Air–sea exchange of CO<sub>2</sub> at a Northern California coastal site along the California Current upwelling system

Abstract

Abstract. It is not well understood whether coastal upwelling is a net CO2 source to the atmosphere or a net CO2 sink to the ocean due to high temporal variability of air–sea CO2 exchange (CO2 flux) in coastal upwelling zones. Upwelling transports heterotrophic, CO2 enriched water to the surface and releases CO2 to the atmosphere, whereas the presence of nutrient-rich water at the surface supports high primary production and atmospheric CO2 uptake. To quantify the effects of upwelling on CO2 flux, we measured CO2 flux at a coastal upwelling site off of Bodega Bay, California, with the eddy covariance technique during the summer of 2007 and the fall of 2008, and the bulk method with partial pressure of CO2 of surface water (pCO2) data from November 2010 to July 2011. Variations in sea surface temperatures (SST) and alongshore wind velocity suggest that the measurement period in 2007 coincided with a typical early summer upwelling period and the measurement period in 2008 was during a typical fall relaxation period. A strong source of CO2 (~ 1.5 ± 7 SD (standard deviation) g C m−2 day−1) from the ocean to the atmosphere during the upwelling period was concurrent with high salinity, low SST, and low chlorophyll density. In contrast, a weak source of CO2 flux (~ 0.2 ± 3 SD g C m−2 day−1) was observed with low salinity, high SST and high chlorophyll density during the relaxation period. Similarly, the sink and source balance of CO2 flux was highly related to salinity and SST during the pCO2 measurement periods; high salinity and low SST corresponded to high pCO2, and vice versa. We estimated that the coastal area off Bodega Bay was likely an overall source of CO2 to the atmosphere based on the following conclusions: (1) the overall CO2 flux estimated from both eddy covariance and pCO2 measurements showed a source of CO2; (2) although the relaxation period during the 2008 measurements were favorable to CO2 uptake, CO2 flux during this period was still a slight source; (3) salinity and SST were found to be good predictors of the CO2 flux for both eddy covariance and pCO2 measurements, and 99% of the historical SST and salinity data available between 1988 and 2011 fell within the range of our observations in May–June 2007, August–September 2008 and November 2010–July~2011, which indicates that our data set was representative of the annual variations in the sea state. Based on the developed relationship between pCO2, SST and salinity, the study area between 1988 and 2011 was estimated to be an annual source of CO2 of ~ 35 mol C m−2 yr−1. The peak monthly CO2 flux of ~ 7 mol C m−2 month−1 accounted for almost 30% of the dissolved inorganic carbon in the surface mixed layer.

Diurnal to annual changes in latent, sensible heat, and CO2 fluxes over a Laurentian Great Lake: A case study in Western Lake Erie

“…There were 36%, 50%, and 35% of LE, H, and F CO2 , respectively, that passed the quality checks as described above. The similar data gaps were also shown in Ikawa et al [2013] and Podgrajsek et al [2014b] in aquatic flux measurements. About 14% of our data gaps resulted from the occasional malfunction of sonic anemometer during heavy rainfall and snowfall periods.…”

Temporal variations in air‐sea CO2 exchange near large kelp beds near San Diego, California

“…The computation of eddy covariance was performed half‐hourly, following Ikawa et al . []. Density correction due to sensor heating increased CO 2 flux by 0.039 g C m −2 h −1 [ Burba et al ., ].…”

Analysis of the PKT correction for direct CO<sub>2</sub> flux measurements over the ocean

“…Prytherch et al (2010a) went further and presented a correction method (called the Peter K. Taylor -PKT -method), which has since been used in several publications to correct OP CO 2 fluxes (e.g. Prytherch et al, 2010b;Lauvset et al, 2011;Edson et al, 2011;Huang et al, 2012;Ikawa et al, 2013). Huang et al (2012) reported that the PKT correction did bring some of their CO 2 flux measurements closer to the bulk flux estimate, but found that for small water vapour fluxes the PKT method overcorrected the CO 2 flux and, in some cases, even resulted is a reversal of the flux direction.…”

“…Huang et al (2012) reported that the PKT correction did bring some of their CO 2 flux measurements closer to the bulk flux estimate, but found that for small water vapour fluxes the PKT method overcorrected the CO 2 flux and, in some cases, even resulted is a reversal of the flux direction. Ikawa et al (2013) reported that the PKT correction resulted in increased scatter when applied to coastal tower-based CO 2 flux measurements, and decided not to apply the correction. A selection of the publications mentioned above are also listed in Table 1 together with a brief description of the deployed IRGAs and findings relevant to this contribution.…”