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

Abstract

The accelerated rate of increase in the atmospheric carbon dioxide (CO<sub>2</sub>) and the substantial fraction of anthropogenic CO<sub>2</sub> 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 °C) and total alkalinity plus computed total dissolved inorganic carbon CO<sub>2</sub> concentration (C<sub>T</sub>) 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 CO<sub>2</sub> 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<sub>2</sub>, C<sub>ANT</sub>. C<sub>T</sub> at constant salinity, NC<sub>T</sub>, increased at a rate of 1 μmol kg<sup>−1</sup> yr<sup>−1</sup> in the first 200 m, linked to an <i>f</i>CO<sub>2</sub> increase of 1.7±0.7 μatm yr<sup>−1</sup> in both the atmosphere and the ocean. Consequently, the ESTOC site has also become more acidic, −0.0018±0.0003 units yr<sup>−1</sup> over the first 100 m, whereas the carbonate ion concentrations and CaCO<sub>3</sub> 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<sub>T</sub> increases at a rate of 0.69, 0.61 and 0.48 μmol kg<sup>−1</sup> yr<sup>−1</sup>, 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 CO<sub>2</sub> for the decade was 66±3 mol m<sup>−2</sup>. A model fitting indicated that the column inventory of C<sub>ANT</sub> increased from 61.7 mol m<sup>−2</sup> in the year 1994 to 70.2 mol m<sup>−2</sup> in 2004. The ESTOC site is presented by way of a reference site to follow C<sub>ANT</sub> changes in the North Atlantic Sub-tropical gyre

Variability and trends of ocean acidification in the Southern California Current System: A time series from Santa Monica Bay

“…The temporal variations of pH and aragonite saturation in the upper 300 m of the water column at SMBO are at least a factor of 5 more pronounced than those seen at the subtropical time series sites [ Dore et al ., ; Bates et al ., ; González‐Dávila et al ., ]. This high variability is largely driven by nonseasonal variations, which are caused by intermittent upwelling and relaxation events and mesoscale processes, but also includes interannual variability associated in part with El Niño Southern Oscillation.…”

“…In the open ocean, surface pH is remarkably uniform in space and time [ Feely et al ., ]. As a result, the ocean acidification‐induced reduction in pH is easily detectable at the long‐term time series sites in the subtropical gyres with only a few years of observations [ Dore et al ., ; Bates et al ., ; González‐Dávila et al ., ]. The saturation state with regard to aragonite, Ω arag , varies substantially more in the open ocean.…”

“…The saturation state with regard to aragonite, Ω arag , varies substantially more in the open ocean. But still, clear long‐term secular trends in Ω arag were detected at all subtropical open ocean time series sites [ Bates et al ., ; González‐Dávila et al ., ; Doney et al ., ]. Given these small “natural” variations and the anticipated progression of ocean acidification, open ocean waters will very soon experience conditions that are far outside this variability range [ Friedrich et al ., ].…”

Slow acidification of the winter mixed layer in the subarctic western North Pacific

“…The acidification of sea surface water has been well documented over the past three decades with time series data at CO 2 monitoring sites in the subpolar North Atlantic Ocean (Iceland Sea and Irminger Sea) [ Olafsson et al ., ], the temperate South Pacific (Munida Time Series) [ Currie et al ., ], and the tropical and subtropical North Atlantic and Pacific Oceans: Bermuda Atlantic Time‐series Study (BATS) [ Bates et al ., ], Hawaii Ocean Time series (HOT) [ Dore et al ., ], European Station for Time series in the Ocean at the Canary Islands (ESTOC) [ González‐Dávila et al ., ], and the Carbon Retention In A Colored Ocean sites in the North Atlantic (CARIACO) [ Astor et al ., ]. At most sites, the surface seawater pH has declined at rates of 0.0013–0.0018 year −1 in response to changes in atmospheric CO 2 induced by the release of anthropogenic CO 2 [ Bates et al ., ].…”

Reconciliation of pH25 and pHinsitu acidification rates of the surface oceans: A simple conversion using only in situ temperature

“…The pH of seawater reflects directly the state of the acid‐base systems of the oceans (Marion et al ). It has attracted much attention recently, as it reflects the seawater acidification of the oceans under the influence of the increasing atmospheric CO 2 concentration (Dore et al ; Olafsson et al ; Byrne et al ; Gonzalez‐Davila et al ; Ishii et al ; Bates et al ; Lui and Chen ; Lui et al ), which has in turn been caused by the fact that since the industrial revolution, humans have released a massive amount of CO 2 , so‐called anthropogenic CO 2 , to the atmosphere. The global oceans absorb around one third of the anthropogenic CO 2 , increasing their CO 2 concentration but reducing their pH and the saturation state of calcium carbonate through the air‐sea CO 2 exchange, adversely affecting marine ecosystems (Sabine et al ; Dore et al ; Feely et al ; Olafsson et al ; Bates et al ).…”