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 Unstable Density increases with depth 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 Intermediate Deep Bottom 0-200m 300-2000m

Atlantic Ocean NADW AAIW AABW SASW

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