ABSTRACT

The association of ice algae with exopolymeric substances (EPS) and the role of EPS in other forms of microbial adhesion, suggest that EPS are important in algal attachment to ice. This attachment appears to be episodically overcome during seasonal ice melt, based on evidence that algae leave the ice in local pulses. Evidence suggests several physical mechanisms that detach algae from ice, but quantitative data that would allow prediction of algal release from ice do not exist. Funds are provided to support research that combines controlled laboratory experiments in specially-designed ice tanks with field observations of coastal fast-ice bottom communities near Barrow, AK. The research will address how ice algae attach to ice, the physical processes that may cause flux of algae out of the ice, and the biogeochemical characteristics of particles released from ice under different conditions.

The role of EPS in attachment of algae to sea ice will be assessed in experiments using artificially-created, sea-ice sheets colonized by ice algae. The time course of algal flux from the ice during melting will be compared between ice enriched in EPS and ice with chemically-degraded EPS. Additional experiments will focus on four specific mechanisms that potentially trigger the release of algae from sea ice: a) excess density and loss of attachment sites, b) flushing by surface meltwater, c) local heating due to light absorption, and d) under-ice currents. Each mechanism will be experimentally isolated to determine its impact on algal flux out of experimental ice sheets. For each mechanism, the minimal conditions necessary to trigger an algal pulse from the ice will be quantified for comparison with field observations. During these experiments, biogeochemically-relevant characteristics of the particles released from the ice will also be measured, including: size, sinking rate, and organic carbon, organic nitrogen, chlorophyll, and EPS concentrations. Complementary field studies are proposed in each year of the proposed research. Time series of algal abundance in the ice and water column will be used to identify release events. Comparison to time series of physical variables relevant to the four proposed detachment mechanisms will allow assessment of the factors that may have triggered the pulses.

Algae that are attached to the ice form a significant portion of the primary production in ice-covered seas. Thus, understanding the processes associated with their attachment to and detachment from the ice will enhance our understanding of the food web of polar seas, its spatial variability, and its potential response to global climate change.

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