An international intercomparison of stable carbon isotope composition measurements of dissolved inorganic carbon in seawater

Abstract

We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (δ13C‐DIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000 m in the northeastern Atlantic Ocean. The between‐lab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11‰ (1σ). The multi‐lab average δ13C‐DIC value reported for the deep seawater sample was consistent within 0.1‰ with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the between‐lab standard deviation to 0.06‰. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/uncertainty target proposed by the Global Ocean Observing System (±0.05‰) is attainable, but only if an aqueous phase reference material for δ13C‐DIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a “Certified” or internally consistent “consensus” value for δ13C‐DIC can be assigned to various batches.

Extensive remineralization of peatland-derived dissolved organic carbon and acidification in the Sunda Shelf Sea, Southeast Asia

“…At NTU, final δ 13 C values were obtained after instrumental drift correction, blank correction for standards (Assayag et al, 2006;Humphreys et al, 2016), and calibration using NBS-18 (δ 13 C = −5.01‰) and Estremoz (δ 13 C = 1.63‰) calcium carbonate standards. All δ 13 C values of the samples were further corrected by accounting for the difference between the international consensus value of δ 13 C DIC of the Dickson CRM (0.78‰) (Cheng et al, 2019) and our laboratory measurements of δ 13 C DIC of the Dickson CRM at NTU (the magnitude of this correction was mostly below 0.4‰). The standard deviation for δ 13 C of DIC measurements over multiple years at UC Davis is reported as ±0.1‰ (https://stableisotopefacility.ucdavis.edu/) and at NTU was ±0.2‰ (Carrara marble, n = 24, 4 runs).…”

Interlaboratory test for stable carbon isotope analysis of dissolved inorganic carbon in geothermal fluids

“…Various factors were identified as the causes of these discrepancies: sample homogeneity, reference materials, synthetic samples, alteration during storage and transportation, etc. Recently, Cheng et al reported consistent results of an international intercomparison for the δ 13 C DIC value of seawater.…”

When a mid-ocean ridge encroaches a continent: Seafloor-type hydrothermal activity in Lake Asal (Afar Rift)

“…Overall, unlike an open and evolved modern ocean with δ 13 C ranging from -6.56 to +3.10‰ (Cheng et al, 2019), δ 18 O ranging from -1.5 to +1.8‰ (Carpenter and Lohmann, 1995) and positive Zn isotope composition (δ 66 Zn = +0.34‰; John et al, 2005) the ocean at "embryonic" stage has heavy both C and O isotope composition (δ 13 C > 6‰, δ 18 O > 4‰; Table 7) and negative Zn isotope composition (δ 66 Zn average = -0.06‰). Calcium isotope compositions of both types of ocean are similarly heavy: δ 44 Ca open evolved ocean = 1.92‰ (Fantle and Tipper, 2014), δ 44 Ca "embryonic" ocean = 1.22-1.64‰ (Table 7).…”