10:45 AM - 12:15 PM
[ACG44-P08] Interannual variations of upper-ocean salinity in the North Pacific in the Argo era
Keywords:salinity, North Pacific, Argo float
Salinity is one of the essential factors that determine the ocean state. This quantity controls the circulation through seawater density and affects ocean temperature indirectly, probably leading to air-sea interaction. Salinity is also utilized when looking for a footprint of changes in hydrological cycle. Although the number of salinity observations were limited before the Argo era, the development of the Argo observation system has enabled us to reveal the clearer picture of spatiotemporal variations of salinity. Studies on the recent climate changes have indicated that the global contrast of the upper-ocean salinity has increased as a results of strengthening of hydrological cycle: subtropical regions of high salinity have become more saline, subarctic and tropical regions of low salinity have become fresher.
The variability of salinity, especially in the upper ocean, is closely tied to climate change. Ocean numerical models still need relaxation of sea surface salinity (SSS) to climatology to avoid salinity drift. It is crucially meaningful to reveal salinity variations based on observations without relying on simulations. The author aims at identifying spatial patterns of salinity change in the North Pacific that were not clearly recognized before the Argo era. A dataset named “the Grid Point Value of the Monthly Objective Analysis (MOAA-GPV)” is analyzed in this study. This has a spatial resolution of 1°×1° horizontally and 25 standard pressure levels from 10 dbar to 2000 dbar. The grid point values of salinity and temperature are obtained from Argo floats and other in situ observations through a two-dimensional optimum interpolation method.
Decadal-scale changes of salinity were dominant above 400 dbar in the North Pacific. Fresher anomalies of salinity appeared in the late 2000s and/or the first half of the 2010s in the eastern and western regions, where salinity increased in the latter half. On the other hand, salinization occurred in the central Pacific in the first half of the 2010s and freshened in the latter half. The changes were almost limited to above 400 dbar, but they were relatively large even below 400 dbar off Sanriku coast of Japan, Kamchatka and Siberia. The salinity changes in the 2010s almost corresponded to that of freshwater flux, but horizontal shifts of the subtropical and subarctic gyres also contributed to the variations. In the regions off North America, advection of anomalies on isopycnal surfaces affected salinity increases in subsurface layers.
The variability of salinity, especially in the upper ocean, is closely tied to climate change. Ocean numerical models still need relaxation of sea surface salinity (SSS) to climatology to avoid salinity drift. It is crucially meaningful to reveal salinity variations based on observations without relying on simulations. The author aims at identifying spatial patterns of salinity change in the North Pacific that were not clearly recognized before the Argo era. A dataset named “the Grid Point Value of the Monthly Objective Analysis (MOAA-GPV)” is analyzed in this study. This has a spatial resolution of 1°×1° horizontally and 25 standard pressure levels from 10 dbar to 2000 dbar. The grid point values of salinity and temperature are obtained from Argo floats and other in situ observations through a two-dimensional optimum interpolation method.
Decadal-scale changes of salinity were dominant above 400 dbar in the North Pacific. Fresher anomalies of salinity appeared in the late 2000s and/or the first half of the 2010s in the eastern and western regions, where salinity increased in the latter half. On the other hand, salinization occurred in the central Pacific in the first half of the 2010s and freshened in the latter half. The changes were almost limited to above 400 dbar, but they were relatively large even below 400 dbar off Sanriku coast of Japan, Kamchatka and Siberia. The salinity changes in the 2010s almost corresponded to that of freshwater flux, but horizontal shifts of the subtropical and subarctic gyres also contributed to the variations. In the regions off North America, advection of anomalies on isopycnal surfaces affected salinity increases in subsurface layers.