Icebergs and the implications for the seafloor fauna
Few scour marks indicate that the Larsen ice shelf broke gently apart
Everyone knows icebergs, but only a few know about their implications when they hit the bottom of the sea. Icebergs that are scraping over the seafloor or getting stuck on underwater elevations cause enormous disturbance events. Entire faunal assemblages are wiped out during such events. However, they also create a diverse relief, which is usually marked by "bulldozed" areas as well as ploughed sediments or piles of rock. This new, unoccupied habitat is quickly seized by mobile pioneer species. Often, patchworks of different recolonization stages form and are thereby enhancing species diversity.
Initially, the assumption prevailed that in the Larsen A and B area the seafloor fauna is strongly shaped by iceberg scouring. After the collapse of the ice shelf a lot of smaller icebergs were created over a very short time period. When more icebergs exist, it increases the destruction potential of icebergs to the seafloor. However judging from our findings, quite the opposite seems to be true. Only shallow areas of the Larsen A and B area were affected by relatively few icebergs. This could indicate that the actual break off event was only half as spectacular as other glacier events like the calving in Alaska. If we assume that the break off happened slowly but steadily, it would explain the few numbers of iceberg scours. Therefore, the bottom fauna did not directly suffer as much as expected. It is also intriguing that no or only very few patches of different colonization stages were apparent. There are two possible explanations. It could be either the very slow growth of organisms and their speed of recolonization, or the fact that the present fauna, in contrast to other areas of Antarctic, is not yet adapted to such scouring events.
Underwater photographs show a large rocky surface scoured by an iceberg. In an undisturbed area in immediate vicinity of the scour, a starfish with an unusually high number of arms seems to have settled. Parallel iceberg scours can easily be seen on the soft sediment. A vase-shaped glass sponge, a translucent sea squirt, and a stalked feather star also inhabit this area.
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