Deconvolving the (delta)18O seawater component from subseasonal coral (delta)18O and Sr/Ca at Rarotonga in the southwestern subtropical Pacific for the period 1726 to 1997

In this paper, we present a brief review of the thermodynamic equilibrium of binary solid solution–aqueous solution (SS-AS) systems and derive an expression that allows us to evaluate the supersaturation or undersaturation of a given aqueous solution with respect to the whole range of solid compositions: the (delta)(x) function. Such an expression is based on the two conditions that define the SS-AS thermodynamic equilibrium. The derivation of the new supersaturation function, (delta)(x), was made by considering in detail the compositional relationships between solid and aqueous phases. To represent the new formulation on Lippmann diagrams, we have defined a new thermodynamic concept: the "actual activity." In addition, we show how our supersaturation function behaves for both ideal and subregular solid solutions. The behaviour and applicability of both the (delta) (x) function and a previous supersaturation function, (beta)(x), defined by Prieto et al. (1993), is discussed.