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 (pCO2W) 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 pCO2W (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, pCO2W, 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 pCO2W and FCO2 had high credibility of being different between periods. During La Niña conditions (2010–2011), maximum pCO2W and FCO2 values were higher, and the minimum values were lower, than during “normal,” El Niño, and Blob conditions. The pCO2W 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.