A¨ıt-Ameur, N. and Goyet, C.: Distribution and transport of natural and anthropogenic CO2 in the Gulf of Ca´diz, Deep-Sea Res., II, 53, 1329-1343, 2006.
Anderson, L. A. and Sarmiento, J. L.: Redfield ratios of remineralization determined by nutrient data analysis, Global Biogeochem. Cycles, 8, 65-80, 1994.
Bates, N. R.: Interannual variability of oceanic CO2 and biogeochemical properties in the western North Atlantic subtropical gyre, Deep Sea Res., Part II, 48, 1507-1528, 2001.
Bates, N. R.: Interannual variability of the oceanic CO2 sink in the subtropical gyre of the North Atlantic Ocean over the last two decades, J. Geophys. Res., 112, C09013, doi:10.1029/2006JC003759, 2007.
Bates, N. R., Michaels, A. F., and Knap, A. H.: Seasonal and interannual variability of the oceanic carbon dioxide system at the U.S. JGOFS Bermuda Atlantic Time-series Site, Deep Sea Res., Part II, 43, 347-383, 1996.
Brewer, P. G.: Direct observation of the oceanic CO2 increase. Geophys. Res. Lett., 5, 997-1000, 1978.
Brix, H., Gruber, N., and Keeling, C. D.: Interannual variability of the upper ocean carbon cycle at station ALOHA near Hawaii, Global Biogeochem. Cycles, 18, GB4019, doi:10.1029/2004GB002245, 2004.
Chen, C. T. A. and Millero, F. J.: Gradual increase of oceanic CO2, Nature, 277, 205-206, 1979.
Chou, W. C., Sheu, D. D., Chen, C. T. A., Wang, S. L., and Tseng, C. M.: Seasonal variability of carbon chemistry at the SEATS time-series site, northern South China Sea between 2002 and 2003, Terr. Atmos. Oceanic Sci., 16, 445-465, 2005.
Chou, W. C., Sheu, D. D., Lee, B. S., Tseng, C. M., Chen, C. T. A., Wang, S. L., and Wong, G. T. F.: Depth distributions of alkalinity, TCO2 and δ13CTCO2 at SEATS time-series site in the northern South China Sea, Deep-Sea Res., II, 54, 1469-1485, 2007.
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.