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Comment by program_whiz | Hacker News Reader

This article shows that we can reliably cause phytoplankton blooms, but doesn't link it with actual "carbon removal". I suppose CO2 is temporarily removed in the form of the bloom, but I believe historically these blooms have a low efficiency for "permanent capture" because the plankton decay or are consumed. The only way to effectively capture would be to somehow create the bloom, then sink the phytoplankton en masse deep within the ocean where the would be neither eaten or decayed. Maybe possible with the right setup, but hard to scale.

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I've heard of capture technologies that literally pump organic matter down far enough that it sinks to the seabed (high enough pressure collapses air bubbles and results negative buoyancy). The problem is that your pumps need to operate using less carbon than you capture (easy with solar?) and that they need to be durable enough to pump billions of gallons of seawater with low maintenance (much harder, salt is terrible for machines).

Why can't we make pumps that withstand salt, dammit. It seems pathetic.

How about like a medical pump? Have a flexible polyurethane tube that's squidged by cams to pump the seawater through it. The cams stay in the dry.

It has to handle solids. Something more like a sewage pump.

Couldn't they front a pump with a macerator?

Just because we wants something doesn't mean we can have it, or at least not at a price we will accept.

Even if you get it to the seabed, the majority will be remineralised there. And if you pump enough down there to bury significant amounts of organic carbon, the bottom waters will likely become hypoxic as a result.

Diatoms sink when dead and we have decent ideas about the rate at which this happens.

How much of the carbon stays in the animal eating the bloom? I would think while it's tricky to calculate assuming them being eaten is bad might not be true. Of course we might end up making farting whales and adding loads of methane to the atmosphere knowing our luck...

Whenever we try playing god it seems we generally mess things up a few times so we'd need to monitor the actual outcomes in reduced CO2 in the atmosphere over several decades. It seems extremely high risk to assume there won't be unintended consequences...

I am curious of what happens to all the other nutrients in the bloom. There is more than just carbon-oxygen-hydrogen in those corpses that are then tied up when they are removed from the carbon cycle. Does anyone here know how that works?

Sequestering algae is how petroleum is produced. Does petroleum contain only hydrogen and carbon?

Hydrocarbons straight from the ground definitely contain a bunch of other crap, somewhat famously sulfur. I don't know what happens to the N and O, though.

This scenario is pretty similar to the Azolla event:

https://en.wikipedia.org/wiki/Azolla_event

Where "event" in this case is something that happened over an 800 000 years interval.

> the resulting draw-down of carbon dioxide has been speculated to have helped reverse the planet from the "greenhouse Earth" state of the Paleocene-Eocene Thermal Maximum, when the planet was hot enough for turtles and palm trees to prosper at the poles, to the current icehouse Earth known as the Late Cenozoic Ice Age.

Time to buy a condo in the Greater McMurdo area?

There are water bodies (Black Sea?) that are very poor at depths, so matter decays very slowly. Bogs aka peatlands are also like that, you can literally preserve meat and other organics, and let it sediment.

https://www.csiro.au/en/news/all/articles/2022/august/sinkin...

"phytoplankton are estimated to capture 10-20 billion tons of carbon dioxide each year."

also, https://en.wikipedia.org/wiki/Biological_pump

So how it works is, you grow the bloom in a massive pond. Wait for it to fully fill up, skim half the pond, add more nutrients and then agitate. With the algae you skimmed off you dry it out then compress it into a brick and burry it. In a 100K years we can the burn it for coal power again. And then repeat that until you've grown enough biomass to match the amount of Carbon put in the atmosphere since the industrial revolution.

Does this expend less carbon than you captured? Skimming, gathering, transport, drying, compression, burying. I assume to reach "gigatons captured per year" this would require heavy machinery and industrial buildout. Not that its impossible, I'm just not sure its a net-negative in CO2.

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