Testing a portable infrared CO2 gas system for the coastal region

Orion Norzagaray, Universidad Autonoma de Baja California UABC, Instituto de Investigaciones Oceanológicas, Ensenada, BJ, Mexico, Alicia Guadalupe Uribe López, Universidad Autónoma de Baja California, Facultad de Ciencias Marinas, Ensenada, BJ, Mexico, Jose Martin Martín Hernandez-Ayon, Autonomous University of Baja California UABC, Instituto de Investigaciones Oceanológicas, Ensenada, BJ, Mexico, Jonatan Santander-Cruz, Universidad Autónoma de Baja California, Ensenada, BJ, Mexico, Adán Mejía-Trejo, Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanologicas, Ensenada, BC, BJ, Mexico, Luz Martínez, Universidad Autónoma de Baja Calfornia, Ensenada, BJ, Mexico and Francisco Chavez, Monterey Bay Aquarium Research Institute, Moss Landing, CA, United States
Despite their reduced area (7%), the biogeochemical processes that controls the CO2 system are more intense in coastal oceans compared to open ocean regions, due to the continental influence or physical processes. Such interactions contribute with the spatial and temporal variability, leading to controversy the role of coastal oceans in the global carbon budget as a net sources or sinks. To determine the latter, a common practice is to derive the partial pressure of the CO2gas (pCO2, µatm) from discrete sampling of dissolved inorganic carbon (DIC, µmolkg-1), total alkalinity (TA, µmolkg-1) and/or pH. However, in order to obtain to obtain a continuous sampling, the most reliable way to quantify the partial pressure of this gas is to measure it directly in the field. In this work we propose two objectives: (1) evaluate the precision of an portable system using a infrared CO2 gas analyzer (LICOR 840-A, ± 2 ppm, MBARI) to measure the molar fraction of CO2gas (xCO2, ppm), and (2) define if Bahia de los Angeles, a Mexican coastal region influenced by upwelling, as a CO2 source or sink. In order to evaluate the performance of the portable system, the xCO2 measured values were contrasted with discrete samples of DIC (± 3 µmol kg-1), TA (± 3 µmol kg-1) and pH (±0.001 pH units). Our results showed that the internal calibration using dry standard gases (475 ± 0.3 ppm and CO2-free air) worked properly to match discrete samplings, showing a discrepancy of ± 11.6 ppm (± 2.3%) with xCO2 values derived from TA-DIC, while the use of pH showed a offset around 100 ppm. Finally, the pCO2 transect measured with the infrared portable system along the bay showed that the study area was a source of CO2 (3.15 to 4.73 mmol C m-2 d-1).