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
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 Low Latitudes Tropical Zone Mid Latitudes Temperate Zone
Comparison High Latitudes Polar Zone Verticalprofiles 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 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 4C and
decreases with lower temperature Salt water is more dense than
fresh water Density always increases with depth If it doesnt, the
water column is unstable (well mixed) 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?
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
Salinity Amount of dissolved material per amount of liquid
(g salt/kg water) part per thousand (ppt, ) Water Salinity Fresh
water 40 ppt 7 7 8 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 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 Measuring Salinity Refractometer measures salinity
Average salinity 35 ppt Prism platform Eyepiece Measuring Density
Hydrometers measure density
Fresh water density ~ g/cm3 Density increases as the water gets
more salty - hydrometer floats higher 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
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