Ocean Properties & Structure

Question 1

Pressure in ocean

Answer 1

• 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)

Question 2

Pressure’s effect on water density

Answer 2

• Desnity increases linearly with pressure
• However, the change is relatively small, water is almost incompressible (compared to air)

Question 3

What drives changes in ocean temperature?

Answer 3

• 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

Question 4

Ocean temperature & solar radiation

Answer 4

• Changes with latitude based on angle of the sun

Question 5

Sea surface temperature (SST)

Answer 5

Question 6

Transects & profiles

Answer 6

Question 7

Temp vs depth

Answer 7

• 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

Question 8

Geographic variations in temp

Answer 8

• Polar oceans: little variation with depth
• Equitorial ocean: large variation with depth

Question 9

Seasonal variations in temp

Answer 9

Question 10

In-situ temp vs potential temp

Answer 10

• 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)

Question 11

Surface salinity mostly controlled by what?

Answer 11

• 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

Question 12

Sea surface salinity map

Answer 12

Question 13

1. Is total ocean salinity changing on geologic time scales?
2. Do the ratio of salt ions vary in the ocean?
3. Does the salinity of the ocean vary in space and time?

Answer 13

1. No
2. No
3. Yes

Question 14

Saliniy vs depth

Answer 14

• 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

Question 15

Density from temp / salinity

Answer 15

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

Question 16

How to calculate density

Answer 16

• Temp and salinity combine to calculate density

Question 17

Range of properties in ocean

Answer 17

90% of all seawater falls in range:
* Temp between -2 to 10
* Salinity between 33% to 35%

Question 18

When two waters of same density mix

Answer 18

Water w different temp and salinity can have same density
When mix can result in diff desnity
Nonlinear equation of state for desnity

Question 19

How do we measure temperature and salinity in the ocean?

Answer 19

CTD = conduvitivity temperature depth sensor
Can also measure other properties like oxygen

Question 20

Conductivity is a proxy for salinity

Answer 20

Question 21

CTDs

Answer 21

Deployed from ships and moorings
Now CTDs also deployed on autonomous platforms such as Argo Floats

Question 22

Remote sensing of ocean surface from satellite & aircraft

Answer 22

*

Question 23

In-situ vs remote