Seasonal Air-Sea CO₂ Flux Dynamics in Colombia's Gorgona Marine Area During La Niña 2021-2022

Simon Gutierrez^1*Alberto Acosta¹Paula Andrea Murcia Zambrano¹Rafael Preciado Garcia¹Andrea Corredor Acosta²Jose Martin Hernandez-Ayon³Luz De Lourdes A. Coronado-Álvarez³Lucía Carolina Kahl⁴Ruiz Pino Diana⁵

• ¹Pontifical Javeriana University, Bogotá, Colombia
• ²Centro FONDAP de Investigación en Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Instituto de Acuicultura y Ciencias Ambientales, Universidad Austral de Chile, Puerto Montt, Chile
• ³Autonomous University of Baja California, Mexicali, Baja California, Mexico
• ⁴Departamento Oceanografía, Servicio de Hidrografía Naval. Av. Montes de Oca 2124, Buenos Aires, Argentina
• ⁵UMR7159 Laboratoire d'Océanographie et du Climat Expérimentations et Approches Numériques (LOCEAN), Paris, Île-de-France, France

This study highlights the importance of in situ measurements for future improvement of predictive models of air-sea CO₂ fluxes in the Eastern Tropical Pacific. In the waters surrounding Gorgona island (National Natural Park in the Colombian Pacific), CO₂ fluxes along with physical, chemical, and biological variables were measured in the main contrasting seasons (upwelling, post-upwelling), during La Niña (2021-2022) characterized by a cool-water anomaly (-0.78°C), increased precipitation (59%) and higher river discharge (44%), exceeding multi-year averages. The net CO₂ flux (calculated for nine months) was near neutral (0.01049 ± 0.00014 mol C m⁻²) with a bimodal seasonal dynamic, that is: (I) six months of post-upwelling conditions with slightly positive fluxes (0.00929 ± 0.000147 mol C m⁻²) associated to high precipitation (746.4 ± 214.7, mean ± SD), SST (27.5 ± 0.4), pCO₂w (567 ± 97.5 μatm) and low pH values (7.869 ± 0.040); and (II) three months of upwelling with neutral/slightly negative fluxes (0.00119 ± 0.00010 mol C m⁻²) associated to low precipitation (165.8 ± 82.4, mean ± SD), SST (26.5 ± 0.2), pCO₂w (461 ± 92.8 μatm) and high pH conditions (7.968 ± 0.048). La Niña (2021-2022) seems to amplify the pCO₂w (316–839 μatm) variability through enhanced vertical (Ekman Pumping) and horizontal (Zonal Ekman Transport and tides) water transport and freshwater inputs. Permanent tropical stratification (thermocline between 10 and 40.1 m) limited deep CO₂-rich waters reach the surface, which, together with the biological uptake modulated CO₂ outgassing due to high productivity (evidenced by Chl-a and ΔDIC values). Overall, the results suggested that within the two explored seasons, physical and biological interactions modulated the magnitude of the CO₂ flux, being relatively low when compared with other typical tropical estuaries and oceanic sources. We highlight the importance of long temporal in situ measurements (physical-biological dynamics) in the Eastern Tropical Pacific, to refine predictive models of air-sea CO₂ fluxes under neutral conditions and ENSO events.