukchi Sea to the East Siberian SeaWater temperature, salinity, and depth have been shown to possess a significant effect on the community structure of the mesozooplanktonPatterns of interannual mesozooplankton communities have been fluctuated horizontally from south to north on a regional bathymetric basis This is the first comprehensive Arctic zooplankton study from the Chukchi Sea to the East Siberian Sea Water temperature, salinity, and depth have been shown to possess a significant effect on the community structure of the mesozooplankton Patterns of interannual mesozooplankton communities have been fluctuated horizontally from south to north on a regional bathymetric basis

Satellite observations and modeling data have suggested a significant increase in net primary production in the Arctic Ocean over the last decade due to retreating sea ice and the development of light availability caused by Arctic warming. Subsequently, under‐ice blooms (UIBs) are being recognized as an important phenomenon from the traditional perspective. However, the role of sea‐ice algae in UIBs is still unknown due to the limited availability of continuous observations. We analyzed data on primary producer‐derived lipid biomarkers from sinking particles collected over 1 year using time‐series sediment traps on the East Siberian Sea and Chukchi Sea slopes. Based on the seasonal changes in sympagic organic carbon derived from the data of the ice proxy (IP25) flux and pelagic biomarkers, such as highly branched isoprenoid trienes, epi‐brassicasterol and dinosterol, a UIB was identified in summer 2018 on the East Siberian Sea slope. Compared to the nutrient distribution on the Chukchi Sea slope, the UIB on the East Siberian Sea slope might have been triggered by the nutrient supply. The estimated flux‐weighted mean sympagic organic carbon value measured during the UIB period (May−August) was 1.04 mg m−2d−1on the East Siberian Sea slope, approximately five times greater than recorded that on the Chukchi Sea slope (0.23 mg m−2d−1) during the same period. Our findings suggest that the importance of sea‐ice algae as primary producers has increased as the UIB phenomenon has become more important in the Arctic Ocean and that sea‐ice environments face changes due to Arctic warming. The production of phytoplankton in the Arctic Ocean is dramatically increasing due to sea‐ice losses caused by Arctic warming. This increase in production can also be observed in the production of phytoplankton living under sea ice. We determined the origins of these phytoplanktons through a chemical analysis of particles falling from the sea surface to the sea bottom in the Arctic Ocean. Considerable under‐ice phytoplanktonic growth caused by the nutrient supply was identified on the East Siberian Sea slope. In particular, the production of under‐ice phytoplankton on the East Siberian Sea slope was confirmed to increase by approximately five times compared to that measured on the Chukchi Sea slope during the high‐growth period (May−August). Our study suggests that under‐ice phytoplankton may play an increasingly important role as primary producers in the Arctic Ocean, a region in which sea‐ice environments face changes due to Arctic warming. Under‐ice blooms may be enhanced by the development of light availability and triggered by the nutrient supplyThe flux of ice‐related organic carbon during under‐ice blooms increased five times compared to that measured in nonbloom conditionsLipid biomarker analysis approach using sinking particles could be an important solution for understanding the under‐ice blooms Under‐ice blooms may be enhanced by the development of light availability and triggered by the nutrient supply The flux of ice‐related organic carbon during under‐ice blooms increased five times compared to that measured in nonbloom conditions Lipid biomarker analysis approach using sinking particles could be an important solution for understanding the under‐ice blooms

The centric diatom order Thalassiosirales includes all diatoms with a fultoportula (strutted process), a feature now recognized as a synapomorphy for the lineage. Within Thalassiosirales, Thalassiosirais perhaps the most taxonomically and morphologically diverse genus, and at least two distinct morphological groups have been recognized within it. Group “A” Thalassiosiraspecies, which include the type species, T. nordenskioeldii, have short inward and long outward extensions of the strutted processes and a labiate process on the valve mantle. Group “B” species have exceptionally long inward and reduced outward extensions of the strutted processes, and a labiate process on the valve face. We collected and cultured Thalassiosira ritscheri, which has a combination of group A and B characters. It has a labiate process on the valve face and reduced outward extensions of the strutted processes. We show for the first time that T. ritscherihas short inward, A-type extensions of the strutted processes. A phylogenetic interpretation of these conditions suggests a close relationship between T. ritscheriand the traditionally held group “B” species. Species diagnosed by the autapomorphic condition of a labiate process away from the valve mantle, including many group “B” Thalassiosiraspecies, are transferred into Shionodiscusgen. nov.

T.A. Klochkova, S.-H. Kang, G.Y. Cho, C.M. Pueschel, J.A. West andG.H. Kim. 2006. Biology of a terrestrial green alga, Chlorococcumsp. (Chlorococcales, Chlorophyta), collected from the Miruksazi stupa in Korea. Phycologia45: 349–358. DOI: 10.2216/04-58.1A terrestrial chlorophyte, Chlorococcumsp., was isolated from the stone walls of Miruksazi stupa, which is a national treasure of Korea. The alga was one of the dominant organisms contributing to biodeterioration of the monument and it grew extensively on the walls of the inner room of the stupa, which had been sealed for more than 5 yr before we started this experiment. Chlorococcumsurvived in darkness during that time as dormant, warty, thick-walled spores. The resting spores revived in freshwater medium and released numerous unicellular progeny, which were isolated into a unialgal culture. The isolate was subjected to 18S rDNA phylogenetic analysis as well as ultrastructure and life cycle studies. In addition, the effect of salinity stress was investigated using sterile enriched seawater as a medium. Chlorococcumsp. grew in seawater culture medium for more than 5 mo and reproduced by aplanospores.

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As Arctic warming accelerates, the underwater acoustic environment in the Arctic Ocean is rapidly changing. We present the first results of passive acoustic monitoring in the marginal ice zone of the East Siberian Sea (ESS). A high sea ice concentration (SIC) and seasonal variations in ice cover make the ESS an ideal region to verify how ambient sound levels respond to natural physical processes and anthropogenic activities during summer. Our observations show that the sound level in the ESS exhibits a strong negative correlation with SIC, and the sound level in September, which was higher than that in other months, was 16 dB higher than the annual average. This increase resulted from geophony and anthrophony with the reduction in the SIC, and sound level increased by 13 dB without anthrophony. Our results indicate that ambient sound level in the Arctic Ocean may increase as climate change accelerates sea ice melting. Arctic ambient noise is expected to increase by the dramatic retreat of sea ice coverage in recent years. We present the first study to validate the effects of both geophony and anthrophony on the ambient noise associated with the great reduction of sea ice in the East Siberian Sea (ESS), Arctic Ocean, one of the acoustically primitive places on Earth. ESS is the relatively quiet sea in the presence of solid sea ice compared to other places in the Arctic Ocean, whereas ambient noise level shows a clear seasonal variability, largely determined by sea ice conditions. During open water season, ambient noise level is highly increased showing 16 dB higher than the annual average. This increase results from geophony and anthrophony and the ambient sound level increased by 13 dB without Anthrophony. Our results indicate that Arctic ambient noise will be highly increased by the effect of geophonic and anthrophonic noise in the future as climate change accelerates sea ice melting. These observations are of sufficiently broad interest for the public as well as the scientific community since they provide vital scientific evidence to develop a mitigation strategy for marine ecology and marine pollution in the Arctic Ocean. The ambient sound level in the East Siberian Sea, showing a negative correlation with the sea ice concentration (SIC), is highest in SeptemberThe ambient sound level increased by 16 dB because of geophony and anthrophony with the reduction in the SICThe ambient sound level may increase with accelerated sea ice melting in the future The ambient sound level in the East Siberian Sea, showing a negative correlation with the sea ice concentration (SIC), is highest in September The ambient sound level increased by 16 dB because of geophony and anthrophony with the reduction in the SIC The ambient sound level may increase with accelerated sea ice melting in the future

C2Symmetric and meso-iodo hydroxy ammonium chlorides generated from 2and 5have been cyclized under basic conditions to produce various heterocycles chemoselectively, which comprise tetrahydrofurans 7and 19, piperidines 13, 15and 21, and pyrrolidines 17and 18.

Atlantic‐origin cold saline water has previously not been considered an important contributor to the nutrient supply in the Pacific Arctic due to the effective insulation by the overlying Pacific‐origin waters that separate the surface mixed layer from the deeper Atlantic Water. Based on hydrographic observations in the northwestern Chukchi Sea from 2015 to 2017, we demonstrate that the intrusion of Atlantic‐origin cold saline water into the halocline boundary between Pacific and Atlantic‐origin waters in 2017 lifted Pacific‐origin nutrients up to the surface layer. We find that the cyclonic atmospheric circulation in 2017 was considerably strengthened, leading to lateral intrusions of two bodies of cold halocline water from the Eurasian marginal seas into the northwestern Chukchi Sea. Our results reveal that the intrusions of cold halocline waters caused unprecedented shoaling of the nutricline and anomalously high surface phytoplankton blooms in typically highly oligotrophic surface waters in the region during summer. Nutrient depletion, especially nitrogen, in Arctic surface waters during the summer is common due to biological uptake and intense stratification caused by sea ice melting and riverine water inputs, which restricts the upward mixing of nutrients into the euphotic zone. Although Atlantic‐origin cold saline water has previously not been considered an important contributor to the nutrient supply in the Pacific Arctic, the results presented here show that the intrusion of Atlantic‐origin cold saline water into the halocline boundary layer between Pacific and Atlantic‐origin waters in the summer of 2017 was an essential mechanism responsible for transporting Pacific‐origin nutrients to the surface layer, leading to anomalously high surface phytoplankton blooms in typically highly oligotrophic surface waters in the northwestern Chukchi Sea. The nutricline shoaling by an intrusion of Atlantic‐origin cold saline water was observed in the northwestern Chukchi Sea in 2017Pacific‐origin nutrients were lifted up to the surface layer by the intrusion of Atlantic‐origin cold saline waterThe enhanced cyclonic ocean circulation triggered a pronounced transport of Atlantic‐origin cold saline water to the western Arctic Ocean The nutricline shoaling by an intrusion of Atlantic‐origin cold saline water was observed in the northwestern Chukchi Sea in 2017 Pacific‐origin nutrients were lifted up to the surface layer by the intrusion of Atlantic‐origin cold saline water The enhanced cyclonic ocean circulation triggered a pronounced transport of Atlantic‐origin cold saline water to the western Arctic Ocean

The zooplankton community composition in the Pacific Arctic Ocean depends heavily on the sea ice and hydrodynamic conditions. The calanoid copepod Calanus hyperboreusis a dominant Arctic zooplankton, but its diet sources in the Pacific Arctic are unclear. C. hyperboreusindividuals were collected in the northern Chukchi Sea (NCS) and the northern‐East Siberian Sea (NESS), which display contrasting chlorophyll abundance and sea ice concentration in summer 2018. Nitrogen isotopes of individual amino acid and fatty acid compositions were measured to determine its trophic level (TL) and dominant diet. C. hyperboreuscollected in the NCS had higher TL values (3.0 ± 0.2) and a relatively low proportion of C20:5(n‐3). In the NESS, C. hyperboreushad lower TL values (2.7 ± 0.2) and a larger percentage of C20:5(n‐3), suggesting a greater proportion of diatoms in its diet. Spatial TL variations of C. hyperboreusbetween the NCS and NESS may be caused by variations in phytoplankton composition (micro‐phytoplankton vs. nano‐ and picophytoplankton) as a result of surface seawater stratification triggered by the inflow of sea ice meltwater as well as summer Bering Sea water through the Bering Strait. These results suggest that the filter‐feeding copepod C. hyperboreuscould be a useful indicator to understand trophic dynamics in zooplankton food web. The Pacific region of the Arctic Ocean experiences different annual volumes of freshwater inflow, resulting in changes to its water‐mass structure. In 2018, we harvested Calanus hyperboreus, a dominant Arctic zooplankton, from the northern Chukchi Sea (NCS) and northern‐East Siberian Sea (NESS). Sea ice concentrations and phytoplankton abundance varied between the regions. We analyzed the fatty acid composition and amino acid nitrogen isotope ratios to determine its diet sources and trophic dynamics, respectively. We found that C. hyperboreuscollected in the NCS occupied higher trophic levels and had a low proportion of diatom‐marker fatty acids. In contrast, in the NESS, C. hyperboreusoccupied lower trophic levels and had a larger percentage of diatom‐marker fatty acids, suggesting diatom accounted for a large portion of its diet in the NESS compared with the NCS. Analysis of amino acid nitrogen isotope and fatty acid composition of C. hyperboreusrevealed a shift in trophic levels and diets, respectively. The trophic level of Calanus hyperboreuswas correlated with the proportion of fatty acid marker of diatom between two contrasting areasThe likely driver of this was variations in phytoplankton community related to stratification caused by sea ice meltwater inflow in summerC. hyperboreuscould be an indicator organism to understand trophic dynamics in zooplankton food web in the Arctic Ocean The trophic level of Calanus hyperboreuswas correlated with the proportion of fatty acid marker of diatom between two contrasting areas The likely driver of this was variations in phytoplankton community related to stratification caused by sea ice meltwater inflow in summer C. hyperboreuscould be an indicator organism to understand trophic dynamics in zooplankton food web in the Arctic Ocean

Phytoplankton in the Arctic Ocean are subject to nitrogen limitation in the summer, however, how severely the nitrogen stress affects phytoplankton physiology remains largely unknown. In the summers of 2015–2018, we examined the distribution of phytoplankton photophysiological properties across two contrasting regions of the Arctic Ocean with distinctly different levels of nitrogen availability in the upper water column. We quantified the extent of nitrogen stress using a highly sensitive fluorescence induction and relaxation system to obtain continuous underway measurements and via discrete sample analyses of phytoplankton physiology, as well as nutrient enrichment incubations. The results revealed vast regions in the Chukchi Sea where phytoplankton photosynthesis was severely nitrogen‐stressed. Thereby, the maximum quantum yield of photochemistry in photosystem II showed only a small decrease (12 ± 9%) relative to its nutrient‐replete values, while the maximum photosynthetic electron transport rates under saturating irradiance were impaired to a greater extent (40 ± 17%). This phytoplankton photosynthesis response is indicative of a severe nitrogen limitation, which results in dramatic reduction in growth and net primary production rates. Nutrient enrichment incubations also revealed a marked increase in large‐size phytoplankton growth (>10 μm) after the nitrogen stress was alleviated, suggesting that the larger cells were more susceptible to nitrogen stress. These results are important for understanding how regional nitrogen fluxes control variability in the primary production and phytoplankton community structure and how these processes might change with rapid climate changes in the Arctic Ocean. Nutrient availability is the main bottom‐up controls of phytoplankton physiology and growth in the upper ocean. The distribution of nutrient limitation in the global ocean varies greatly in space and time, so phytoplankton responses to this factor are essential for understanding the marine ecosystem. Although nitrogen limitation was previously shown in the Arctic Ocean in the summer, how nitrogen stress affects phytoplankton physiology remains largely unknown. This study investigates, with high spatial resolution, the distribution of phytoplankton physiological status and quantifies the effects of nitrogen stress in the western Arctic Ocean. Our results revealed severe nitrogen limitation in the summer that results in dramatic reduction in growth and net primary production in this region of the ocean. Therefore, alterations in nitrogen fluxes along with climate change in the Arctic Ocean would be important for controlling phytoplankton growth and primary production in this region. Regional nitrogen availability in the Arctic Ocean is an important factor determining the physiological status of phytoplanktonSevere nitrogen limitation reduces gross photosynthetic rates of phytoplankton in the western Arctic Ocean in summer by approximately 40%Large‐sized phytoplankton are more susceptible to nitrogen stress in the Arctic Ocean

Enantioselective intramolecular iodoetherification of disubstituted γ-hydroxyalkenes has been intended using NIS in the presence of 0.2 equivalents of (R)-Binol-Ti(IV) complex to procure the corresponding tetrahydrofurans in up to 65% ee.