Experimental formation of sea ice: importance of water circulation and wave action for incorporation of phytoplankton and bacteria |
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Authors: | Jürgen Weissenberger Sönnke Grossmann |
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Institution: | (1) Norsk Hydro ASA, P.O. Box 2560, N-3901 Porsgrunn, Norway e-mail: jurgen.weissenberger@hre.hydro.com, fax: 35 92 2302, NO;(2) Alfred-Wegener-Institut für Polar-und Meeresforschung, Postfach 12 01 61, 27515 Bremerhaven, Germany, DE |
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Abstract: | The efficiency of physical concentration mechanisms for enrichment of algae and bacteria in newly formed sea-ice was investigated
under defined conditions in the laboratory. Sea-ice formation was simulated in a 3,000 l tank under different patterns of
water movement. When ice formed in an artificially generated current pattern, algal cells were substantially enriched within
the ice matrix. Enrichment factors for chlorophyll a calculated from the ratio between the concentrations in ice and underlying water reached values of up to 53. Repeated mixing
of ice crystals into the water column, as well as flow of water through the new ice layer, contributed to the enrichment of
algae in the ice. Wave action during ice formation revealed lower phytoplankton enrichment factors of up to 9. Mixing of floating
ice crystals with underlying water and pumping of water into the ice matrix by periodical expansion and compression of the
slush ice layer were responsible for the wave-induced enrichment of algal cells. Physical enrichment of bacteria within the
ice was negligible. Bacterial biomass within new ice was enhanced only when the concentration of algae was high. At low algal
biomass, bacteria experienced substantial losses in the ice, most likely due to brine drainage, which were not observed for
the microalgae. Bacterial cells are therefore not scavenged by ice crystals and the observed enrichment and sustainment of
bacterial biomass within newly formed ice depend on their attachment to cells or aggregates of algae. Division rates of bacteria
changed only slightly during ice formation.
Received: 21 October 1997 / Accepted: 9 April 1998 |
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