1. Lab 5 Physical and Chemical Properties of Sea Water
Temperature, salinity & their effects on density
Dissolved oxygen and seasonality in the upper ocean
Nutrient profiles

2. Temperature
The Sun supplies the largest source of energy at the surface of the Earth
The distribution of temperature in the oceans is related to solar radiation
Surface waters are warmer than deep waters, and surface water is warmer at the equator than at the poles

3. Low Latitudes
Tropical Zone
Mid Latitudes
Temperate Zone
Comparison
High Latitudes
Polar Zone
Vertical profiles
A profile is a plot of a water property versus depth (see typical temperature profile to right) 
Mixed layer
Wind/waves
Thermocline
Area of large temp change with depth
Deep Water
Relatively constant temp

4. Density Temperature AND salinity effects on Density:
Salinity: a measure of the salt concentration of water - the total amount of
dissolved material in grams in one kilogram of sea water (parts per thousand – ppt)
Higher salinity means more dissolved salts.
Colder water is more dense than warm water
This is true for sea water, but fresh water
density reaches a maximum at 4°C and decreases with lower temperature
Salt water is more dense than fresh water
Density always increases
with depth
If it doesn’t, the
water column is
unstable (well mixed)

5. Dissolved oxygen (DO) Typical DO profile.
How is Oxygen introduced into the water?
How can temperature and seasons affect DO depth profiles like the one you see here?

6. Nutrient Profiles Marine organisms need nutrients to photosynthesize
Nutrients: several forms of nitrogen and phosphorus
Organisms take up nutrients at surface layers, nutrients depleted
When organisms die, they decompose and nutrients are replenished to water column (remineralization) and sink
These nutrients are upwelled to surface where depleted once again my photosynthesizing organisms.
depth

7. Salinity Amount of dissolved material per amount of liquid
(g salt/kg water)
part per thousand (ppt, ‰)
Water Salinity
Fresh water <0.5 ppt
Brackish ppt
Seawater ~35 ppt
Hypersaline >40 ppt 7 7

8. 8

9. Class Exercise
Measure temperature stratification and indicate thermoclines in varying salinities
Measure salinity with a refractometer & measure density with a hydrometer and correlate measurements
Study dissolved oxygen depth profiles and effect of temperature

10. Temperature Experiment
We will conduct an experiment on 2 water samples (freshwater an salt water):
To measure temperature profiles and
To identify the thermocline zone created by heating tanks from above with lamps
Lamp

11. Measuring Salinity Refractometer measures salinity
Average salinity 35 ppt
Prism
platform
Eyepiece

12. Measuring Density Hydrometers measure density
Fresh water density ~ g/cm3
Density increases as the water gets more salty - hydrometer floats higher

13. Plotting Density vs. Salinity
First plot points of KNOWN measured salinity and density (see points graphed below)
Draw “Best Fit Line” through points – A line on a scatter plot which can be drawn near the points to more clearly show the trend between two sets of data.
Use Best Fit Line to determine an UNKNOWN variable based on a KNOWN variable:
Known
Density A
Best Fit
Line
Determine
Correlating
Salinity A
Density
Salinity