Description: The stable carbon isotope composition of dissolved inorganic carbon (δ13C-DIC) can be used to quantify fluxes within the carbon system. For example, knowing the δ13C signature of the inorganic carbon pool can help in describing the amount of anthropogenic carbon in the water column. The measurements can also be used for evaluating modeled carbon fluxes, for making basin-wide estimates of anthropogenic carbon, and for studying seasonal and interannual variability or decadal trends in interior ocean biogeochemistry. For all these purposes, it is not only important to have a sufficient amount of data, but these data must also be internally consistent and of high quality. In this study, we present a δ13C-DIC dataset for the North Atlantic which has undergone secondary quality control. The data originate from oceanographic research cruises between 1981 and 2014. During a primary quality control step based on simple range tests, obviously bad data were flagged. In a second quality control step, biases between measurements from different cruises were quantified through a crossover analysis using nearby data of the respective cruises, and values of biased cruises were adjusted in the data product. The crossover analysis was possible for 24 of the 32 cruises in our dataset, and adjustments were applied to 11 cruises. The internal accuracy of this dataset is 0.017 ‰.

Description: The stable carbon isotope composition of dissolved inorganic carbon (δ13CDIC) in seawater was measured in samples collected during June—July 2014 in the subpolar North Atlantic. Sample collection was carried out on the RRS James Clark Ross cruise JR302, part of the "Radiatively Active Gases from the North Atlantic Region and Climate Change" (RAGNARoCC) research programme. The observed δ13CDIC values for cruise JR302 fall in a range from 0.07 ‰ to +1.95 ‰, relative to the Vienna Peedee Belemnite standard. From duplicate samples collected during the cruise, the 1σ precision for the 341 results is 0.08 ‰, which is similar to our previous work and other studies of this kind. We also performed a cross-over analysis using nearby historical δ13CDIC data, which indicated that there were no significant systematic offsets between our measurements and previously published results. We also included seawater reference material (RM) produced by A. G. Dickson (Scripps Institution of Oceanography, USA) in every batch of analysis, enabling us to improve upon the calibration and quality-control procedures from a previous study. The δ13CDIC is consistent within each RM batch, although its value is not certified. We report δ13CDIC values of 1.15 ± 0.03 ‰ and 1.27 ± 0.05 ‰ for batches 141 and 144 respectively. Our JR302 δ13CDIC data can be used – along with measurements of other biogeochemical variables – to constrain the processes that control DIC in the interior ocean, in particular the oceanic uptake of anthropogenic carbon dioxide and the biological carbon pump. Our δ13CDIC results are available from the British Oceanographic Data Centre – doi:10.5285/22235f1a-b7f3-687f-e053-6c86abc0c8a6.

Description: 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. High-profile 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.

Description: Shelf seas play an important role in the global carbon cycle, absorbing atmospheric carbon dioxide (CO2) and exporting carbon (C) to the open ocean and sediments. The magnitude of these processes is poorly constrained, because observations are typically interpolated over multiple years. Here, we used 298500 observations of CO2 fugacity (fCO2) from a single year (2015), to estimate the net influx of atmospheric CO2 as 26.2 ± 4.7 Tg C yr−1 over the open NW European shelf. CO2 influx from the atmosphere was dominated by influx during winter as a consequence of high winds, despite a smaller, thermally-driven, air-sea fCO2 gradient compared to the larger, biologically-driven summer gradient. In order to understand this climate regulation service, we constructed a carbon-budget supplemented by data from the literature, where the NW European shelf is treated as a box with carbon entering and leaving the box. This budget showed that net C-burial was a small sink of 1.3 ± 3.1 Tg C yr−1, while CO2 efflux from estuaries to the atmosphere, removed the majority of river C-inputs. In contrast, the input from the Baltic Sea likely contributes to net export via the continental shelf pump and advection (34.4 ± 6.0 Tg C yr−1).

Description: The stable isotopic composition of particulate organic carbon (δ13CPOC) in the surface waters of the global ocean can vary with the aqueous CO2 concentration ([CO2(aq)]) and affects the trophic transfer of carbon isotopes in the marine food web. Other factors such as cell size, growth rate and carbon concentrating mechanisms decouple this observed correlation. Here, the variability in δ13CPOC is investigated in surface waters across the south subtropical convergence (SSTC) in the Atlantic Ocean, to determine carbon isotope fractionation (ϵp) by phytoplankton and the contrasting mechanisms of carbon uptake in the subantarctic and subtropical water masses. Our results indicate that cell size is the primary determinant of δ13CPOC across the Atlantic SSTC in summer. Combining cell size estimates with CO2 concentrations, we can accurately estimate "p within the varying surface water masses in this region. We further utilize these results to investigate future changes in "p with increased anthropogenic carbon availability. Our results suggest that smaller cells, which are prevalent in the subtropical ocean, will respond less to increased [CO2(aq)] than the larger cells found south of the SSTC and in the wider Southern Ocean. In the subantarctic water masses, isotopic fractionation during carbon uptake will likely increase, both with increasing CO2 availability to the cell, but also if increased stratification leads to decreases in average community cell size. Coupled with decreasing δ13C of [CO2(aq)] due to anthropogenic CO2 emissions, this change in isotopic fractionation and lowering of δ13CPOC may propagate through the marine food web, with implications for the use of δ13CPOC as a tracer of dietary sources in the marine environment.

Description: Marine dissolved organic matter (DOM) presents key thermodynamic properties that are not yet fully constrained. Here, we report the distribution of binding sites occupied by protons (i.e., proton affinity spectra) and parametrize the median intrinsic proton binding affinities (log K̅H) and heterogeneities (m), for DOM samples extracted from the North Atlantic. We estimate that 11.4 ± 0.6% of C atoms in the extracted marine DOM have a functional group with a binding site for ionic species. The log K̅H of the most acidic groups was larger (4.01–4.02 ± 0.02) than that observed in DOM from coastal waters (3.82 ± 0.02), while the chemical binding heterogeneity parameter increased with depth to values (m1= 0.666 ± 0.009) ca. 10% higher than those observed in surface open ocean or coastal samples. On the contrary, the log K̅H for the less acidic groups shows a difference between the surface (10.01 ± 0.08) and deep (9.22 ± 0.35) samples. The latter chemical groups were more heterogeneous for marine than for terrestrial DOM, and m2 decreased with depth to values of 0.28 ± 0.03. Binding heterogeneity reflects aromatic carbon compounds’ persistence and accumulation in diverse, low-abundance chemical forms, while easily degradable low-affinity groups accumulate more uniformly in the deep ocean.