[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,

Abstract. The Atlantic and Arctic Oceans are critical components of the global carbon cycle. Here we quantify the net sea–air CO2 flux, for the first time, across different methodologies for consistent time and space scales for the Atlantic and Arctic basins. We present the long-term mean, seasonal cycle, interannual variability and trends in sea–air CO2 flux for the period 1990 to 2009, and assign an uncertainty to each. We use regional cuts from global observations and modeling products, specifically a pCO2-based CO2 flux climatology, flux estimates from the inversion of oceanic and atmospheric data, and results from six ocean biogeochemical models. Additionally, we use basin-wide flux estimates from surface ocean pCO2 observations based on two distinct methodologies. Our estimate of the contemporary sea–air flux of CO2 (sum of anthropogenic and natural components) by the Atlantic between 40° S and 79° N is −0.49 ± 0.05 Pg C yr−1, and by the Arctic it is −0.12 ± 0.06 Pg C yr−1, leading to a combined sea–air flux of −0.61 ± 0.06 Pg C yr−1 for the two decades (negative reflects ocean uptake). We do find broad agreement amongst methodologies with respect to the seasonal cycle in the subtropics of both hemispheres, but not elsewhere. Agreement with respect to detailed signals of interannual variability is poor, and correlations to the North Atlantic Oscillation are weaker in the North Atlantic and Arctic than in the equatorial region and southern subtropics. Linear trends for 1995 to 2009 indicate increased uptake and generally correspond between methodologies in the North Atlantic, but there is disagreement amongst methodologies in the equatorial region and southern subtropics.

[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

A well documented, publicly available, global data set of surface ocean carbon dioxide (CO₂) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO₂ Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO₂, which had been subject to quality control (QC). Many additional CO₂ data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC), were retrieved from data originators, public websites and other data centres. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO₂ data points from the global oceans and coastal seas, spanning four decades (1968–2007). Three types of data products are available: individual cruise files, a merged complete data set and gridded products. With the rapid expansion of marine CO₂ data collection and the importance of quantifying net global oceanic CO₂ uptake and its changes, sustained data synthesis and data access are priorities

A well documented, publicly available, global data set for surface ocean carbon dioxide (CO₂) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO₂ Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO₂, which had been subject to quality control (QC). SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO₂ data from the global oceans and coastal seas, spanning four decades (1968–2007). The SOCAT gridded data is the second data product to come from the SOCAT project. Recognizing that some groups may have trouble working with millions of measurements, the SOCAT gridded product was generated to provide a robust regularly spaced fCO₂ product with minimal spatial and temporal interpolation which should be easier to work with for many applications. Gridded SOCAT is rich with information that has not been fully explored yet, but also contains biases and limitations that the user needs to recognize and address