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 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

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)

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 <0.5 ppt Brackish 0.5-30 ppt Seawater ~35 ppt Hypersaline >40 ppt 7 7

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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 ~ 1.000 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