Oceanography Unit Section One Properties of Seawater
Read through the notes below or on-line and answer the questions 1-11 from the notes.
I. Oceans
II. Composition
III. Pressure
IV. Density & Temperature
V. Research
I. 4 major oceans on Earth
1. Atlantic Ocean (2nd largest) longest north to south
2. Arctic Ocean- (smallest)
3. Indian Ocean
4. Pacific Ocean - (largest) covers 33% of the Earth; contains 50% of Earth's salt water
II. Composition
A. Dissolved gases - greater % in cold water
1. Nitrogen
2. Oxygen
3. Carbon dioxide
B. Salinity - a measure of the dissolved solids in seawater
1. Avg. ocean salinity = 34.5 g/kg (or ppt. parts per
thousand) If you evaporate 1000 grams of sea water,
35 grams of solid minerals (salts) will be left behind.
2. Measured with instruments that test for electric
conductivity; the more conductive the higher the salinity
3. Sources of ocean salinity include: volcanoes; erosion
carried by glaciers, streams, and waves breaking on shore
4. Salinity decreases where large amounts of fresh water are
entering any ocean:
a. mouth of a river
b. area where glacier enter the ocean
c. areas of heavy rainfall (equator)
Ex. Baltic Sea Salinity = 30.0 g/kg because many
rivers and glaciers drain into it.
5. Salinity increases where climates are hot and dry because
evaporation is taking away fresh water and leaving salts
behind:
a. Latitudes between 200 - 300 north & south latitude
Ex. Mediterranean Sea & Red Sea
Salinity = 40.0 g/kg
b. Polar waters where sea ice forms. Only fresh water
forms ice and the salt gets left behind
III. Pressure - the force per unit area
A. Pressure at the bottom of the Marianas Trench is 1000 times greater than standard
atmospheric temperature. Depth is about 11,000 m or 36,000 ft. There is so much water
pushing down from above at this depth that the force is 7.8 tons per square in.
B. Doubling water depth doubles pressure
IV. Density - the mass per volume of an object.
A. Density of fresh water is greatest at approx. 4 0C (40 0F) Increasing or decreasing
temperature from this # causes a decrease in density.
B. As salinity increases the temperature of maximum density and the freezing temperature
decrease.
C. Seawater density and temperature are inversely proportional
1. As temperature of seawater increases density decreases.
2. As temperature of seawater decreases density increases
D. Temperature has a greater effect on the density of seawater than salinity does.
V. The Argo Ocean Profiling Network
1. International project to monitor ocean temperature, salinity, and currents to improve the
understanding of Earth's climates
2. Click here for the lab portion of this section.
Questions:
Fill in or circle the correct response. Use your notes as a reference
1. The salinity of seawater increases when [(water evaporates)(sea ice melts)].
2. The most abundant ions in seawater are [(chloride & calcium) (chloride & sodium) (sodium & calcium)]
3. Temperature is typically [(more important than) (equally important as) (less important than) salinity in controlling seawater density.
4. The largest ocean is the ______Ocean.
5. Cold water contains [(more) (less)] dissolved gases than warm water.
6. The average ocean salinity is [30.0 g/kg) (34.5 g/kg) (40.0 g/kg)].
7. Salinity of the Mediterranean Sea is [(greater) (less)] than the salinity of the Atlantic Ocean. Remembering that denser water sinks, the Mediterranean seawater that enters the Atlantic Ocean will [(sink below) (stay above)] the Atlantic seawater.
8. When swimming in Florida or the Bahamas (latitudes between 20-30 degrees north)a swimmer can expect the water to be [(less salty) (more salty)] than the seawater he or she swam in at the Jersey Shore.
9. Seawater density and temperture are [(directly)(indirectly) proportional meaning when temperture increases salinity [(increases) (decreases)].
10. There is a link to a [(bar graph) (line graph) (pie chart)] for the dissolved ions found in seawater.
11. Fill in the following with: Average salinity (34.5‰.), lower than average salinity (34.5‰↓),
or higher than average salinity (34.5 ‰↑)
Station 2: Located where the Congo River empties into the ocean; high average temperature; abundant rainfall throughout the year.
Station 3: Located at 26 0C N latitude; climate hot & dry
Station 4: Located deep below the surface on the floor of the Pacific Ocean; water temperature 1 0C
Station 5: Located off the east coast of Canada where ice-filled arctic currents meet warm Gulf Stream waters; abundant fog & precipitation
DENSITY-DRIVEN OCEAN CIRCULATION LAB
In this activity, we examine actual temperature and salinity profiles in the upper 2000 m of the ocean to identify a water mass. A water mass is a volume of seawater that is relatively uniform in density and is identifiable based on its temperature, salinity, and other properties
The source of data for this portion of the investigation is measurements made by the Argo Ocean Profiling Network, an international project to monitor ocean temperature, salinity, and currents to better understand Earth’s climate system. (Argo is the name of the ship sailed by the Greek mythological hero Jason.) Launched in Fall 2000, Argo will deploy by ship or aircraft some 3000 floats on the ice-free portion of the ocean by 2003. Analogous to a radiosonde in the atmosphere, a float obtains vertical profiles of temperature and salinity in the ocean. As shown in Image 1, the instrument is programmed to sink to a depth of about 2000 m, drifting at that level for 10 to 14 days, then slowly rise, measuring temperature and salinity through the ocean layers as it makes its way to the surface. At the surface, data is transmitted to a communications satellite and the probe begins another cycle. Each float is expected to be operational for 4 to 5 years. Image 2 is a plot of temperature and salinity profiles obtained by Argo float 422. Float 422 was located at 32.6 degrees N, 72.4 degrees W in the Atlantic Ocean east of North Carolina (shown on the map on the lower right) on February 6th 2002 when the plotted data were reported. Profiles of temperature and salinity variations with depth are plotted in the large diagram on the left. As a ratio salinity has no units and may be written as a pure number, but for convenience we express salinity in practical salinity units (psu). The temperature scale (in °C) is horizontally along the top while the salinity scale (in psu). The left axis shows pressure in decibars increasing from the surface downward. Pressure in decibars corresponds numerically to depth in meters so, for example, a pressure of 800 decibars occurs at a depth of about 800 m. On this image, the red on-screen (or light gray on printed copy) line (with triangles) on the left is the temperature profile and the blue on-screen (or black on printed copy) dotted line on the right is the salinity profile. Label the two profiles.
Fill in or circle the correct response. Use the on-line lab portion for the questions below.
1. The water pressure is 1200 decibars at an ocean depth of ______meters.
2. According to the plotted temperature profile, seawater temperature [(increases) (decreases) (is essentially constant)] from the ocean surface down to a depth of about 150 m. The total temperature change from the surface down to a depth of 150 m is about [(3)(6)] Celsius degrees. This is the near-surface seasonal thermocline that develops in spring and persists through summer and much of the fall.
3. From a depth of about 150 m down to about 400 m, both temperature and salinity decrease [(at a rapid rate) (only slightly)]. The main thermocline, characteristic of the low and mid-latitude ocean, extends from a depth of about 400 m to a depth of about [(1200)(2000)] m.
4. At a depth of 2000 m, seawater temperature is about [(2)(4)(6)] °C and salinity is about [(34.5)(35.0)(35.5)] psu.
5. Image 3 is a plot of temperature and salinity profiles obtained by Argo float 544. Float 544 was located at 34.8 degrees N, 124.8 degrees W in the Pacific Ocean west of Pismo Beach, California (shown on the map on the lower right) on 23 October 2001 when the plotted data were reported. On this image, the on-screen red (or light gray on printed copy) line (with triangles) is the temperature profile and the on-screen blue (or black on printed copy) dotted line is the salinity profile. Label the two profiles.
6. Floats 544 and 422 are located essentially at the same latitude with float 544 representing conditions associated with the California Current and float 422 representing conditions associated with the Gulf Stream.
7. Compare the temperature profiles for floats 422 and 544. From the surface down to a depth of 150 m, the water temperature off the California coast is [(lower) (higher)] than the water temperature off the North Carolina coast. This temperature contrast is consistent with the relatively [(cold) (warm)] California Current and [(cold) (warm)] Gulf Stream.
8. Image 4 shows the Argo float 422 for 22 October 2002 compared to 6 February 2002. Compared to the plot from October the February plot shows [(a faster) (the same) (less of a) rate of decrease in temperature. This is due to the change in received solar radiation for that latitude from Oct. - Feb.
9. Image 5 shows Argo float 422 is roughly off the coast of the Carolinas. At first the float moved [(northward) (southward) (eastward) (westward)] and than moved [(northwest) (southwest) (northeast) (southeast)] to its present location.