5:15 PM - 7:15 PM
[ACG36-P04] Shoaling of main thermocline over the North Pacific subtropical gyre
Keywords:Main thermocline depth, North Pacific Subtropical Gyre
The main thermocline depth, the lower boundary of the surface wind-driven circulation, plays a crucial role in determining the ocean’s capacity to absorb heat from the atmosphere. However, long-term changes in the main thermocline depth and its causes remain poorly understood.
To address this point, we try to investigate the changes in the main thermocline depth over the North Pacific subtropical gyre, using in-situ ocean observational data and atmospheric reanalysis datasets. In this study, we use the depth of the 12°C isotherm as an indicator for main thermocline depth. First, we explore temperature and density behaviors from repeat hydrographic sections along the 137°E conducted by the Japan Meteorological Agency from 1972 to 2023. Results indicate that the main thermocline depth has a shoaling trend of around 43 meters per century between approximately 15°N and 25°N.
To examine whether or not this shallowing occurs across the entire North Pacific subtropical gyre, we constructed a gridded dataset of the main thermocline depth using observational data from the World Ocean Database 2023, covering the period of 1970 to 2023. Our results indicate a shoaling trend of approximately 25 meters per century over the North Pacific subtropical gyre. To investigate the cause of this trend, we examined wind stress curl fields. Results indicate that, in addition to a northward shift in wind stress curl, as reported in recent studies, a weakening trend, i.e., cyclonic trend, has emerged. This change in atmospheric forcing likely contributes to the observed main thermocline depth shoaling.
To address this point, we try to investigate the changes in the main thermocline depth over the North Pacific subtropical gyre, using in-situ ocean observational data and atmospheric reanalysis datasets. In this study, we use the depth of the 12°C isotherm as an indicator for main thermocline depth. First, we explore temperature and density behaviors from repeat hydrographic sections along the 137°E conducted by the Japan Meteorological Agency from 1972 to 2023. Results indicate that the main thermocline depth has a shoaling trend of around 43 meters per century between approximately 15°N and 25°N.
To examine whether or not this shallowing occurs across the entire North Pacific subtropical gyre, we constructed a gridded dataset of the main thermocline depth using observational data from the World Ocean Database 2023, covering the period of 1970 to 2023. Our results indicate a shoaling trend of approximately 25 meters per century over the North Pacific subtropical gyre. To investigate the cause of this trend, we examined wind stress curl fields. Results indicate that, in addition to a northward shift in wind stress curl, as reported in recent studies, a weakening trend, i.e., cyclonic trend, has emerged. This change in atmospheric forcing likely contributes to the observed main thermocline depth shoaling.