5:15 PM - 7:15 PM
[ACG36-P11] Variation in North Pacific Cetral Mode Water aboundance due to atmospheric and oceanic changes and its propagation to each distribution region
Keywords:North Pacific Central Mode Water, Pacific Decadal Oscillation, oceanic heat loss, mixed layer depth
The annual variations in North Pacific Central Mode Water (CMW) abundance have been suggested by annual variations in the development of the winter mixed layers (MLs) that contribute to CMW formation. Also, significant correlation between the PDO index, Pacific Decadal Oscillation (PDO) index defined as the projections of monthly mean SST anomalies onto their first EOF vectors in the North Pacific (North of 20°N), and CMW volume throughout subtropical gyre has been indicated. These results suggested that the CMW volume variations are associated with PDO.
Since CMW is subject to alteration and dissipation during its transport over a wide region, the variability in abundance associated with atmospheric and oceanic fluctuations will likely differ from region to region. Also, the potential density of CMW ranges widely from σθ=25.7 kg m-3 to 26.4 kg m-3. Depending on density, the effect of atmospheric and oceanic fluctuations differs, reflecting the difference in formation region. Thus, volume variations of CMW are expected to vary with density classes. Therefore, in this study, we aimed to clarify the difference in CMW volume in each region and density classes and the relationship between volume and atmospheric and oceanic fluctuations by dividing the CMW distribution region into the western part of the formation region, the eastern part of the formation region, stagnant region and dissipation region, and by further analyzing by density class.
CMW volume variations corresponding to the PDO index were found throughout the region from the gridded data of temperature and salinity based on Argo profiles (Roemmich-Gilson Argo climatology). Additionally, the correlation between CMW volume and PDO index was more significant for CMW with lighter density classes in each region. We analyzed the relationship between ML contributing to CMW formation and the PDO index using the atmospheric reanalysis dataset (ERA5) and sea surface temperature dataset (OTSST) based on satellite observation. As a result, when the PDO index is in a positive phase (westerly wind strengthening period), an increase in the average oceanic heat loss in winter (December, January, and February) that contributes to the development of ML was observed in the eastern part of the CMW formation region (33°N-43°N, 180°-160°W). Furthermore, a positive and significant correlation was found between the mixed layer depths (MLDs) in March and oceanic heat loss in winter. In this region, the water corresponding to the CMW with σθ= 26.3 kg m-3 to 26.4 kg m-3 outcrops when the ML is the most developed in March, and there is a significant positive correlation between PDO index in winter and average CMW volume in April to June in the eastern part of the formation region for these density classes. In the eastern part of the CMW formation region, it was revealed that oceanic heat loss fluctuations are associated with PDO. These fluctuations contribute to ML development and affect CMW formation.
Only in the western part of the CMW formation region (33°N-43°N, 145°E-180°), the water corresponding to the CMW with σθ= 26.3 kg m-3 to 26.4 kg m-3 outcrops. We analyzed CMW volume variations in the western part of the formation region for these density classes; we found a long-period variation that is suggested to correspond to the PDO index. To identify this short-scale variations factor, we analyzed relationships between oceanic heat loss in winter in the peripheral region (35°N-45°N, 145°E-180°W) where σθ=26.3 kg m-3 to σθ=26.4 kg m-3 water outcrops, MLD in March and east edge location where σθ=26.3 kg m-3 water outcrop in March. As a result, 2-4-year fluctuations of wintertime oceanic heat loss were observed, and MLD and outcrop location fluctuations that correspond to these variations were found. This suggests that CMW volume variations of high-density classes in the western part of the formation region are caused by 2-4-year scale fluctuations of wintertime oceanic heat loss.
Since CMW is subject to alteration and dissipation during its transport over a wide region, the variability in abundance associated with atmospheric and oceanic fluctuations will likely differ from region to region. Also, the potential density of CMW ranges widely from σθ=25.7 kg m-3 to 26.4 kg m-3. Depending on density, the effect of atmospheric and oceanic fluctuations differs, reflecting the difference in formation region. Thus, volume variations of CMW are expected to vary with density classes. Therefore, in this study, we aimed to clarify the difference in CMW volume in each region and density classes and the relationship between volume and atmospheric and oceanic fluctuations by dividing the CMW distribution region into the western part of the formation region, the eastern part of the formation region, stagnant region and dissipation region, and by further analyzing by density class.
CMW volume variations corresponding to the PDO index were found throughout the region from the gridded data of temperature and salinity based on Argo profiles (Roemmich-Gilson Argo climatology). Additionally, the correlation between CMW volume and PDO index was more significant for CMW with lighter density classes in each region. We analyzed the relationship between ML contributing to CMW formation and the PDO index using the atmospheric reanalysis dataset (ERA5) and sea surface temperature dataset (OTSST) based on satellite observation. As a result, when the PDO index is in a positive phase (westerly wind strengthening period), an increase in the average oceanic heat loss in winter (December, January, and February) that contributes to the development of ML was observed in the eastern part of the CMW formation region (33°N-43°N, 180°-160°W). Furthermore, a positive and significant correlation was found between the mixed layer depths (MLDs) in March and oceanic heat loss in winter. In this region, the water corresponding to the CMW with σθ= 26.3 kg m-3 to 26.4 kg m-3 outcrops when the ML is the most developed in March, and there is a significant positive correlation between PDO index in winter and average CMW volume in April to June in the eastern part of the formation region for these density classes. In the eastern part of the CMW formation region, it was revealed that oceanic heat loss fluctuations are associated with PDO. These fluctuations contribute to ML development and affect CMW formation.
Only in the western part of the CMW formation region (33°N-43°N, 145°E-180°), the water corresponding to the CMW with σθ= 26.3 kg m-3 to 26.4 kg m-3 outcrops. We analyzed CMW volume variations in the western part of the formation region for these density classes; we found a long-period variation that is suggested to correspond to the PDO index. To identify this short-scale variations factor, we analyzed relationships between oceanic heat loss in winter in the peripheral region (35°N-45°N, 145°E-180°W) where σθ=26.3 kg m-3 to σθ=26.4 kg m-3 water outcrops, MLD in March and east edge location where σθ=26.3 kg m-3 water outcrop in March. As a result, 2-4-year fluctuations of wintertime oceanic heat loss were observed, and MLD and outcrop location fluctuations that correspond to these variations were found. This suggests that CMW volume variations of high-density classes in the western part of the formation region are caused by 2-4-year scale fluctuations of wintertime oceanic heat loss.