Variability of pCO2 and FCO2 in the Mexican Pacific during 25 years

Oceanographic features acting on different spatial-temporal scales influence the variation in the partial pressure of CO2 (pCO2) and ocean-atmosphere CO2 flux (FCO2). In this work, we regionally characterize regions of variability in the Mexican Pacific (MP) based on these chemical properties. We also evaluate the seasonal and interannual changes of each region: in the California Current System (CCS), Cabo Corrientes (CC), and Gulf of Tehuantepec (GT) regions. Sea surface temperature (SST), salinity, wind, pCO2, and FCO2 data from 1993 to 2018 were analyzed. Bayesian t-tests (95% credibility intervals) determined showed that the three regions had high probabilities of being different. Typical FCO2 values in the CCS were higher (- 27.6-29.8 mmol C m- 2 d-1) than those of the CC and GT regions (- 19.9-25.8 and - 11.8-12.5 mmol C m- 2 d-1, respectively). The highest positive seasonal variation of FCO2 (mean +/- standard deviation) was found in the CCS and CC (-4.6 +/- 4.2 mmol C m-2 d- 1) regions during spring, and in the GT region (1.2 +/- 2 mmol C m- 2 d-1) in autumn due to the strong northerly winds. It was found that during ENSO conditions the MP was a source (4.0 and 3.9 mol C m- 2 y-1 for El Nin similar to o and La Nin similar to a, respectively), although on average over the last 25 years included in the study the MP acted as a slight-CO2 sink (-10.9 +/- 0.005 mol C m-2).