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Identifying ocean acidification and its controlling mechanisms is an important priority within the broader question of understanding how sustained anthropogenic CO2 emissions are harming the health of the ocean. Through extensive analysis of observational data products for ocean inorganic carbon, here we quantify the rate at which acidification is proceeding in the western tropical Pacific Warm Pool, revealing ‐0.0013 ±0.0001 yr‐1 for pH and ‐0.0083±0.0007 yr‐1 for the saturation index of aragonite for the years 1985‐2016. However, the mean rate of total dissolved inorganic carbon increase (+0.81 ±0.06 μmol kg‐1 yr‐1) sustaining acidification was ~20% slower than what would be expected if it were simply controlled by the rate of atmospheric CO2 increase and transmitted through local air‐sea CO2 equilibration. Joint Lagrangian and Eulerian model diagnostics indicate that the acidification of the Warm Pool occurs primarily through the anthropogenic CO2 that invades the ocean in the extra‐tropics, is transported to the tropics through the thermocline shallow overturning circulation, and then re‐emerges into surface waters within the tropics through the Equatorial Undercurrent from below. An interior residence time of several years to decades, acting in conjunction with the accelerating CO2 growth in the atmosphere, can be expected to contribute to modulating the rate of Warm Pool acidification. Key Points Progress of ocean acidification in the western tropical Pacific Warm Pool was identified using the data of oceanic CO2 measurements The rate of oceanic CO2 increase here was ~20% lower than that expected from the growth rate of the mixing ratio of CO2 in the atmosphere Inter‐gyre exchange of anthropogenic CO2 within the thermocline predominantly controls the rate of acidification in this region

To investigate the dynamics and environmental drivers of CO 2 flux through the winter snowpack in a dwarf bamboo ecosystem (Hokkaido, northeast Japan), we constructed an automated sampling system to measured CO 2 concentrations at five different levels in the snowpack, from the base to the upper snow surface. Using a gas diffusion approach, we estimated an average apparent soil CO 2 flux of 0.26 μmol m −2 s −1 during the snow season (December–April); temporally, the CO 2 flux increased until mid-snow season, but showed no clear trend thereafter; late-season snow-melting events resulted in rapid decreases in apparent CO 2 flux values. Air temperature and subnivean CO 2 flux exhibited a positive linear relationship. After eliminating the effects of wind pumping, we estimated the actual soil CO 2 flux (0.41 μmol m −2 s −1 ) to be 54% larger than the apparent flux. This study provides new constraints on snow-season carbon emissions in a dwarf bamboo ecosystem in northeast Asia.

We evaluated the nighttime CO2 flux (ecosystem respiration) on Rishiri Island, located at the northern tip of Hokkaido, Japan, from 2009 to 2011, by using the relationship between atmospheric 222Rn and CO2 concentrations. The annual mean CO2 flux was 1.8 μmol m−2 s−1, with a maximum monthly mean in July (4.6 ± 2.6 μmol m−2 s−1) and a broad minimum from December to March (0.33 ± 0.29 μmol m−2 s−1). The annual mean was comparable to fluxes at the JapanFlux sites in northern Japan. During the season of snow cover (mid-December to early April), the CO2 flux was low (0.45 ± 0.43 μmol m−2 s−1). Total annual respiration was estimated at 679 ± 174 g cm−2, about 8 % of which occurred during the season of snow cover.

The Southern Ocean is an important region for investigation because it has a major effect on global air-to-sea CO2 fluxes and because of the ocean acidification resulting from the uptake of anthropogenic carbon, leading to serious consequences for marine ecosystems in the near future. We estimated long-term trends of ocean acidification in surface waters of the Pacific sector of the Southern Ocean, based on the summer observational records of oceanic CO2 partial pressure and related surface properties during 1969–2003. The computed pH time series exhibited substantial decreasing trends in the extensive region from the subtropical to polar zones. The mean rates of pH decrease over the 35-year period were 0.0011 to 0.0013 yr−1 in the zones north of the Polar Front and were larger in the polar zone (0.0020 yr−1). The contribution of trends in sea surface temperature to the trends of pH decrease was small in all zones. The high rate of pH decrease in the polar zone was attributed to the supply of dissolved inorganic carbon from lower layers, enhanced by intensified wind stress and superimposed onto the accumulation of anthropogenic CO2. A preliminary evaluation of thermodynamic changes in the upper carbonate system, using observational results, projected that the polar zone south of the Polar Front would be undersaturated with respect to aragonite in summer after 80 years.

The recent uptake of anthropogenic carbon by the ocean brings about changes in the surface-ocean carbon cycle that could result in ocean acidification with subsequent serious effects on marine ecosystems. We evaluated the trend of ocean acidification in the surface layer of extensive regions of the subtropical North Pacific using synthesized data for partial pressure of CO2 for the past 40 years because no precise pH data were available. The results show significant trends of acidification (a pH decrease of 0.01 to 0.02 per decade) over the subtropical North Pacific. The rate of pH decrease, after excluding the contribution from changes in sea surface temperature, was highest in the eastern subtropical region. In this region in particular, the intrusion of subarctic waters with high concentrations of dissolved inorganic carbon could have contributed to the relatively high rate of acidification. Comparisons of the estimated rate of pH decrease for the past 26 years with those for the decade following 1969 and for 50 years into the future suggest an acceleration of acidification in recent years, as well as in the future, depending on the scenario of future anthropogenic CO2 emission.

We have investigated the seasonal and inter-annual variations of the difference in partial pressure of CO2 between surface seawater (pCO2sea) and overlying air (pCO2air) and the air-sea CO2 flux in the mid-latitudes of the western North Pacific (WNP; 25-40°N, 140-170°E) and eastern North Pacific (ENP; 25-40°N, 120-150°W) from 1999 to 2006 using the latest voluntary observation ship data. In the WNP and ENP, the area-averaged ΔpCO2 (pCO2air - pCO2sea) was at its minimum in late summer (-4.6 to 6.7 μatm in the WNP and -32.5 to -20.5 μatm in the ENP) and at its maximum in late winter (51.0 to 59.8 μatm in the WNP and 35.1 to 46.2 μatm in the ENP). The WNP acts as a moderate sink for atmospheric CO2 (4.1 to 5.5 mmol m^[-2] d^[-1]), while the ENP acts as a weak sink (1.1 to 1.9 mmol m^[-2] d^[-1]). Because ΔpCO2 is mainly controlled by pCO2sea, we have evaluated the effect of the factors controlling pCO2sea : sea surface temperature (SST), salinity (SSS), dissolved inorganic carbon (TCO2), and total alkalinity (AT). In the WNP, not only SST but also TCO2 plays an important role in the seasonal pCO2sea variation, while the SST could only explain most of the pCO2sea variation in the ENP. From 1999 to 2006, pCO2sea increased at a significantly lower rate (0.53±0.11 μatm yr^[-1]) than pCO2air (1.81±0.01 μatm yr^[-1]) in the WNP, and at a slightly lower rate in the ENP (1.32±0.16 μatm yr^[-1]). The air-sea CO2 flux increased at a rate of 0.19±0.05 mmol m^[-2] d^[-1] yr^[-1] in the WNP and 0.09±0.03 mmol m^[-2] d^[-1] yr^[-1] in the ENP, suggesting that the WNP is a stronger sink for atmospheric CO2.

The oceanic carbon cycle in the tropical-subtropical Pacific is strongly affected by various physical processes with different temporal and spatial scales, yet the mechanisms that regulate air-sea CO2 flux are not fully understood due to the paucity of both measurement and modeling. Using a 3-D physical-biogeochemical model, we simulate the partial pressure of CO2 in surface water (pCO2sea) and air-sea CO2 flux in the tropical and subtropical regions from 1990 to 2004. The model reproduces well the observed spatial differences in physical and biogeochemical processes, such as: (1) relatively higher sea surface temperature (SST), and lower dissolved inorganic carbon (DIC) and pCO2sea in the western than in the central tropical-subtropical Pacific, and (2) predominantly seasonal and interannual variations in the subtropical and tropical Pacific, respectively. Our model results suggest a non-negligible contribution of the wind variability to that of the air-sea CO2 flux in the central tropical Pacific, but the modeled contribution of 7% is much less than that from a previous modeling study (30%; McKinley et al., 2004). While DIC increases in the entire region SST increases in the subtropical and western tropical Pacific but decreases in the central tropical Pacific from 1990 to 2004. As a result, the interannual pCO2sea variability is different in different regions. The pCO2sea temporal variation is found to be primarily controlled by SST and DIC, although the role of salinity and total alkalinity, both of which also control pCO2sea, need to be elucidated by long-term observations and eddy-permitting models for better estimation of the interannual variability of air-sea CO2 flux.

Data of the partial pressure of carbon dioxide in surface seawater (pCO2sw) collected in the western equatorial Pacific (144°E - 160°W, 5°S - 5°N) since the 1980's have been used to determine the spatial variability and decadal trends in pCO2sw. A total of 109 cruises since 1983, including 30 cruises since 1990 with total dissolved inorganic carbon (TCO2) measurements, are synthesized for this zone. The western equatorial Pacific warm/fresh surface water where T ≥ 29.0 ℃ and S ≤ 34.8 is nitrate-depleted and it is moderately supersaturated with CO2 (0 < ΔpCO2 (= pCO2sw - pCO2air) / μatm < 40). A slight CO2 undersaturation (-20 < ΔpCO2 / μatm < 0) was also observed on many cruises where thin, low density layers (σt < 21.4) capped barrier layers. The undersaturation may result from net biological uptake of CO2 due to nitrogen fixation. Excluding the data in such a extremely light waters, we determined changes in the linear growth rate of pCO2sw of +0.3 ± 1.3 μatm year^[-1] for 1985 - 1990, +2.2 ± 0.7 μatm year^[-1] for 1990 - 1999, and -0.2 ± 1.0 μatm year^[-1] for 1999 - 2004. The rate of increase was +1.5 ± 0.2 μatm year^[-1] for the entire period (1985 - 2004). The variation in the rate of increase of pCO2sw is fairly consistent with the change in the rate of increase of salinity-normalized TCO2 from +2.1 ± 0.4 μmol kg^[-1] year^[-1] during 1992 - 1999 to +0.4 ± 0.9 μmol kg^[-1] year^[-1] during 1999 - 2004. These changes are anti-correlated with the decadal variation in the geostrophic mass transport from subtropics of both hemispheres into the equatorial zone in the Pacific.

An automatic measuring system for the partial pressure, pCO2, of atmospheric and oceanic carbon dioxide was developed. The system was mounted on a moored buoy for routine observation of maritime meteorology in the East China Sea. CO2 observations were conducted from June 29, 1997 to January 6, 1998. During the observation period, the atmospheric pCO2 showed little variation (341–365 μatm), whereas pCO2 in the surface water varied significantly (308–408 μatm). In the summer, pCO2 was higher in the surface water than in the overlying atmosphere, implying that this area was a source for atmospheric CO2, though it became a sink after late September. Time-series data clearly exhibited significant short-term variations in the oceanic pCO2, i.e. sudden variations during the passage of typhoons, and diurnal variations driven by the diurnal variations in the sea-surface temperature under calm conditions. The effects of typhoons on ocean–atmosphere CO2 exchange at the surface could differ, depending on the relative position of the mooring site with respect to the center of the moving typhoons. These differences result from the different contributions of sea-surface cooling, entrainment, and upwelling. The efflux enhanced by three typhoons accounted for 60% of the efflux of CO2 in the warm season. It is suggested that typhoons have a significant impact on the carbon cycle in the western subtropical North Pacific.

2006年12月から2007年3月まで北海道利尻島(45°07′N, 141°12′E)において大気中CO2とO3の濃度測定を実施した。観測されたCO2とO3濃度は数分から数ヶ月の時間スケールで変動しており、12月から2月中旬までの期間CO2濃度はO3濃度の変動と逆相関を示した。この逆相関はユーラシア大陸の高緯度地域及び利尻島での土壌呼吸によるCO2排出と地表でのO3分解消失によって引き起こされるものと考えられた。12月から2月中旬までの逆相関とは対照的に、2月中旬以降大気中CO2濃度とO3濃度は、時折正相関を示した。これら高濃度のCO2とO3は日本及び朝鮮半島の人為起源による排出・輸送の影響を受けていることが示唆された。

Measurements of atmospheric CO2 were made continuously at a height of 34 m in Sapporo (lat 43.1°N, long 141.3°E), located in northern Japan, from November 2004 to December 2005. Air samples for measurements of atmospheric CO, CH4, and CO2 were also taken in Sapporo and Ishikari Hama (lat 43.3°N, long 141.4°E), facing the Japan Sea, at 10- to 14-day intervals during the same period. In Sapporo, the atmospheric CO2 data showed clear diurnal and seasonal variations. During the diurnal variation, the maximum CO2 concentration occurred in the morning and the broad minimum in the daytime. The daily mean value of atmospheric CO2 in the daytime (11-16 JST) was at a maximum in winter to spring and a minimum in summer. From December to February, the daytime atmospheric CO2 concentration was about 8-13 ppm higher than that in the background air at Ishikari Hama; from July to August, it was nearly equal to that of the background air. In winter, the atmospheric CO concentrations in Ishikari Hama and Sapporo showed a good correlation with atmospheric CO2 (10 ppb CO/ppm CO2, r = 0.82). However, atmospheric CH4 remained fairly constant against CO2 change. In summer, CO2 flux by the photosynthesis of terrestrial vegetation between 11 and 16 JST was nearly equal to that of area-averaged CO2 emission (between Ishikari Hama and Sapporo) due to human activities, which was estimated to be 11 μmol m-2s-1 in the catchment area.

Since February 1992, measurements of atmospheric CO2 at 200 m above the ground have been taken from a meteorological tower (lat 36.1°N, long 140.1°E, 25 m a.s.l.) in Tsukuba, central Japan. We have examined seasonal/long-term variations in atmospheric CO2, based on atmospheric 85Kr, a noble gas with well-known source and sink terms, monitored continuously at weekly intervals in Tsukuba since May 1995. During the annual cycle, the daily mean values of atmospheric CO2 in the afternoons (1300-1600 JST) showed maximum in late April, except in 2002, and minimum in late August or early September. The seasonal variations in atmospheric 85Kr, which is low in summer and high in winter, were caused by the seasonal variations in the large-scale atmospheric circulation, and latitudinal distribution of atmospheric 85Kr. Compared with seasonal variations in atmospheric 85Kr, the draw-down (DD) and buildup (BU) for atmospheric CO2 occurred about 1 week and 3 weeks later, respectively. The peak-to-trough amplitude of de-trended seasonal variations in atmospheric CO2 concentrations ranged from 11 to 14 ppm. A decrease in the seasonal CO2 minimum occurred with a decrease in the 85Kr concentration, showing the effect of air mass transport from different origins. Unlike the minimum, the maximum CO2 did not vary as expected from the air mass transport. The daily mean values of atmospheric CO2 increased at an average rate of 2.0 ppm yr−1, with a range from −0.5 to 4 ppm yr−1. While both CO2 and 85Kr are emitted into the atmosphere, due to energy consumption, the growth rate of atmospheric CO2 showed a pattern different from that of atmospheric 85Kr (0.03 Bq m−3 yr−1).

A calibration system of standard gases for atmospheric methane measurements using a gas chromatograph equipped with a flame ionization detector was developed at the Meteorological Research Institute (MRI) in 1993 and later at the Japan Meteorological Agency (JMA) in 2000. Calibration results for the two systems exhibited good agreement. Although the primary standard gases of the MRI and JMA were prepared independently using the gravimetric method, their methane standard scales were quite similar, (a difference of less than 1 ppb). A comparison of gravimetric standards prepared by several Japanese gas companies showed a methane scale difference within ∼5 ppb relative to the primary standards of the MRI. These gravimetric-scale differences were primarily caused by methane impurities in the diluent air used for standard gas preparation. Long-term storage experiments indicated that the methane contents of standard gases were stable in high-pressure cylinders for 8-9 years. No significant drift of methane was found in any of the standard gases in the MRI; however, to evaluate the stability of the JMA standards, data collected over a longer period of time is required. We evaluated the differences between the methane scales of the MRI and other laboratories based on the previous intercomparison experiments. The differences found in the standard scales used by different laboratories were largely due to the diverse origins of the primary standard gases.

We observed the partial pressure of oceanic CO2, pCO2 sea, and related surface properties in the westernmost region of the subarctic North Pacific, seasonally from 1998 to 2001. The pCO2 sea in the Oyashio region showed a large decrease from winter to spring. In winter, pCO2 sea was higher than 400 μatm in the Oyashio region and this region was a source of atmospheric CO2. In spring, pCO2 sea decreased to extremely low values, less than 200 μatm (minimum, 139 μatm in 2001), around the Oyashio region with low surface salinity and this region turned out to be a strong sink. The spatial variations of pCO2 sea were especially large in spring in this region. The typical Oyashio water with minimal mixing with subtropical warm water was extracted based on the criterion of potential alkalinity. The contribution of main oceanic processes to the changes in pCO2 sea from winter to spring was estimated from the changes in the concentrations of dissolved inorganic carbon and nutrients, total alkalinity, temperature and salinity observed in surface waters in respective years. These quantifications indicated that photosynthesis made the largest contribution to the observed pCO2 sea decreases in all years and its magnitude was variable year by year. These year-to-year differences in spring biological contribution could be linked to those in the development of the density stratification due to the decrease in surface salinity. Thus, the changes in the surface physical structure could induce those in pCO2 sea in the Oyashio region in spring. Furthermore, it is suggested that the direction and magnitude of the air-sea CO2 flux during this season could be controlled significantly by the onset time of the spring bloom.

In the marginal ice zone (MIZ) of the Southern Ocean south of Australia at 140°E, the net community production (NCP) above the remnant temperature-minimum (Tmin) layer was evaluated in the austral summer of 1994/95 on the basis of the deficit in normalized total inorganic carbon (NTCO2) by reference to the NTCO2 in the remnant Tmin layer (2182 μmol kg−1 at S=34). The NCP integrated from the preceding late winter ranged from 4 to 16 gC m−2 in December 1994 and from 6 to 30 gC m−2 in January 1995, showing a tendency to increase with time and distance from the ice edge. The biological TCO2 drawdown and temperature-rise after the retreat of sea ice were the dominant factors controlling the spatial and temporal variability of CO2 partial pressure in surface seawater (pCO2sw) in the seasonal ice zone including the MIZ. The water beneath the sea ice is considered to be significantly CO2-supersaturated in winter, but the effect of biological CO2 uptake in summer on average was larger than that of the temperature-rise after the retreat of the sea ice. Hence, the pCO2sw showed a tendency to decrease with time and distance from the ice edge in the MIZ. The community uptake ratio of ΔSi/ΔC/ΔN/ΔP estimated from the deficits in silicic acid, TCO2, nitrate+nitrite and phosphate above the Tmin layer was 39/54/8.7/1 in the MIZ. The community uptake ratios of ΔSi/ΔP (=39) and ΔSi/ΔN (=4.5) were even higher than the uptake ratios by the diatom-dominated phytoplankton assemblage in the field incubation experiments under iron-deficit conditions (ΔSi/ΔP=26, ΔSi/ΔN=1.9–2.1; Takeda, Nature 393 (1998) 774). These results suggest that phosphorus and nitrogen, as well as carbon, in biogenic particulate matter have undergone significant preferential remineralization compared with silicate through heterotrophic activities in the surface layer.

To elucidate modulation of the CO2 system in the mixed layer of the northwestern North Pacific by a spring phytoplankton bloom, we conducted extensive oceanographic observations for two periods (May 13–15 and 24–28, 1999) during the MR99-K02 cruise by the R/V Mirai. During the first survey period, we found a patch of typical bloom conditions around lat 44.7°N, long 155.8°E (Stn 1), where the surface seawater partial pressure of CO2 (pCO2) dropped to a level lower than 200 μatm, accompanied by high fluorescence reaching 10 mg m−3 (arbitrary unit). By comparing the vertical profiles of salinity-normalized total CO2 (nTCO2) and nitrate+nitrite (nNOx) between Stn 1 and Stn 2 (a pre-bloom station), we found that drawdown of nTCO2 (approx. 109 μmol kg−1) and nNOx (approx. 20 μmol kg−1) occurred in the mixed layer. During the second survey period, spatial variations in the chemical properties at the sea surface in the survey area were not as conspicuous as found in the first survey period, but the drawdown of nTCO2 and nNOx extended to deeper layers at the selected stations (Stns 3–5) than at Stn 1, in association with deepening of the mixed layers. The air–sea CO2 fluxes calculated from the formula of Liss and Merlivat (In: Buat-Menard, P. (Ed.), The Role of Air–Sea Exchange in Geochemical Cycling. NATO ASI Series C: Mathematical and Physical Science, Vol. 185, 1986, pp. 113–127) were approximately −12 to −16 mmol m−2 d−1 (i.e. into the ocean) around Stns 1, 3, and 4, while the CO2 flux was approximately 3 mmol m−2 d−1 around Stn 2. For the nTCO2 drawdown, the influence of CaCO3 production/dissolution was estimated to be negligible, because salinity-normalized total alkalinity+nNOx was almost constant against changes in nTCO2. ΔC/ΔN (mol/mol) ratios were approximately 5.6 at Stns 1, 3, and 4, which is significantly smaller than the classical Redfield ratio of 6.6 and close to the particulate organic carbon to nitrogen ratio (5.8) obtained at Stn 3. From significant ratios against ΔSi, biological activity by diatoms was inferred to have caused the observed nTCO2 drawdown. Observed ΔSi/ΔN ratios of about 2.0 were higher than the reported biomass ratio of diatoms (1.0), implying a more dominant role for diatom-related activity, and close to the reported ratios for iron-limited diatoms. Analyses of covariations in nTCO2 and nutrients revealed that nTCO2 would be higher when nSiO4, not nNOx or nPO4, was completely depleted, implying regulation by silicate. We can summarize the carbon budget in the mixed layer as follows: Contributions of vertical diffusive transport and air–sea exchange of CO2 to total changes of nTCO2 were small, accounting at most for 3% and 10%, respectively. Net community productivity (NCP) at Stns 1, 3, and 4 was approximately 1300–1600 mg C m−2 d−1, if one assumes the beginning of the spring phytoplankton bloom to be May 1, and approximately 1000–1100 mg C m−2 d−1, if one assumes it to be April 23. The estimated values for NCPs were close to values in a bloom condition, reported elsewhere.

The equatorial Pacific consists of two regions that have distinct hydrological features and ecosystem dynamics: the warm pool to the west and the Pacific Equatorial Divergence (PEQD). The two regions are separated by well-defined fronts in salinity, pCO2, and macronutrients. Both the input of macronutrients in the two regions and their zonal extension are influenced primarily by the El Nino Southern Oscillation (ENSO) variability, which may be depicted by the Southern Oscillation Index (SOI). Thus, a quantitative relationship can be established between the longitude of the front and the SOI (Geophys. Res. Lett. 23 (1996) 1781–1784), allowing an assessment of the zonal extension of the two regions. In the PEQD, equatorial transects have shown that there is much temporal and spatial stability of biomass and fluxes of the biological pump, regardless of variations in macronutrient concentrations. This is a consequence of the High Nutrient Low Chlorophyll (HNLC) status of the waters, where primary production is not limited by the input of macronutrients. Moreover, the lack of an E–W gradient in the biological parameters supports the view that micronutrient inputs also should be more or less constant with longitude along the equator. A review of temporal variability on scales ranging from ENSO cycles to diel cycles leads to the conclusion that much of the biomass and flux variations along equatorial transects may be ascribed to temporary meridional transport by Tropical Instability Waves (TIW). In the warm pool, primary production is regulated by the input of macronutrients to the photic zone. These inputs from the deep nutricline depend on the ENSO cycle and temporary events. However, primary production is less than in the PEQD. A monthly estimate of the biological pump was made for the period 1980–2000 and the 1°N–1°S band of the divergence, west of the Galapagos Islands, on the assumption that: the longitude of the front was directly related to the SOI; there were no zonal variations in biological parameters; and mean rate values could therefore be used for primary production, new production, particle sinking and fluxes due to diel migration. The average longitude of the front was 178°W, and mean new production was 106–134 Mt C yr−1; it was 76–96 Mt C yr−1 during strong El Nino years and 114–144 Mt C yr−1 during other years. These variations between the two ENSO situations are less than those of published CO2 fluxes to the atmosphere, a result that can be ascribed to the particularly stable HNLC system.

Measurements of partial pressure of CO2 in surface waters (pCO2w) and overlying air (pCO2a) were made in the central and western equatorial Pacific from October 1997 to February 1998 within the period of the 1997/1998 El Nino, which was reported to be the strongest El Nino event on record. The distribution of the pCO2w showed a pattern driven by the eastward movement of western Pacific warm pool and thermodynamic effects (temperature and salinity), which was different from those of the moderate 1986/1987 El Nino and non-El Nino periods. Due to the eastward movement of the warm pool with sea surface temperature (SST) higher than 28.5 °C and sea surface salinity (SSS) lower than 34.5, the pCO2w between 180° and 163°W (347–364 μatm) was almost equal to that of the air (351 μatm). Between 143°E and 180°, the pCO2w tended to increase toward the west (387 μatm at 0°, 144°E in December 1997) along with the SST and SSS. West of 143°E in January 1998, a steep change in pCO2w ranging from 320 to 365 μatm occurred while retaining high SST (>28.5 °C) and SSS (>34.5). This was caused by the advection of surface water from the southern low latitudes that had been affected by biological activity (New Guinea Coastal Current). From December 1997 to January/February 1998, the SSS was usually higher than 34.5 west of 180°, which was significantly high compared to the western equatorial Pacific warm pool. This was probably due to the decrease of the net fresh water input for the western equatorial Pacific and/or the northward migration of surface water from the Southern Hemisphere. The CO2 outflux from the central and western equatorial Pacific (5.5°S–5.5°N, 139.5°E–159.5°W) was estimated to be 0.027 Pg-C/year in December 1997 and 0.038 Pg-C/year in January/February 1998. This presents a significant decrease from the CO2 outflux during the non-El Nino periods (0.34 Pg-C/year in January/February 1989, 0.11 Pg-C/year in September/November 1990) and a slight one from the moderate 1986/1987 El Nino period (0.055 Pg-C/year in January/February 1987). Following the El Nino–Southern Oscillation phenomena, CO2 outflux varied largely in the central equatorial Pacific and little in the western equatorial Pacific.

Seasonal variation in total inorganic carbon (TCO 2 ) in surface waters of the western North Pacific (137°–152°E) subtropical gyre was analyzed on the basis of measurements of TCO 2 and partial pressure of CO 2 ( p CO 2 sw). The controlling processes including vertical mixing, horizontal advection, and net air–sea CO 2 transport, as well as biological activity, were quantified. The seasonal increase in normalized TCO 2 (NTCO 2 ) from autumn to winter, ranging from 19 to 37 μmol kg −1 in the northern part of the subtropical gyre between 24°N and 30°N, was predominantly accounted for by the upward supply of TCO 2 due to enhanced vertical mixing. The contribution of horizontal advection, estimated from monthly meridional NTCO 2 distributions and the monthly advection field of the Meteorological Research Institute (MRI)'s 3D-ocean general circulation model, was insignificant. Analyses of the mixed-layer NTCO 2 budget revealed that biological activity was playing an important role in the decrease in surface NTCO 2 from winter to summer. Annual net community production reached 48±19 gC m −2 between 24°N and 30°N, and 19±16 gC m −2 between 15°N and 23°N.

Atmospheric 85 Kr and 133 Xe have continuously been monitored since 1995 (weekly averages) at the Meteorological Research Institute, Tsukuba. Elevated 85 Kr concentrations observed in spring and fall of 1995–1997 are the result of two factors, the operation of the PNC Tokai nuclear plant and secondly the seasonal change of prevailing wind directions. Elevated 85 Kr levels arising from releases of the Tokai plant are interpreted in a semi-quantitative fashion using the daily 85 Kr release data and available meteorological data. During periods without the influence of the Tokai plant, 85 Kr background concentrations (1.3 Bq/m3 of air) are similar to those for latitudes between 35 and 40°N. Background concentrations show a continuous increase with time and pronounced seasonal variations. The yearly increase rate of about 2.5% observed between 1996 and 1998 is very similar to European observations. The features of the seasonal variations are minimum values during summer and maximum values during winter. 133 Xe concentrations are not influenced by major local sources. One observation of a high 133 Xe concentration in June 1996 can be interpreted as originating from a Chinese underground nuclear test conducted earlier in the same month.

AbstracL Air samples at 8-13 km were collected regularly using a commercial airliner to obtain long-term measurements of carbon monoxide (CO) mixing ratio in the upper troposphere over the western Pacific between Australia and Japan during April 1993 - December 1997. The measurements in 1997 clearly reveal an anomalous CO increase during September to November in the Southern Hemisphere, with a maximum of 320-380 ppb around 20°S in October. Tropical biomass burning, not urban/industrial emissions, was the main source for the enhanced CO in 1997. A similar southern-spring increase due to biomass burning was observed in previous years. The peaks showed a large interannual variation associated with the El Nino/Southern Oscillation (ENSO) events. The largest CO spring peak appeared during the strong El Nino event in 1997, while the weak La Nina year of 1996 was marked by a largely suppressed CO spring peak. The outgoing longwave radiation (OLR) anomaly is largest during the El Nino events indicating that the events cause a longer drought in the tropics and significantly influence the enlargement of biomass burning in tropical Southeast Asia. Thus the most likely cause for the ENSO-cycle CO variability is a year-to-year change of biomass-burning emissions mainly from Southeast Asia. The appearance of the CO spring peak in the southern subtropics is discussed on the basis of the possible long-range transport of biomass-burning CO from Southeast Asia to the upper troposphere over the western South Pacific.

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.

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.

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.

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

In order to measure the CO 2 mixing ratios in air equilibrated with seawater (xCO 2 S ), we tested a multi-layered composite hollow-fiber membrane (MHF) module aboard the TS Hokuto-maru in the North Pacific in January-February 1996 and July-August 1996. The MHF module is much smaller (300 cm 3 ) than the currently used shower-head type equilibrator (110 dm 3 installation volume). The mean difference in xCO 2 S (ΔxCO 2 S ) values between the two systems determined 14 minutes apart was 1.6 ppm with a standard deviation of 2.2 ppm (n = 73) for the southbound cruise in January, and -1.9 ppm with a standard deviation of 1.8 ppm (n = 103) for the northbound cruise in February, 1996. The difference in average ΔxCO 2 S between the two legs was mainly caused by the effect of water temperature difference between the shower-head type equilibrator and the MHF module. By taking into account the effect on xCO 2 S of water-temperature difference between the two equilibrators, the mean ΔxCO 2 S was as low as 0.1 ppm (n = 732) with a standard deviation of 3.7 ppm for the cruise in July-August 1996. These results indicate that no systematic difference exists between the two equilibrators. The MHF has potential for future use as an equilibrator that is compact and easy to install.

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.

A new automatic flask sampling system for the Boeing 747 commercial airliner was developed to observe CO 2 and CH 4 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 CO 2 and CH 4 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 CH 4 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.

Since April 1986, measurements of the CO2 concentration in the surface air have been conducted at the Meteorological Research Institure (MRI, 36°04′ N, 140°07′ E, 25 m above sea level) in Tsukuba, located 50 km northeast of Tokyo, Japan. The CO2 data measured over times between 11:00 Japan Standard Time (JST) and 16:00 JST (C N ) were considered to be representative of the air (within a few ppmv) in the planetary boundary layer. To evaluate the representative CO2 level on a spatial scale larger than that of the C N record, the CO2 data with hour-to-hour variation less than 1 ppmv were selected (C P ). Comparison of these data with those of Ryori (39°02′ N, 141°50′ E), a continental station operated by the Japan Meteorological Agency, indicates that the C P record provides a representative CO2 level in the air on spatial scales of at least a few hundred kilometers. The C N record allows an investigation of the internanual changes in photosynthesis/respiration against changes in climatological parameters. Within a small temperature anomaly (ca.±1 °C) respiration is sensitive to the temperature change, while photosynthesis is less sensitive. When the temperature anomaly is large, however, photosynthesis and respiration tend to be competitive.

[1] Recent changes in oceanic CO2 partial pressure (pCO2sea) have attracted increasing interest as they relate to the increase in atmospheric CO2 and climate change. We report decadal changes in the growth rates of pCO2sea in latitudinal zones from 3°N to 33°N along the repeat hydrographic line at 137°E in the western North Pacific in winter. The growth rates of pCO2sea for 1999–2009 (−0.3 ± 0.9 [mean ± 1σ] to 1.7 ± 0.5 μatm yr−1) were lower than those for 1984–1997 (0.7 ± 0.3 to 2.2 ± 0.6 μatm yr−1) at most latitudes, indicative of the recent notable deceleration of pCO2sea increase. For latitudes around 10–20°N, we attribute the reduction in the growth rate of pCO2sea for 1999–2009 primarily to the reduction in the contribution from dissolved inorganic carbon (DIC) originating from a reduction in carbon accumulation associated with the expansion of the western Subtropical Gyre towards the south.

Experiments were performed to determine the equilibrium as well as kinetic stable nitrogen and oxygen isotope fractionations between aqueous dissolved and gaseous N2O. The equilibrium fractionations, defined as the ratio of the isotopic abundance ratios (15R and 18R, respectively) of gaseous and dissolved N2O were found to be 0.99925 for 15 N 14 N and 0.99894 for 18 O 16 O at 298.2 K. No temperature dependence could be observed over the temperature range of 273.2–317.7 K outside experimental error. At 298.2 K the kinetic fractionation factors during N2O invasion ( 15 α in = 15 R ( invaded ) 15 R ( gas ) , and 18αin defined similarly) were 1.0000 and 0.9992, respectively, and during N2O evasion ( 15 α ev = 15 R ( evaded ) 15 R ( aq.solution ) and 18αev defined similarly) were 0.9993 and 0.9981, respectively. The resulting changes in δ-values during air to sea transfer of N2O are 0.0 and −0.8‰, and for sea to air transfer −0.7 and −1.9‰, for N and O, respectively. These results are in agreement with the hypothesis that the oceans would be a large source for N2O in the atmosphere considering the fact that 15δ and 18δ of dissolved N2O were found to be slightly heavier than those in air.

[1] Oceanic methane (CH_4) was examined in the South Pacific and the Southern Ocean from December 2001 to February 2002. From the oligotrophic South Pacific (10°S) to the Subtropical Front (STF), we observed the maximum concentrations of CH_4 in the subsurface layer which ranged from 2.7 to 3.9 nmol kg^. South of the STF, higher levels of CH_4 were often detected in both the surface and the subsurface layers. Elevated surface CH_4 concentrations (3.4-6.1 nmol kg^) south of the STF tended to be higher than those north of the STF. Higher CH_4 were often concomitant with an increase in chlorophyll a levels in the Seasonal Ice Zone (SIZ). Considering that phytoplankton does not generate methane directly, the high CH_4 production probably resulted from the grazing processes of Antarctic krill and/or zooplankton fed on phytoplankton and the subsequent microbial methanogenesis in addition to the aerobic CH_4 production in the water column. Present results showed a good relation between surface CH_4 data (, r = 0.68, n = 49, p < 0.001). The sea-air fluxes estimated during our survey were from 2.4 to 4.9 mol CH_4 km^ d^ between 10°S and the PF (54°S), and from 0.8 to 2.3 mol CH_4 km^ d^ south of the PF, where the sea-air CH_4 flux was largely affected by the wind speed.

Ocean acidification resulting from increases in present and future atmospheric CO2 levels could seriously affect diverse coastal and oceanic ecosystems. In this work, we determine that a significant trend in ocean acidification is superposed on the large seasonal and interannual variabilities of acidity in surface waters off the south coast of Honshu, Japan, based on our repeated observations of partial pressure of CO2 (pCO2), total inorganic carbon (TCO2), and pH. Multiple regression analysis of TCO2 as a function of temperature, salinity, and timing of observations shows that TCO2 increased at a rate of + 1.23 ± 0.40 μmol kg^[-1] yr^[-1] for the period 1994-2008, while no long-term change has been determined for total alkalinity calculated from TCO2 and pCO2 in seawater. These results indicate that pH and the aragonite saturation state (Ωarag) are decreasing at a rate of -0.020 ± 0.007 decade^[-1] and -0.12 ± 0.05 decade^[-1], respectively. If future atmospheric CO2 levels keep increasing as predicted by the Intergovernmental Panel on Climate Change emission scenario A1FI, which postulates intensive fossil fuel use associated with very rapid economic growth, a further reduction of -0.8 to -1.0 in Ωarag is likely in the next 50 years. Such a rapid reduction of Ωarag could have negative impacts on a variety of calcareous organisms.

Measurements of atmospheric methane at 11–13 km were made over the Pacific from 65°N to 65°S by two research flights (INSTAC II, February – March, 1990, and III, October, 1990). Relatively low concentrations were observed in the high latitudes, indicating intrusion of stratospheric methane at 11–13 km. Methane distributions in the tropical and subtropical regions showed north to south gradients and longitudinal gradients from west to central Pacific. During almost the same period of the INSTAC III flight, atmospheric methane in the marine boundary air was measured on boad a research vessel in the Pacific from 35°N to 20°S. In the Northern Hemisphere, methane concentrations in the marine boundary air showed relatively higher values compared with those at 11–13 km. However, the relative methane levels between lower and upper air were reversed between 10°N and the equator, where the Intertropical Convergence Zone (ITCZ) was located. Such positive vertical gradient appearing around the ITCZ was maintained to the mid-latitudes of the Southern Hemisphere. These results strongly suggests that methane-rich air in the Northern Hemisphere was actively transported upward at the ITCZ and then meridionally transported through the upper troposphere into the Southern Hemisphere.

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 CO 2 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. DOI: 10.1111/j.1600-0889.2010.00474.x

Methane concentrations were determined for air samples collected over the western Pacific and the Antarctic Ocean in the years from 1978 to 1986. The latitudinal distribution from 35°N to 65°S revealed a decrease in methane concentration towards south, with two sharp gradients around 20°N and the intertropical convergence zone (ITCZ). The methane concentrations south of ITCZ were much lower than those in the Northern Hemisphere. The average concentrations of methane in samples collected over the western North Pacific (9°N–24°N) indicate an almost linear increase from 1978 to 1986 with no significant fluctuation of the annual rate of methane increase. The average rate of the increase from 1978 to 1986 was calculated to be 17 ± 2 ppb/yr over the western North Pacific, and that over the Antarctic Ocean was estimated to be 16–17 ppb/yr from 1978 to 1984.

Air samples were collected during the test and southbound flight (from Tokyo, Japan to Biak, Indonesia) of International Strato/Tropospheric Air Chemistry I in March 1989 (INSTAC-I). The air samples collected at 4 - 5 km height were subjected to CH4 and CO2 measurement at first, and then CO2 was extracted to measure the carbon isotopic ratio. The concentration of CO2 (ppm, molefraction in dry air) was high over and near the Japan Islands, and shows a little hump around 13°N. The relationship between carbon isotopic ratio and concentration of atmospheric CO2 shows that the high concentration over and near the Japan Islands and a hump around 13°N are caused by the CO2 released by the fossil fuel consumption and/or land plants respiration. The concentration of CH4 (ppm, mole fraction in dry air) was linearly proportional to that of CO2, which suggests a fairly constant ratio between CH4 flux and CO2 flux south of 35°N.

Measurements of partial pressure of CO2 in surface waters (pCO2sw) and overlying air (pCO2air) were made intermittently in the central and western equatorial Pacific from January 1987 to January 2003. We estimated the long-term trend of the pCO2sw in the high nutrient low chlorophyll (HNLC) region and the western Pacific warm pool. The spatial distribution of pCO2sw in the HNLC region could be expressed as a linear function of sea surface temperature (SST) and concentration of macronutrients ([NO2−]+[NO3−]), and in the western Pacific warm pool as a function of SST and sea surface salinity (SSS). By using an average SST (27.4 °C) and concentration of nitrate and nitrite (3.9 μmol/kg) in the HNLC region and the average SST (29.6 °C) and SSS (34.29) in the western Pacific warm pool between 1987 and 2003, we obtained pCO2sw values for respective cruises. The growth rate of pCO2sw due to increases in atmospheric CO2 was calculated to be 1.4±0.5 μatm/yr in the HNLC region and 1.3±0.3 μatm/yr in the western Pacific warm pool. The sea−air CO2 flux in the equatorial Pacific since 1998 was evaluated by using underway pCO2sw data measured by Japan Meteorological Agency, Meteorological Research Institute (JMA/MRI), National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory (NOAA/PMEL), and NOAA, Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML). From 1998 to 2003 the sea−air CO2 flux in the equatorial Pacific (5°N–10°S, 140°E–90°W) showed lowest flux in January/February 1998 (0.1±0.1 Pg C/yr, 1997/98 El Nino), and highest (0.9±0.4 Pg C/yr) in January/February 2001, suggesting significant interannual variations in sea−air CO2 flux in the equatorial Pacific. In October 2002−January 2003, which was within a weak El Nino period, the CO2 flux in the equatorial Pacific was 0.5±0.3 Pg C/yr, almost same as that of the non-El Nino period. In this period, sea−air CO2 flux in the central and western equatorial Pacific decreased considerably to the same level of January/February 1998, but that in the eastern equatorial Pacific remained fairly constant.

[1] An empirical method is presented for the estimation of basin-scale distribution of partial pressure of carbon dioxide (pCO 2 ) in the North Pacific using satellite-derived sea surface temperature (SST), chlorophyll-a concentrations (chl a), and climatological sea surface salinity (SSS). In this approach, multiple regression equations were developed to compute mixed layer dissolved inorganic carbon (DIC) based on SST, SSS and Chl a, whereas mixed layer total alkalinity (TA) was linearly regressed with SSS. The DIC-SST relation exhibited three different slopes at SST 27.5°C. Therefore data have been grouped with reference to SST. Regression equations were developed for two seasons (spring and summer). The regression errors for DIC and TA were 10.5 and 5 μmol kg -1 , respectively. The pCO 2 was computed from the estimated DIC and TA using dissociation constants given by Mehrbach et al. (1973), refit by Dickson and Millero (1987). The derived pCO 2 agreed with the shipboard pCO 2 observations within an error of 17-23 μatm. The sensitivity test on the regression equations for DIC estimation indicated that SSS is the most influencing parameter, followed by SST and Chl a. Using the monthly average SST and Chl a fields derived from the Advanced Very High Resolution Radiometer (AVHRR) and SeaWiFS (Sea-viewing Wide Field of view Sensor), respectively, and climatological SSS, monthly basin-scale pCO 2 fields were computed. The statistical model derived pCO 2 results are in agreement with underway pCO 2 in the North Pacific. This study strongly suggests that satellite-based techniques are promising tools for estimation of pCO 2 fields on a basin scale but the associated error bars are larger than required to study anthropogenic carbon uptake by the oceans. Incorporation of more in situ shipboard data may help in refining the estimating equations and reducing the errors further.

[1] The long-term trend of the partial pressure of CO2 in surface seawater (pCO2sea) in late-January to early-February during the past two decades was examined in the western North Pacific along the repeat line at 137°E from 3°N to 34°N. The growth rate of pCO2sea at each 1° in latitude ranged from +1.3 ± 0.2 to +2.1 ± 0.3 μatm yr−1, and the average was +1.7 ± 0.2 μatm yr−1. The growth of pCO2sea is attributable mainly to the uptake of anthropogenic CO2 in surface water and, to a small extent, to the regional changes in sea surface temperature (SST). The net air-to-sea CO2 flux in January–February that accounts for 40 to 60% of the annual flux remained at a similar level in the subtropical regions (7°N to 34°N). In the equatorial region (3°N to 6°N), however, a slight increase in the CO2 efflux was seen.

[1] We measured oceanic methane in the western part of the Sea of Okhotsk in 1998, 1999, and 2000. An anomalously high methane concentration was found in near-bottom water above the shelfbreak (∼200 m) off northeast Sakhalin every year: up to 488 nmol kg−1 in 1998, 981 nmol kg−1 in 1999, and 556 nmol kg−1 in 2000. This anomalously high concentration can be used to trace the water with density range 26.6 to 26.8 σθ in the upper Dense Shelf Water. In the shelf off east Sakhalin, a strong stratification caused by freshwater from Amur River controlled the upward transport of methane through the suppression of vertical convection. The calculated methane flux was largest in the northeastern shelf region of Sakhalin (88 mol CH4 km−2 d−1). In the western part of the Sea of Okhotsk (0.73 × 106 km2, 51% of total Sea of Okhotsk area), the emission rate of methane was 11 Gg CH4 yr−1.

As part of the JGOFS field program, extensive CO2 partial-pressure measurements were made in the atmosphere and in the surface waters of the equatorial Pacific from 1992 to 1999. For the first time, we are able to determine how processes occurring in the western portion of the equatorial Pacific impact the sea–air fluxes of CO2 in the central and eastern regions. These 8 years of data are compared with the decade of the 1980s. Over this period, surface-water pCO2 data indicate significant seasonal and interannual variations. The largest decreases in fluxes were associated with the 1991–94 and 1997–98 El Nino events. The lower sea–air CO2 fluxes during these two El Nino periods were the result of the combined effects of interconnected large-scale and locally forced physical processes: (1) development of a low-salinity surface cap as part of the formation of the warm pool in the western and central equatorial Pacific, (2) deepening of the thermocline by propagating Kelvin waves in the eastern Pacific, and (3) the weakening of the winds in the eastern half of the basin. These processes serve to reduce pCO2 values in the central and eastern equatorial Pacific towards near-equilibrium values at the height of the warm phase of ENSO. In the western equatorial Pacific there is a small but significant increase in seawater pCO2 during strong El Nino events (i.e., 1982–83 and 1997–98) and little or no change during weak El Nino events (1991–94). The net effect of these interannual variations is a lower-than-normal CO2 flux to the atmosphere from the equatorial Pacific during El Nino. The annual average fluxes indicate that during strong El Ninos the release to the atmosphere is 0.2–0.4 Pg C yr−1 compared to 0.8–1.0 Pg C yr−1 during non-El Nino years.

International audience; 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.

Methane and carbon monoxide in the surface seawater and the overlying atmosphere were measured in the equatorial Pacific from 160°E and 160°W. Both gases were supersaturated with respect to the atmosphere. The longitudinal distribution of oceanic methane showed an interannual variation between 1987 to 1990. This variation suggested that the production and/or transport of methane were largely changed by a strong upwelling during the 1988/89 La Nina event. The measurements of oceanic carbon monoxide in 1994 showed higher concentrations in the central and eastern regions than in the western region. This longitudinal distribution was mainly related to the solar radiation intensity. Carbon monoxide concentrations showed clear diurnal cycles that had a phase delay of 3–4 hours against the solar radiation cycle. However, the change rate of carbon monoxide concentration with time coincided well with the solar radiation pattern with no phase lag, suggesting that the rate of photochemical production quickly responded to the solar radiation intensity. A higher carbon monoxide concentration was observed in a water depth of 3 m rather than 5 m, suggesting a steep concentration gradient. From these results, it is concluded that longitudinal, interannual and vertical variations of the both gases are important for more accurate estimation on total oceanic fluxes in the tropical Pacific.

In order to determine the seasonal and interannual variability of the CO 2 released to the atmosphere from the equatorial Pacific, we have developed p CO 2 -temperature relationships based upon shipboard oceanic CO 2 partial pressure measurements, p CO 2 , and satellite sea surface temperature, SST, measurements. We interpret the spatial variability in p CO 2 with the help of the SST imagery. In the eastern equatorial Pacific, at 5°S, p CO 2 variations of up to 100 μatm are caused by undulations in the southern boundary of the equatorial upwelled waters. These undulations appear to be periodic with a phase and a wavelength comparable to tropical instability waves, TIW, observed at the northern boundary of the equatorial upwelling. Once the p CO 2 signature of the TIW is removed from the Alize II cruise measurements in January 1991, the equatorial p CO 2 data exhibit a diel cycle of about 10 matm with maximum values occurring at night. In the western equatorial Pacific, the variability in p CO 2 is primarily governed by the displacement of the boundary between warm pool waters, where air–sea CO 2 fluxes are weak, and equatorial upwelled waters which release high CO 2 fluxes to the atmosphere. We detect this boundary using satellite SST maps. East of the warm pool, Δ P is related to SST and SST anomalies. The 1985–97 CO 2 flux is computed in a 5° wide latitudinal band as a combination of Δ P and CO 2 exchange coefficient, K , deduced from satellite wind speeds, U . It exhibits up to a factor 2 seasonal variation caused by K -seasonal variation and a large interannual variability, a factor 5 variation between 1987 and 1988. The interannual variability is primarily driven by displacements of the warm pool that makes the surface area of the outgassing region variable. The contribution of Δ P to the flux variability is about half the contribution of K . The mean CO 2 flux computed using either the Liss and Merlivat (1986) or the Wanninkhof (1992) K – U parametrization amounts to 0.11 GtC yr −1 or to 0.18 GtC yr −1 , respectively. The error in the integrated flux, without taking into account the uncertainty on the K – U parametrization, is less than 31%. DOI: 10.1034/j.1600-0889.1999.00025.x

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO 2 in the free troposphere between 5 and 11 km. Continuous measurements of CO 2 mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O 3 , were also observed using continuous measuring systems at the same time. CO 2 over the northern Pacific (35°N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO 2 was quite similar to that of CO, but the relationship between CO 2 and O 3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO 2 variation. On the other hand, the CO 2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO 2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO 2 distributions over the western Pacific. Very low mixing ratios of O 3 of less than 20 ppb were distributed in the latitude band of 15–30°N at 11 km, reflecting the effects of transport from the equatorial region. DOI: 10.1111/j.1600-0889.2004.00088.x

High concentrations of carbon monoxide (CO) were observed in October 1997 at the upper troposphere of the western tropical Pacific. Transport from the potential sources of CO due to biomass burnings in the tropics was investigated by using a global chemical transport model (CTM) driven by assimilated meteorological data provided from European Centre for Medium-Range Weather Forecasts (ECMWF). A CTM evaluation simulation using water vapor showed that the amount of vertical transport of moisture by large-scale flow was consistent with the precipitation predicted at the convective zone. A series of CTM simulations using 10-day emission periods of an artificial material with lifetime of 60 days indicated that vertical lifting of surface air at the Indonesian archipelago occurred in the concentrated convections west of Sumatra Island. No evidence was found that CO from the Amazon region or Africa significantly contributed to high concentrations in the western tropical Pacific. Transport formed a large-scale anvil below the tropopause by rapid vertical transport and by divergence flow. The average time required for the transport from Kalimantan and Sumatra Island to the point of high CO concentration was about 15 days. High concentrations at an altitude of 10 km in the Southern Hemisphere were transported by large-scale subsidence from the upper tropospheric maximum, which was presumably produced from the sources at Kalimantan and Sumatra Island. Estimated emissions of CO in September and October from Kalimantan and Sumatra were substantially larger than the previous estimates. Omission of chemical reaction was a possible problem for the overestimate, but not significant. The possible problems in the transport were incorrect CTM transport due to insufficient horizontal (2.5×2.5°) and vertical resolution of the CTM, and to inaccuracy in the wind fields at the upper part of the troposphere and a divergent flow pattern in the upper part of the troposphere. DOI: 10.1034/j.1600-0889.2002.00271.x

Since February 1992, measurements of atmospheric CO 2 at 200 m above the ground have been taken from a meteorological tower (lat 36°04′ N, long 140°07′ E, 25 m a.s.l.) in Tsukuba, central Japan. A diurnal variation of atmospheric CO 2 at 200 m was clearly observed in summer and less clearly in winter. In summer, the maximum occurred a few hours after dawn and the minimum in the late afternoon; in winter, the CO 2 mixing ratio was fairly constant because of temperature inversion below 200 m. The daily mean values of atmospheric CO 2 in the afternoon (1300–1600 JST), selected as they were close to the representative values in the planetary boundary layer, were as high as 4 to 6 ppm greater than at stations in remote areas of the same latitudinal zone. This was mainly due to CO 2 emissions from anthropogenic sources in central Japan. The peak-to-trough amplitude of the seasonal variation, caused by the CO 2 exchange between the air and the land biosphere, ranged from 11 to 14 ppm. Year-to-year changes in the seasonal variation of atmospheric CO 2 during the period from May to July were correlated well with the surface air temperature among climate variables that affect the photosynthesis/respiration of the land biosphere. The change in CO 2 mixing ratio of the detrended seasonal variation from May to July increased with the surface air temperature, which was suggestive of the larger temperature dependence of respiration rate as compared with that of photosynthesis rate. Over the period from 1993 to 1999, the annual mean of the CO 2 mixing ratio increased from 363.0 ppm to 374.6 ppm. The growth rate from February 1992 to January 2000 showed a large interannual variability ranging from −0.8 to 4.6 ppm yr −1 with a mean rate of 2.0 ppm yr −1 . DOI: 10.1034/j.1600-0889.2001.01163.x

During 1968 to 72, scientists of the Meteorological Research Institute/Japan Meteorological Agency measured CO 2 in the surface seawater and overlying air in the Pacific Ocean quasicontinuously to examine CO 2 exchange between the sea and the atmosphere. From the data remaining in our laboratory from that time, we re-evaluated the partial pressure of CO 2 in surface seawater ( p CO s 2 ) by taking into account pressure broadening effects due to the use of CO 2 -in-N 2 standards, the use of chemical desiccant (Mg(ClO 4 ) 2 ), calibration using background air data, seawater temperature rise between the equilibrator and sea surface, the WMO CO 2 mole fraction scale, and differences in pressure during the oceanic CO 2 measurements from those of standards and background air in the nondispersive infra-red gas analyser cell. The overall uncertainty of p CO s 2 measurements for the cruises from 1968 to 1970 was estimated to be less than 3.6 μatm, which allowed us to evaluate temporal variations in the carbonate system over a few decades, but uncertainty was higher (> 10 μatm) for the cruise from 1971 to 1972 because of serious malfunctions of the system. The re-evaluated p CO s 2 data from 1968 to 1970 exhibit patterns similar to those observed at the same place and time of year (within 30 days) in 1982/83, 1988, 1995 and 1996, but compared with levels in the 1980s and 1990s the p CO s 2 level was clearly lower in the wide area of the Pacific except south of the Subtropical Front (STF; 47°S) in the Australian sector. The observed p CO s 2 increased by 34 ± 5 μatm ( n = 133) for the area 7°N to 35°N, 138°E to 147°E from February 1969 to February 1995, 29 ± 5 μatm ( n = 247) for the area 9°N to 35°N, 138°E to 165°E from February 1970 to February/March 1996, 26 ± 7 μatm ( n = 224) for the area 29°N to 51°N, 170°W from April 1970 to April 1988, and 41 ± 9 μatm ( n = 165) for the area 10°S to 45°S, 148°E to 166°E from January/February 1969 to January/February 1995. In the northern subtropics (7°N to 35°N, 138°E to 147°E), we estimated the long-term increase (35 ± 6 μatm, n = 133) after removing seasonal variations that were obtained from the p CO s 2 -sea surface temperature (SST) relationship. Observed and seasonally adjusted increases were nearly equal to those of the partial pressure of CO 2 in the air (1.4 μatm yr −1 ) over the same time intervals. South of the STF, p CO s 2 increase as found in the subtropics was not detected, mostly due to the large variability of p CO s 2 (250 to 380 μatm in 1968/69) on small spatial scales. The average p CO s 2 south of the STF showed large variations on time scales of months and years that affect the estimation of the growth rate of atmospheric CO 2 . DOI: 10.1034/j.1600-0889.1999.t01-3-00007.x

Measurements of CO 2 in marine boundary air and in surface seawater of the central and western Pacific west of 150°W were made during the period from September to December 1990. The meridional section along 150°W showed pCO 2 (sea) maximum over 410 µ atm between the equator and 3°S due to strong equatorial upwelling. In the equatorial Pacific between 150°W and 179°E, pCO 2 (sea) decreased gradually toward the west as a result of biological CO 2 uptake and surface sea temperature increase. Between 179°E and 170°E, the pCO 2 (sea) decreased steeply from 400 µ atm to 350 µ atm along with a decrease of salinity. West of 170°E, where the salinity is low owing to the heavy rainfall, pCO 2 (sea) was nearly equal to pCO 2 (air). The distribution of the atmospheric CO 2 concentration showed a considerable variability (± 3 ppm) in the area north of the Intertropical Convergence Zone due to the regional net source-sink strength of the terrestrial biosphere. The net CO 2 flux from the sea to the atmosphere in the equatorial region of the central and western Pacific (15°S−10°N, 140°E−150°W) was evaluated from the ΔpCO 2 distribution and the several gas transfer coefficients reported so far. It ranged from 0.13 GtC year -1 −0.29 GtC year -1 . This CO 2 outflux is thought to almost disappear during the period of an El Nino event. DOI: 10.1034/j.1600-0889.47.issue4.5.x