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

Fig. 9.20.a

Fig. 9.20.b

Fig. 9.20.c

The Layered Oceans

• Surface– 0-200m

• Intermediate– 300-2000m

• Deep– 2000-4000m

• Bottom– >4000m

Atlantic Ocean

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

Mediterranean Sea

Thermohaline Circulation

• Ocean radiator

Thermohaline Circulation

• Freshwater lid– Very cold freshwater runoff at high latitudes– Very low density does not sink

– Fjords and semi-enclosed bays

Global Currents

Fig. 9.25

Measuring the Currents

• Highly sophisticated equipment:

Measuring the Currents

Measuring the Currents• Current Meters

Measuring the Currents

• Doppler current meter– Emits sound of known

frequency – Measures frequency of

returning echoes