TEMPORAL AND SPATIAL VARIATIONS IN ATMOSPHERIC AND OCEANIC CO2 IN THEWESTERN NORTH PACIFIC FROM 1990 TO 1993 - POSSIBLE LINK TO THE 1991 92 ENSO EVENT/

The results of atmospheric and oceanic CO2 observations conducted by t he Japan Meteorological Agency in the western North Pacific are presen ted for the period 1990-1993, covering an El Nino/Southern Oscillation (ENSO) event (onset: spring, 1991; withdrawal: summer, 1992). The atm ospheric CO2 concentration over the region south of 30 degrees N incre ased drastically between 1990 and 1991 during the winter (4.0 ppmv) an d summer (4.5 ppmv), although the values are not seasonally adjusted. Over the other two years of observations, the growth rates were smalle r or at times negative. Oceanic CO2, which is expressed in units of th e mole fraction (ppmv) in dry air equilibrated with seawater, showed a significant increase, especially in low latitudes during both seasons of the years 1991-1993, compared to the 1990 values. Oceanic CO2, nor malized at a constant temperature: also revealed a significant increas e, with larger and smaller magnitudes for winter and summer, respectiv ely. This implies that the increased summer oceanic CO2 results mostly from changes in surface seawater temperature, while for that in winte r, other factors, unknown at present, are more related to the increase d oceanic CO2. Calculated values of Delta pCO(2) and CO2 flux at the a ir-sea interface reveal that in winter, the region north of 10 degrees N acts as a sink of CO2, with a maximum net flux of similar to -10.0 mmol . m(-2). d(-1). The region south of 10 degrees N, however, at tim es becomes a weak source of CO2, with a maximum net flux of 2.4 mmol . m-2 . d(-1) In summer, the western North Pacific becomes a weak sourc e or is almost in equilibrium with atmospheric CO2. The increase in wi nter oceanic CO2 or Delta pCO(2), as related to the 1991/92 ENSO event , is not as distinct as in the 1982/83 ENSO event, although lower temp eratures and higher salinity in the surface seawater were commonly fou nd during both the events. The response of the CO2 flux in the tropica l western North Pacific to the 1991/92 ENSO event was rather small com pared to the magnitude of the rate changes obtained in previous result s for the central or eastern tropical Pacific.