Methodology of CRW Ocean Acidification Products Computation of Sea Surface pCO2,sw Fields

Sea surface pCO_2,sw is computed as a function of CO₂ gas solubility using an regionally specific empirical relationship according to (Gledhill et al., in press):

Where y_o = -51.2 ± 0.3, A = 350.7±12.3x10³, B = 30.3±0.1x10^-2 for oceanic surface waters of the Greater Caribbean. The temperature and salinity dependent gas solubility coefficient (K₀, moles kg^-1 atm^-1) is calculated according to Weiss [1974] in Near-Real-Time using the 1/4-degree gridded fields of daily NOAA NCDC OI AVHRR + AMSR-E SST OI.2 (henceforth referred to as SST_OI) and HYCOM+NCODA SSS. Archived data generated for dates prior to December 2003 were generated using climatological salinities obtained from NOAA NODC World Ocean Atlas and for dates prior to June 2002 the model applies NOAA NCDC OI AVHRR SST.

Atmospheric CO₂ partial pressure (pCO_2,air) is computed according to:

where sea-level pressure (SLP) is obtained from NOAA NCEP, water vapor pressure (pH₂O) is calculated as a function of SST_OI according to the empirical formula offered by Cooper et al., [1998], and the dry atmospheric CO₂ mole fraction data (XCO₂) are obtained from the NOAA GMD Carbon Cycle Cooperative Global Air Sampling Network [Thoning et al., 1995]. As quality controlled XCO₂ flask data are made available from Key Biscayne, Fl (25.7°N) and Ragged Point, Barbados (13.2°N), they are interpolated to derive daily estimates and linearly regressed to account for any latitudinal gradient across the region in the fashion employed by Olsen et al., [2004]. However, there is considerable latency between the collection of the flask samples, analysis and quality control. Therefore, the Near-Real-Time model generates 'preliminary' estimates based on non-linear regression models of XCO₂ at Key Biscayne and Ragged Point, As QC values are made available the data are reprocessed to 'final' status.

For Near-Real-Time estimates of atmospheric CO2 mole fraction data (XCO2) the model depends on non-linear regression fits of flask sample data obtained from Key Biscayne, Fl (25.7°N) and Ragged Point, Barbados (13.2°N) and available from NOAA GMD CCCG.