[1] The long-term trends and average seasonal variability in the upper ocean inorganic carbon observations were investigated at the ESTOC Station (the European Time Series in the Canary Islands), on the basis of an existing 10-year series (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004). Hydrographic temperature and salinity, together with the pH in total scale at 25°C (pH T ), total alkalinity (A T ), partial pressure of CO 2 expressed as fugacity (fCO 2 ), computed dissolved inorganic carbon (C T ) and fluxes of CO 2 (FCO 2 ) reveal substantial variability over the years. Seasonal detrended data of salinity-normalized C T (NC T ) and experimental fCO 2 show upward trends of 0.99 ± 0.20 mmol kg À1 yr À1 and 1.55 ± 0.43 matm yr À1 , respectively, indicating direct control over the C T concentration due to increased atmospheric CO 2 concentration. Our series of experimental pH T data confirm the acidification of surface waters in the east Atlantic Ocean, with an interannual decrease of 0.0017 ± 0.0004 pH units yr À1. Interannual trends were examined by determining the variance in biogeochemical anomalies over time. The resulting anomalies in temperature and salinity revealed two scenarios in the ESTOC site, where there are periods of cooler and fresher water than the mean, driven by variations in winter mixed-layer depths, and periods with inverse temperature and salinity anomaly relationships, related to seasonal changes in the position of the subtropical gyre. Hydrographic and biogeochemical anomalies at ESTOC were linked to large-scale climate variability indexes, such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA). A delay of around 3 years in the oceanic response to the NAO best correlates with the anomalies observed for temperature (0.83), salinity (0.56), alkalinity (0.49), C T (0.41), fCO 2 (0.57) and the depth of the mixed layer (À0.64) with p < 0.05. The seasonal variability and its link-in to the large-scale climate variability of the North Atlantic subtropical gyre has been studied using the two long series, BATS and ESTOC.Citation: Santana-Casiano, J. M., M. González-Dávila, M.-J. Rueda, O. Llinás, and E.-F. González-Dávila (2007), The interannual variability of oceanic CO 2 parameters in the northeast Atlantic subtropical gyre at the ESTOC site, Global Biogeochem. Cycles, 21, GB1015,

[1] A 2-year record of mixed layer measurements of CO 2 partial pressure (pCO 2 ), nitrate, and other physical, chemical, and biological parameters at a time series site in the northeast Atlantic Ocean (49°N/16.5°W) is presented. The data show average undersaturation of surface waters with respect to atmospheric CO 2 levels by about 40 ± 15 matm, which gives rise to a perennial CO 2 sink of 3.2 ± 1.3 mol m À2 a À1 . The seasonal pCO 2 cycle is characterized by a summer minimum (winter maximum), which is due to the dominance of biological forcing over physical forcing. Our data document a rapid transition from deep mixing to shallow summer stratification. At the onset of shallow stratification, up to one third of the mixed layer net community production during the productive season had already been accomplished. The combination of high prestratification productivity and rapid onset of stratification appears to have caused the observed particle flux peak early in the season. Mixed layer deepening during fall and winter reventilated CO 2 from subsurface respiration of newly exported organic matter, thereby negating more than one third of the carbon drawdown by net community production in the mixed layer. Chemical signatures of both net community production and respiration are indicative of carbon overconsumption, the effects of which may be restricted, though, to the upper ocean. A comparison of the estimated net community production with satellite-based estimates of net primary production shows fundamental discrepancies in the timing of ocean productivity.

[1] Seasonal patterns in hydrography, partial pressure of CO 2 , fCO 2 , pH t , total alkalinity, A T , total dissolved inorganic carbon, C T , nutrients, and chlorophyll a were measured in surface waters on monthly cruises at the European Station for Time Series in the Ocean at the Canary Islands (ESTOC) located in the northeast Atlantic subtropical gyre. With over 5 years of oceanographic data starting in 1996, seasonal and interannual trends of CO 2 species and air-sea exchange of CO 2 were determined. Net CO 2 fluxes show this area acts as a minor source of CO 2 , with an average outgassing value of 179 mmol CO 2 m À2 yr À1 controlled by the dominant trade winds blowing from May to August. The effect of short-term wind variability on the CO 2 flux has been addressed by increasing airsea fluxes by 63% for 6-hourly sampling frequency. The processes governing the monthly variations of C T have been determined. From March to October, when C T decreases, mixing at the base of the mixed layer (11.5 ± 1.5 mmol m À3 ) is compensated by air-sea exchange, and a net organic production of 25.5 ± 5.7 mmol m À3 is estimated. On an annual scale, biological drawdown accounts for the decrease in inorganic carbon from March to October, while mixing processes control the C T increase from October to the end of autumn. After removing seasonality variability, f CO 2sw increases at a rate of 0.71 ± 5.1 matm yr À1 , and as a response to the atmospheric trend, inorganic carbon increases at a rate of 0.39 ± 1.6 mmol kg À1 yr À1 . Citation: González-Dávila, M., J. M. Santana-Casiano, M.-J. Rueda, O. Llinás, and E.-F. González-Dávila, Seasonal and interannual variability of sea-surface carbon dioxide species at the European Station for