Methodology of CRW Ocean Acidification Products General Approach

Fully describing the carbonic acid system requires that, in addition to temperature and salinity, at least two of the carbonate parameters (pCO_2,sw, A_T, DIC, pH) be known. To achieve this, we compute daily fields of total alkalinity (A_T) and carbon dioxide partial pressure (pCO_2,sw) through the application of a variety of modeled and remotely sensed environmental parameters. Sea surface pCO₂,sw is estimated using an empirical model relating the differential between sea surface and atmospheric CO₂ partial pressure (ΔpCO₂ = pCO_2,sw - pCO_2,air) to changes in CO₂ gas solubility (K₀). Sea surface A_T is derived using the empirical relationships offered by Lee et al. [2006] describing (sub)tropical surface A_T as a function of SSS and SST. Monthly composites of these A_T and pCO_2,sw fields are then coupled to solve the carbonic acid system using the CDIAC Program for CO₂ System Calculations [Lewis and Wallace, 1998]. The carbonate equilibria calculations used the Mehrbach et al. [1973] formulations of the K1 and K2 dissociation constants as refit by Dickson and Millero [1987]. A more detailed describtion of the methods employed are given in Gledhill et al. (2008).

Monthly composites of SST, SSS, pCO2,sw, and A_T are used as inputs to the CDIAC CO2 System Program to solve for the carbonic acid system and obtain maps including carbonate ion and aragonite saturation state (see the flow chart above).