title: Composition, buoyancy regulation and fate of ice algal aggregates in the Central Arctic Ocean.
abstract: 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.
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Mar
authors.initials: M
authors.lastname: Fernández-Méndez
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Wenzhöfer
authors.affiliation: Polar Biological Oceanography, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany; MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany.
authors.forename: Ilka
authors.initials: I
authors.lastname: Peeken
authors.affiliation: Nordic Centre for Earth Evolution, University of Southern Denmark, Odense, Denmark; Greenland Climate Research Centre, Nuuk, Greenland.
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Sørensen
authors.affiliation: Nordic Centre for Earth Evolution, University of Southern Denmark, Odense, Denmark; Greenland Climate Research Centre, Nuuk, Greenland; Marine Biogeochemistry, Scottish Association for Marine Science, Oban, United Kingdom; Arctic Research Centre, University of Aarhus, Aarhus, Denmark.
authors.forename: Ronnie N
authors.initials: RN
authors.lastname: Glud
authors.affiliation: HGF-MPG Group for Deep Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany; HGF-MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine Microbiology, Bremen, Germany; MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Boetius
mesh_terms: D000222:Adaptation, Physiological; D001110:Arctic Regions; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis*; D000077194:Chlorophyll A; D003080:Cold Temperature; D017377:Diatoms / Q000378:metabolism*; D017753:Ecosystem; D005615:Freezing; D046448:Ice Cover; D009584:Nitrogen / Q000378:metabolism; D009792:Oceans and Seas; D010788:Photosynthesis / Q000502:physiology*
chemical_list: D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen; D000077194:Chlorophyll A