Abstract
During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum year.
Highlights
The ongoing thinning and loss of Arctic sea ice will lead to changes in the surface energy budget of the Arctic Ocean [1,2] and will have far-reaching ramifications for both sympagic and pelagic ecosystems [3]
Seawater and meltwater samples as well as melted sea ice samples to be analysed for chlorophyll (Chl a), particulate organic carbon (POC) and nitrogen (PON) were filtered onto 25 mm Ø GF/F and pre-combusted (500°C for 4 h) GF/F filters, respectively
A roughly 0.5 m thick freshwater layer was separated from the underlying seawater by a sharp density gradient detected in cracks and openings in the ice at approximately the ice-water interface
Summary
The ongoing thinning and loss of Arctic sea ice will lead to changes in the surface energy budget of the Arctic Ocean [1,2] and will have far-reaching ramifications for both sympagic (iceassociated) and pelagic ecosystems [3]. At the base of the Arctic sea ice ecosystem, have to cope with being released into freshening surface water during the melt season. Due to their inherent stickiness, they are prone to aggregation [11] and subsequent sedimentation [12].
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