Answer:
increase; decrease
Step-by-step explanation:
The oceans absorb 25 % to 30 % of CO₂ emissions quickly and about 85 % in the long term.
Thus, carbon dioxide levels in the ocean increase.
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Dissolved CO₂ is involved in several equilibria.
(1) CO₂(g) ⇌ CO₂(aq)
(2) CO₂(aq) + H₂O(ℓ) ⇌ H₂CO₃(aq)
(3) H₂CO₃(aq) + H₂O(ℓ) ⇌ HCO₃⁻(aq) + H₃O⁺(aq)
(4) HCO₃⁻(aq) + H₂O(ℓ) ⇌ CO₃²⁻(aq) + H₃O⁺(ℓ)
Reaction(3) accounts for most of the increase in hydronium ion concentration.
pH = -log[H₃O⁺]
As [H₃O⁺] increases, pH decreases.
Sea surface pH has decreased from 8.25 to 8.07 since the Industrial Revolution. This corresponds to a 50% increase in hydronium ions in the oceans.
We can see these effects in the NOAA graph below.
