Everyone knows that the bulk of an iceberg is underwater, so what happens when they hit the sea floor? Icebergs that scrape over the sea floor or get stuck on underwater elevations cause enormous disturbance events. Entire faunal assemblages are wiped out during such events. Scraping icebergs leave behind a diverse landscape, 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 thus enhance species diversity.

Initially, scientists assumed that the seafloor fauna of the Larsen A and B area would have been strongly affected by iceberg scouring. When an ice shelf collapses, many smaller icebergs form in a short period of time. When more icebergs exist, the destruction potential of icebergs on the seafloor increases.

Our findings suggest something else happened at Larsen. 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 not as spectacular as other glacier events, like the calvings in Alaska. If we assume that the break-off happened slowly but steadily, this can explain the low number of iceberg scours we found, and it implies the bottom fauna did not suffer as much as we expected.

It is also intriguing that we found very few patches of different colonization stages. There are two possible explanations for this: It could because of the very slow growth of organisms and the speed of their recolonization, or else because 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. A starfish with an unusually high number of arms seems to have settled in an undisturbed area in the immediate vicinity of the scour. 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.

Text: Stephanie Langner
Photographs: Julian Gutt