Ocean Water Characteristics

Ocean Water Characteristics Ocean circulation has two primary components: surface ocean currents and deep-ocean circulation. While surface currents like the famous Gulf Stream are driven primarily by the prevailing world winds, the deep-ocean circulation is largely the result of differences in ocean water density (mass per unit volume of a substance). A density current is the movement (flow) of one body of water over, under, or through another caused by the density differences and gravity. Variations in salinity and temperature are the two most important factors in creating the density differences that result in the deep-ocean circulation. Salinity Salinity is the amount of dissolved solid material in water, expressed as parts per thousand part of water. The symbol for parts per thousand is 0/00. Although there are many dissolved salts in seawater, sodium chloride (common table salt) is the most abundant. Variations in the salinity of seawater are primarily a consequence of changes in the water content of the solution. In regions where evaporation is high, the proportionate amount of dissolved material is seawater is increased by removing the water and leaving behind the salts. On the other hand in areas of high precipitation and high runoff, the additional water dilutes seawater and lowers the salinity. Since the factors that determine the concentration of salts in seawater are not constant from the equator to the poles, the salinity of seawater also varies with latitude and depth.

Salinity-Density Experiment This experiment will help you gain a better understanding of how salinity affects the density of water. Step 1 Fill a graduated cylinder with cool tap water up to the level of a rubber band which has been placed near the top of the cylinder. Step 2 Fill a test tube about ½ full of solution A (saltwater) and pour it slowly into the cylinder. Observe and describe what happens. Observations: __________________________________________________________ ______________________________________________________________________ Step 3 Repeat steps 1 and 2 two additional times and measure the time required for the front edge of the seawater to travel from the rubber band to the bottom of the cylinder. Record the times for each test in Data Table I. Make certain that you drain the cylinder after each trial and refill it with fresh water and use the same amount of solution with each trial.

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Ocean Water Characteristics

Table I. Salinity-density Experiment Data Table Solution A B Solution B plus salt

Timed Trial #1

Timed Trial #2

Avg. of both times

XXXXXXXXXXX

XXXXXXXXX

Step 4 Determine the travel time two times for solutions B exactly as you did with solution A, and enter your data in Table I. Step 5 Fill a test tube about ½ full of solution B and add to it some additional salt. Then shake the test tube vigorously to dissolve the salt. Determine the travel time of this solution (as before) and enter the data in Table I. Step 6 Clean all glassware thoroughly. Rinse well to remove all salt.

Questions 1. Since the solution that traveled fastest had the greatest density, which solution was most dense? _______________________ 2. Write a brief summary of the results of your salinity-density experiment.

Table II list the approximate surface water salinity at various latitudes in the Atlantic and Pacific Oceans. Using the data, construct a salinity curve for each ocean on the graph (Fig. 1). Use a different colored pencil for each ocean. Answer the following questions. 3. At which latitudes are the highest surface salinities? 4. What are two factors that control the salts in seawater? 5. Refer to the factors listed in question 4. What is the cause of the difference in surface water salinity between equatorial and subtropical regions in the Atlantic Ocean? 6. Of the two oceans, which has the higher average surface salinity? 7. Suggest a reason for the difference in the average surface salinity between the oceans.

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Ocean Water Characteristics

Table II. Ocean surface water salinity (in parts per thousand) at various latitudes in the Atlantic and Pacific Oceans. Latitude 60o N 50o 40o 30o 20o 10o 0o 10o 20o 30o 40o 50o 60o S

Atlantic Ocean (0/00) 33.0 33.7 34.8 36.7 36.8 36.0 35.0 35.9 36.7 36.2 35.3 34.3 33.9

Pacific Ocean (0/00) 31.0 32.5 33.2 34.2 34.2 34.4 34.3 35.2 35.6 35.7 35.0 34.4 34.0

Figure 2 shows how ocean water salinity varies with depth at different latitudes. Using Figure 2 and your text, answer the following questions. 8. In general, salinity (increases/decreases) with depth in the equatorial and tropical regions, and (increases/decreases) with depth at high latitudes. 9. Why are the surface salinities higher that the deep-water salinities in the lower latitudes? 10. What is the halocline? Label the halocline on Figure 2. 11. Below the halocline the salinity of ocean water (increases rapidly/ remains fairly constant/decreases rapidly).

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Ocean Water Characteristics

Ocean Water Temperatures Seawater temperature is the most extensively determined variable of the oceans because it is easily measured and has an important influence on marine life. Like salinity, ocean water temperatures vary from equator to pole and change with depth. Temperature, like salinity, also affects the density of seawater. However, the density of seawater is more sensitive to temperature fluctuations than salinity. Cool surface water, which has a greater density than warm water, forms in the polar regions, sinks and flows toward the tropics.

Temperature-Density Experiment Conduct the following experiment to observe the effects of temperature on the density of water

Step 1 Fill a graduated cylinder with cold tap water up the level of the rubber band. Step 2 Put 2-3 drops of dye in a test tube and fill it ½ full with hot tap water. Step 3 Pour the contents of the test tube slowly into the cylinder and record your observations. _____________________________________________________________________ _____________________________________________________________________ Step 4 Empty the cylinder and refill it with hot water. Step 5 Add a test tube full of cold water and 2-3 drops of dye to some ice in a beaker. Stir the solution for a few seconds. Fill the test tube ¾ full with some liquid (no ice) from the beaker. Pour this cold liquid slowly into the cylinder and record your observations. _____________________________________________________________________ _____________________________________________________________________ Step 6 Clean the glassware.

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Ocean Water Characteristics

Questions 1. Given equal salinities, (cold/warm) seawater would have the greatest density. 2. Write a brief summary of your temperature density experiment.

Table III show the average surface temperature and density of seawater at various latitudes. Using the data in Table III, plot a line on the graph in Figure 3 for temperature and a separate, different color, line for density. Then answer the questions. 3. (Warm/cool) surface temperatures and (high/low) surface densities occur in the equatorial regions. While at high latitudes, (warm/cool) surface temperatures and (high/low) surface densities are found. 4. What is the reason for the fact that higher average surface densities are found in the Southern Hemisphere? Earlier in these experiments you concluded that surface salinities were greatest at about 30oN and 30oS. 5. Refer to the density curve in Figure 3. What evidence supports the fact that the temperature of seawater is more of a controlling factor of density than salinity? Table III. Idealized ocean surface water temperatures and densities at various latitudes. Latitude 60o N 40o 20o 0o 20o 40o 60o S

Surface Temperature (oC) 5 13 24 27 24 15 2

Surface Density (g/cm3) 1.0258 1.0259 1.0237 1.0238 1.0241 1.0261 1.0272

Figure 4 shows how ocean water temperature varies with depth at different latitudes. Questions 6. Temperature decreases most rapidly with depth at (high/low) latitudes. Give the reason that the decrease with depth is most rapid at these latitudes. 7. What is the thermocline? Label the thermocline on the Figure 4. 8. Below the thermocline the temperature of ocean water (increases rapidly/remains fairly constant/decreases rapidly).

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