From: Andy Soos, ENN
Published June 3, 2011 08:15 AM

Iceberg Fertilizer

Iceberg are just frozen water. Water picks up other stuff when it freezes whether as dissolved or scraped up. Icebergs calving off of Antarctica are shedding substantial iron — the equivalent of a growth-boosting vitamin — into waters starved of the mineral, a new set of studies demonstrates. This iron is fertilizing the growth of microscopic plants and algae, transforming the waters adjacent to ice floes into teeming communities of everything from tiny shrimplike krill to fish, birds and sometimes mammals. Iron is a trace element necessary for photosynthesis in all plants. It is highly insoluble in sea water and is often the limiting nutrient for phytoplankton growth. Large phytoplankton blooms can be created by supplying iron to iron-deficient ocean waters.


An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. An iceberg's composition is almost entirely ice, with some stones and rocks. It is jagged and rough. Some are really big and others are rather small. Icebergs are usually white in color. When the water freezes, whatever is in it that is dissolved will stay with the iceberg until it melts.

By releasing iron into the Southern Oceans, melting icebergs are fueling the growth of plankton - which help to remove a substantial amount of CO2 from the atmosphere.

Iron is an essential nutrient, a lack of which limits the growth of plant life in the Southern Ocean. The main source of this iron is believed to be from atmospheric dust, but new evidence from the University of Leeds shows that icebergs could provide at least as much absorbable iron into the ocean.

Consideration of iron's importance to phytoplankton growth and photosynthesis dates back to the 1930s when English biologist Joseph Hart speculated that the ocean's great desolate zones (areas apparently rich in nutrients, but lacking in plankton activity or other sea life) might simply be iron deficient. Little further scientific discussion of this issue was recorded until the 1980s, when oceanographer John Martin renewed controversy on the topic with his marine water nutrient analyses. His studies indicated it was indeed a scarcity of iron micronutrients that was limiting phytoplankton growth and overall productivity in these regions.

Supporting evidence from the Weddell Sea in the Southern Ocean shows that iron from melting icebergs acts as a fertilizer for plant life in the surrounding ocean. This in turn reduces the level of C02 in the atmosphere.

"We've found a new source of iron delivery into the Southern Ocean, in the form of iron nanoparticles embedded in icebergs," says Prof Rob Raiswell, a professor of sedimentary geochemistry at the University of Leeds.

"This source has previously been overlooked because the iron in glacial sediments was assumed to be too inert for plankton to use, but we have discovered iron oxide nanoparticulates that can be easily absorbed."

The research, funded by a Leverhulme Emeritus Fellowship and published in the journal Geochemical Transactions, used samples from icebergs and glaciers in Antarctica which were analyzed using high resolution microscopy and chemical extraction methods to identify the iron nanoparticles.

"We have reason to think that the iceberg delivery of nanoparticulate iron oxides during the last Ice Age (18000-21000 years ago) was a significant factor in maintaining the cold climate and the associated low C02 concentrations. And if icebergs mitigated against climate warming in the past they should have the capacity to do so in the near future," comments Raiswell.

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