Hisayuki Y. Inoue

Aircraft observation of carbon dioxide at 8–13 km altitude over the western Pacific from 1993 to 1999

Abstract The spatial and temporal variations of atmospheric CO2 at 8–13 km from April 1993 to April 1999 were observed by measuring CO2 mixing ratios in samples collected biweekly from a commercial airliner between Australia and Japan. The CO2 growth rate showed a considerable interannual variation, with a maximum of about 3 ppm yr−1 during late 1997. This variation is related to the El Niöo/Southern Oscillation (ENSO) events. A year-to-year change related to the ENSO events was also found in the latitudinal distribution pattern of the CO2 annual mean between 30°N and 30°S. The averaged CO2 seasonal cycle in the Northern Hemisphere gradually decayed toward the equator, and a relatively complicated variation with a double seasonal maximum appeared in the Southern Hemisphere. A significant yearly change of the seasonal cycle pattern was observed in the Southern Hemisphere. The impact of a tropical biomass-burning injection on the upper tropospheric CO2 was estimated on the basis of the CO data from the same airliner observation.

Close coupling between seasonal biological production and dynamics of dissolved inorganic carbon in the Indian Ocean sector and the western Pacific Ocean sector of the Antarctic Ocean

The distribution of total dissolved inorganic carbon (DIC) in surface sea water and the upper water column of the seasonal ice zone in the Antarctic Ocean between 30°E and 150°E was investigated in the austral summer 1992/1993. In February–March 1993, total DIC content of surface seawater in the seasonal ice zone showed large spatial variability, ranging from 2064 to 2166 μmol kg-1. Biological activity played an important role in the deficit of total DIC in Prydz Bay, in the marginal ice zones (MIZ) near Lutzow-Holm Bay and Casey Bay, and in the offshore regions near 63°S, 100°E, while the decrease in total DIC due to meltwater input from the receding sea ice was also significant in those MIZ and in the area off the West Ice Shelf. From the analyses of total DIC concentration in the coldest waters (t<−1.7°C) of the subsurface temperature minimum layer, we deduced a characteristic value of normalized total DIC concentration (2184.0±3.7 μmol kg-1 at S=34) for the winter mixed layer over the wide area we investigated. Seasonally integrated net community production (NCP) in summer and its ΔCT/ΔN/ΔP ratios were calculated on the basis of the difference in normalized total DIC and nutrients concentrations between the winter mixed layer and the Summer Surface Water. Large spatial variations in the NCP, ranging from 10 to 48 gC m-2, and different ΔCT/ΔN/ΔP consumption ratios, typically 58/9.2/1 and 84/9.0/1, suggest the high variability of organic matter production and of its impact on both the air-sea CO2 exchange and export of carbon from the photic layer to the deeper waters in the seasonal ice zone of the Antarctic Ocean.

The international at-sea intercomparison of fCO2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean

The ‘International Intercomparison Exercise of fCO2 Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO2) systems, one discrete fCO2 system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO2 measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final fCO2 were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO2 in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO2 measurements can be made in good agreement (±3 μatm) with underway fCO2 data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO2 results. Calculation of fCO2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO2 measurements.

Measurements of atmospheric CO2 and CH4 using a commercial airliner from 1993 to 1994

Abstract A new automatic flask sampling system for the Boeing 747 commercial airliner was developed to observe CO2 and CH4 mixing ratios in the upper atmosphere at altitudes of 9–13 km. It was confirmed by a test flight that sample air collected using our system was useful for precise measurements of the trace gases in the upper atmosphere. Monthly air sampling was performed over the western Pacific between Narita in Japan and Cairns in Australia during 1993–1994. Measurements of both CO2 and CH4 in the Northern Hemisphere showed a clear seasonal cycle that was largely influenced by the seasonal variation in the lower troposphere. A significant decrease of mixing ratio during the winter season was observed in the CH4 variation, suggesting the intrusion of lower stratospheric air into the upper troposphere. The seasonal variation of both the gases gradually decayed toward the equator, but a different seasonal cycle appeared in the Southern Hemisphere. This change indicated the significance of meridional transport of both gases through the upper troposphere into the Southern Hemisphere. The mixing ratio level of both gases showed a recent increase in the upper troposphere.

Carbon isotopic fractionation during the CO2 exchange process between air and sea water under equilibrium and kinetic conditions

Abstract Carbon isotopic fractionation during the air/sea exchange process is not fully understood at present. Information on the equilibrium and kinetic fractionation factors is an essential requirement, together with the value of the CO 2 partial pressure, for understanding the carbon cycle in the atmosphere and marine environments. Using a specially designed countercurrent equilibrator system, the fractionation factors between gaseous CO 2 and dissolved inorganic carbon in sea water were determined under both kinetic and equilibrium conditions. The following results were obtained: kinetic fractionation factor for air to sea ( α as ) is 0.998 at 288.2 K; kinetic fractionation factor for sea to air ( α sa ) is 0.990; equilibrium fractionation factor ( α eq ) is 0.991 at pH = 8.3 and 288.2 K. From these results, the carbon isotopic ratio of CO 2 passed through the air/ sea interface is estimated to be about −10 %. for air to sea and −8 %. for sea to air when CO 2 exchange takes place between air ( δ 13 C = −8 %.) and surface sea water ( δ 13 C = 2 %.) at 288.2 K.

Changes in longitudinal distribution of the partial pressure of CO2 (pCO2) in the central and western equatorial Pacific, west of 160°W

We describe spatial and temporal variations in the partial pressure of carbon dioxide (pCO2) in the central and western equatorial Pacific on the basis of measurements conducted for the periods between 1987 and 1994. Surface water pCO2 data indicate the significant differences in longitudinal distribution depending on the ocean conditions. We examine the relationship between the area showing higher surface pCO2 values and the El Nino/Southern Oscillation phenomenon by using the Southern Oscillation Index. Results indicate that the area showing higher surface pCO2 values correlates with the SOI, which suggests significant intra- and interannual fluctuations of CO2 outflux from the central and western equatorial Pacific.

Aircraft measurements of trace gases between Japan and Singapore in October of 1993, 1996, and 1997

Carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) mixing ratios were measured in discrete air samples from aircraft between Japan and Singapore in October. The mixing ratios of all trace gases at 9–12 km were enhanced over the South China Sea in 1997 compared with those in 1993 and 1996. Vertical distributions of all trace gases over Singapore in 1997 also showed largely elevated mixing ratios at all altitudes. These distributions indicate a wide outflow of trace gases from intense biomass burning in the southeast Asia regions in the very strong El Nino year. The enhanced trace gases showed a strong linear correlation between CH4 and CO, and between CO and CO2, with the regression slopes of 0.051 (ΔCH4 ppb/ΔCOppb) and 0.089 (ΔCOppb/ΔCO2ppb). The emission ratios are characteristic of fires with relatively lower combustion efficiency from the tropical rain forest and peat lands in Kalimantan and Sumatra of Indonesia.

Carbon monoxide in the upper troposphere over the western Pacific between 1993 and 1996

Air samples at 8.5–13 km were collected regularly using a commercial airliner between Australia and Japan, and they were measured for CO mixing ratios to obtain time series data from April 1993 to July 1996. When averaged over 12 latitudinal bands between 30°N and 30°S, two overall features emerge from these data. First, CO levels in the upper troposphere decreased in all latitudinal bands. Second, the seasonal cycle showed significant differences between the northern and southern hemispheres. In the southern hemisphere a strong maximum in the CO mixing ratio (up to around 90 ppb) was found in October-November. The most likely source for this enhanced CO is tropical biomass burning. Methane oxidation and transport of industrial CO from the northern hemisphere were estimated as relatively minor sources during the austral spring. Air mass trajectories indicate that an extremely high CO level of ∼130 ppb observed in November 1994 between 10° and 20°S was due to enhanced biomass burning in Southeast Asia and/or northern Australia. On the other hand, air mass trajectories for the 20°-30°S region indicate that CO-rich air from biomass burnings over southern Africa or South America was transported across the South Indian Ocean within ∼1 week by the strong westerly winds around the subtropical jet. Thus it is concluded that a rapid horizontal transport coupled with deep convection plays an important role in the appearance of the CO spring peak in the upper troposphere over the western South Pacific.

Decreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific

We estimated long-term trends of ocean acidification in surface waters in latitudinal zones from 3°N to 33°N along the repeat hydrographic line at 137°E in the western North Pacific Ocean. Estimates were based on the observational records of oceanic CO2 partial pressure and related surface properties over the last two decades. The computed pH time series both for 25 yr in winter (late January.early February) and for 21 yr in summer (June.July) exhibited significant decreasing trends in the extensive subtropical to equatorial zones, with interannual variations that were larger in summer. The calculated rates of pH decrease ranged from 0.0015 to 0.0021 yr-1 (average, 0.0018 ± 0.0002 yr-1) in winter and from 0.0008 to 0.0019 yr-1 (average, 0.0013 ) 0.0005 yr-1) in summer. The thermodynamic effects of rising sea surface temperature (SST) accounted for up to 44% (average, 15%) of the trend of pH decrease in the subtropical region in winter, whereas a trend of decreasing SST slowed the pH decrease in the northern subtropical region (around 25°N) in summer. We used the results from recent trends to evaluate future possible thermodynamic changes in the upper ocean carbonate system.

Tropospheric carbon monoxide and hydrogen measurements over Kalimantan in Indonesia and northern Australia during October, 1997

During the PACE-5 campaign over Australia and Indonesia in October 1997, we used an aircraft to measure carbon monoxide (CO) and hydrogen (H2). Latitudinal distributions of CO and H2 clearly showed a large increase from northern Australia to Kalimantan in Indonesia. Elevated CO levels over northern Australia were observed only in the smoke plumes of savanna fires. A thick smoke haze from forest fires over Kalimantan contained very high CO mixing ratios of 3 to 9 ppm. These enhanced CO mixing ratios correlated well with increased concentrations of H2, nitrogen oxides (NOx), and aerosols. Emission ratios from biomass burning in Kalimantan ranged 0.06 0.1 for H2/CO (ppb/ppb), 0.0002 to 0.0005 for NOx/CO (ppb/ppb), and 0.43 to 1.0 for number of aerosols/CO (cm−3/ppb). These values were much lower than emission ratios in northern Australia. This difference suggests that the biomass burning in Indonesia was intense and that, due to a strong El Nino event, an unique composition of trace gases was formed in the smoke haze.