First, we know from these small-scale experiments that when you fertilize the ocean with iron, you change the structure of the phytoplankton community. Different species bloom than were there before, and when you change this structure, you change the structure of the entire food web that relies on these species.

Second, when you make organic carbon in a phytoplankton bloom it settles to the deep ocean where there is no light, and therefore no new production of oxygen from photosynthesis. You get consumption of oxygen by the bacteria that consume this organic carbon in their metabolism. This respiration can cause anoxic zones or low oxygen zones, depending on the magnitude of the bloom.

When you have anoxic zones, you could also have methanogenic bacteria that create methane gas, which is a greenhouse gas more potent than CO2.

imageNow this is just one illustration of how all of these biogeochemical cycles are coupled. When you fiddle with one, you're inevitably going to change other dimensions of the system. Likewise, if you were to fertilize with nitrogen, which others will discuss later, you will dramatically change the global nitrogen cycle. If you do it to a large enough degree, you could also stimulate nitrifying bacteria and denitrifying bacteria. One of the byproducts of those processes is nitrous oxide, which is another powerful greenhouse gas that also reacts with ozone.

Another proposal on the table is to fertilize with iron in regions where isn't excess N and P, with the goal of stimulating nitrogen fixation by cyanobacteria. This would have a similar effect on the nitrogen cycle.


imageLarge scale iron fertilization could also cause problems "downstream". If one fertilizes, say, the entire Southern Ocean with iron, and the phytoplankton take up the nitrogen and phosphorus there, it will not be available to fuel productivity in other areas of the oceans when that water finds its way back to the surface via the global ocean conveyor belt.

To sum up, I just want to tell a short story. Sometimes when I'm trying to talk to people about the complexities of the ocean ecosystem and the risks in undertaking a large manipulation like this, I draw a very imperfect analogy between the oceans and the human body. I explain that it is like trying to develop modern medicine with no understanding of the physiology and anatomy of the human body. On one occasion somebody jumped in and said, "That's exactly how modern medicine was developed!"

After a quiet pause, another person in the room jumped in and rescued me, and said, "Yes, but there's only one ocean."

It's a little chilling to think about it that way, but I hope we keep that in mind in our discussions over the next three days. It is impossible to predict the cumulative long-term consequences of large-scale ocean fertilization. You certainly can't predict them from short-term experiments. They simply don't scale up. Models can help us understand and bound the possibilities but they can't tell us what will happen. It's an extraordinarily complex system.

With that, I'll turn it over to the rest of the speakers, who will go into all of these dimensions in detail.

Back to Top Page | 1 | 2 | 3 |

American Society of Limnology & Oceanography - © Copyright 2002
Disclaimer & Directions for Downloading
Site Design Credits