As levels of carbon dioxide increase in the atmosphere, we could expect oceanic carbon dioxide levels to and oceanic ph to .

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.