Temporal variations of water pCO2 and the air–water CO2 flux at a coastal location in the southern California Current System: diurnal to interannual scales

Abstract

The aim of this work was to identify processes that cause surface CO₂ partial pressure (pCO_2W) and air–water CO₂ flux (FCO₂) variations at a coastal location in the California Current System, from semidiurnal to interannual time scales. Such processes may include sea breeze, upwelling, El Niño/Southern Oscillation (ENSO) cycle, and “The Blob” (strong positive temperature anomalies in the NE Pacific). Sea surface  temperature  (SST,  2008–2014)  and  pCO_2W  (2008–2015)  time  series  were  generated  with  data  collected from  a  MAPCO₂  buoy anchored at 100 m depth and 5 km from Punta Banda (31.6ºN, 116.6ºW), Baja California, México. There were significant changes in SST, pCO_2W, and FCO₂ that lasted periods that were as short as a few hours and as large as interannual time frames. Spectral analysis showed significant semidiurnal, diurnal, ~15-d, and ~28-d components of variation. Time series were divided into periods according to the Multivariate ENSO Index and the Blob event. Bayesian t tests show that both pCO_2W and FCO₂ had high credibility of being different between periods. During La Niña conditions (2010–2011), maximum pCO_2W and FCO₂ values were higher, and the minimum values were lower, than during “normal,” El Niño, and Blob conditions. The pCO_2W range during this La Niña event was from 131 to 864 µatm, and the FCO₂ range was from–6.9 to 40.4 mmol C·m^–2·d^–1. The FCO₂ range during the Blob was from near equilibrium to ~2.5 mmol C·m^–2·d^–1. The extreme values for the FCO₂ integral (± standard error), for all periods, were –57.0 ± 0.01 mmol C·m^–2 for El Niño, and 257.0 ± 0.03 mmol C·m^–2 for La Niña. Themean FCO₂ value (± standard error) was 0.04 ± 0.02 mol C·m^–2·yr^–1. The buoy location was found to be a very weak source of CO₂ during thestudy period.