Grist had a couple more links on Planktos.
Planktos estimates that 25 percent of the carbon assimilated by phytoplankton from carbon dioxide in the air becomes locked up in the deep ocean once it dies and sinks below 1,600 feet. Considering this, along with the scale of the ocean and the larger quantity of plankton that occupied it 30 years ago, Coleman claims that restoring the sea to its original algae level could catch and hold about 50 percent of all of the carbon dioxide released every year by cars, power plants, and all other human-induced sources.
Some scientists are skeptical, calling the company’s estimates extremely optimistic. “You can make that calculation on paper,” says Nicholas Meskhidze, an assistant professor at the School of Marine, Earth and Atmospheric Sciences at North Carolina State University, “But whether it actually works that way in the ocean I don’t think is known.”
Meskhidze and John Marra, a biological oceanographer at Columbia University’s Lamont-Doherty Earth Observatory, estimate that just five percent of the carbon assimilated by phytoplankton sinks into the deep ocean, and only one percent ends up buried in sediment, far less carbon sequestration than Coleman predicts.
One of the reasons this occurs, explains Marra, is that in their slow descent to the deep, few phytoplankton actually reach the ocean floor after they die. “The phytoplankton isn’t going to just rocket down to the bottom, they’re not like little bullets or little pebbles,” says Marra, “They sink 50 to 100 meters per day and that’s generally slow enough that they can be eaten or attacked by bacteria.” As a result, the sequestered carbon is then re-released to the atmosphere. “[It] ends up as a sort of zero sum game,” says Marra.
Additionally, iron-seeding experiments that have been conducted since 1981, in Marra’s view, have never been conclusive enough to label the ocean as a reliable carbon sink. “It’s controversial,” he says. “It seems like every time [researchers] have done one of these iron enrichment experiments, they get a different result.”Source
And the headline at the Ottawa Citizen (same story as National Post, below):