Abstract. Atmospheric oxygen (O2) and carbon dioxide (CO2) variations in the
North Pacific were measured aboard a cargo ship, the New Century 2
(NC2), while it cruised between Japan and the United States between
December 2015 and November 2016. A fuel cell analyzer and a nondispersive
infrared analyzer were used for the measurement of O2 and
CO2, respectively. To achieve parts-per-million precision for the
O2 measurements, we precisely controlled the flow rates of the
sample and reference air introduced into the analyzers and the outlet
pressure. A relatively low airflow rate (10 cm3 min−1) was
adopted to reduce the consumption rate of the reference gases. In the
laboratory, the system achieved measurement precisions of 3.8 per meg for
δ(O2 ∕ N2), which is commonly used to express
atmospheric O2 variation, and 0.1 ppm for the CO2 mole
fraction. After the in situ observation started aboard NC2, we found that
the ship's motion caused false wavy variations in the O2 signal
with an amplitude of more than several tens of ppm and a period of about
20 s. Although we have not resolved the problem at this stage, hourly
averaging considerably suppressed the variation associated with ship motion.
Comparison between the in situ observation and flask sampling of air
samples aboard NC2 showed that the averaged differences (in situ–flask)
and the standard deviations (±1σ) are −2.8 ± 9.4 per meg
for δ(O2 ∕ N2) and −0.02 ± 0.33 ppm
for the CO2 mole fraction. We compared 1 year of in situ data for
atmospheric potential oxygen (APO; O2 +1.1×CO2)
obtained from the broad middle-latitude region
(140∘ E–130∘ W, 29∘ N–45∘ N) with
previous flask sampling data from the North Pacific. This comparison showed
that longitudinal differences in the seasonal amplitude of APO, ranging from
51 to 73 per meg, were smaller than the latitudinal differences.
In situ observation of atmospheric oxygen and carbon dioxide in the North Pacific using a cargo ship
