Our preferred approach to geoengineering the carbon cycle, if one is deemed to be essential, is a gradual seeding of iron into the Southern Ocean to feed the phytoplankton and eventually sequester the carbon in the briny deep, either as sinking dead plankton cells or more probably as fish and whale poop.
But there's more to the story. If you prepare the iron to the plankton's taste you get a lot bigger effect.
From the American Geophysical Union's EOS, October 30:
A new study of seafloor sediments suggests reactions in the atmosphere convert dust-borne iron into forms more readily taken up by phytoplankton.
Windblown iron carried on dust particles from the Sahara travels long distances. The critical nutrient is ferried to plants in the Amazon and to phytoplankton in the Atlantic Ocean and elsewhere. But much of this iron is initially locked up in molecules that are not bioavailable—cells simply can’t use it.
New research published in Frontiers in Marine Science shows that the farther this iron travels on windblown dust, the more bioavailable it becomes because of chemical reactions it undergoes while in the atmosphere.
Iron is essential for some of life’s most basic processes, playing a key role in biomolecules responsible for photosynthesis, DNA repair, and more. It’s a key constraint on the growth of phytoplankton, the bedrock of ocean ecosystems and a major driver of the planet’s carbon cycle. Iron-rich dust from the Sahara can therefore have a tremendous impact on distant ecosystems.
“There are neat interconnections across huge scales of time and space,” said Vernon Morris, an atmospheric scientist at Arizona State University who was not involved with the study. Morris leads a project called AEROSE (Aerosols and Ocean Science Expeditions) that has been following Saharan dust storms across the North Atlantic since 2004.
Connecting Air and Ocean
Making the chemical link between what happens to iron-rich dust in the atmosphere and what happens to it in the oceans has been challenging. Researchers have measured total iron levels in ocean floor sediment cores, but this approach doesn’t consider whether that iron was in forms that organisms can use, said Timothy Lyons, a biogeochemist at the University of California, Riverside, and a coauthor of the new study....
....MUCH MORE
Related:
Plankton Week: “Give me a half tanker of iron, and I will give you an ice age.”
The headline quote is from oceanographer John Martin during a 1988 lecture at Woods Hole Oceanographic Institution. Here's NASA's Earth Observatory archive page on the statement.
It is a bit of an exaggeration, you may need ten of those Valemax bulk carriers, currently the second largest ships in the world at 400,000 dwt (Euronav's two TI oil tankers at 441,000 dwt are bigger), to make an environmental change but what a change it would be. The orders of magnitude of carbon the iron-fed plankton would sequester are almost mind-boggling:
...Martin gathered the results of the incubation experiments and laid out the evidence in support of the Iron Hypothesis together with some back‐of‐the‐envelope calculations and presented his findings at a Journal Club lecture at Woods Hole Oceanographic Institution in July of 1988. He estimated that using a conservative Fe : C ratio that 300,000 tons of iron in the Southern Ocean induce the growth of phytoplankton that could draw down an estimated two billion tons of carbon dioxide. Then, putting on his best Dr. Strangelove accent, he suggested that “with half a ship load of iron….I could give you an ice age.” The symposium broke up with laughter and everyone retired to the lawn outside the Redfield Building for beers (from Chisholm and Morel, Editors, preface to: What controls phytoplankton production in nutrient‐rich areas of the open sea? Limnology and Oceanography, 36, 8 December 1991).
As repeated in "John Holland Martin: From Picograms to Petagrams and Copepods to Climate"
—Bulletin of Limnology and Oceanography, Wiley. 25 March 2016
....Coming up tomorrow, the Pope, and a Vancouver stock promoter.
Our series thus far:
October 27
Plankton Week: "Metal deposits from Chinese coal plants end up in the Pacific Ocean, research shows"
October 26
"Plankton Bloom Heralded Earth’s Greatest Extinction"
