Air–Water CO2 Fluxes and Net Ecosystem Production Changes in a Baja California Coastal Lagoon During the Anomalous North Pacific Warm Condition

Abstract

The present study examines the temporal variability of air–water CO2 fluxes (FCO2) and seawater carbonate chemistry in a Baja California coastal lagoon during an exceptionally warm anomaly that was developed in Northeast Pacific coasts during 2014. This oceanographic condition led to a summer-like season (weak upwelling condition) during the study period, which reached a maximum surface temperature anomaly of 2 °C in September 2014. San Quintin Bay acts as a source of CO2 to the atmosphere in 2014 (3.3 ± 4.8 mmol C m−2 day−1) with the higher positive fluxes mainly observed in summer months (9.0 ± 5.3 mmol C m−2 day−1). Net ecosystem production (NEP) switched seasonally between net heterotrophy and net autotrophy during the study period, with an annual average of 2.2 ± 7.1 mmol C m−2 day−1, which indicates that San Quintin Bay was a net autotrophic system during the atypical warm oceanographic condition in 2014. This pattern of seasonal variations in the carbon balance at San Quintin Bay appears to be linked to the life cycle of benthic communities, which play an important role in the whole-ecosystem metabolism. Under the limited input from external sources coupled with an increase in seawater temperatures, the recycled benthic carbon and nutrient fluxes play a major role to sustain water-column processes within the bay. Since the upwelling condition may influence the magnitude of the air–water CO2 fluxes, our results clearly indicated that San Quintin Bay is a net source of carbon to the atmosphere regardless of the adjacent oceanic conditions. Our study sheds light on the carbon dynamics and its metabolic implications in a shallow coastal ecosystem under a regional warm anomaly and contributes potentially relevant information in view of the likely future scenario of global climate change.