Figure 6

Likely solubility orders of fish carbonate phases and their theoretical fates in different surface seawater scenarios in The Bahamas. Solubility orders (left) are based on existing data for similar phases of biogenic (where available) and synthetic origins. Differences between the columns reflect a disparity in published solubility data for HMC. Data are from: 1) Morse and Mackenzie¹⁹ (and references therein); 2) Hull and Turnball⁶⁴; 3) Walter and Morse¹⁷; 4) Brečević and Nielsen²³ and Clarkson et al.⁶⁵. Phases below the dashed line are thermodynamically unstable (Ω < 1) under normal surface seawater (SSW) conditions in The Bahamas. Based on these solubility data, a plot of CaCO₃ ion concentration product (ICP; i.e. [Ca²⁺][CO₃ ²⁻]) for seawater (practical salinity 35; temperature 25 °C; ρCO₂ 400 µatm) versus total alkalinity illustrates the predicted stabilities of these phases relative to SSW in The Bahamas (right; modified after Morse et al.³⁵ with the kind permission of Elsevier). ICP values for normal and platform interior (Inner GBB) waters are plotted (solid circles) along with equilibrium ICP values for relevant carbonate phases (dashed lines; Ω = 1); these phases being more stable the further their equilibrium ICP values are below seawater ICP. Uncertainties regarding brucite and ACMC solubilities are discussed in Supplementary Note 1, but available data suggest both phases are highly unstable in SSW.