Estimation of the oceanic pCO(2) in the North Atlantic from VOS lines in-situ measurements : parameters needed to generate seasonally mean maps

Automated instruments on board Volunteer Observing Ships (VOS) have provided high-frequency pCO(2) measurements over basin-wide regions for a decade or so. In order to estimate regional air-sea CO2 fluxes, it is necessary to interpolate between in-situ measurements to obtain maps of the marine pCO(2). Such an interpolation remains, however, a difficult task because VOS lines are too distant from each other to capture the high pCO(2) variability. Relevant physical parameters available at large scale are thus necessary to serve as a guide to estimate the pCO(2) values between the VOS lines. Satellites do not measure pCO(2) but they give access to parameters related to the processes that control its variability, such as sea surface temperature (SST). In this paper we developed a method to compute pCO(2) maps using satellite data (SST and CHL, the chlorophyll concentration), combined with a climatology of the mixed-layer depth (MLD). Using 15 401 measurements of surface pCO(2) acquired in the North Atlantic between UK and Jamaica, between June 1994 and August 1995, we show that the parameterization of pCO(2) as a function of SST, CHL and MLD yields more realistic pCO(2) values than parameterizations that have been widely used in the past, based on SST, latitude, longitude or SST only. This parameterization was then used to generate seasonal maps of pCO(2) over the North Atlantic. Results show that our approach yields the best marine pCO(2) estimates, both in terms of absolute accuracy, when compared with an independent data set, and of geographical patterns, when compared to the climatology of Takahashi et al. (2002). This suggests that monitoring the seasonal variability of pCO(2) over basin-wide regions is possible, provided that sufficient VOS lines are available