Abstract
Abstract. The accelerated rate of increase in atmospheric carbon dioxide and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic signatures of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, CANT. CT at constant salinity, NCT, increased at a rate of 0.85 μmol kg−1 yr−1 in the mixed layer, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr−1, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg−1 yr−1 at 300, 600, and 1000 m, respectively. The general processes controlling the vertical variations of alkalinity and the inorganic carbon distribution were computed by considering the pre-formed values, the production/decomposition of organic matter and the formation/dissolution of carbonates. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, increasing to 35% at 3685 m. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented as a reference site to follow CANT changes in the Northeast Atlantic Sub-tropical gyre.
Highlights
Atmospheric carbon dioxide (CO2) levels have increased by nearly 40%, from the pre-industrial levels of around 280 ppmv to 384 ppmv in 2007 (Solomon et al, 2007)
The seasonal variability of the four carbon parameters for the surface water at ESTOC can be seen in previous studies by Santana-Casiano et al (2007) whereas the factors contributing to the long-term variation observed in the mixed layer reported for the 1995–2004 period has previously been published in Gonzalez-Davila et al (2007)
The slope of the regression line indicates an increase in the mixed layer N CT content of 0.90 ± 0.6 μmol kg−1 yr−1, equivalent to an annual f CO2 increase of 1.5 ± 0.9 μatm yr−1, similar to the value observed in the atmospheric CO2 increase for the period 1995 to 2004
Summary
Atmospheric carbon dioxide (CO2) levels have increased by nearly 40%, from the pre-industrial levels of around 280 ppmv (parts per million volume) to 384 ppmv in 2007 (Solomon et al, 2007). Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle There are several long-term ocean time series observations of seawater CO2 that have allowed the evaluation of inter-annual trends of surface seawater CO2 and air-sea CO2 fluxes. The seasonal variability of the four carbon parameters for the surface water at ESTOC can be seen in previous studies by Santana-Casiano et al (2007) whereas the factors contributing to the long-term variation observed in the mixed layer reported for the 1995–2004 period has previously been published in Gonzalez-Davila et al (2007). The influence of anthropogenic CO2 in the water column has been taken into consideration
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
