Influence of the advection of water masses in the Ballenas Channel on the CO2 system in Bahía de los Angeles (Mexico)

The surface waters of the Ballenas Channel (BC) are characterized by thermohaline and biogeochemical conditions that depend on the water masses present. Since these surface waters are transported into Bahía de los Ángeles (BLA), it is relevant to assess their timing, intensity and biogeochemical implications on a seasonal scale. For this purpose, the seasonal and spatial variability of temperature, salinity, dissolved inorganic carbon (DIC) and total alkalinity (TA), were quantified over 19 discrete monthly monitoring campaigns that covered 12 stations in BLA from June 2017 to October 2019. In addition, vertical CTD profiles of thermohaline, apparent oxygen utilization (AOU), and nitrate were obtained for the purposes of identifying the water masses present and determining how they change by season. It was found that the dynamics of DIC, AOU, nitrate, and temperature in BLA respond to the presence of Subtropical Subsurface Water (SSW), evident by the enrichment of the bay with high DIC and nitrate concentrations during winter, but during summer occurs the opposite, with the presence of the Gulf of California Water (GCW). In addition, zonation analysis within BLA indicated three regions consistently found along the year, attributed to different physical and biogeochemical processes. Finally, we also interpreted the data in the context of the interannual variability due to ENSO events by using a relationship between observed temperature–DIC data. A 20-year calculated DIC (DICcalc) time series for an area near BLA indicated that during summer periods under the influence of La Niña events, the DICcal in front to BLA could be 10-12μmol kg −1 higher than El Niño events. These high DIC values, likely promoted by an increased volume of SSW in the BC, is accompanied by a higher nutrients concentration, suggesting that the interannual variability must interact with biological processes within BLA and other adjacent embayment’s in this region.