Abstract
In recent years, global warming due to an increase in atmospheric CO2 concentrations is the most urgent concern for maintaining sustainable development in the future. The ocean is one of the most important reservoirs, acting as a sink for the increasing atmospheric CO2. However, there remain considerable uncertainties in estimates of the oceanic CO2 uptake. In the western North Pacific, the Japan Meteorological Agency has periodically conduted on board observations of oceanic CO2 and hydrographic properties from 3° N to 34° N along 137° E every winter since the early 1980s. The 26-year observation records exhibited increasing long-term trends of oceanic CO2 with similar growth rates to those of atmospheric CO2 in the extensive subtropical to equatorial zones, suggesting a persistent invasion of anthropogenic CO2 into the ocean from the atmosphere. The recent uptake of anthropogenic carbon by the ocean has given rise to changes in the chemical equilibrium of the surface ocean CO2 system, resulting in a reduction of seawater pH, i.e., ocean acidification. It is important to fully understand the mechanisms of the changes in the carbonate system responding to the climate shift for future predictions of the role of the western North Pacific in global carbon cycles.
