Gen Hashida

Temporal and spatial variations of oceanic pCO 2 and air–sea CO 2 flux in the Greenland Sea and the Barents Sea

In order to elucidate the seasonal and interannual variations of oceanic CO2 uptake in the Greenland Sea and the Barents Sea, the partial pressure of CO2 in the surface ocean (pCO2sea) was measured in all seasons between 1992 and 2001. We derived monthly varying relationships between pCO2sea and sea surface temperature (SST) and combined them with the SST data from the NCEP/NCAR reanalysis to determine pCO2sea and air–sea CO2 flux in these seas. The pCO2sea values were normalized to the year 1995 by assuming that pCO2sea increased at the same growth rate (1.5 μatm yr-1) of the pCO2 in the air (pCO2air) between 1992 and 2001. In 1995, the annual net air–sea CO2 fluxes were evaluated to be 52 ± 20 gC m-2 yr-1 in the Greenland Sea and 46 ± 18 gC m-2 yr-1 in the Barents Sea. The CO2 flux into the ocean reached its maximum in winter and minimum in summer. The wind speed and Δ pCO2 ( = pCO2 air – pCO2sea) exerted a greater influence on the seasonal variation than the sea ice coverage. The annual CO2 uptake examined in this study (70◦–80◦N, 20◦W–40◦E) was estimated to be 0.050 ± 0.020 GtCyr-1 in 1995. The interannual variation in the annual CO2 uptake was found to be positively correlated with the North Atlantic Oscillation Index (NAOI) via wind strength but negatively correlated with Δ pCO2 and the sea ice coverage. The present results indicate that the variability in wind speed and sea ice coverage play a major role, while that in ΔpCO2 plays a minor role, in determining the interannual variation of CO2 uptake in this area.

Variations of constituents of individual sea-salt particles at Syowa station, Antarctica

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea-salt chemistry in the coastal Antarctic regions, individual sea-salt particles were analysed using a scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDX). Individual particle analysis indicates that more sea-salt particles were modified in fine particles (0.2–2 µm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter—spring. In particular, sea-salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO2 and H2SO4 but also volatile sulfur species (e.g. CH3SO3H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea-salt particles (S-rich, Mg-rich, K-rich and Ca-rich) from the surface of snow and sea ice, particularly in September—October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea-salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea-salt particles could rise to approximately 0.5 nmol m−2 day−1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non-sea-salt (nss)-SO2−4 and CH3SO−3 and ~10% of total atmospheric sulfur species (nss-SO2−4, CH3SO−3 and SO2). In contrast, the estimated NO−3 scavenging rate by sea-salt particles was ~0.2 nmol m−2 day−1, which is similar to the dry deposition rate of HNO3+N2O5 (approximately 0.2–0.3 nmol m−2 day−1). Hence, sea-salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.

Carbon dioxide variations in the stratosphere over Japan, Scandinavia and Antarctica

Systematic collections of stratospheric air samples have been conducted over Japan since 1985 using a balloon-borne cryogenic sampler. The collection of stratospheric air samples was also carried out twice over Scandinavia and once over Antarctica. Vertical profiles of CO2 concentration thus obtained over these locations were quite similar to each other; CO2 concentration decreased with increasing altitude in the lower stratosphere and reached an almost constant value in the mid-stratosphere. δ13C of stratospheric CO2observed over these locations enriched with increasing altitude. A negative correlation between δ13C and CO2 concentration with Δδ13C/ΔCO2 of −0.02‰ ppmv−1 was found in the lower stratosphere. Although CO2 concentration was almost constant in the mid-stratosphere, the δ13C enrichment was observed in succession. δ18O of stratospheric CO2 also enriched with increasing altitude. The enrichment was significant; δ18O was almost 0‰ at the tropopause and reached a maximum value of about 11‰ at a layer with N2O concentration of about 10 ppbv. A compact relation between δ18O and N2O concentration was consistently observed for these locations. Stratosperic CO2 over Japan showed a secular increase with an average rate of 1.4 ppmv yr−1 for the period 1985–2000. The secular increase was not constant with time, and temporal stagnation of the CO2 increase was observed in 1997.

Validation of the Improved Limb Atmospheric Spectrometer‐II (ILAS‐II) Version 1.4 nitrous oxide and methane profiles

This study assesses polar stratospheric nitrous oxide (N(2)O) and methane (CH(4)) data from the Improved Limb Atmospheric Spectrometer-II (ILAS-II) on board the Advanced Earth Observing Satellite-II (ADEOS-II) retrieved by the Version 1.4 retrieval algorithm. The data were measured between January and October 2003. Vertical profiles of ILAS-II volume mixing ratio (VMR) data are compared with data from two balloon-borne instruments, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B) and the MkIV instrument, as well as with two satellite sensors, the Odin Sub-Millimetre Radiometer (SMR) for N(2)O and the Halogen Occultation Experiment (HALOE) for CH(4). Relative percentage differences between the ILAS-II and balloon/satellite data and their median values are calculated in 10-ppbv-wide bins for N(2)O (from 0 to 400 ppbv) and in 0.05-ppmv-wide bins for CH(4) (from 0 to 2 ppmv) in order to assess systematic differences between the ILAS-II and balloon/satellite data. According to this study, the characteristics of the ILAS-II Version 1.4 N(2)O and CH(4) data differ between hemispheres. For ILAS-II N(2)O VMR larger than 250 ppbv, the ILAS-II N(2)O agrees with the balloon/SMR N(2)O within +/- 20% in both hemispheres. The ILAS-II N(2)O in the VMR range from 30-50 to 250 ppbv (corresponding to altitudes of similar to 17-30 km in the Northern Hemisphere (NH, mainly outside the polar vortex) and similar to 13-21 km in the Southern Hemisphere (SH, mainly inside the polar vortex) is smaller by similar to 10-30% than the balloon/SMR N(2)O. For ILAS-II N(2)O VMR smaller than 30 ppbv (>similar to 21 km) in the SH, the differences between the ILAS-II and SMR N(2)O are within +/- 10 ppbv. For ILAS-II CH(4) VMR larger than 1 ppmv ( similar to 30 km) and the ILAS-II CH(4) for its VMR smaller than 1 ppmv (>similar to 25 km) only in the NH, are abnormally small compared to the balloon/satellite data.

Annual-layer determinations and 167 year records of past climate of H72 ice core in east Dronning Maud Land, Antarctica

Abstract To determine annual layers for reconstructing the past environment at annual resolution from ice cores, we employed snow-stake data back to 1972, tritium content, solid electrical conductivity measurements (ECM) and stratigraphic properties for the 73m ice core at the H72 site, east Dronning Maud Land, Antarctica. the average annual surface mass balance at H72 is 307 mma–1w.e. during the last 27 years from continuous accumulation data, 317 mma–1 w.e. according to the densification model and 311 mma–1 w.e. according to the average surface mass balance for 167 years based on annual-layer counting. the ECM age is closely coincident with tritium age, and corresponds with the snow-stake record back to AD 1972 from the surface to 15 m depth. the H72 ice core is dated as AD 1831by ECMat 73.16 mdepth.The time series of yearly surface mass balance at H72 shows an almost constant 311 mm a–1 w.e. for the last 167 years. the oxygen-isotope records indicate a significant trend to lower values, with negative gradient of 1.7% (100 years)–1.

Variations of stratospheric trace gases measured using a balloon-borne cryogenic sampler

Abstract For a better understanding of the cycles of atmospheric trace gases, we have continued to systematically collect air samples in the stratosphere over Japan since 1985, using a balloon-borne cryogenic sampler. The collection of the stratospheric air samples was also made twice over the Scandinavian Peninsula in 1997 and once over Japanese Antarctic station, Syowa in 1998. The air samples collected were analyzed not only for the concentrations of CO2, CH4, N2O and various halocarbons but also for their isotopic ratios. These measurements revealed that, in general, the concentrations of all gas components decreased and their isotopic ratios increased with increasing height, due to influence of atmospheric transport and photochemical destruction in the stratosphere. However, detailed inspection of the results indicated that the observed vertical profiles of the respective components were quantitatively different, depending on location and time. Stratospheric CO2 over Japan showed the secular increase with an average rate of 1.4 ppmv/year for the period 1985–1999.

Reconstruction of past variations of δ 13 C in atmospheric CO 2 from its vertical distribution observed in the firn at Dome Fuji, Antarctica

Temporal variations of δ13C of atmospheric CO2 in the past have been reconstructed from the δ13C values of CO2 observed in firn at Dome Fuji, Antarctica. The effective diffusivities of CO2 in firn were estimated for Dome Fuji and another Antarctic site, H72. The age distributions of 13CO2 in firn were first calculated by using a one-dimensional diffusion model, and then the past values of the atmospheric δ13C were derived by using an iterative procedure so that the calculated and observed vertical profiles of δ13C of CO2 in firn agreed with each other. This reconstruction method was also applied to the CH4 concentration to confirm its validity. The values of the atmospheric δ13C thus estimated were in good agreement with those from direct atmospheric measurements at Syowa Station, Antarctica, even for the levelling off of the secular decrease observed in the first half of the 1990s. The statistical uncertainty of the iterative procedure was examined by adding normal pseudo-random numbers to the observed δ13C values in firn. We also calculated the δ13C values for firn at H72 using the reconstructed history of the atmospheric δ13C, and its vertical profile was found to be in close agreement with the observational result.

Concentration variations of atmospheric CO2 observed at Syowa Station, Antarctica from 1984 to 2000

Systematic and continuous measurements of the atmospheric CO2 concentration have been carried out at Syowa Station, Antarctica since February 1984. The measurement system was renewed in 1995, but the continuity of the data from the two systems was confirmed by operating them simultaneously. The CO2 data taken for 17 years from 1984 to 2000 showed clear evidence for a seasonal cycle, a secular trend and interannual variations. The seasonal cycle was variable from year to year, with especially larger amplitudes in 1992 and 1998 and a large phase delay in 1993. A rapid increase in the CO2 concentration was observed in 1987, 1994 and 1998 in association with ENSO events. The average rate of the secular CO2 increase for the last 17 years was calculated to be 1.49 ppmv yr−1. Short-term CO2 variations with amplitudes of around 1.0 ppmv were found in the austral summer season of several years after 1990, probably due to an intrusion of CO2-depleted air mass into the Antarctic region.

Balloon operation for stratospheric air sampling at Antarctica

Abstract On January 3rd, 1998, a cryogenic air sampling experiment was carried out at Syowa Station (69S, 40E), which is the first successful trial in the world for collection of large amount of stratospheric air over the Antarctic. The samples are analyzed for CO 2 , CH 4 , CFCs, and C and O isotope ratios in CO 2 in the laboratories. As the meteorological conditions for launching and payload recovery are both critical, feasibility on wind conditions over Syowa Station was studied in detail. The balloon launching operations had to be performed without a specialist. Facilities for balloon launching, tracking, and other support systems were newly designed for ready-to- and easy-to-use. Realtime remote support from Japan for the balloon launching and flight control operations was applied using a computer network linked by INMARSAT.