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Comment by emmelaich | Hacker News Reader

How does it cause depletion in other areas?

FWIW, I think the danger of excessive blooms is overstated. Most of the ocean is a desert nutritionally.

The flow and distribution of nutrients in the ocean follow weak gradients from their underlying sources in a kind of thermodynamic equilibrium. Some areas will have nutrient excesses based on geography, geochemistry, and limitations on consumption rate due to dependencies on other nutrients.

If iron is the rate limiting ingredient, then when you seed an area with iron a bunch of other nutrients are consumed in the process that currently are not being consumed. This changes the chemical equilibrium driving those other nutrient flows in the ocean and may stop critical nutrients flows into areas that rely on them. Any major local change to nutrient balance changes the equilibrium and thermodynamic gradients of the entire system.

In hindsight this is kind of obvious. There are similar equilibrium problems in large chemical reactors too and the ocean is just a giant reactor vessel to a first approximation. I think the original assumption was that the ocean is so big that no one would notice but long distance effects on local nutrient balances were observed such that increased sequestration productivity in one area was at least partially offset by losses of productivity in other areas due to new nutrient bottlenecks.

In principle modeling the entire system would allow one to inject the right nutrients at the right handful of spots to maximize aggregate sequestration performance with minimal risk. Building such models is still very much beyond us.

How does consumption of a nutrient stop its production?

I only use my common sense here, but it doesn't stop the production it just prevents the transport from the source to the destination through the area that was previously iron deficient and couldn't use the fully the other nutrient which passed on to another area.

It's not stopping the production, but changing the flow.

suppose there's a flow of nutrients of type A from area one to area two. Currently, iron is the chokepoint in nutrient consumption of A, so that A is never completely consumed while going from one to two.

By adding excess iron into area one, or in the middle of the region between this flow from area one to two, you now have the possibility to consume A completely as iron no longer limits A's consumption.

So what happens to area two's consumption of A, if it became more scarce? May be nothing - or may be you now have another choke point of resources that wasn't there previously, leading to a change. If you weren't sure if this change would occur, or dont know, perhaps adding iron to area one is not a good idea, until such outcomes have been studied and acertained first.

Sorry about a naive question. If additional nutrients causes imbalance due to taking nutrients from other areas. Cant we add those nutrients in as well?

I am starting to think China will be the first to experiment with this in large enough scale.

theoretically yes, but this draws you away from the original objective of effective sequestration

Wouldn't this only be an effect that happens on a small scale? It means that you'll see large changes elsewhere from small blooms in the ocean because of depletion elsewhere. Ok. But that cannot occur if you do this to an entire ecosystem (which can be the ocean, sure, but perhaps doing it to a large lake first would make more sense.

Second aren't we already doing large scale iron fertilization of the oceans? Not "intentionally" but simply rivers with human economic or residential activity along them.

It's kind of too obvious to notice, but the ocean is largely contiguous and interconnected. Any "local" effect can be distributed clear across the planet by ocean currents in a matter of days.

  aren't we already doing large scale iron fertilization of the oceans

Usually the opposite actually. Dams impede a massive amount of sediment from flowing into the oceans. Most large rivers near humans have multiple dams at this point.

In iron sulfate fertilization you're only adding two nutrients (iron and sulfur). Now that nutrient is in excess in one area so metabolic uptake of all nutrients increases locally, creating a concentration gradient that reduces nutrients available elsewhere. This leads to one of the other limiting nutrients like phosphorus or nitrogen preventing growth of other life forms in another location since the concentration gradient created by the phytoplankton sucked it away. Also sulfur concentration changes metabolic pathways through epigenetic effects so there are other effects just within the phytoplankton that depend on the species that happens to be present that will determine what the exact concentration gradient would look like. The dynamic of nutrients shifting of the metabolome makes modeling and risk assessment difficult since some species are known to produce toxins which can bioaccumulate. https://en.wikipedia.org/wiki/Phycotoxin

Not sure if it's a time to cry about the loss of a bush of roses when the forests are burning. Any natural iron supplementation like blowing the dust from Sahara or a river carrying out to the ocean waters full of red soil should be causing similar effects. Granted, rivers are likely carry other nutrients, often in excess, but this also does disrupt what grows or not in the surrounding areas.

Iron fertilization may still be pointless since the effectiveness is being debated afaik. On the other hand if it does work well for a competitive price compared to other methods, I would rather have a fish in the middle of the ocean full of algal neurotoxins and lower global temperature than the same fish cooked. No need to at it though.

Adding sulfur as a nutrient to the ocean is unlikely to have much effect, as seawater already contains about 3 ppm sulfate, thousands of times the concentration of iron.

It causes hypoxic zones in the water near the blooms, because the excessive blooms take up all the oxygen in the water leading to hypoxic and deadly conditions afterwards. That's why you often see so many dead fish around excessive blooms, all the oxygen is used up.

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