The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004

Abstract

Abstract. The accelerated rate of increase in atmospheric carbon dioxide and the substantial fraction of anthropogenic CO 2 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 (C T ) 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 CO 2 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 CO 2 , C ANT . C T at constant salinity, NC T , increased at a rate of 0.85 µmol kg −1 yr −1 in the mixed layer, linked to an f CO 2 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 CaCO 3 saturation states have also decreased over time. NC T 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 Correspondence to: M. González-Dávila (mgonzalez@dqui.ulpgc.es) of calcium carbonate, increasing to 35% at 3685 m. The total column inventory of anthropogenic CO 2 for the decade was 66 ± 3 mol m −2 . A model fitting indicated that the column inventory of C ANT 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 C ANT changes in the Northeast Atlantic Sub-tropical gyre.

Variability of the ocean carbon cycle in response to the North Atlantic Oscillation

“…In contrast to the more northern areas, DpCO 2 measured at two locations in the subtropical gyre, ESTOC (e.g. Santana-Casiano et al, 2007;Gonzalez-Davila et al, 2010) and BATS (e.g. Bates, 2001Bates, , 2007, has remained more or less constant over time.…”

Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean

“…These ocean carbon cycle and ocean acidification data provide critically needed observational tests of global coupled ocean-atmosphere models and allow attribution of changes to both anthropogenic and natural causes (e.g., Le Quéré et al, 2010). Repeat hydrographic sections provide a means of quantifying basinwide ocean uptake of anthropogenic CO 2 (e.g., Friis et al, 2005;Brown et al, 2010;Wanninkhof et al, 2010). Alternatively, higher frequency observations of the changes in seawater chemistry due to uptake of anthropogenic CO 2 have been collected at a few ocean time-series near various islands,…”

Ocean Reference Stations

“…At present, funding from the governments of Spain and the Canary Islands comes primarily through the Canary Oceanic Platform (PLOCAN; http://plocan.eu). For more information on ESTOC, see and González-Dávila et al (2010). ESTOCS is part of the EuroSITES network and its websites can be found at: http://www.eurosites.info/estoc.php and http://www.estoc.es/.…”