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

[摘要] The accelerated rate of increase in atmospheric carbon dioxide and thesubstantial fraction of anthropogenic CO₂ emissions absorbed by theoceans are affecting the anthropocenic signatures of seawater. Long-termtime series are a powerful tool for investigating any change in oceanbio-geochemistry and its effects on the carbon cycle. We have evaluated theESTOC (European Station for Time series in the Ocean at the Canary islands)observations of measured pH (total scale at 25 °C) and total alkalinityplus computed total dissolved inorganic carbon concentration (C_T) from1995 to 2004 for surface and deep waters, by following all changes inresponse to increasing atmospheric carbon dioxide. The observed values forthe surface partial pressure of CO₂ from 1995 to 2008 were also takeninto consideration. The data were treated to better understand thefundamental processes controlling vertical distributions in the EasternNorth Atlantic Ocean and the accumulation of anthropogenic CO₂,C_ANT. C_T at constant salinity, NC_T, increased at a rate of0.85 μmol kg⁻¹ yr⁻¹ in the mixed layer, linked to anfCO₂ increase of 1.7±0.7 μatm yr⁻¹ in both the atmosphereand the ocean. Consequently, the mixed layer at ESTOC site has also becomemore acidic, −0.0017±0.0003 units yr⁻¹, whereas the carbonate ionconcentrations and CaCO₃ saturation states have also decreased overtime. NC_T increases at a rate of 0.53, 0.49 and 0.40 μmol kg⁻¹ yr⁻¹at 300, 600, and 1000 m, respectively. The generalprocesses controlling the vertical variations of alkalinity and theinorganic carbon distribution were computed by considering the pre-formedvalues, the production/decomposition of organic matter and theformation/dissolution of carbonates. At 3000 m, 30% of the inorganiccarbon production is related to the dissolution of calcium carbonate,increasing to 35% at 3685 m. The total column inventory of anthropogenicCO₂ for the decade was 66±3 mol m⁻². A model fittingindicated that the column inventory of C_ANT increased from 61.7 mol m⁻²in the year 1994 to 70.2 mol m⁻² in 2004. The ESTOC site ispresented as a reference site to follow C_ANT changes in the NortheastAtlantic Sub-tropical gyre.

[学科分类] 地球化学与岩石