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Comment by hwillis | Hacker News Reader

why does removing carbonates cause the ocean to absorb more CO2, though? Calcium and magnesium oxide aren't just floating around the ocean waiting to absorb more CO2. Removing salts does not lower oceanic acidity.

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The ocean and the atmosphere exist in an equilibrium there is a 'balance' of relative concentration of CO2. Because CO2 can dissolve in water as CO3 and HCO3 the concentration is skewed to a higher concentration in oceans. When we take out CO2 from the oceans we lower the relative concentration, so we shift it out of balance. So the entire ocean becomes the surface area for re-absorbing CO2 from the atmosphere to re-establish that balance!

But the re-absorbed CO2 will come from new limestone dissolving into calcium bicarbonate, not from atmospheric CO2.

You'll be adding more CO2 to the air -increasing oceanic acidification- while increasing the ocean's ability to dissolve more CaCO3. Far from fighting global warming it sounds like this will put exactly as much CO2 into the atmosphere and double the leaching impact on shellfish and coral.

I am shit at chemistry and would really like cement to not release CO2, but I don't understand this.

Wait, no, why? As far as I understand the process of limestone dissolving into oceans is the long term (on the scale of millions of years) process and is based on rivers dissolving limestone so would not be affected by the ocean changes; in the short term (days/years/centuries) it would be balanced simply by CO2 exchange between the atmosphere and what's dissolved in the ocean.

Yeah absolutely, the CO2 balance comes from re-equilibration with the atmosphere. The rivers replenish calcium content on a longer time scale. But as you point out we're in no danger of running out of calcium in the oceans

Same question! As I understand it: CO2 pulled out of the ocean is replenished by atmospheric CO2, because limestone in the ocean dissolves too slowly to make up for the imbalance and it more readily comes in from the air. But if that's true, then the calcium will actually not be replenished quickly in the ocean (not sure what the significance of this is)! If it were true that the calcium is dissolved fast enough to replenish, then there must also be CO2 released from underwater limestone? Which means extracting Ca and CO2 will not remove any atmospheric CO2 really.

Alternatively, we do end up extracting Ca from the ocean that is not replenished (there's probably so much we don't care) and rely on the atmospheric CO2 to correct ph balance of the ocean?

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