In recent years, the progression of global warming has led to increasingly serious impacts on marine environments.
Because the oceans absorb approximately one-fourth of the carbon dioxide (CO2) emitted by human activities, "ocean acidification" has been progressing as CO2 emissions increase. When seawater becomes more acidic, the concentration of carbonate ions decreases, lowering the saturation state of calcium carbonate. This may adversely affect organisms that play important roles in marine ecosystems, such as corals, shellfish, and plankton, which use calcium carbonate to form their skeletons or shells.
A research team led by Senior Researcher Maki Noguchi Aita of the Research Institute for Global Change at the Japan Agency for Marine-Earth Science and Technology analyzed changes in seawater temperature and other variables over a 25-year period from 1999 to 2023. The analysis was based on field observations conducted by the R/V Mirai at Station K2 (47°N, 160°E), located off the Kamchatka Peninsula in the western subarctic North Pacific, and on satellite data. The results revealed that the sea surface temperature in this area has been rising at an annual rate of 0.056℃, indicating that the warming rate is 1.87 times higher than that in the waters surrounding Japan. The pH, an indicator of ocean acidification, has been decreasing by 0.0014 per year. This rate of change was nearly the same as the global average across all seasons. On the other hand, no long-term changes were observed in the annual average concentrations of nutrients required for phytoplankton growth, such as silicate, phosphate, and nitrate. However, decadal-scale variations were observed, with nutrient concentrations increasing in May and decreasing in July.
This study has greatly advanced our understanding of ocean acidification and long-term variations in biological production in the subarctic North Pacific. The research team aims to improve predictions of marine environmental changes through continued observations at Station K2.
(Article: Masanori Nakajo)
