Density Structure
• Surface Processes– Temperature– Salinity– Pressure
Changes with Depth
• Density– Pycnocline
– σt = density – 1000 kg/m3
Changes with Depth
• Temperature– Thermocline
• Salinity– Halocline
Changes with Depth
• Stable– Density increases with depth
• Unstable– Density decreases with depth– Leads to overturn & mixing of water column
The Layered Oceans
• Surface– 0-200m
• Intermediate– 300-2000m
• Deep– 2000-4000m
• Bottom– >4000m
Pacific Ocean
• Layers difficult to distinguish
• No large source of deep water
Indian Ocean
• No deep water• Fairly uniform mixture
Arctic Ocean
• Density controlled more by salinity• Circulation confined to < 500m
Thermohaline Circulation
• Freshwater lid– Very cold freshwater runoff at high latitudes– Very low density does not sink
– Fjords and semi-enclosed bays
Measuring the Currents
• Highly sophisticated equipment:
Measuring the Currents• Current Meters
Measuring the Currents
• Doppler current meter– Emits sound of known
frequency – Measures frequency of
returning echoes