Experimental set-up.

<p>For each treatment (in triplicate; T = 18.9±0.1°C), the target A_T (total alkalinity in µmol kg⁻¹), pH_T and Ω_a (saturation state of the seawater with respect to aragonite) are indicated. pH_T was controlled by bubbling ambient or high-CO₂ air. A_T was decreased in T4 by HCl addition and increased in T5 by NaHCO₃ addition. In T4, calcium concentrations have been increased above ambient levels by CaCl₂ addition. See text for more details.