Algal communities attached to free-drifting, Antarctic icebergs

Disintegration of the Antarctic Peninsula's eastern ice shelves has increased the population of icebergs traversing the Weddell Sea, but until recently little was known about their ecological impact on the pelagic environment. Here we describe a class of algal communities that occur on the submerged flanks of large, free-drifting, glacially-derived tabular icebergs. We used remotely operated vehicles to examine these icebergs directly for the first time, to survey the algal communities and collect material for shipboard laboratory studies. The communities, principally diatoms, were associated with a characteristic cupped configuration of the ice surface, and they served as feeding sites for aggregations of Antarctic krill. Production rate measurements indicate that these communities are providing a substantial contribution to regional primary production in summer. As the number of icebergs grows, the number of algae communities may also be increasing, along with their cumulative contribution to organic carbon flux.