Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe datasets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics and cement production data, respectively, while emissions from Land-Use Change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent Dynamic Global Vegetation Models forced by observed climate, CO2 and land cover change (some including nitrogen-carbon interactions). We compare the variability and mean land and ocean fluxes to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004–2013), EFF was 8.9 ± 0.4 GtC yr−1, ELUC 0.9 ± 0.5 GtC yr−1, GATM 4.3 ± 0.1 GtC yr−1, SOCEAN 2.6 ± 0.5 GtC yr−1, and SLAND 2.9 ± 0.8 GtC yr−1. For year 2013 alone, EFF grew to 9.9 ± 0.5 GtC yr−1, 2.3% above 2012, contining the growth trend in these emissions. ELUC was 0.9 ± 0.5 GtC yr−1, GATM was 5.4 ± 0.2 GtC yr−1, SOCEAN was 2.9 ± 0.5 GtC yr−1 and SLAND was 2.5 ± 0.9 GtC yr−1. GATM was high in 2013 reflecting a steady increase in EFF and smaller and opposite changes between SOCEAN and SLAND compared to the past decade (2004–2013). The global atmospheric CO2 concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that EFF will increase by 2.5% (1.3–3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO2 yr−1), 65% above emissions in 1990, based on projections of World Gross Domestic Product and recent changes in the carbon intensity of the economy. From this projection of EFF and assumed constant ELUC for 2014, cumulative emissions of CO2 will reach about 545 ± 55 GtC (2000 ± 200 GtCO2) for 1870–2014, about 75% from EFF and 25% from ELUC. This paper documents changes in the methods and datasets used in this new carbon budget compared with previous publications of this living dataset (Le Quéré et al. 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_2014). Italic font highlights significant methodological changes and results compared to the Le Quéré et al. (2014) manuscript that accompanies the previous version of this living data.
.

The variability of the Atlantic meridional overturning circulation (AMOC) has considerable impacts on the global climate system. Past studies have shown that changes in the South Atlantic control the stability of the AMOC and drive an important part of its variability. That is why significant resources have been invested in a South (S)AMOC observing system. In January 2017, the RV Maria S. Merian conducted the first GO-SHIP hydrographic transect along the SAMOC-Basin Wide Array (SAMBA) line at 34.5°S in the South Atlantic. This paper presents estimates of meridional volume, freshwater (MFT), and heat (MHT) transports through the line using the slow varying geostrophic density field and direct velocity observations. An upper and an abyssal overturning cell are identified with a strength of 15.64 ± 1.39 Sv and 2.4 ± 1.6 Sv, respectively. The net northward MHT is 0.27 ± 0.10 PW, increasing by 0.12 PW when we remove the observed mesoscale eddies with a climatology derived from the Argo floats data set. We attribute this change to an anomalous predominance of cold core eddies during the cruise period. The highest velocities are observed in the western boundary, within the Brazil and the Deep Western Boundary currents. These currents appear as a continuous deep jet located 150 km off the slope squeezed between two cyclonic eddies. The zonal changes in water masses properties and velocity denote the imprint of exchange pathways with both the Southern and the Indian oceans.

We present new estimates of the regional North Atlantic (15-80g ¯N) CO2 flux for the 2000-2017 period using atmospheric CO2 measurements from the NOAA long-term surface site network in combination with an atmospheric carbon cycle data assimilation system (GEOS-Chem-LETKF, Local Ensemble Transform Kalman Filter). We assess the sensitivity of flux estimates to alternative ocean CO2 prior flux distributions and to the specification of uncertainties associated with ocean fluxes. We present a new scheme to characterize uncertainty in ocean prior fluxes, derived from a set of eight surface pCO2-based ocean flux products, and which reflects uncertainties associated with measurement density and pCO2-interpolation methods. This scheme provides improved model performance in comparison to fixed prior uncertainty schemes, based on metrics of model-observation differences at the network of surface sites. Long-term average posterior flux estimates for the 2000-2017 period from our GEOS-Chem-LETKF analyses are -0.255¯±¯0.037¯PgC¯yr-1 for the subtropical basin (15-50g ¯N) and -0.203¯±¯0.037¯PgC¯yr-1 for the subpolar region (50-80g ¯N, eastern boundary at 20g ¯E). Our basin-scale estimates of interannual variability (IAV) are 0.036¯±¯0.006 and 0.034¯±¯0.009¯PgC¯yr-1 for subtropical and subpolar regions, respectively. We find statistically significant trends in carbon uptake for the subtropical and subpolar North Atlantic of -0.064¯±¯0.007 and -0.063¯±¯0.008¯PgC¯yr-1¯decade-1; these trends are of comparable magnitude to estimates from surface ocean pCO2-based flux products, but they are larger, by a factor of 3-4, than trends estimated from global ocean biogeochemistry models.

The authors regret that we omitted acknowledgement of the ‘iFADO EAPA_165/2016 that covered work at the PAP-SO’. The authors would like to apologise for any inconvenience caused.

The ocean is currently a significant net sink for anthropogenically remobilised CO2, taking up around 24% of global emissions. Numerical models predict a diversity of responses of the ocean carbon sink to increased atmospheric concentrations in a warmer world. Here, we tested the hypothesis that increased atmospheric forcing is causing a change in the ocean carbon sink using a high frequency observational dataset derived from underway pCO2 (carbon dioxide partial pressure) instruments on ships of opportunity (SOO) and a fixed-point mooring between 2002 and 2016. We calculated an average carbon flux of 0.013 Pg yr−1 into the ocean at the Porcupine Abyssal Plain (PAP) site, consistent with past estimates. In spite of the increase in atmospheric pCO2, monthly average seawater pCO2 did not show a statistically significant increasing trend, but a higher annual variability, likely due to the decreasing buffer capacity of the system. The increasing ΔpCO2 led to an increasing trend in the estimated CO2 flux into the ocean of 0.19 ± 0.03 mmol m−2 day−1 per year across the entire 15 year time series, making the study area a stronger carbon sink. Seawater pCO2 variability is mostly influenced by temperature, alkalinity and dissolved inorganic carbon (DIC) changes, with 77% of the annual seawater pCO2 changes explained by these terms. DIC is in turn influenced by gas exchange and biological production. In an average year, the DIC drawdown by biological production, as determined from nitrate uptake, was higher than the DIC increase due to atmospheric CO2 dissolution into the surface ocean. This effect was enhanced in years with high nutrient input or shallow mixed layers. Using the rate of change of DIC and nitrate, we observed Redfieldian carbon consumption during the spring bloom at a C:N ratio of 6.2 ± 1.6. A comparison between SOO and PAP sustained observatory data revealed a strong agreement for pCO2 and DIC. This work demonstrates that the study area has continued to absorb atmospheric CO2 in recent years with this sink enhancing over time. Furthermore, the change in pCO2 per unit nitrate became larger as surface buffer capacity changed.

AbstractThe ocean is a sink for ~25% of the atmospheric CO2 emitted by human activities, an amount in excess of 2 petagrams of carbon per year (PgC yr−1). Time-resolved estimates of global ocean-atmosphere CO2 flux provide an important constraint on the global carbon budget. However, previous estimates of this flux, derived from surface ocean CO2 concentrations, have not corrected the data for temperature gradients between the surface and sampling at a few meters depth, or for the effect of the cool ocean surface skin. Here we calculate a time history of ocean-atmosphere CO2 fluxes from 1992 to 2018, corrected for these effects. These increase the calculated net flux into the oceans by 0.8–0.9  PgC yr−1, at times doubling uncorrected values. We estimate uncertainties using multiple interpolation methods, finding convergent results for fluxes globally after 2000, or over the Northern Hemisphere throughout the period. Our corrections reconcile surface uptake with independent estimates of the increase in ocean CO2 inventory, and suggest most ocean models underestimate uptake.

AbstractThe contemporary air‐sea flux of CO2 is investigated by the use of an air‐sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air‐sea gas transfer velocity are used to evaluate the combined standard uncertainty resulting from several sources of error. Depending on expert opinion, a standard uncertainty in transfer velocity of either ~5% or ~10% can be argued and that will contribute a proportional error in air‐sea flux. The limited sampling of upper ocean fCO2 is readily apparent in the Surface Ocean CO2 Atlas databases. The effect of sparse sampling on the calculated fluxes was investigated by a bootstrap method, that is, treating each ship cruise to an oceanic region as a random episode and creating 10 synthetic data sets by randomly selecting episodes with replacement. Convincing values of global net air‐sea flux can only be achieved using upper ocean data collected over several decades but referenced to a standard year. The global annual referenced values are robust to sparse sampling, but seasonal and regional values exhibit more sampling uncertainty. Additional uncertainties are related to thermal and haline effects and to aspects of air‐sea gas exchange not captured by standard models. An estimate of global net CO2 exchange referenced to 2010 of −3.0 ± 0.6 Pg C/year is proposed, where the uncertainty derives primarily from uncertainty in the transfer velocity.

AbstractThe North Atlantic Ocean is a region of intense uptake of atmospheric CO2. To assess how this CO2 sink has evolved over recent decades, various approaches have been used to estimate basin‐wide uptake from the irregularly sampled in situ CO2 observations. Until now, the lack of robust uncertainties associated with observation‐based gap‐filling methods required to produce these estimates has limited the capacity to validate climate model simulated surface ocean CO2 concentrations. After robustly quantifying basin‐wide and annually varying interpolation uncertainties using both observational and model data, we show that the North Atlantic surface ocean fugacity of CO2 (fCO2−ocean) increased at a significantly slower rate than that simulated by the latest generation of Earth System Models during the period 1992–2014. We further show, with initialized model simulations, that the inability of these models to capture the observed trend in surface fCO2−ocean is primarily due to biases in the models' ocean biogeochemistry. Our results imply that current projections may underestimate the contribution of the North Atlantic to mitigating increasing future atmospheric CO2 concentrations.

The ability to routinely quantify global carbon dioxide (CO2) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and international coordination have made it possible to measure CO2 absorption by the oceans to a greater degree of accuracy than is possible in terrestrial landscapes. These advances, combined with new satellite‐based Earth observation capabilities, increasing public availability of data, and cloud computing, provide important opportunities for addressing critical knowledge gaps. Furthermore, Earth observation in synergy with in‐situ monitoring can provide the large‐scale ocean monitoring that is necessary to support policies to protect ocean ecosystems at risk, and motivate societal shifts toward meeting C emissions targets; however, sustained effort will be needed.

The role ships play in atmospheric, oceanic, and biogeochemical observations is described with a focus on measurements made within 100 m of the ocean surface. Ships include merchant and research vessels, cruise liners and ferries, fishing vessels, coast guard, military, and other government-operated ships, yachts, and a growing fleet of automated surface vessels. The present capabilities of ships to measure essential climate/ocean variables and the requirements from a broad community to address operational, commercial, and scientific needs are described. Following the guidance from the OceanObs'19 organizing committee, the authors provide a vision to expand observations needed from ships to understand and forecast the exchanges across the ocean-atmosphere interface. The vision addresses (1) recruiting vessels to improve both spatial and temporal sampling, (2) conducting multi-variate sampling on ships, (3) raising technology readiness levels of automated shipboard sensors and ship-to-shore data communications, (4) advancing quality evaluation of observations, and (5) developing a unified data management approach for observations and metadata that meets the needs of a diverse user community. Recommendations are made focusing on integrating private and autonomous vessels into the observing system, investing in sensor and communications technology development, developing an integrated data management structure that includes all types of ships, and moving towards a quality evaluation process that will result in a subset of ships being defined as mobile reference ships that will support climate studies. We envision a future where commercial, research, and privately-owned vessels are making multivariate observations using a combination of automated and human-observed measurements. All data and metadata will be documented, tracked, evaluated, distributed, and archived to benefit users of marine data. This vision looks at ships as a holistic network, not a set of disparate commercial, research, and/or third-party activities working in isolation, to bring these communities together for the mutual benefit of all.

Ocean biological processes play an important role in the global carbon cycle via the production of organic matter and its subsequent export. Often, this flux is assumed to be in steady state; however, it is dependent on nutrients introduced to surface waters via multiple mechanisms, some of which are likely to exhibit both intra-annual and interannual variability leading to comparable variability in ocean carbon uptake. Here we test this variability using surface (5 m) inorganic nutrient concentrations from voluntary observing ships and satellite-derived estimates of chlorophyll and net primary production. At lower latitudes, the seasonality is small, and the monthly averages of nitrate:phosphate are lower than the canonical 16:1 Redfield ratio, implying nitrogen limitation, a situation confirmed via a series of nutrient limitation experiments conducted between Bermuda and Puerto Rico. The nutrient seasonal cycle is more pronounced at higher latitudes, with clear interannual variability. Over a large area of the midlatitude North Atlantic, the winters of 2009/2010 and 2010/2011 had nitrate values more than 1μmol L−1 higher than the 2002–2017 average, suggesting that during this period, the system may have shifted to phosphorus limitation. This nitrate increase meant that, in the region between 31° and 39° N, new production calculated from nitrate uptake was 20.5g C m−2 in 2010, more than four times higher than the median value of the whole observing period. Overall, we suggest that substantial variability in nutrient concentrations and biological carbon uptake occurs in the North Atlantic with interannual variability apparent over a number of different time scales.

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere - the "global carbon budget" - is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFF) are based on energy statistics and cement production data, while emissions from land use and land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the last decade available (2008-2017), EFF was 9.4±0.5 GtC yrĝ'1, ELUC 1.5±0.7 GtC yrĝ'1, GATM 4.7±0.02 GtC yrĝ'1, SOCEAN 2.4±0.5 GtC yrĝ'1, and SLAND 3.2±0.8 GtC yrĝ'1, with a budget imbalance BIM of 0.5 GtC yrĝ'1 indicating overestimated emissions and/or underestimated sinks. For the year 2017 alone, the growth in EFF was about 1.6 % and emissions increased to 9.9±0.5 GtC yrĝ'1. Also for 2017, ELUC was 1.4±0.7 GtC yrĝ'1, GATM was 4.6±0.2 GtC yrĝ'1, SOCEAN was 2.5±0.5 GtC yrĝ'1, and SLAND was 3.8±0.8 GtC yrĝ'1, with a BIM of 0.3 GtC. The global atmospheric CO2 concentration reached 405.0±0.1 ppm averaged over 2017. For 2018, preliminary data for the first 6-9 months indicate a renewed growth in EFF of +2.7 % (range of 1.8 % to 3.7 %) based on national emission projections for China, the US, the EU, and India and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. The analysis presented here shows that the mean and trend in the five components of the global carbon budget are consistently estimated over the period of 1959-2017, but discrepancies of up to 1 GtC yrĝ'1 persist for the representation of semi-decadal variability in CO2 fluxes. A detailed comparison among individual estimates and the introduction of a broad range of observations show (1) no consensus in the mean and trend in land-use change emissions, (2) a persistent low agreement among the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) an apparent underestimation of the CO2 variability by ocean models, originating outside the tropics. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding the global carbon cycle compared with previous publications of this data set (Le Quéré et al. 2018, 2016, 2015a, b, 2014, 2013).

The oceanic uptake of anthropogenic CO2 causes pronounced changes to the marine carbonate system. High quality pCO2 measurements with good temporal and spatial coverage are required to monitor the oceanic uptake, identify regions with pronounced carbonate system changes, and observe the effectiveness of CO2 emission mitigation strategies. There are currently several instruments available, but many are unsuitable for autonomous deployments on in situ platforms such as gliders, moorings and Argo floats. We assess currently available technology on its suitability for in situ deployment, with a focus on optode technology developments. Optodes for pCO2 measurements provide a promising new technological approach, and were successfully calibrated over the range of 280–480 μatm applying modified time-domain dual lifetime referencing. A laboratory precision of 0.8 μatm (n = 10) and a response time (τ90) of 165 s were achieved, and with further development pCO2 optodes may become as widely used as their oxygen counterparts.

The exchange of mass, heat, salt and anthropogenic carbon (Cant) between the South Atlantic, south of 24°S, and adjacent ocean basins is estimated from hydrographic data obtained during 2008–2009 using an inverse method. Transports of anthropogenic carbon are calculated across the western (Drake Passage), eastern (30°E) and northern (24°S) boundaries. The freshwater overturning transport of 0.09 Sv is southward, consistent with an overturning circulation that exports freshwater from the North Atlantic, and consistent with a bistable Meridional Overturning Circulation (MOC), under conditions of excess freshwater perturbation. At 30°E, net eastward Antarctic Circumpolar Current (ACC) transport, south of the Subtropical Front, is compensated by a 15.9 ± 2.3 Sv westward flow along the Antarctic boundary. The region as a whole is a substantial sink for atmospheric anthropogenic carbon of 0.51 ± 0.37 Pg C yr−1, of which 0.18 ± 0.12 Pg C yr−1 accumulates and is stored within the water column. At 24°S, a 20.2 Sv meridional overturning is associated with a 0.11 Pg C yr−1 Cant overturning. The remainder is transported into the Atlantic Ocean north of 24°S (0.28 ± 0.16 Pg C yr−1) and Indian sector of Southern Ocean (1.12 ± 0.43 Pg C yr−1), having been enhanced by inflow through Drake Passage (1.07 ± 0.44 Pg C yr−1). This underlines the importance of the South Atlantic as a crucial element of the anthropogenic carbon sink in the global oceans.

The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO2 values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water fCO2 values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water fCO2 has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. Highprofile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) "living data" publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al. 2013; Sabine et al. 2013; Bakker et al. 2014). Individual data set files, included in the synthesis product, can be downloaded here: doi:10.1594/PANGAEA.849770. The gridded products are available here: doi:10.3334/CDIAC/OTG.SOCAT-V3-GRID.

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere-the "global carbon budget"-is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates and consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models. We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ± reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2006-2015), EFF was 9.3±0.5 GtC yr-1, ELUC 1.0±0.5 GtC yr-1, GATM 4.5±0.1 GtC yr-1, SOCEAN 2.6±0.5 GtC yr-1, and SLAND 3.1±0.9 GtC yr-1. For year 2015 alone, the growth in EFF was approximately zero and emissions remained at 9.9±0.5 GtC yr-1, showing a slowdown in growth of these emissions compared to the average growth of 1.8%yr-1 that took place during 2006-2015. Also, for 2015, ELUC was 1.3±0.5 GtC yr-1, GATM was 6.3±0.2 GtC yr-1, SOCEAN was 3.0±0.5 GtC yr-1, and SLAND was 1.9±0.9 GtC yr-1. GATM was higher in 2015 compared to the past decade (2006-2015), reflecting a smaller SLAND for that year. The global atmospheric CO2 concentration reached 399.4±0.1 ppm averaged over 2015. For 2016, preliminary data indicate the continuation of low growth in EFF with C0.2% (range of-1.0 to C1.8 %) based on national emissions projections for China and USA, and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. In spite of the low growth of EFF in 2016, the growth rate in atmospheric CO2 concentration is expected to be relatively high because of the persistence of the smaller residual terrestrial sink (SLAND) in response to El Ninõ conditions of 2015-2016. From this projection of EFF and assumed constant ELUC for 2016, cumulative emissions of CO2 will reach 565±55 GtC (2075±205 GtCO2) for 1870-2016, about 75% from EFF and 25% from ELUC. This living data update documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this data set (Le Quéré et al. 2015b, a, 2014, 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center.

We present high-resolution autonomous measurements of carbon dioxide partial pressure p(CO2) taken in situ at the Porcupine Abyssal Plain sustained Observatory (PAP-SO) in the northeast Atlantic (49° N, 16.5° W; water depth of 4850 m) for the period 2010-2012. Measurements of p(CO2) made at 30 m depth on a sensor frame are compared with other autonomous biogeochemical measurements at that depth (including chlorophyll a fluorescence and nitrate concentration data) to analyse weekly to seasonal controls on p(CO2) flux in the inter-gyre region of the North Atlantic. Comparisons are also made with in situ regional time series data from a ship of opportunity and mixed layer depth (MLD) measurements from profiling Argo floats. There is a persistent under-saturation of CO2 in surface waters throughout the year which gives rise to a perennial CO2 sink. Comparison with an earlier data set collected at the site (2003-2005) confirms seasonal and inter-annual changes in surface seawater chemistry. There is year-to-year variability in the timing of deep winter mixing and the intensity of the spring bloom. The 2010-2012 period shows an overall increase in p(CO2) values when compared to the 2003-2005 period as would be expected from increases due to anthropogenic CO2 emissions. The surface temperature, wind speed and MLD measurements are similar for both periods of time. Future work should incorporate daily CO2 flux measurements made using CO2 sensors at 1 m depth and the in situ wind speed data now available from the UK Met Office Buoy.

Using measurements of the surface-ocean CO2 partial pressure (pCO2) and 14 different pCO2 mapping methods recently collated by the Surface Ocean pCO2 Mapping intercomparison (SOCOM) initiative, variations in regional and global sea-air CO2 fluxes are investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCO2 seasonality, in line with previous estimates. In terms of interannual variability (IAV), all mapping methods estimate the largest variations to occur in the eastern equatorial Pacific. Despite considerable spread in the detailed variations, mapping methods that fit the data more closely also tend to agree more closely with each other in regional averages. Encouragingly, this includes mapping methods belonging to complementary types - taking variability either directly from the pCO2 data or indirectly from driver data via regression. From a weighted ensemble average, we find an IAV amplitude of the global sea-air CO2 flux of 0.31 PgC yr1 (standard deviation over 1992-2009), which is larger than simulated by biogeochemical process models. From a decadal perspective, the global ocean CO2 uptake is estimated to have gradually increased since about 2000, with little decadal change prior to that. The weighted mean net global ocean CO2 sink estimated by the SOCOM ensemble is -1.75 PgC yr1 (1992-2009), consistent within uncertainties with estimates from ocean-interior carbon data or atmospheric oxygen trends.

Using measurements of the surface-ocean CO2 partial pressure (pCO2) and 14 different pCO2 mapping methods recently collated by the Surface Ocean pCO2 Mapping intercomparison (SOCOM) initiative, variations in regional and global sea-air CO2 fluxes have been investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCO2 seasonality, in line with previous estimates. In terms of interannual variability (IAV), all mapping methods estimate the largest variations to occur in the Eastern equatorial Pacific. Despite considerable spead in the detailed variations, mapping methods with closer match to the data also tend to be more consistent with each other. Encouragingly, this includes mapping methods belonging to complementary types - taking variability either directly from the pCO2 data or indirectly from driver data via regression. From a weighted ensemble average, we find an IAV amplitude of the global sea-air CO2 flux of 0.31 PgC yr-1 (standard deviation over 1992-2009), which is larger than simulated by biogeochemical process models. On a decadal perspective, the global CO2 uptake is estimated to have gradually increased since about 2000, with little decadal change prior to 2000. The weighted mean total ocean CO2 sink estimated by the SOCOM ensemble is consistent within uncertainties with estimates from ocean-interior carbon data or atmospheric oxygen trends.

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates as well as consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2, and land-cover change (some including nitrogen-carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2005-2014), EFF was 9.0 ± 0.5 GtC yrg'1, ELUC was 0.9 ± 0.5 GtC yrg'1, GATM was 4.4 ± 0.1 GtC yrg'1, SOCEAN was 2.6 ± 0.5 GtC yrg'1, and SLAND was 3.0 ± 0.8 GtC yrg'1. For the year 2014 alone, EFF grew to 9.8 ± 0.5 GtC yrg'1, 0.6 % above 2013, continuing the growth trend in these emissions, albeit at a slower rate compared to the average growth of 2.2 % yrg'1 that took place during 2005-2014. Also, for 2014, ELUC was 1.1 ± 0.5 GtC yrg'1, GATM was 3.9 ± 0.2 GtC yrg'1, SOCEAN was 2.9 ± 0.5 GtC yrg'1, and SLAND was 4.1 ± 0.9 GtC yrg'1. GATM was lower in 2014 compared to the past decade (2005-2014), reflecting a larger SLAND for that year. The global atmospheric CO2 concentration reached 397.15 ± 0.10 ppm averaged over 2014. For 2015, preliminary data indicate that the growth in EFF will be near or slightly below zero, with a projection of g'0.6 [range of g'1.6 to +0.5] %, based on national emissions projections for China and the USA, and projections of gross domestic product corrected for recent changes in the carbon intensity of the global economy for the rest of the world. From this projection of EFF and assumed constant ELUC for 2015, cumulative emissions of CO2 will reach about 555 ± 55 GtC (2035 ± 205 GtCO2) for 1870-2015, about 75 % from EFF and 25 % from ELUC. This living data update documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this data set (Le Quéré et al. 2015, 2014, 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP-2015).

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2, and land-cover-change (some including nitrogen-carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004-2013) EFF was 8.9 ± 0.4 GtC yr-1, ELUC 0.9 ± 0.5 GtC yr-1, GATM 4.3 ± 0.1 GtC yr-1, SOCEAN 2.6 ± 0.5 GtC yr-1, and SLAND 2.9 ± 0.8 GtC yr-1. For year 2013 alone, EFF grew to 9.9 ± 0.5 GtC yr-1, 2.3% above 2012, continuing the growth trend in these emissions, ELUC was 0.9 ± 0.5 GtC yr-1, GATM was 5.4 ± 0.2 GtC yr-1, SOCEAN was 2.9 ± 0.5 GtC yr-1, and SLAND was 2.5 ± 0.9 GtC yr-1. GATM was high in 2013, reflecting a steady increase in EFF and smaller and opposite changes between SOCEAN and SLAND compared to the past decade (2004-2013). The global atmospheric CO2 concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that EFF will increase by 2.5% (1.3-3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO2 yr-1), 65% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the global economy. From this projection of EFF and assumed constant ELUC for 2014, cumulative emissions of CO2 will reach about 545 ± 55 GtC (2000 ± 200 GtCO2) for 1870-2014, about 75% from EFF and 25% from ELUC. This paper documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this living data set (Le Quéré et al. 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP-2014).

© 2014. The Authors. The magnitude of marine plankton net community production (NCP) is indicative of both the biologically driven exchange of carbon dioxide between the atmosphere and the surface ocean and the export of organic carbon from the surface ocean to the ocean interior. In this study the seasonal variability in the NCP of five biogeochemical regions in the North Atlantic was determined from measurements of surface water dissolved oxygen and dissolved inorganic carbon (DIC) sampled from a Volunteer Observing Ship (VOS). The magnitude of NCP derived from dissolved oxygen measurements (NCPO2) was consistent with previous geochemical estimates of NCP in the North Atlantic, with an average annual NCPO2 of 9.5 ± 6.5 mmol O 2. m -2. d -1. Annual NCPO2 did not vary significantly over 35° of latitude and was not significantly different from NCP derived from DIC measurements (NCP DIC ). The relatively simple method described here is applicable to any VOS route on which surface water dissolved oxygen concentrations can be accurately measured, thus providing estimates of NCP at higher spatial and temporal resolution than currently achieved.

© 2014. The Authors. The magnitude of marine plankton net community production (NCP) is indicative of both the biologically driven exchange of carbon dioxide between the atmosphere and the surface ocean and the export of organic carbon from the surface ocean to the ocean interior. In this study the seasonal variability in the NCP of five biogeochemical regions in the North Atlantic was determined from measurements of surface water dissolved oxygen and dissolved inorganic carbon (DIC) sampled from a Volunteer Observing Ship (VOS). The magnitude of NCP derived from dissolved oxygen measurements (NCPO2) was consistent with previous geochemical estimates of NCP in the North Atlantic, with an average annual NCPO2 of 9.5 ± 6.5 mmol O 2. m -2. d -1. Annual NCPO2 did not vary significantly over 35° of latitude and was not significantly different from NCP derived from DIC measurements (NCP DIC ). The relatively simple method described here is applicable to any VOS route on which surface water dissolved oxygen concentrations can be accurately measured, thus providing estimates of NCP at higher spatial and temporal resolution than currently achieved.

The variability in the storage of the oceanic anthropogenic CO2 (Cant) on decadal timescales is evaluated within the main water masses of the Subtropical North Atlantic along 24.5°N. Inorganic carbon measurements on five cruises of the A05 section are used to assess the changes in Cant between 1992 and 2011, using four methods (δC*, TrOCA, ϕCT0, TTD). We find good agreement between the Cant distribution and storage obtained using chlorofluorocarbons and CO2 measurements in both the vertical and horizontal scales. Cant distribution shows higher concentrations and greater decadal storage rates in the upper layers with both values decreasing with depth. The greatest enrichment is obserbed in the central water masses, with their upper limb showing a mean annual accumulation of about 1μmolkg-1yr-1 and the lower limb showing, on average, half that value. We detect zonal gradients in the accumulation of Cant. This finding is less clear in the upper waters, where greater variability exists between methods. In accordance with data from time series stations, greater accumulation of Cant is observed in the upper waters of the western basin of the North Atlantic Subtropical Gyre. In intermediate and deep layers, the zonal gradient in the storage of Cant is more robust between methods. The much lower mean storage rates found along the section (

The Surface Ocean CO2 Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO2 (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface water fCO 2 values) and extended data coverage (from 1968-2007 to 1968-2011). The quality control criteria, while identical in both versions, have been applied more strictly in version 2 than in version 1. The SOCAT website (http://www.socat.info/) has links to quality control comments, metadata, individual data set files, and synthesis and gridded data products. Interactive online tools allow visitors to explore the richness of the data. Applications of SOCAT include process studies, quantification of the ocean carbon sink and its spatial, seasonal, year-to-year and longerterm variation, as well as initialisation or validation of ocean carbon models and coupled climate-carbon models. © Author(s) 2014. CC Attribution 3.0 License.

Water column dissolved inorganic carbon and total alkalinity were measured during five hydrographic sections in the Atlantic Ocean and Drake Passage. The work was funded through the Strategic Funding Initiative of the UK's Oceans2025 programme, which ran from 2007 to 2012. The aims of this programme were to establish the regional budgets of natural and anthropogenic carbon in the North Atlantic, the South Atlantic, and the Atlantic sector of the Southern Ocean, as well as the rates of change of these budgets. This paper describes in detail the dissolved inorganic carbon and total alkalinity data collected along east"west sections at 47° N to 60° N, 24.5° N, and 24° S in the Atlantic and across two Drake Passage sections. Other hydrographic and biogeochemical parameters were measured during these sections, and relevant standard operating procedures are mentioned here. Over 95% of dissolved inorganic carbon and total alkalinity samples taken during the 24.5° N, 24° S, and the Drake Passage sections were analysed onboard and subjected to a first-level quality control addressing technical and analytical issues. Samples taken along 47° N to 60° N were analysed and subjected to quality control back in the laboratory. Complete post-cruise second-level quality control was performed using crossover analysis with historical data in the vicinity of measurements, and data were submitted to the CLIVAR and Carbon Hydrographic Data Office (CCHDO), the Carbon Dioxide Information Analysis Center (CDIAC) and and will be included in the Global Ocean Data Analyses Project, version 2 (GLODAP 2), the upcoming update of Key et al. (2004). © Author(s) 2014.

We present a new observation-based estimate of the global oceanic carbon dioxide (CO2) sink and its temporal variation on a monthly basis from 1998 through 2011 and at a spatial resolution of 1×1. This sink estimate rests upon a neural network-based mapping of global surface ocean observations of the partial pressure of CO2 (pCO2) from the Surface Ocean CO2 Atlas database. The resulting pCO2 has small biases when evaluated against independent observations in the different ocean basins, but larger randomly distributed differences exist particularly in high latitudes. The seasonal climatology of our neural network-based product agrees overall well with the Takahashi et al. (2009) climatology, although our product produces a stronger seasonal cycle at high latitudes. From our global pCO2 product, we compute a mean net global ocean (excluding the Arctic Ocean and coastal regions) CO2 uptake flux of -1.42 ± 0.53 Pg C yr-1, which is in good agreement with ocean inversion-based estimates. Our data indicate a moderate level of interannual variability in the ocean carbon sink (±0.12 Pg C yr-1, 1σ) from 1998 through 2011, mostly originating from the equatorial Pacific Ocean, and associated with the El Niño-Southern Oscillation. Accounting for steady state riverine and Arctic Ocean carbon fluxes our estimate further implies a mean anthropogenic CO2 uptake of -1.99 ± 0.59 Pg C yr-1 over the analysis period. From this estimate plus the most recent estimates for fossil fuel emissions and atmospheric CO2 accumulation, we infer a mean global land sink of -2.82 ± 0.85 Pg C yr-1 over the 1998 through 2011 period with strong interannual variation.

The Atlantic Ocean is one of the most important sinks for atmospheric carbon dioxide (CO2), but this sink has been shown to vary substantially in time. Here we use surface ocean CO2 observations to estimate this sink and the temporal variability from 1998 through 2007 in the Atlantic Ocean. We benefit from (i) a continuous improvement of the observations, i.e. the Surface Ocean CO2 Atlas (SOCAT) v1.5 database and (ii) a newly developed technique to interpolate the observations in space and time. In particular, we use a two-step neural network approach to reconstruct basin-wide monthly maps of the sea surface partial pressure of CO2 (pCO2) at a resolution of 1° × 1°. From those, we compute the air-sea CO2 flux maps using a standard gas exchange parameterization and high-resolution wind speeds. The neural networks fit the observed pCO2 data with a root mean square error (RMSE) of about 10 μatm and with almost no bias. A check against independent time-series data and new data from SOCAT v2 reveals a larger RMSE of 22.8 μatm for the entire Atlantic Ocean, which decreases to 16.3 μatm for data south of 40 °N. We estimate a decadal mean uptake flux of -0.45 ± 0.15 Pg C yr-1 for the Atlantic between 44 °S and 79 °N, representing the sum of a strong uptake north of 18 °N (-0.39 ± 0.10 Pg C yr-1), outgassing in the tropics (18 °S-18 °N, 0.11 ± 0.07 Pg C yr-1), and uptake in the subtropical/temperate South Atlantic south of 18 °S (-0.16 ± 0.06 Pg C yr-1), consistent with recent studies. The strongest seasonal variability of the CO2 flux occurs in the temperature-driven subtropical North Atlantic, with uptake in winter and outgassing in summer. The seasonal cycle is antiphased in the subpolar latitudes relative to the subtropics largely as a result of the biologically driven winter-to-summer drawdown of CO2. Over the 10 yr analysis period (1998 through 2007), sea surface pCO2 increased faster than that of the atmosphere in large areas poleward of 40 °N, while in other regions of the North Atlantic the sea surface pCO2 increased at a slower rate, resulting in a barely changing Atlantic carbon sink north of the Equator (-0.01 ± 0.02 Pg C yr-1 decade-1). Surface ocean pCO2 increased at a slower rate relative to atmospheric CO2 over most of the Atlantic south of the Equator, leading to a substantial trend toward a stronger CO2 sink for the entire South Atlantic (-0.14 ± 0.02 Pg C yr-1 decade-1). In contrast to the 10 yr trends, the Atlantic Ocean carbon sink varies relatively little on inter-annual timescales (±0.04 Pg C yr-1; 1 σ). © Author(s) 2013.

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. © 2013 Author(s).

As a response to public demand for a well-documented, quality controlled, publically available, global surface ocean carbon dioxide (CO2) data set, the international marine carbon science community developed the Surface Ocean CO2 Atlas (SOCAT). The first SOCAT product is a collection of 6.3 million quality controlled surface CO2 data from the global oceans and coastal seas, spanning four decades (1968-2007). The SOCAT gridded data presented here 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 CO2 fugacity (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 (e.g. regional differences in the seasonal cycles), but also contains biases and limitations that the user needs to recognize and address (e.g. local influences on values in some coastal regions). © 2013 Author(s).

The oceans are an important sink for anthropogenically produced CO(2), and on time scales longer than a century they will be the main repository for the CO(2) that humans are emitting. Our knowledge of how ocean uptake varies (regionally and temporally) and the processes that control it is currently observation-limited. Traditionally, and based on sparse observations and models at coarse resolution, ocean uptake has been thought to be relatively invariant. However, in the few places where we have enough observations to define the uptake over periods of many years or decades, it has been found to change substantially at basin scales, responding to indices of climate variability. We illustrate this for three well-studied regions: the equatorial Pacific, the Indian Ocean sector of the Southern Ocean, and the North Atlantic. A lesson to take from this is that ocean uptake is sensitive to climate (regionally, but presumably also globally). This reinforces the expectation that, as global climate changes in the future owing to human influences, ocean uptake of CO(2) will respond. To evaluate and give early warning of such carbon-climate feedbacks, it is important to track trends in both ocean and land sinks for CO(2). Recent coordinated observational programmes have shown that, by organization of an observing network, the atmosphere-ocean flux of CO(2) can, in principle, be accurately tracked at seasonal or better resolution, over at least the Northern Hemisphere oceans. This would provide a valuable constraint on both the ocean and (by difference) land vegetation sinks for atmospheric CO(2).

Recent data suggest the accumulation of anthropogenic carbon dioxide (△Canth) in the subtropical North Atlantic is not occurring at a steady rate throughout the water column. Carbon measurements from three transatlantic cruises along 24.5°N in 1992, 1998, and 2004 were investigated for changes in Canth using both a back-calculation shortcut technique and extended multiple linear regression. For three time periods (1992-1998, 1998-2004, and 1992-2004) we observed spatial and vertical changes in Canth storage, along with a general increase in total concentration. In the surface layers, total dissolved inorganic carbon (TCO 2) and Canth concentrations increased in line with atmospheric CO2 levels: TCO2 +8.8 ± 0.5 μmol kg-1 for 1992-1998 and +8.6 ± 0.5 μmol kg-1 for 1998-2004 and Canth +8.0 ± 0.2 μmol kg-1 for 1992-1998 and +6.8 ± 0.3 mmol kg-1 for 1998-2004. In deeper waters, △Canth was significantly different than zero for all depths above 5000 dbar between 1992 and 2004, while on a subdecadal timescale, significant variability was observed for △Canth at a depth range of 800-1000 dbar. Evidence is presented for the arrival at 24.5°N at depth of freshly ventilated Labrador Sea Water from the subpolar North Atlantic between 1992 and 1998, as well as consistent smaller △Canth signals alongside the Mid-Atlantic Ridge. This is in addition to low-level, stable increases identified in the deep eastern basin between 1992 and 2004, the first time that △Canth has been detected and confirmed by new measurements of carbon tetrachloride and CFC-11 from 2004. These results highlight the importance of the subtropics as a site for long-term C anth storage away from the surface. © 2010 by the American Geophysical Union.

Future climate change as a result of increasing atmospheric CO2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary production and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic Ocean for the period between 2005 and 2007. Monthly observations were made between the English Channel and the Bay of Biscay using a ship of opportunity program. During the colder winter of 2005/2006, the maximum depth of the mixed layer reached up to 650 m in the Bay of Biscay, whilst during the warmer (by 2.6 a± 0.5 a°C) winter of 2006/2007 the mixed layer depth reached only 300 m. The inter-annual differences in late winter concentrations of nitrate (2.8 ± 1.1 μmol l−1) and dissolved inorganic carbon (22 a± 6 μmol kg−1, with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the chlorophyll α-fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO2 fluxes (ranging from +3.7 to ĝ̂'4.8 mmol mĝ̂'2 d−1) showed an increased oceanic CO2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences. ©Author(s) 2010. CC Attribution 3.0 License.

A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al. 2002. Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 μatm y-1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 μatm y-1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niño periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air-sea CO2 flux is estimated using the sea-air pCO2 difference and the air-sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979-2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N-14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y-1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of -0.70 Pg-C y-1 for the northern and -1.05 Pg-C y-1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of -2.5 tons-C month-1 km-2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°-62°S), the mean annual flux is small (-0.06 Pg-C y-1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be -1.6±0.9 Pg-C y-1, which includes an undersampling correction to the direct estimate of -1.4±0.7 Pg-C y-1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y-1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be -2.0±1.0 Pg-C y-1 in 2000. © 2008 Elsevier Ltd.

Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO2) for the North Atlantic on a 1° latitude by 1° longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO 2. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFS-MODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437 μatm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 μatm, which equals to just above 3 per cent of an average pCO2 value in the in situ dataset. The seasonal pCO2 cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO2 fluxes or improvement of seasonal and interannual marine CO2 cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences.

As part of the U.K. contribution to the international Surface Ocean - Lower Atmosphere Study, a series of three related projects - DOGEE, SEASAW, and HiWASE - undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosol-size spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurements campaigns. © 2009 American Meteorological Society.

Highly accurate and precise measurements of marine carbon components are required in the study of the marine carbon cycle, particularly when investigating the causes for its variability from seasonal to interannual timescales. This is especially true in the investigation of the consequences of anthropogenic influences. The analysis of any marine carbon component requires elaborate instrumentation, most of which is currently used onboard ships, either in manual or automated mode. Technological developments result in more and more instruments that have sufficient long-term reliability so that they can be deployed on commercial ships, surface moorings, and buoys, whilst the great technological and operational challenges mean that only few sensors have been developed that can be used for sub-surface in situ measurements on floats, robots, or gliders. There is a special need for autonomous instruments and sensors that are able to measure a combination of different components, in order to increase the spatial and temporal coverage of marine carbon data. This paper describes analytical techniques used for the measurement of the marine dissolved carbon components, both inorganic and organic: the fugacity of CO 2, total dissolved inorganic carbon, pH, alkalinity, and dissolved organic carbon. By pointing out advantages, disadvantages, and/or challenges of the techniques employed in the analysis of each component, we aim to aid non-carbon marine scientists, sensor developers and technologists, in the decision of which challenges to address in further development. © 2013 Author(s).

The primary instrumentation that deals with the problems of parameterizing the physical exchange of gases and aerosol at the air-sea interface has been described while some additional details of measurement systems and techniques have been provided. The measurement systems being discussed include the autoflux, wave measurements, aerosol measurements, bubble measurements, DMS measurements and surface film measurements. The autoflux is an autonomous system for making continuous direct measurements of air-sea fluxes while also support the mean meteorological parameters. As for wave measurements, the shipborne wave recorders (SBWRs) were the ones being used as it consist of two pairs of accelerometers and pressure sensors. Meanwhile, the compact lightweight aerosol spectrometer probe (CLASP) was used for the aerosol flux measurement which was specifically designed for the direct use in eddy covariance flux measurements of marine aerosol.

The oceans are a major sink for atmospheric carbon dioxide (CO2). Historically, observations have been too sparse to allow accurate tracking of changes in rates of CO2 uptake over ocean basins, so little is known about how these vary. Here, we show observations indicating substantial variability in the CO2 uptake by the North Atlantic on time scales of a few years. Further, we use measurements from a coordinated network of instrumented commercial ships to define the annual flux into the North Atlantic, for the year 2005, to a precision of about 10%. This approach offers the prospect of accurately monitoring the changing ocean CO2 sink for those ocean basins that are well covered by shipping routes.

We examine observations from 1990 to 2006 from four voluntary observing ships and two time-series stations in the North Atlantic, fitting a sinusoidal annual cycle and linear year-on-year trend at all locations where there are sufficient data. Results show that in the subtropical regions, sea-surface fCO2 has closely followed the increasing trend in atmospheric fCO2. In contrast, farther north, sea-surface fCO2 has increased faster than fCO2 in the atmosphere. The resulting ΔfCO2, driving air-sea flux of CO2, has therefore decreased in the North Atlantic, particularly at higher latitudes, as has the annual mean air-sea flux. Several underlying causes may have led to the observed changes in sea-surface fCO2. Low-frequency modes, such as the North Atlantic Oscillation, lead to changes in the sea-surface temperature, in sea-surface circulation and in vertical mixing, affecting sea-surface fCO2 through biogeochemical processes. A comparison with measurements covering a longer time period shows that the sea-surface fCO2 rise has accelerated since 1990 in the northern North Atlantic. © 2008 Elsevier Ltd.

Observational studies report a rapid decline of ocean CO2 uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physicalbiological numerical simulations forced with interannually varying atmospheric conditions for the period 1979-2004. In the simulations, surface ocean water mass properties and CO2 system variables exhibit substantial multiannual variability on subbasin scales in response to wind-driven reorganization in ocean circulation and surface warming/cooling. The simulated temporal evolution of the ocean CO2 system is broadly consistent with reported observational trends and is influenced substantially by the phase of the North Atlantic Oscillation (NAO). Many of the observational estimates cover a period after 1995 of mostly negative or weakly positive NAO conditions, which are characterized in the simulations by reduced North Atlantic Current transport of subtropical waters into the eastern basin and by a decline in CO2 uptake. We suggest therefore that air-sea CO2 uptake may rebound in the eastern temperate North Atlantic during future periods of more positive NAO, similar to the patterns found in our model for the sustained positive NAO period in the early 1990s. Thus, our analysis indicates that the recent rapid shifts in CO2 flux reflect decadal perturbations superimposed on more gradual secular trends. The simulations highlight the need for long-term ocean carbon observations and modeling to fully resolve multiannual variability, which can obscure detection of the long-term changes associated with anthropogenic CO2 uptake and climate change. Copyright 2008 by the American Geophysical Union.

A time series of observations from merchant ships between the U.K. and the Caribbean is used to establish the variability of sea surface pCO2 and air-to-sea flux from the mid-1990s to early 2000s. We show that the sink for atmospheric CO2 exhibits important interannual variability, which is in phase across large regions from year to year. Additionally, there has been an interdecadal decline, evident throughout the study region but especially significant in the northeast of the area covered, with the sink reducing >50% from the mid-1990s to the period 2002-2005. A review of available observations suggests a large region of decrease covering much of the North Atlantic but excluding the western subtropical areas. We estimate that the uptake of the region between 20°N and 65°N declined by ∼0.24 Pg C a-1 from 1994/1995 to 2002-2005. Declining rates of wintertime mixing and ventilation between surface and subsurface waters due to increasing stratification, linked to variation in the North Atlantic Oscillation, are suggested as the main cause of the change. These are exacerbated by a contribution from the changing buffer capacity of the ocean water, as the carbon content of surface waters increases. Copyright 2007 by the American Geophysical Union.