Composition, Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean

PLOS ONE, Dec 2019

Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8–35 and 9–40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m−2, maintaining an estimated net primary production of 0.4–40 mg C m−2 d−1, and accounted for 3–80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities.

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Composition, Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean

Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean. PLoS ONE 9(9): e107452. doi:10.1371/journal.pone.0107452 Composition, Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean Mar Ferna ndez-Me ndez 0 Frank Wenzho fer 0 Ilka Peeken 0 Heidi L. Srensen 0 Ronnie N. Glud 0 Antje Boetius 0 Kay C. Vopel, Auckland University of Technology, New Zealand 0 1 HGF-MPG Group for Deep Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum fu r Polar- und Meeresforschung , Bremerhaven, Germany , 2 HGF- MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine Microbiology , Bremen, Germany, 3 Polar Biological Oceanography , Alfred-Wegener- Institut Helmholtz-Zentrum f u r Polar- und Meeresforschung , Bremerhaven, Germany, 4 MARUM , Center for Marine Environmental Sciences, University of Bremen , Bremen, Germany, 5 Nordic Centre for Earth Evolution , University of Southern Denmark , Odense, Denmark , 6 Greenland Climate Research Centre , Nuuk, Greenland, 7 Marine Biogeochemistry , Scottish Association for Marine Science , Oban , United Kingdom , 8 Arctic Research Centre, University of Aarhus , Aarhus , Denmark Sea-ice diatoms are known to accumulate in large aggregates in and under sea ice and in melt ponds. There is recent evidence from the Arctic that such aggregates can contribute substantially to particle export when sinking from the ice. The role and regulation of microbial aggregation in the highly seasonal, nutrient- and light-limited Arctic sea-ice ecosystem is not well understood. To elucidate the mechanisms controlling the formation and export of algal aggregates from sea ice, we investigated samples taken in late summer 2011 and 2012, during two cruises to the Eurasian Basin of the Central Arctic Ocean. Spherical aggregates densely packed with pennate diatoms, as well as filamentous aggregates formed by Melosira arctica showed sign of different stages of degradation and physiological stoichiometries, with carbon to chlorophyll a ratios ranging from 110 to 66700, and carbon to nitrogen molar ratios of 8-35 and 9-40, respectively. Sub-ice algal aggregate densities ranged between 1 and 17 aggregates m22, maintaining an estimated net primary production of 0.4-40 mg C m22 d21, and accounted for 3-80% of total phototrophic biomass and up to 94% of local net primary production. A potential factor controlling the buoyancy of the aggregates was light intensity, regulating photosynthetic oxygen production and the amount of gas bubbles trapped within the mucous matrix, even at low ambient nutrient concentrations. Our data-set was used to evaluate the distribution and importance of Arctic algal aggregates as carbon source for pelagic and benthic communities. - Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All data are available in the public repository PANGAEA. http://doi.pangaea.de/10.1594/PANGAEA.832345. Funding: HLS and RNG were supported by the Commission for Scientific Research in Greenland (KVUG;GCRC6507), the European Research Council through an Advanced Grant (ERC-2010-AdG20100224), the Danish National Research Foundation (DNRF53) and the Danish Council for Independent Research (12-125843). This study was supported by the European Research Council Advanced Investigator grant 294757 to AB. Additional support came from the Helmholtz Association and the Max Planck Society. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. In the Arctic Ocean, sea ice and water column microbial communities both contribute to photosynthetic production, but the relative importance of the pelagic versus the sympagic communities depends on season and geographical region [1]. Depending on light availability, the ice-algal growth season begins in April, and ends in September [2]. The total amount of productivity and standing stock formed seasonally in the water below the ice in the Central Arctic is constrained by light, as well as nutrient availability in the euphotic zone. Annual production in the ice-covered Central Arctic is estimated to be 910 g C m22 yr21, which is very low even compared to other oligotrophic oceans [3,4]. Previous investigations before 1997 have indicated a significant annual contribution by sea-ice algae to total photosynthetic productivity, on the order of 457% [3,5,6]. The wide range (010 g C m22 yr21) of sea ice primary production rates including the Arctic shelves is due to a very high spatial variability [3]. Sub-ice algae can accumulate substantial biomass in the Central Arctic basins, at times exceeding 80% of the standing stock [5]. They offer an additional food source to planktonic grazers in early spring [6] and in late autumn when other food sources are scarce [7,8]. Also their c (...truncated)


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Mar Fernández-Méndez, Frank Wenzhöfer, Ilka Peeken, Heidi L. Sørensen, Ronnie N. Glud, Antje Boetius. Composition, Buoyancy Regulation and Fate of Ice Algal Aggregates in the Central Arctic Ocean, PLOS ONE, 2014, Volume 9, Issue 9, DOI: 10.1371/journal.pone.0107452