Importance of this Topic
The Seasonal Thermocline,
Subduction and the Ventilation
of the Main Thermocline
To Name Just a Few:
1. Heat Exchange between Ocean Atmosphere
2. Interannual Recurrence of SST anomalies
3. Nutrient Recirculation in the Subtropics
4. Solubility Pump and CO2 Sequestration
Seasonal Heating and Cooling of the
Ocean Surface
Seasonal Thermocline
Entrainment and Detrainment
1
Variation in the Depth of the Seasonal
Thermocline
Vertical Temperature Profiles of Tropical,
Mid Latitude and Polar Oceans
Mixed Layer
Seasonal
Thermocline
Permanent
Thermocline Region
Mixed Layer Depth
Summer
Winter
At the end of winter, water in the seasonal thermocline is
at its maximum density and overlies the main therocline
2
Surface Distribution of
Density
Subduction
Ventilation of the Main
Thermocline
Vertical Distribution of
Density
3
Ekman Pumping
Surface Water Convergence
and Subsequent Downwelling
Geostrophic Flow
Ekman Layer Convergence
4
Ekman Layer and Mixed Layer
Thickness Determined by Wind Only
Thickness
Determined
by Wind
Mixing and
Convective
Overturning
Surface Distribution of
Density
Enhanced Annual Buoyancy Flux (additional heat
input) in Year-2 Leads to Sallower Seasonal
Thermocline in Winter
Fluid is entrained
into the seasonal
thermocline during
winter
Fluid is subducted into main
thermocline during spring
but has the WINTER TS
characteristics!!
The above scenario leads to net annual transfer of seasonal
thermocline water into the main thermocline. Note: If year-2 had
been colder main thermocline water would have been transferred to
the surface mixed layer
Annual Subduction Rates (meters/Y)
Eq. 2, Williams, 2001
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