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As part of the second phase of the Regional Carbon Cycle Assessment and Processes project (RECCAP2), we present an assessment of the carbon cycle of the Atlantic Ocean, including the Mediterranean Sea, between 1985 and 2018 using global ocean biogeochemical models (GOBMs) and estimates based on surface ocean carbon dioxide (CO2) partial pressure (pCO2 products) and ocean interior dissolved inorganic carbon observations. Estimates of the basin-wide long-term mean net annual CO2 uptake based on GOBMs and pCO2 products are in reasonable agreement (−0.47 ± 0.15 PgC yr−1 and −0.36 ± 0.06 PgC yr−1, respectively), with the higher uptake in the GOBM-based estimates likely being a consequence of a deficit in the representation of natural outgassing of land derived carbon. In the GOBMs, the CO2 uptake increases with time at rates close to what one would expect from the atmospheric CO2 increase, but pCO2 products estimate a rate twice as fast. The largest disagreement in the CO2 flux between GOBMs and pCO2 products is found north of 50°N, coinciding with the largest disagreement in the seasonal cycle and interannual variability. The mean accumulation rate of anthropogenic CO2 (Cant) over 1994–2007 in the Atlantic Ocean is 0.52 ± 0.11 PgC yr−1 according to the GOBMs, 28% ± 20% lower than that derived from observations. Around 70% of this Cant is taken up from the atmosphere, while the remainder is imported from the Southern Ocean through lateral transport

The dynamic and thermohaline characteristics of the Atlantic Ocean linked to the Atlantic Meridional Overturning Circulation (AMOC) give it a specific role in the accumulation of heat and CO2, either of natural or anthropogenic origin (Cant), from the surface layer to the deep waters, significantly mitigating the impacts of anthropogenic climate change. Here, we evaluate the annual mean, long-term trends, seasonal cycle and interannual variability of net sea-air CO2 fluxes (FCO2) between 1985 and 2018 based on observation products (pCO2-products) and global ocean biogeochemical models (GOBMs) for the Atlantic from 30ºS to the Nordic Seas (~79ºN) and the Mediterranean. The mean contemporary FCO2 (sum of anthropogenic and natural components) is estimated to be 0.362 ± 0.067 and 0.47 ± 0.15 Pg C yr-1 using pCO2-products and GOBMs, respectively. The GOBMs show consistent growth trends in CO2 uptake with rates similar to the atmospheric CO2 growth, however trends obtained from CO2-products show a sharp increase from the pre-2000 period to the post-2000 period. There is overall agreement between pCO2-products and GOBMs results for mean values, seasonal cycle and interannual variability in all biomes, except for the North Atlantic subpolar biome, where pCO2-products show lower mean values, larger trends, and a different seasonal cycle than GOBMs. The GOBMs and pCO2-products show very concordant values in equatorial and subtropical regions, where CO2 variability is strongly determined by temperature. For the period 1994-2007, GOBMs show concordant values in annual Cant storage rate with carbonate marine system observations (Gruber et al., 2019) with values of 0.506 ± 0.106 Pg C yr-1 vs 0.673 ± 0.066 Pg C yr-1, respectively. The Cant storage rate agreement between GOBMs and observations are also registered in the different biomes, although in both permanently stratified subtropical in North and South Atlantic biomes, the storage rates in GOBMs show a larger spread with their

Around 31% of carbon dioxide derived from human activities (Canth) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Sabine et al., 2004). This accumulation helps to mitigate atmospheric carbon dioxide (CO2), but in turn leads to severe consequences on marine systems (IGBP, IOC, SCOR, 2013). Both components of CO2, i.e. anthropogenic and natural, present high variability and uncertainties difficult to observe and quantify. In particular, the Canth signal represents a small fraction of the total dissolved inorganic carbon pool (CT) and it is not directly distinguishable from the natural component, resulting in the emergence of back-calculation techniques (Brewer 1978; Chen and Millero, 1979) to derive it indirectly. Over the years, back-calculation techniques have undergone remarkable improvements (Gruber et al., 1996; Sabine et al., 2004; Touratier et al., 2004, 2007; Vázquez-Rodríguez et al., 2009a, 2009b, 2012), resulting in different methods for estimating Canth that, despite providing helpful and advanced results, show various biases and limitations. Here, we present a new approach for estimating Canth that relies on a back-calculation methodology, purely based on carbon data, and provides results that show good agreement with previous global Canth climatologies. Our approach mainly differs from previous methodologies by pioneering using the transport matrix output from a data‐assimilating ocean circulation inverse model (TMI: Total Matrix Intercomparison; Gebbie and Huybers, 2010) to obtain preformed properties, instead of the historical use of Optimum Multiparameter analysis (OMP). This improvement prevents from the need to use (sub)surface-property linear regressions to estimate preformed alkalinity or air-sea CO2 disequilibrium, and allows introducing different corrections for denitrification and, as a novelty, oxygen disequilibrium

During the FIGURE-CARING cruise (https://doi.org/10.17600/18002940) on board the RV/Atlantic Explorer (21-30 Jul 2022), CTD-rosette discrete water samples were taken to measure pH and total alkalinity (TA), by means of a JASCO V-750 double beam spectrophotometer and an automatic potentiometric titrator "Titrando 809 Metrohm", respectively. The first, located in the air-conditioned RV/AE laboratory (End Lab), the latter, located ashore at the Institute of Marine Research (IIM-CSIC; Vigo, Spain). Further details on the water sampling/storage procedure can be found in the cruise report (Benavides and Carracedo, 2022; https://doi.org/10.13155/96692). The processing steps by parameter, as well as the QC and the final data, are described/shown in this data report. The corresponding datafile is provided as a CSV file (Carracedo et al., 2022; https://doi.org/10.17882/96728).

Since the industrial revolution, human activities have emitted large amount of anthropogenic carbon (Cant) into the atmosphere through the burning of fossil fuel, the production of cement and land-use change. Via air-sea gas exchange, the ocean absorbs roughly a third of Cant, meaning that Cant is an additional source of carbon for the ocean. In particular, the North Atlantic is known to be a region with a high storage capacity of Cant. Whereas the distribution of Cant in the upper layers of the North Atlantic is well documented, its transport to the abyssal ocean and the mechanisms behind its deep redistribution remain scarcely described. To shed light on this research gap, we use a database provided by ~70 Deep-Argo floats equipped with oxygen sensors and located in the North Atlantic that allow us to explore the deep pathways of Cant. First, the macronutrients and carbon variables (pH, total alkalinity, total inorganic carbon and pCO2) are estimated with bayesian neural networks (CANYON-B and CONTENT) from the temperature, salinity and oxygen data of the floats. Second, Cant concentrations in the water column are then estimated with back-calculation methods. Here we present the first results of our study

The OVIDE section, composed of a hundred top-to-bottom stations from Portugal to Greenland, has been visited biennially since 2002. Collected data show a strong variability of both the Atlantic Meridional Overturning Circulation (AMOC) and of the water mass properties. The OVIDE-AMOC timeseries built upon the Argo array and altimetry has been updated and validated with the in-situ cruise estimates. It shows a strong seasonal variability and, on longer time scales, significant transition in 2014, from moderate (19 Sv) to strong (23 Sv) amplitude, along with the development of a fresh and cold anomaly in the upper 800m over the eastern subpolar Atlantic, discussed in the literature and observed at the OVIDE section. Through a composite analysis of both transport and property data, we compare the 2002-2012 OVIDE average with the 2014-2018 average and analyze the evolutions of the transports of the different water masses with special attention to LSW, which has been largely renewed since 2014 through deep convection in the western subpolar gyre

About 30% of the carbon dioxide derived from human activities (CANTH) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Friedlingstein et al., 2021), with the North Atlantic (NA) being one of the largest CANTH sinks per unit area (Khatiwala et al., 2013; Sabine et al., 2004). In the NA, oceanic CANTH uptake strongly relies on the meridional overturning circulation and the associated regional winter deep convection. In fact, the formation and deep spreading of Labrador Sea Water stands as a critical CANTH gateway to intermediate and abyssal depths. The NA CANTH uptake has fluctuated over the years according to changes in the North Atlantic Oscillation. Biennial observation of the marine carbonate system along the Go-Ship A25-OVIDE section has allowed us assessing the decadal and interannual variability of the CANTH storage in the subpolarNA from 2002 to 2021. In this study, we investigate 1) the trend of CANTH and 2) the relationship between the CANTH saturation, the apparent oxygen utilization, and the ventilation of the water masses between the A25-OVIDE section and the Greenland-Iceland-Scotland sills during 2002-2021. We divided the A25-OVIDE section into three main basins (Irminger, Iceland, and Eastern NA). Our results show that the Irminger Basin presents a more homogenous CANTH profile and higher CANTH saturation values at depth than the other two basins, which is related to the pronounced convective activity in the Irminger Basin. In contrast, the Eastern NA Basin has higher CANTH values at the surface due to its higher surface temperature, but its deep water masses show the lowest CANTH values since they are the less ventilated in the section. Our analysis also reveals that, overall, the NA CANTH storage has increased during 2002-2021, but varied according to the ventilation changes. While the Eastern NA water masses experienced a relatively constant, although shallower, average ventilation, the Irminger and Iceland Basins underwent a less

Despite covering only 15% of the global oceanic area, the North Atlantic (NA) accumulates one of the highest contents of anthropogenic CO2 (CANTH) in the ocean, storing 23% of the oceanic CANTH (Sabine et al., 2004). In terms of CANTH increase, large regions of the NA recorded average rates of 1.2 ± 0.1 mol m-2 yr-1 during 1994-2007, doubling the global oceanic rate of CANTH increase of 0.65 ± 0.08 mol m-2 yr-1 (Gruber et al., 2019). In the NA, high CANTH concentrations penetrate to mid and abyssal depths as a result of the formation and deep spreading of Labrador Sea Water. These processes are linked to the meridional overturning circulation and winter convection occurring in the NA subpolar gyre. Differences in CANTH storage rates have been observed between different phases of the NA Oscillation (NAO), attributed to both changes in CANTH concentration and decreases in volumetric water mass census (Fröb et al., 2018). There has been a 50% slowdown in the rate of CANTH increase in the NA subpolar gyre between 1994 and 2007, coinciding with a period of low NAO. Biennial observation of the marine carbonate system along the GOSHIP A25-OVIDE section has allowed assessing the long-term and interannual variability of the CANTH storage in the subpolar NA from 2002 to 2018. In this research, we determined the increases of CANTH in the water masses present between the OVIDE section and the Nordic sills. The average accumulation rate CANTH in the water column between the A25-OVIDE section and the sills was 0.90 ± 0.08 mol m-2 yr-1 (0.041 ± 0.003 Pg-C yr-1) for 2002-2021, being 61% higher than the 0.54 ± 0.06 mol m-2 yr-1 observed for 1997-2006 (low NAO). The increase in the CANTH accumulation rate during 2002-2021 is mainly found in the Irminger and Iceland basins and is mainly associated with the period of high NAO that occurred after 2014. In these two basins, the CANTH accumulation rates during the high NAO double those found during the low NAO

Marta López, PhD student at IIM-CSIC, & Marcos Fontela, ERC at the Centre of Marine Science of Algarve (CCMAR), work at BOCATS2 research project. They'll show us how they do their research aboard the Research Vessel Sarmiento de Gamboa (part of the Spanish Research Council fleet) in their trip along the GOSSIP section in the North Atlantic Ocean