Already C. Darwin acting as geologist describes that icebergs can carry large boulders and he argues that “…the bottom of the Antarctic Sea, and the shores of its islands, must already be scattered with masses of foreign rock.”
But icebergs are much more important then producing all sorts of dropstones, and not always they presence is causing a tragedy.
Melting icebergs in the Antarctic Ocean are slowing down the global warming - the icebergs release glacial sediments and fertilize the circumstanding Oceans, causing an algal bloom.
Rob Raiswell and his research team, studying the sediment transports of icebergs on board of the British icebreaker "Endurance", has discovered minute iron rich particles enclosed in the ice. Iron is a limiting factor of algal growth in the circumpolar ocean, and is only available in the sea by wind-transport of iron oxides from the southern continents, like the desert regions of Africa. But now an iceberg armada seems to provide enough of iron for a future massive algal bloom.
The alga during growth and reproduction assimilate carbon dioxide, and so maybe help to regulate the amount of this greenhouse gas in the atmosphere. Raiswell estimates that the icebergs can transport up to 120.000 tons of iron in the polar ocean, and the resulting algal growth has until now assimilated 2,6 billion tons of carbon dioxid. This phenomena will probably increase in the near future - the rising global temperatures has a positive effect on the flow velocity of the icecaps of the Antarctic continent- the production of icebergs in the Antarctic sea, providing much more fertilizer to the algae. This mechanism is significant, affirms Raiswell, but in any case not sufficient to stop the global warming, but to mitigate his effects. Furthermore, it is still not clear if the trapped carbon dioxide will effectively be deposited with the remains of the algae on the bottom of the sea, and remain there for a longer timescale, preventing a greenhouse effect, or otherwise return trough the food chain and seawater back in the atmosphere.