Air-sea CO2 fluxes in a tropical region of the Mexican Pacific.

The ocean can emit or capture CO₂ to the atmosphere. This characteristic is dynamic, therefore is necessary to know the CO₂ flow studies (FCO₂) and characterize the forcing agents. In the Mexican Pacific, some FCO₂ studies have been carried out, which are mostly concentrated in the California Current system, which leaves a gap of information in other regions such as the tropical Pacific. With the objective to know the FCO₂ in the Mexican tropical Pacific (from Cabo Corrientes, Jalisco, to Acapulco, Guerrero), two oceanographic campaigns were carried out aboard the R/V El Puma of the UNAM, in April 2017 and April 2018. To understand the oceanographic dynamics in the study area, satellite images of sea surface temperature (SST) and photosynthetic chlorophyll pigments (CHL) were used. With a CTD-SeaBird, vertical temperature and salinity profiles were made, wind recording was taken, and surface water aliquots were taken for the determination of dissolved inorganic carbon (DIC) and total alkalinity (TA), with these the FCO₂ calculation was performed. The T-S diagrams show the presence of Tropical Surface Water (TSW) in the firsts meters of the water column and, below it, Subtropical Subsurface Water (StSsW); this is related to an oxygen minimum zone (OMZ) and is rich in DIC. The SST images showed for both campaigns three regions: to the south with warm water, in the north with less warm water, and on the coast of Cabo Corrientes extending to Manzanillo, Colima, with cold water, agreeing with the greatest photosynthetic activity area (> 20 mg m^-3), that suggests intense coastal upwellings for this time. In the northern of study area (Cabo Corrientes, Manzanillo and Maruata) the FCO₂ show contrasting scenarios for the two campaigns, in 2017 was a carbon emitter and in 2018 as a sink. In 2017, the values maximum (minimums) of FCO₂ were 9.48 mmol C m^-2 d^-1 (-0.58 mmol C m^-2 d^-1), and in 2018 were 0.52 mmol C m^-2 d^-1 (-13.20 mmol C m^-2 d^-1).