Factors determining the ocean–atmosphere CO₂ flux variability in 5 coastal zones of the Gulf of California

The Gulf of California (GC) features many oceanographic processes. It communicates with the Pacific Ocean via a surface water outflow (0–200 m) with relatively low dissolved inorganic carbon (DIC) values and a water inflow (200–600 m) with high DIC values. Data on the marine carbon system in the GC are scarce and most have been taken from the Midriff Islands region, in the central part of the gulf. We explored possible forcing agents that control the ocean–atmosphere CO₂ flux (fCO₂) variability in 5 coastal zones of the GC. We carried out 6 oceanographic cruises in 5 regions: off northern Sinaloa in September 2016 (NAV2016) and in March 2017 (NAV2017), in the Guaymas Basin (central gulf) in September 2016 (GUA2016), in Concepción Bay (Baja California Sur) in July 2017 (BC2017), in Mulegé (Baja California Sur) in July 2017 (MUL2017), and off Mazatlán (southern gulf) in July 2017 (MAZ2017). We measured temperature, salinity, DIC, and total alkalinity and calculated the surface water partial pressure of CO₂ and fCO₂. We also used sea surface height anomaly with geostrophic flow, sea surface temperature, and chlorophyll concentration data from satellite imagery to generate composites for the sampling days. The lowest temperature, highest DIC, and negative fCO₂ were registered in NAV2017. NAV2016, GUA2016, and BC2017 showed the highest tempera-tures; and MUL2017 and MAZ2017, intermediate temperatures. The most contrasting fCO₂ values occurred in GUA2017 (0.56 ± 0.46 mmol C·m^–2·d–1) and MAZ2017 (–2.26 ± 1.85 mmol C·m^–2·d–1). In general, fCO₂ is determined by the oceanographic conditions of each study area.