An internally consistent dataset of <i>δ</i><sup>13</sup>C-DIC in the North Atlantic Ocean – NAC13v1

Abstract

Abstract. The stable carbon isotope composition of dissolved inorganic carbon (δ 13 C-DIC) can be used to quantify fluxes within the carbon system. For example, knowing the δ 13 C 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 δ 13 C-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 ‰.The dataset is available via the Carbon Dioxide Information Analysis Center (CDIAC) at http://cdiac.ornl. gov/oceans/ndp_096/NAC13v1.html, doi:10.3334/CDIAC/OTG.NAC13v1.

20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models

“…As reported by Voelker et al (2016), studies that are consistent with the notion of constant c i /c a include early work by Wong et al (1979) measuring A and g of leaves in a chamber, and a range of tree-ring δ 13 C studies (Saurer et al, 2004;Ward et al, 2005;Bonal et al, 2011;Franks et al, 2013), as well as a metaanalysis of FACE experiments (Ainsworth and Long, 2005). The European δ 13 C tree-ring records analyzed by Frank et al (2015) and Saurer et al (2014) also point to a moderate control towards a constant c i /c a ratio.…”

“…Furthermore, δ 13 C observations allow identification of the imprint of fossil-fuel carbon in atmospheric air to quantify regional-tolocal-scale land carbon sources and sinks (Torn et al, 2011;Vardag et al, 2016), or to evaluate air-sea transfer velocity parameterizations (Krakauer et al, 2006). The δ 13 C data from the modern ocean are applied to infer the oceanic uptake of anthropogenic carbon (Heimann and Maier-Reimer, 1996;Gruber et al, 1999;Sonnerup and Quay, 2012;Becker et al, 2016), while paleoproxy δ 13 C data from ocean sediments and ice cores permit inference of land carbon changes between the last glacial maximum and the current warm period (Shackleton, 1977;Ciais et al, 2012;Peterson et al, 2014). Paleo-δ 13 C data are also used to trace water mass, circulation and biological productivity changes on glacialinterglacial timescales and during past abrupt events Schmittner and Somes, 2016), to disentangle processes of past glacial-interglacial carbon-cycle changes Schneider et al, 2013;Eggleston et al, 2016), and of ancient climate events (Kennett and Stott, 1991;Korte and Kozur, 2010).…”

Otolith δ13C values as a metabolic proxy: approaches and mechanical underpinnings

“…The variation of freshwater d 13 C DIC values is strongly dependent on geological chemistry, water metabolism and biogeochemical process. By contrast, d 13 C DIC values are relatively constant in marine systems, with values that generally vary between 0 and 3% on the horizontal spatial scale, and ,1% in the vertical gradient (Kroopnick 1985;Tagliabue and Bopp 2008;Schmittner et al 2013;Becker et al 2016). In addition to spatial variations, temporal differences in the exchanges between the atmosphere and the ocean.…”

Author response to reviews

“…The small changes in discrimination, an increase in iWUE proportional to the atmospheric CO 2 increase, and approximately constant c i /c a over the 20th century as reconstructed by our tree-ring compilation and simulated by LPX-Bern is consistent with most, but not all, studies. As reported by Voelker et al (2016), studies that are consistent with the notion of constant c i /c a include early work by Wong et al (1979) measuring A and g of leaves in a chamber, and a range of tree-ring δ 13 C studies (Saurer et al, 2004;Ward et al, 2005;Bonal et al, 2011;Franks et al, 2013), as well as a metaanalysis of FACE experiments (Ainsworth and Long, 2005). The European δ 13 C tree-ring records analyzed by Frank et al (2015) and Saurer et al (2014) also point to a moderate control towards a constant c i /c a ratio.…”

“…Furthermore, δ 13 C observations allow identification of the imprint of fossil-fuel carbon in atmospheric air to quantify regional-tolocal-scale land carbon sources and sinks (Torn et al, 2011;Vardag et al, 2016), or to evaluate air-sea transfer velocity parameterizations (Krakauer et al, 2006). The δ 13 C data from the modern ocean are applied to infer the oceanic uptake of anthropogenic carbon (Heimann and Maier-Reimer, 1996;Gruber et al, 1999;Sonnerup and Quay, 2012;Becker et al, 2016), while paleoproxy δ 13 C data from ocean sediments and ice cores permit inference of land carbon changes between the last glacial maximum and the current warm period (Shackleton, 1977;Ciais et al, 2012;Peterson et al, 2014). Paleo-δ 13 C data are also used to trace water mass, circulation and biological productivity changes on glacialinterglacial timescales and during past abrupt events Schmittner and Somes, 2016), to disentangle processes of past glacial-interglacial carbon-cycle changes Schneider et al, 2013;Eggleston et al, 2016), and of ancient climate events (Kennett and Stott, 1991;Korte and Kozur, 2010).…”