That proved true again this week when a group of Indian and German researchers gave their first report from the biggest ever experiment in geo-engineering: an expedition to pour iron into the Southern Ocean, a vast area that encircles Antarctica, to stimulate a giant bloom of phytoplankton.I am glad they were able to conduct this experiment. I am curious as to how much additional biomass they get per ton of iron, and how much it cost.
Those researchers, led by Wajih Naqvi and Victor Smetacek, created a bloom of phytoplankton by fertilising an area of 300 square kilometres with six tonnes of iron sulphate, which dissolves in water. In two weeks the bloom’s mass doubled. But it also proved to be extremely tasty for small crustaceans called copepods, which gobbled the phytoplankton up so quickly that even with further iron fertilisation the bloom stopped growing. As a result, only a small amount of CO2 was dispatched to the ocean floor.
The problem lay with the species of phytoplankton in the bloom. In previous experiments the blooms had consisted of a group of algae known as diatoms. As diatoms have shells made of silica they are protected from copepods and so are more likely to die without being eaten and thus take take their carbon to the ocean floor. But in the area where the researchers were working natural blooms had already depleted much of the silicic acid, which the diatoms use for shellmaking. The result was that the beneficiaries of the iron were instead groups of algae such as Phaeocystis, which are among the most heavily grazed by copepods.
Since silicic-acid levels are naturally low across about two-thirds of the Southern Ocean, the expedition’s results suggest that iron-fertilisation would remove less CO2 from the atmosphere than optimists had hoped. Although that is a setback for proponents of large-scale iron-fertilisation, the results from the Polarstern expedition have given researchers lots to work on, including the role predators play in reducing algal blooms. And the results in one part of the ocean may be different from those in another because, as Ulrich Bathmann of the Wegener Institute points out, ecosystems in the sea are at least as diverse as those on the land. So the team may make another voyage to discover more.
I am all for this type of geo-engineering testing, but I don't agree with the conclusion that it needs to be modified to produce more diatoms and less phytoplankton. Better that there is more food at the bottom of the food chain that will then result in greater harvests of fish and larger populations of whales than more CO2 at the bottom of the ocean.
via The Economist and Planktos Science