[rjtc]

Most of the ocean is desert lacking the limiting nutrients of nitrogen, phosphorous and iron. If we can cheaply fertilize large swathes of the ocean with these limiting nutrients in a controlled manner, then this could trigger massive algae blooms that on sinking sequester massive amounts of carbon.

[mcguire]

Algae blooms result in de-oxygenated water, no?

(Among other consequences.) https://www.cdc.gov/habs/environment.html

[pvaldes]

it depends on the context

[sacnoradhq]

It doesn't take an unreasonable amount of iron and the sequestering efficiency is 13k:1 C:Fe on a molar basis. https://en.wikipedia.org/wiki/Iron_fertilization

[euroderf]

Do you mean rather: 1:13k Fe:C

From that Wikipedia item,

"Each iron atom converted at least 13,000 carbon atoms into algae."

[ravenstine]

Would we have to continually fertilize the ocean? And at whose expense? It'd be great if such an operation could be profitable, but it there's only so much seaweed people can eat.

[rickydroll]

need more whale poop to keep the fertilization cycle going. https://www.newscientist.com/article/2309262-scientists-want...

https://www.dw.com/en/artificial-whale-poop-could-save-the-p...

and burning Australia is a proven way to generate more plankton. https://nicholas.duke.edu/news/australian-wildfires-triggere....

[analog31]

Unfortunately, fertilizer presently has a large carbon footprint

[ben_w]

Many crop fertilisers have that issue, but fertiliser is not only one thing.

One hypothesis is that algae are limited by some single resource which could be gradually dropped out the back of cargo ships as they cross oceans, seeding carbon-absorbing algal blooms as they go.

(I heard about this nearly 20 years ago, so I assume that has either been tested or banned since then…)

[fosk]

Can’t fertilizer production emission be compartimentalized?

[rjtc]

it depends on the final balance. As mentioned above the ratio for iron is 13k Carbon atoms sequestered for atom of iron.

Keep in mind the vast majority of agricultural yield growth the last century is giving these limiting nutrients as fertilizer for plants, so it is successful and worthwhile for land based farming atleast.