Stable carbon isotopes of dissolved inorganic carbon for a zonal transect across the subpolar North Atlantic Ocean in summer 2014

Abstract. The stable carbon isotope composition of dissolved inorganic carbon (δ¹³C_DIC) 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 δ¹³C_DIC values for cruise JR302 fall in a range from −0.07 to +1.95 ‰, relative to the Vienna Pee Dee 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 δ¹³C_DIC 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 δ¹³C_DIC is consistent within each RM batch, although its value is not certified. We report δ¹³C_DIC values of 1.15 ± 0.03 ‰ and 1.27 ± 0.05 ‰ for batches 141 and 144 respectively. Our JR302 δ¹³C_DIC 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 δ¹³C_DIC results are available from the British Oceanographic Data Centre – doi:10.5285/22235f1a-b7f3-687f-e053-6c86abc0c8a6.