Abstract
Oxygen in the atmosphere undergoes variations and changes in response to biospheric activities, ocean–atmosphere exchange and fossil fuel combustion. Continuous in situ measurements of atmospheric δ(O2/N2) and CO2 mole fraction were started at Ny-Ålesund, Svalbard (78.93°N, 11.83°E, 40 m a.s.l.) in November 2012. Atmospheric potential oxygen (APO) calculated from the measured O2 and CO2 values during November 2012–January 2015 show a clear seasonal cycle with a peak-to-peak amplitude of approximately 50 per meg. The seasonal cycle of APO simulated using an atmospheric transport model, with prescribed oceanic O2, N2 and CO2 fluxes at monthly time intervals, is in excellent agreement with the observed APO. However, in spring and early summer, high values of APO are observed irregularly on a timescale of hours to days. By comparing backward trajectories of air parcels released from the site with distributions of marine net primary production (NPP), and tagged tracer experiments made using the atmospheric transport model for APO, it is found that these high APO fluctuations are primarily attributable to O2 emissions from the Greenland Sea, the Norwegian Sea and the Barents Sea, due to marine biological productivity. Marine net community production, estimated based on the sea-to-air O2 flux derived from observed APO fluctuations, agrees with NPP obtained from satellite observations within an order of magnitude. The results obtained in this study have still some uncertainties, but our continuous observations of atmospheric δ(O2/N2) and CO2 mole fraction at Ny-Ålesund can play an important role in detecting possible changes in the carbon cycle in the near future.
Highlights
Understanding the sources and sinks of O2 and CO2 is important for advancing our knowledge of the global carbon cycle.Atmospheric O2 and CO2 are closely related to each other through terrestrial biospheric photosynthesis and respiration, as well as the combustion of fossil fuel
Signals with periods of longer than 24 months are regarded as the longterm trend, and the average seasonal cycle is approximated by the fundamental and its first harmonics
The results reported by Ishidoya et al (2012b) from mass spectrometry analyses of weekly flask air samples at Ny-Ålesund are presented in Fig. 2, for the period from November 2012 to January 2015
Summary
Understanding the sources and sinks of O2 and CO2 is important for advancing our knowledge of the global carbon cycle.Atmospheric O2 and CO2 are closely related to each other through terrestrial biospheric photosynthesis and respiration, as well as the combustion of fossil fuel. The two gases are exchanged independently between the atmosphere and the ocean. Global oceanic and terrestrial biospheric carbon sinks can be estimated separately by analysing long-term changes in atmospheric O2 and CO2 Variations in atmospheric O2 are usually expressed as a change in the ratio of O2 to N2, as follows (Keeling and Shertz, 1992): (O2∕N2) =. Change of 4.8 per meg in δ(O2/N2) corresponds to 1 μmol mol−1 change in O2, when O2 and CO2 vary in the atmosphere at the –O2:CO2 exchange ratio of 1.0. To eliminate the influence of terrestrial biospheric activity on δ(O2/N2), Stephens et al (1998) defined atmospheric potential oxygen (APO) in per meg unit as follows: APO =
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