Can phytoplankton absorb the excess CO2 in the oceans? Some scientists have suggested this as a solution: adding iron to the ocean’s surface to encourage the growth of these tiny plants. The first to suggest this was oceanographer John Martin in the late 1980s.
In May, 200 countries reached an agreement during the ninth Conference of the Parties (COP 9) to curtail these sea fertilization plans., also referred to as carbon sequestration.
Part of the problem with such a strategy is that, while it’s definitely possible to trigger plant growth by adding iron or other nutrients, it’s not easy to control what grows and what doesn’t.
Addressing this issue, an article in The Newport News-Times goes on to say:
". . . four dozen scientists on a 2002 research venture in the Southern Ocean off Antarctica . . . tested the concept of iron fertilization. They discovered that adding the iron did boost biological productivity and enhance the ocean’s carbon dioxide uptake. But that and about a dozen other experiments involving iron fertilization have proven inconclusive and somewhat disappointing.
“Experiments so far have generally shown an increase in productivity that was less than expected, and it didn’t last long,” noted [scientist Pete] Strutton. “Adding iron also changes the type of phytoplankton that grew, which might have important ecological consequences we don’t yet understand.”
Certain algae, for example, can release toxic substances which, when they accumulate in shellfish, can cause illness, even death, in humans eating them.
Also, an excess of phytoplankton would alter light absorption at the ocean’s surface:
“As you increase phytoplankton levels, you can alter the absorption of light, potentially leading to more heating of the upper ocean and more stratification of ocean waters,” said Strutton. “At the same time you are trying to enhance the growth of plant life in one area, you may be depleting nutrients nearby and affecting adjacent ecosystems.”