Page 43 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

1
2
3
4
2.2 Chemical oceanography 31
Mixed surface layer
Upper water mass
Deepwater mass
Temperature (°C)
0 10 200 10 200 10 200 10 20 0
Wind mixed layer
Shallow thermocline
Deep thermocline
Mixed layer deepening
Shallow thermocline
Deep thermocline
Mixed layer
Deep thermocline
Mixed layer
Shallow thermocline
Deep thermocline
20 40 60 80
100 120
FIGURE 2.4
Summer Fall
Winter
Spring
Surface layer mixing by season.
The density range for seawater is from 1.02200 to 1.030000 g/cm3 (Thurman, 1994). In an ide- alized stable system, the higher density water sinks to the bottom while the lower density water floats to the surface. Water under the extreme pressure of depth will naturally be denser than sur- face water, with the change in pressure (through motion between depths) being realized as heat. Just as the balance of pressure/volume/temperature is prevalent in the atmosphere, so is the temper- ature/salinity/pressure model in the oceans.
A rapid change in density over a short distance is termed a “pycnocline” and can trap any number of energy sources from crossing this barrier, including sound (sonar and acoustic positioning sys- tems), current, and neutrally buoyant objects in the water column (underwater vehicles). Changing operational area from a lower latitude to a higher latitude produces a mean temperature change in
Surface layer by season
Depth (m)
Depth (km)