Latitudinal distribution of atmospheric CO₂ sources and sinks inferred by δ¹³C measurements from 1985 to 1991

Net CO 2 fluxes between the atmosphere and the ocean, and between the atmosphere and the terrestrial biosphere, were estimated by constraining a two‐dimensional atmospheric transport model with the CO 2 concentration and its δ 13 C data obtained from our shipboard measurements in the western Pacific region during the period April 1984 to December 1991. The results obtained for the non‐El Niño and Southern Oscillation (ENSO) years during this time period showed that the ocean acted as a CO 2 sink in middle latitudes of both hemispheres and a CO 2 source around the equator. The results also suggested that during the 1984–1991 period there were biospheric CO 2 sources in southern low and northern middle latitudes, and significant biospheric sinks in northern high latitudes. By comparing the latitudinal distributions of CO 2 source/sink for ENSO years with those for non‐ENSO years, it was found that a considerable amount of CO 2 was released from the terrestrial biosphere in low latitudes in association with the 1986–1987 ENSO event. While the oceanic region from the equator to 30°N acted as an excess CO 2 sink of about 1.0 Gt C y −1 r during 1987 and 1988, the oceanic contributions to the CO 2 anomaly in the atmosphere were less pronounced in the northern high latitudes and in the southern hemisphere. Also, compared with the estimated interannual fluctuations in the atmosphere‐biosphere CO 2 flux, the net CO 2 flux between the atmosphere and the ocean showed relatively less interannual variability.