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We examined temporal variations in the latitudinal distribution of annual mean atmospheric potential oxygen (APO=O2+1.1×CO2), a useful tracer for studying ocean biogeochemical processes. To compute APO, we used atmospheric CO2 and O2 concentrations from flask samples and in-situ measurements onboard commercial cargo ships sailing between Japan and Australia/New Zealand. Most of the observed latitudinal distributions of the annual mean APO for the years 2002–2012 showed equatorial bulges, indicating tropical APO outgassing fluxes. However, the equatorial bulge was noticeably absent during the 2009/2010 El Niño period, especially in the Southern Hemisphere. The temporal variation in the 25–0°S latitudinal APO gradient correlated significantly with the El Niño/Southern Oscillation (ENSO); the equatorward APO gradients decreased (increased) during the El Niño (La Niña) period with a variability of about ±0.1 per meg/degree. Simulated APO based on an atmospheric transport model driven by climatological/constant flux fields and reanalysis meteorological data reproduced the overall characteristic of the observed temporal variation in the APO gradients well, suggesting that the atmospheric transport contributed substantially to the observed interannual variation in the global APO distributions. However, the model simulation underestimated the variability in the APO gradients by about 25%, compared to the observations. These discrepancies suggest a possibility of the existence of additional APO flux variability in the tropical Pacific, enhancing the ENSO-related variability in the observed APO gradients.

A high precision continuous measurement system has been developed for analysis of the atmospheric O2/N2 and Ar/N2 ratios based on a mass spectrometry method. Sample and reference air flows through an inlet system and only a miniscule amount of each is transferred to the ion source of the mass spectrometer through thermally insulated thin fused silica capillaries. The measured O2/N2 and Ar/N2 values are experimentally corrected for the effects of pressure imbalance between the sample air and reference air during their introduction into the mass spectrometer, as well as for the influence of CO2 concentration and O2/N2 ratio of the sample air. Standard deviations of the measured O2/N2 and Ar/N2 ratios of standard air are ±3.2 and ±6.5 per meg, respectively, for our normal measurement time of 62 seconds. Our standard air is prepared by drying natural air and then stored in 48-L high-pressure cylinders; its O2/N2 and Ar/N2 ratios are stable to within ±1.1 and ±5.8 per meg, respectively, over a period of 11 months. The CO2/N2 ratio is also simultaneously measured by this system, and converted to CO2 concentration with a precision better than ±0.3 ppm using an experimentally determined relationship. This system has been field tested in Tsukuba, Japan since February 2012. Preliminary results show clear seasonal cycles of atmospheric potential oxygen (APO=O2 +1.1×CO2), as well as of Ar/N2. If we ignore the fossil fuel influence, then that part the seasonal APO cycle driven by the air–sea heat flux accounts for 23% of the observed seasonal APO cycle, as estimated from the seasonal cycle of Ar/N2; any residuals are attributed to ocean biology and ventilation.

Detailed observations of O2:CO2 exchange ratios were conducted in a cool temperate deciduous forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11±0.01 and 1.02±0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O2/N2 ratio and the CO2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87±0.02) than in the nighttime (1.03±0.02) with a daily mean value of 0.94±0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a one-box canopy O2/CO2 budget model simulation of net turbulent O2 and CO2 fluxes between the atmosphere and the forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O2 and CO2 fluxes depend sensitively on the forest ecosystem processes.

A high precision continuous measurement system has been developed for analysis of the atmospheric O2/N2 and Ar/N2 ratios based on a mass spectrometry method. Sample and reference air flows through an inlet system and only a miniscule amount of each is transferred to the ion source of the mass spectrometer through thermally insulated thin fused silica capillaries. The measured O2/N2 and Ar/N2 values are experimentally corrected for the effects of pressure imbalance between the sample air and reference air during their introduction into the mass spectrometer, as well as for the influence of CO2 concentration and O2/N2 ratio of the sample air. Standard deviations of the measured O2/N2 and Ar/N2 ratios of standard air are ±3.2 and ±6.5 per meg, respectively, for our normal measurement time of 62 seconds. Our standard air is prepared by drying natural air and then stored in 48-L high-pressure cylinders; its O2/N2 and Ar/N2 ratios are stable to within ±1.1 and ±5.8 per meg, respectively, over a period of 11 months. The CO2/N2 ratio is also simultaneously measured by this system, and converted to CO2 concentration with a precision better than ±0.3 ppm using an experimentally determined relationship. This system has been field tested in Tsukuba, Japan since February 2012. Preliminary results show clear seasonal cycles of atmospheric potential oxygen (APO=O2 +1.1×CO2), as well as of Ar/N2. If we ignore the fossil fuel influence, then that part the seasonal APO cycle driven by the air-sea heat flux accounts for 23% of the observed seasonal APO cycle, as estimated from the seasonal cycle of Ar/N2; any residuals are attributed to ocean biology and ventilation. [ABSTRACT FROM AUTHOR]

Detailed observations of O2:CO2 exchange ratios were conducted in a cool temperate deciduous forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11±0.01 and 1.02±0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O2/N2 ratio and the CO2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87±0.02) than in the nighttime (1.03±0.02) with a daily mean value of 0.94±0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a 1-box canopy O2/CO2 budget model simulation of net turbulent O2 and CO2 fluxes between the atmosphere and the forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O2 and CO2 fluxes depend sensitively on the forest ecosystem processes. [ABSTRACT FROM AUTHOR]

We examined temporal variations in the latitudinal distribution of annual mean atmospheric potential oxygen (APO=O2+1.1×CO2), a useful tracer for studying ocean biogeochemical processes. To compute APO, we used atmospheric CO2 and O2 concentrations from flask samples and in-situ measurements onboard commercial cargo ships sailing between Japan and Australia/New Zealand. Most of the observed latitudinal distributions of the annual mean APO for the years 2002–2012 showed equatorial bulges, indicating tropical APO outgassing fluxes. However, the equatorial bulge was noticeably absent during the 2009/2010 El Niño period, especially in the Southern Hemisphere. The temporal variation in the 25–0°S latitudinal APO gradient correlated significantly with the El Niño/Southern Oscillation (ENSO); the equatorward APO gradients decreased (increased) during the El Niño (La Niña) period with a variability of about ±0.1 per meg/degree. Simulated APO based on an atmospheric transport model driven by climatological/constant flux fields and reanalysis meteorological data reproduced the overall characteristic of the observed temporal variation in the APO gradients well, suggesting that the atmospheric transport contributed substantially to the observed interannual variation in the global APO distributions. However, the model simulation underestimated the variability in the APO gradients by about 25%, compared to the observations. These discrepancies suggest a possibility of the existence of additional APO flux variability in the tropical Pacific, enhancing the ENSO-related variability in the observed APO gradients. [ABSTRACT FROM AUTHOR]