Probability of a reduction in the formation rate of the subsurface water in the North Pacific during the 1980s and 1990s

Abstract

Comparing the apparent oxygen utilization (AOU) and apparent CFC tracer ages (τ) between extensive decadal reobservation data along 47°N (’85–’99) and 165°E (’87–’00) lines, we found that both AOU and τ markedly increased over the North Pacific between 26.4–27.4 σ θ . The observed AOU increase was almost consistent with the AOU increase calculated from observed change of τ. Based on a linear trend of increasing AOU over 30 years (’68–’98) in the subpolar region [ Ono et al., 2001], we concluded that the formation rate of the subsurface water in the North Pacific has continuously reduced at least during the last fifteen years. In the North Pacific, the recent uptake rate of oceanic anthropogenic carbon was also estimated as reduced by as much as 10% from the efficiency of anthropogenic carbon absorption in the middle of 1980s.