Abstract

We present 20-year flask sample records of atmospheric CO2, δO2/N2 and APO from the stations Lutjewad (the Netherlands) and Mace Head (Ireland) and a 3-year record from Halley station (Antarctica), including details of the extensive calibration procedure and its stability over time. The results of our inter-comparison involving gas cylinders from various research laboratories worldwide also show that our calibration is of high quality and compatible with the internationally recognised Scripps scale. The measurement records from Lutjewad and Mace Head show similar long-term trends during the period 2002–2018 of 2.31 ± 0.07 ppm yr−1 for CO2 and −21.2 ± 0.8 per meg yr−1 for δO2/N2 at Lutjewad, and 2.22 ± 0.04 ppm yr−1 for CO2 and −21.3 ± 0.9 per meg yr−1 for δO2/N2 at Mace Head. They also show a similar δO2/N2 seasonal cycle with an amplitude of 54 ± 4 per meg at Lutjewad and 61 ± 5 per meg at Mace Head, while CO2 seasonal amplitude at Lutjewad (16.8 ± 0.5 ppm) is slightly higher than that at Mace Head (14.8 ± 0.3 ppm). We show that the observed trends and seasonal cycles are compatible with the measurements from various stations, especially the measurements from Weybourne Atmospheric Observatory (United Kingdom). However, there are remarkable differences in the progression of annual trends between the Mace Head and Lutjewad records for δO2/N2 and APO, which might in part be caused by sampling differences, but also by environmental effects, such as the North Atlantic Ocean oxygen ventilation changes to which Mace Head is more sensitive. The Halley record shows clear trends and seasonality in δO2/N2 and APO, where especially APO agrees well with the continuous measurements at Halley by the University of East Anglia, while CO2 and δO2/N2 present slight disagreements, most likely caused by small leakages during sampling. From our 2002–2018 records, we find good agreement for the global ocean sink: 2.0 ± 0.8 PgC yr−1 and 2.2 ± 0.9 PgC yr−1, based on Lutjewad and Mace Head, respectively. The data presented in this work are available at https://doi.org/10.18160/qq7d-t060 (Nguyen et al., 2021).

Highlights

  • The global carbon cycle is a dynamic system that comprises the exchanges of carbon between various reservoirs and is important for studying human-induced climate change and its impacts (Ciais et al, 2013)

  • Samples at Lutjewad are collected under various conditions and time frequencies, but in this paper we present only the data from flasks collected under local background conditions, defined by van der Laan-Luijkx et al (2010) as flasks taken while the 222Radon activity monitored at the station was less than 3 Bq m-3 and with a CO mole fraction of less than 200 ppb

  • Due to the sensitive nature of oxygen measurements, we conducted an extensive and intensive calibration procedures, which demonstrated a long-term standard deviation for δ(O2/N2) of 13.5 per meg based on our own internal cylinders

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Summary

Introduction

The global carbon cycle is a dynamic system that comprises the exchanges of carbon between various reservoirs and is important for studying human-induced climate change and its impacts (Ciais et al, 2013). By combining the decadal trends of atmospheric CO2 and O2, we can quantify the global land and ocean carbon sinks (Bender et al, 1996; Keeling and Shertz, 1992; Manning and Keeling, 2006; Tohjima et al, 2019). This is because CO2 and O2 cycles are closely coupled – in most processes, there is an anti-correlation in the changes of their mole fraction, except for the oceanic uptake of CO2 (Manning and Keeling, 2006). To quantify the various components of the global 45 carbon cycle, the changes in atmospheric mole fraction of the two species can be used in combination with their stoichiometric exchange ratio (ER), which is the ratio of CO2 and O2 exchanged (consumed/produced) in a process. The ER value varies depending on the process, and is close to 1.1 for photosynthesis/respiration (Severinghaus, 1995) and on average 1.38 for the global mix of fossil fuels (Keeling and Manning, 2014)

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