Ocean Properties & Structure Flashcards
Pressure in ocean
- Linear increase with depth
- Force / area
- unit: N / m^2 (Pascales) [SI units]
- Assumption: hydrostatic balance, vertical accelerations are small
- P = weight of water column / area = mg / A
- P = pgh = gravity * distnce below surface * density of water
- 100,000 Pascales = 1 bar = 10 decibars (db)
Pressure’s effect on water density
- Desnity increases linearly with pressure
- However, the change is relatively small, water is almost incompressible (compared to air)
What drives changes in ocean temperature?
- Radiation from the sun can increase ocean temperature
- Evaporation can decrease ocean temperature
- Heat exchange with the air can either increase or decrease the temperature of the ocean
Ocean temperature & solar radiation
- Changes with latitude based on angle of the sun
Sea surface temperature (SST)
Transects & profiles
Temp vs depth
- Temp is warmest a top, decreases reapidly, and then is relatively uniform the rest of the ocean
- Because the sun’s heat is primarily added to the surface, the temp in the ocean is stringly dependent on depth
- The region at the surface that is mixed by wind is called the mixed layer
- The region below the mixed layer where temp changed rapidly with depth is called the thermocline
Geographic variations in temp
- Polar oceans: little variation with depth
- Equitorial ocean: large variation with depth
Seasonal variations in temp
In-situ temp vs potential temp
- t = in-situ temp: the temp measured directly
- theta = potential temp: the temp the water would have if moved adiabatically to the surface (i.e. removing the effect of pressure on temp)
Surface salinity mostly controlled by what?
- Mostly controlled by evaporation and precipitation
- High lat (polar regions) - LOW salinity
-high precipitation, meltater runoff - Mid lat (desert) - HIGH salinity
-warm dry air and high evaporation - Low lat (tropics) - LOW salinity
-high rainfall and runoff
Sea surface salinity map
- Is total ocean salinity changing on geologic time scales?
- Do the ratio of salt ions vary in the ocean?
- Does the salinity of the ocean vary in space and time?
- No
- No
- Yes
Saliniy vs depth
- The halocline is the region below the mixed layer where salinity changes rapidly with depth
- Low lattitudes: relatively salty surface water
- High latitude: relatively fresh surface water
- Salinity is similar at depth
Density from temp / salinity
The desnity of surface water is controlled by temperature and salinity
Low desnity near equator, higher density near poles
* Almost all controls on density are exerted at the ocean surface
* temp and salinity are conservative properties below the surface
How to calculate density
- Temp and salinity combine to calculate density
When two waters of same density mix
Water w different temp and salinity can have same density
When mix can result in diff desnity
Nonlinear equation of state for desnity
How do we measure temperature and salinity in the ocean?
CTD = conduvitivity temperature depth sensor
Can also measure other properties like oxygen
Conductivity is a proxy for salinity
CTDs
Deployed from ships and moorings
Now CTDs also deployed on autonomous platforms such as Argo Floats
