Shigeyuki Ishidoya

Time and space variations of the O2/N2 ratio in the troposphere over Japan and estimation of the global CO2 budget for the period 2000-2010

ABSTRACT Systematic measurements of the atmospheric O2/N2 ratio have been made using aircraft and ground-based stations in Japan since 1999. The observed seasonal cycles of the O2/N2 ratio and atmospheric potential oxygen (APO) vary almost in opposite phase to that of the CO2 concentration at all altitudes, and their amplitudes and phases are generally reduced and delayed, respectively, with increasing altitude. Simulations of APO using two atmospheric transport models reproduce general features of the observed seasonal cycle, but both models fail to reproduce the phase at an altitude ranging from 8 km to the tropopause. By analysing the observed secular trends of APO and CO2 concentration, and assuming a global net oceanic O2 outgassing of 0.2±0.5 GtC yr−1, we estimate global average terrestrial biospheric and oceanic CO2 uptake for the period 2000–2010 to be 1.0±0.8 and 2.5±0.7 GtC yr−1, respectively.

O 2 :CO 2 exchange ratios observed in a cool temperate deciduous forest ecosystem of central Japan

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.

Observation of O2:CO2 exchange ratio for net turbulent fluxes and its application to forest carbon cycles

An average O2:CO2 exchange ratio for net turbulent O2 and CO2 fluxes in a cool temperate deciduous forest in central Japan was obtained based on an aerodynamic method using continuous measurements of atmospheric O2/N2 ratio and CO2 concentration. The average daily mean O2:CO2 exchange ratio was 0.86 during summer, 2013, a value significantly lower than the 1.1 used as a globally averaged terrestrial biospheric O2:CO2 exchange ratio in a CO2 budget analysis. Using the value of 0.86, along with the O2:CO2 exchange ratio of 1.11 for the ecosystem respiration (RE) and 1.00 for the gross primary production (GPP), the net ecosystem production (NEP) measured with an eddy covariance method was separated into GPP and RE using a one-box canopy O2/CO2 budget model. The estimated average daily-mean GPP and RE values were consistent, within estimation errors, with those estimated from an empirical function of air temperature; the RE values were also comparable to the soil CO2 efflux observed using an open-flow soil chamber method. These results suggest that the simultaneous observation of O2 and CO2 concentrations in a forest has potential as a new tool to evaluate the forest CO2 budget.

Oceanic and terrestrial biospheric CO2 uptake estimated from atmospheric potential oxygen observed at Ny-Ålesund, Svalbard, and Syowa, Antarctica

ABSTRACT Simultaneous measurements of the atmospheric O2/N2 ratio and CO2 concentration were made at Ny-Ålesund, Svalbard, and Syowa, Antarctica for the period 2001–2009. Based on these measurements, the observed atmospheric potential oxygen (APO) values were calculated. The APO variations produced by changes in the oceanic heat content were estimated using an atmospheric transport model and heat-driven air–sea O2 (N2) fluxes, and then subtracted from observed interannual variations of APO. The oceanic CO2 uptake derived from the resulting ‘corrected’ secular trend of APO showed interannual variability of less than ±0.6 GtC yr−1, significantly smaller than that derived from the ‘uncorrected’ trend of APO (±0.9 GtC yr−1). The average CO2 uptake during the period 2001–2009 was estimated to be 2.9±0.7 and 0.8±0.9 GtC yr−1 for the ocean and terrestrial biosphere, respectively. By excluding the influence of El Niño around 2002–2003, the terrestrial biospheric CO2 uptake for the period 2004–2009 increased to 1.5±0.9 GtC yr−1, while the oceanic uptake decreased slightly to 2.8±0.8 GtC yr−1.

A New Compact Cryogenic Air Sampler and Its Application in Stratospheric Greenhouse Gas Observation at Syowa Station, Antarctica

Abstract To collect stratospheric air samples for greenhouse gas measurements, a compact cryogenic air sampler has been developed using a cooling device called the Joule–Thomson (J–T) minicooler. The J–T minicooler can produce liquefied neon within 5 s from high pressure neon gas precooled by liquid nitrogen. The sampler employs liquid neon as a refrigerant to solidify or liquefy sampled atmospheric constituents. Laboratory experiments showed that the sampler is capable of collecting about 3 and more than 7 L STP of air at 25 and 120 hPa, respectively, which corresponds to about 25 and 15 km above ground within 240 s, respectively. The new balloon-borne sampling system, which was set up for Antarctic experiments, consists of the compact sampler, a 2-L high pressure neon gas cylinder, pneumatic and solenoid valves, a controller with a GPS receiver, a telemetry transmitter, and batteries. The size of the sampling system is 300 mm width × 300 mm depth × 950 mm height and it weighs about 22 kg (including liqu...

Development of a new high precision continuous measuring system for atmospheric O 2 /N 2 and Ar/N 2 and its application to the observation in Tsukuba, Japan

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.

Ship-based observations of atmospheric potential oxygen and regional air-sea O 2 flux in the northern North Pacific and the Arctic Ocean

Simultaneous observations of atmospheric potential oxygen (APO=O2+1.1×CO2) and air–sea O2 flux, derived from dissolved oxygen in surface seawater, were carried out onboard the research vessel MIRAI in the northern North Pacific and the Arctic Ocean in the autumns of 2012–2014. A simulation of the APO was also carried out using a three-dimensional atmospheric transport model that incorporated a monthly air–sea O2 flux climatology. By comparing the observed and simulated APO, as well as the observed and climatological air–sea O2 fluxes, it was found that the large day-to-day variation in the observed APO can be attributed to the day-to-day variation in the local air–sea O2 fluxes around the observation sites. It was also found that the average value of the observed air–sea O2 fluxes was systematically higher than that of the climatological O2 flux. This could explain the discrepancy between the observed and simulated seasonal APO cycles widely seen at various northern hemispheric observational sites in the fall season.

Terrestrial biospheric and oceanic CO2 uptakes estimated from long‐term measurements of atmospheric CO2 mole fraction, δ13C, and δ(O2/N2) at Ny‐Ålesund, Svalbard

Systematic observations of CO2 mole fraction, the isotopic ratio δ13C of CO2 and oxygen to nitrogen ratio (δ(O2/N2)) in the atmosphere have been carried out at Ny-Alesund, Svalbard since 1991, 1996 and 2001, respectively. The CO2 mole fraction shows a clear seasonal cycle superimposed on a secular increase with an average rate of 2.0 ppm yr−1 for the period 1996–2013. On the other hand, δ13C and δ(O2/N2) decrease secularly at an average rate of −0.020 ‰ yr−1 for 1996–2013, and −19.9 per meg yr−1 for 2001–2013, respectively. Based on the observed secular trends of the CO2 mole fraction and δ(O2/N2), the average CO2 uptake during 2001–2013 was estimated to be 1.6 ± 0.8 and 2.3 ± 0.5 GtC yr−1 for the terrestrial biosphere and the ocean, respectively. By using the observed CO2 and δ13C, the corresponding CO2 uptake of 1.3 ± 0.6 and 2.6 ± 0.5 GtC yr−1 were obtained for the same period. The estimates from the two methods are in good agreement with each other. The terrestrial biospheric CO2 uptake derived by the latter method showed large inter-annual variability in association with El Nino events. On the other hand, the oceanic uptake increased secularly with less inter-annual variability during 1996–2013.