The export of calcium carbonate (CaCO 3 ) from the surface ocean is poorly constrained. A better understanding of the magnitude and spatial distribution of this flux would improve our knowledge of the ocean carbon cycle and marine biogeochemistry. Here, we investigate controls over the spatial distribution of total alkalinity in the surface global ocean and produce a tracer for CaCO 3 cycling. We took surface ocean bottle data for total alkalinity from global databases (GLODAP, CARINA, PACIFICA) and subtracted the effects of several processes: evaporation and precipitation, river discharge, and nutrient uptake and remineralization. The remaining variation in alkalinity exhibits a robust and coherent pattern including features of large amplitude and spatial extent. Most notably, the residual variation in alkalinity is more or less constant across low latitudes of the global ocean but shows a strong polewards increase. There are differences of ~110 µmol kg -1 and ~85 µmol kg all low salinities to be caused by rainfall. The residual alkalinity data can be used as a tracer to indicate where in the world's ocean most CaCO 3 export from the surface layer takes place, and of future changes in calcification, for instance due to ocean acidification.

Abstract. The stable carbon isotope composition of dissolved inorganic carbon (δ 13 C 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 δ 13 C 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 δ 13 C 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 δ 13 C DIC is consistent within each RM batch, although its value is not certified. We report δ 13 C DIC values of 1.15 ± 0.03 ‰ and 1.27 ± 0.05 ‰ for batches 141 and 144 respectively. Our JR302 δ 13 C 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 δ 13 C DIC results are available from the British Oceanographic Data Centre -doi:10.5285/22235f1a-b7f3-687f-e053-6c86abc0c8a6.

Abstract. 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.

The causes of natural variation in alkalinity in the North Pacific surface ocean need to be investigated to understand the carbon cycle and to improve predictive algorithms. We used GLODAPv2 to test hypotheses on the causes of three longitudinal phenomena in Alk*, a tracer of calcium carbonate cycling. These phenomena are (a) an increase from east to west between 45°N and 55°N, (b) an increase from west to east between 25°N and 40°N, and (c) a minor increase from west to east in the equatorial upwelling region. Between 45°N and 55°N, Alk* is higher on the western than on the eastern side, and this is associated with denser isopycnals with higher Alk* lying at shallower depths. Between 25°N and 40°N, upwelling along the North American continental shelf causes higher Alk* in the east. Along the equator, a strong east-west trend was not observed, even though the upwelling on the eastern side of the basin is more intense, because the water brought to the surface is not high in Alk*. We created two algorithms to predict alkalinity, one for the entire Pacific Ocean north of 30°S and one for the eastern margin. The Pacific Ocean algorithm is more accurate than the commonly used algorithm published by Lee et al. (2006), of similar accuracy to the best previously published algorithm by Sasse et al. (2013), and is less biased with longitude than other algorithms in the subpolar North Pacific. Our eastern margin algorithm is more accurate than previously published algorithms.