The accelerated rate of increase in the atmospheric carbon dioxide (CO₂) and the substantial fraction of anthropogenic CO₂ emissions absorbed by the oceans are affecting the anthropocenic properties 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 &deg;C) and total alkalinity plus computed total dissolved inorganic carbon CO₂ concentration (C_T) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The experimental values for the partial surface 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, C_ANT. C_T at constant salinity, NC_T, increased at a rate of 1 &mu;mol kg^&minus;1 yr^&minus;1 in the first 200 m, linked to an <i>f</i>CO₂ increase of 1.7&plusmn;0.7 &mu;atm yr^&minus;1 in both the atmosphere and the ocean. Consequently, the ESTOC site has also become more acidic, &minus;0.0018&plusmn;0.0003 units yr^&minus;1 over the first 100 m, whereas the carbonate ion concentrations and CaCO₃ saturation states have also decreased over time. The rate of change is to be observed over the first 1000 m, where at 300, 600, and 1000 m the NC_T increases at a rate of 0.69, 0.61 and 0.48 &mu;mol kg^&minus;1 yr^&minus;1, respectively. The vertical distribution of the carbonate system variables are affected by the water mass structure and, to a different extent, controlled by the production/decomposition of organic matter, the formation/dissolution of carbonates, and differences in their respective pre-formed values. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, with a total of 35% at the bottom. The total column inventory of anthropogenic CO₂ for the decade was 66&plusmn;3 mol m^&minus;2. A model fitting indicated that the column inventory of C_ANT increased from 61.7 mol m^&minus;2 in the year 1994 to 70.2 mol m^&minus;2 in 2004. The ESTOC site is presented by way of a reference site to follow C_ANT changes in the North Atlantic Sub-tropical gyre

ABSTRACT. Fe(II) oxidation kinetics were studied in seawater and in seawater enriched with exudates excreted by Phaeodactylum tricornutum as an organic ligand model. The exudates produced after 2, 4, and 8 days of culture at 6.21 10 7 , 2.29 10 8 , and 4.98 10 8 cell L -1 were selected. The effects of pH (7.2-8.2), temperature (5-35 ºC), and salinity (10-36.72) on the Fe(II) oxidation rate were studied. All the data were compared with the results for seawater without exudates (control). The Fe(II) rate constant decreased as a function of culture time and cell concentration in the culture at different pH, temperature, and salinity. All the experimental data obtained in this study were fitted to a polynomial function in order to quantify the fractional contribution of the organic exudates from the diatoms to the Fe(II) oxidation rate in natural seawater. Experimental results showed that the organic exudates excreted by P. tricornutum affect Fe(II) oxidation, increasing the lifetime of Fe(II) in seawater. A kinetic model approach was carried out to account for the speciation of each Fe(II) type together with its contribution to the overall rate.

Labile Fe(II) distributions were investigated in the Sub-Tropical South Atlantic and the Southern Ocean during the BONUS-GoodHope cruise from 34 to 57° S (February–March 2008). Concentrations ranged from below the detection limit (0.009 nM) to values as high as 0.125 nM. In the surface mixed layer, labile Fe(II) concentrations were always higher than the detection limit, with values higher than 0.060 nM south of 47° S, representing between 39% and 63% of dissolved Fe (DFe). Biological production was evidenced. At intermediate depth, local maxima were observed, with the highest values in the Sub-Tropical domain at around 200 m, and represented more than 70% of DFe. Remineralization processes were likely responsible for those sub-surface maxima. Below 1500 m, concentrations were close to or below the detection limit, except at two stations (at the vicinity of the Agulhas ridge and in the north of the Weddell Sea Gyre) where values remained as high as ~0.030–0.050 nM. Hydrothermal or sediment inputs may provide Fe(II) to these deep waters. Fe(II) half life times (<i>t</i>_1/2) at 4 °C were measured in the upper and deep waters and ranged from 2.9 to 11.3 min, and from 10.0 to 72.3 min, respectively. Measured values compared quite well in the upper waters with theoretical values from two published models, but not in the deep waters. This may be due to the lack of knowledge for some parameters in the models and/or to organic complexation of Fe(II) that impact its oxidation rates. This study helped to considerably increase the Fe(II) data set in the Ocean and to better understand the Fe redox cycle

We used 5-year concomitant data of tracers distribution from the BATS (Bermuda Time-series Study) and ESTOC (European Station for Time-Series in the Ocean, Canary Islands) sites to build a 1-D tracer model conservation including horizontal advection and compute net production and shallow remineralization rates at both sites. Net production rates computed below the mixed layer to 110 m from April to December for oxygen, dissolved inorganic carbon and nitrate at BATS (1.34 ± 0.79 mol O₂ m⁻², −1.73 ± 0.52 mol C m⁻² and −125 ± 36 mmol N m⁻²) showed no statistically significant differences compared to ESTOC (1.03 ± 0.62 mol O₂ m⁻², −1.42 ± 0.30 mol C m⁻² and −213 ± 56 mmol N m⁻²). Shallow remineralization rates between 110 and 250 m computed at ESTOC (−3.9 ± 1.0 mol O₂ m⁻², 1.53 ± 0.43 mol C m⁻² and 38 ± 155 mmol N m⁻²) were statistically higher for oxygen compared to BATS (−1.81 ± 0.37 mol O₂ m⁻², 1.52 ± 0.30 mol C m⁻² and 147 ± 43 mmol N m⁻²). Lateral advection, which was more significant at ESTOC, was responsible for the differences in estimated oxygen remineralization rates between both stations. Due to the relevance of the horizontal transport at ESTOC, we cannot assert that the differences in shallow remineralization rates computed for both stations can explain the observed descrepancies in the flux of sinking organic matter