Decadal changes in the bomb-produced radiocarbon in the Pacific Ocean from the 1990s to 2000s

In the 2000s, radiocarbon in dissolved inorganic carbon was measured during the revisit cruises along WOCE (the World Ocean Circulation Experiment) lines conducted in the 1990s in the Pacific Ocean. Comparison of radiocarbon data from the 1990s and 2000s revealed that radiocarbon in the subtropical region decreased in upper thermocline (approx. 0 - 500-m depth) and increased in lower thermocline (approx. 500 - 1500-m depth). In the northeastern and southern subtropical regions, the two opposing directions in radiocarbon change cancelled each other and resulted in small temporal changes in the total inventory of vertical-integrated bomb-produced radiocarbon. On the other hand, the water column inventory of the bomb radiocarbon significantly decreased in the northwestern subtropical region. The different behavior of the bomb radiocarbon change suggests that the turnover time of the thermocline circulation in the northwestern subtropical region is faster than those in the other subtropical regions.