High concentrations of exopolymeric substances in Arctic winter sea ice: implications for the polar ocean carbon cycle and cryoprotection of diatoms |
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| Authors: | C Krembs H Eicken K Junge J W Deming |
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| Institution: | 1. School of Oceanography, University of Washington, P.O. Box 357940, Seattle, WA, USA;2. Geophysical Institute, University of Alaska, Fairbanks, USA;1. Ministry of Education-Shanghai Key Laboratory of Children''s Environmental Health, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China;2. Department of Obstetrics and Gynecology, Shanghai Changhai Hospital, Shanghai, China;3. Institute of Biothermal and Technology, University of Shanghai for Science and Technology, Shanghai, China;1. Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstr. 15, 04318, Leipzig, Germany;2. Biogeochemistry Research Centre, Marine Institute, Plymouth, PL4 8AA, UK;3. Helmholtz Centre for Environmental Research - UFZ, Brückstraße 3a, 39114, Magdeburg, Germany;1. Department of Molecular Biology, Sejong University, 209 Neungdong-ro, Gunja-dong, Gwangjin-gu, Seoul 05006, Republic of Korea;2. Department of Chemistry, Sejong University, 209 Neungdong-ro, Gunja-dong, Gwangjin-gu, Seoul 05006, Republic of Korea;3. Department of Integrative Bioscience and Biotechnology, Sejong University, 209 Neungdong-ro, Gunja-dong, Gwangjin-gu, Seoul 05006, Republic of Korea;1. Vivarmor Nature, 18 C rue du Sabot, 22440, Ploufragan, France;2. Réserve naturelle nationale de la Baie de Saint-Brieuc, site de l’étoile, 22120, Hillion, France;3. Ifremer, Laboratoire Environnement et Ressources Bretagne nord, 38 rue du Port Blanc, 35800, Dinard, France;4. Laboratoire des Sciences de l''Environnement Marin (LEMAR), UMR 6539 CNRS/UBO/IRD/IFREMER, BP 70, 29280, Plouzané, France;5. Sorbonne Université, CNRS, Station Biologique de Roscoff, UMR7144, Place Georges Teissier, CS90074, 29688, Roscoff Cedex, France;6. Université de Rennes 1, BOREA, Muséum National d''Histoire Naturelle, Sorbonne Université, Université de Caen Normandie, Université des Antilles), Campus de Beaulieu, 35000, Rennes, France;7. Saint-Brieuc Agglomération Baie d’Armor, 5 rue du 71ème RI, 22000, Saint-Brieuc, France;1. Department of Environment and Energy, Sejong University, Seoul, 05006, South Korea;2. Department of Environmental Marine Sciences, Hanyang University, Ansan, Gyeonggi do, 15588, South Korea |
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| Abstract: | Exopolymeric substances (EPS) produced by microorganisms play important roles in various aquatic, porous, and extreme environments. Only recently has their occurrence in sea ice been considered. We used macroscopic and microscopic approaches to study the content and possible ecological role of EPS in wintertime fast ice near Barrow, Alaska (71°20′ N, 156°40′ W). Using Alcian blue staining of melted ice samples, we observed high concentrations of EPS in all samples examined, ranging from 0.79 to 7.71 mg xanthan gum equivalents (XGEQV) l−1. Areal conversions to carbon equivalents yielded 1.5−1.9 g C m−2 ice in March and 3.3−4.0 g C m−2 in May (when the ice was thicker). Although EPS did not correlate with macronutrient or pigment data, the latter analyses indicated ongoing or recent biological activity in the ice within temperature horizons of −11°C to −9°C and warmer. EPS correlated positively with bacterial abundance (although no functional relationship could be deduced) and with dissolved organic carbon (DOC) concentrations. Ratios of EPS/DOC decreased at colder temperatures within the core, arguing against physical conversion of DOC to EPS during freezing. When sea-ice segments were maintained at representative winter temperatures (−5°C,−15°C and −25°C) for 3−14 months, the total EPS content increased significantly at rates of 5−47 μg XGEQV l−1 d−1, similar to published rates of EPS production by diatoms. Microscopic images of ice-core sections at these very cold temperatures, using a recently developed non-invasive method, revealed diatoms sequestered in spacious brine pockets, intact autofluorescent chloroplasts in 47% of the (pennate) diatoms observed, and indications of mucus in diatom-containing pores. The high concentrations of EPS detected in these winter ice cores represent a previously unrecognized form of organic matter that may contribute significantly to polar ocean carbon cycles, not only within the ice but after springtime release into the water column. The EPS present in very high concentrations in the brine of these microhabitats appear to play important buffering and cryoprotectant roles for microorganisms, especially diatoms, against harsh winter conditions of high salinity and potential ice-crystal damage. |
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| Keywords: | Arctic Sea ice Polysaccharides Exopolymers Diatom Carbon |
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