Ocean iron fertilization -- reasons to go slow

Climate Feedback summarizes the reasons for caution about one proposed form of tinkering with the oceans to sequester carbon: Investors are backing a geoengineering startup based on the idea of fertilizing the ocean with iron to grow CO2-sequestering phytoplankton, despite recent research that underlines doubts about whether the scheme can work.

The startup, Climos, announced Wednesday that it had received US$3.5 million in venture capital, which it will spend on an environmental impact assessment, scientific workshops to discuss ocean iron fertilization, and international permits for a demo project - all to pave the way for selling carbon offsets from the fertilization technique. It's been less than a month since a rival company called Planktos had to drop a similar business plan for lack of funding, which it blamed on "a highly effective disinformation campaign waged by anti-offset crusaders". I'm guessing Planktos had in mind the activists who opposed such plans at an international policy meeting last year, though a group of ocean and climate scientists also called fertilization offset sales "premature" in a Science commentary (subscription required) soon before Planktos flopped. Climos must be betting its new millions that its proposed assessment, demo project and workshops will put some scientific weight on its side.

But the list of questions is long. The unknown ecological consequences of stimulating phytoplankton blooms first springs to mind, but another unknown is whether CO2 taken up by the plankton would actually end up stored in the deep sea, as hoped. In a press conference at the AGU Ocean Sciences meeting the day after the Climos announcement, researchers Peter Statham, Stephane Blain and Ian Salter described the results of studies on phytoplankton blooms fed naturally by iron that leaches from islands in the Southern Ocean. Their news may be bad for the offsets business.

If carbon is to stay stored underwater for decades or centuries, phytoplankton that have absorbed it must, upon death, sink at least 3,000 metres below the sea surface, the speakers said - but they had found that this probably happens to only about 5% of natural iron-happy blooms. They added, however, that differences between artificial iron fertilization and natural leaching may affect the results in ways that have yet to be analyzed: "present geo-engineering approaches will not mimic natural extended release from islands, the iron will not be [the] same form, and the overall impact on eco-systems is unknown."

Phytoplankton and hydrogen sulfide off the coast of Namibia: Brilliant green colors in the waters of the South Atlantic off the coast of Namibia mark out a large bloom of ocean plants and a hydrogen sulfide eruption. NASA image courtesy of Jeff Schmaltz, MODIS Land Rapid Response Team at NASA GSFC, Wikimedia Commons