Marine Science Name:____________________________________________ Period:___________ Activity: Salinity Properties of Seawater
Objective: During this activity students will become familiar several concepts on ocean salinity, including residence time, chlorinity, conductivity, and how salinity changes in an estuarine system. Procedure: Complete each of the sections below. Residence Time: Residence time is a broadly useful concept that expresses how fast something moves through a system in equilibrium. Elements with long residence times in the ocean tend to be very soluble in sea water and to be evenly mixed throughout the ocean. Elements with short residence times (such as iron and aluminum) are relatively reactive, or insoluble in sea water; they are easily removed and are unevenly distributed throughout the ocean. 1. There are 300 students in this room. If every minute, one student leaves and another arrives, how long does the average student stay in the room? How does this relate to residence time? 2. From the concentration data in the first column of the table below, determine the mass of Na+ and Ca2+ in the ocean. Then determine the residence time for these two dissolved components. *Mass of the oceans (water + salt) = 14,299 x 1020 g How can you explain the difference in the residence time for these two dissolved components? Chlorinity: Of the major ions, the concentration of Cl‐ is the easiest to analyze with reasonable accuracy. The chloride concentration is known as chlorinity, and has the following relationship with salinity: Salinity = 1.80655 x chlorinity (‰) 3. Water from the mouth of the Chesapeake Bay was measured to have a chlorinity value of 16.5‰. What is the salinity of this water? 4. The average salinity of the ocean is 35‰. What is the average chlorinity of the ocean? Marine Science Name:____________________________________________ Period:___________ Conductivity: By 1960, the salinity of sea water was most often measured by a salinometer, which measures the electrical conductivity of the sample. Electrical conductivity, or the ability of a substance to conduct electricity, increases for water as the amount of dissolved ions increase. 5. According to the graph to the right, what is the conductivity of water that has a salinity of 30‰ and a temperature of 15°C? What happens to the conductivity if the temperature of this water increases to 25°C? 6. The chlorinity of a seawater sample is 20‰. What is the conductivity of this sample at 0°C? 7. The average surface water temperature of the Red Sea during the summer is about 25 °C (79 °F) in the north and 30 °C (86 °F) in the south. The average conductivity of water in the northern region of the Red Sea during the summer is 60 x 103 µmhos/cm. What is the average salinity of this water? Seasonal Estuarine Data: Estuaries are marine environments whose salinity levels vary, depending on the river that feeds the estuary and the ocean from which it derives its salinity. Answer the following questions about the Pine Island, FL estuary. 8. Go to this website: http://cdmo.baruch.sc.edu/get/export.cfm I.
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In the first big box, scroll down and select ““Guana Tolomato Matanzas” It is in the NE of Florida. Select “PINE ISLAND” make sure it is the Pine Island with the Data Types “Water Quality” Click “Proceed with this Station”, then click “Graph Data” Choose a date range from the past year Make your first parameter “Specific Conductivity” and your second perimeter “Salinity” Click :Graph” Marine Science Name:____________________________________________ Period:___________ Use the graphs to answer these questions: 9. Why are the two graphs generated similar? 10. What was the highest salinity reading from this year? When was it taken? What could have caused the salinity to be so high at this time? 11. What was the lowest salinity reading from this year? When was it taken? What could have caused the salinity to be so low at this time? 12. When was there a significant rain storm during this year? Explain. Go to this website: http://cdmo.baruch.sc.edu/get/realTime.cfm I.
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In the first big box, scroll down and select “GTMPCWQ ‐ Pellicer Creek”. Click “Specific Cond.: 24 hour chart” (The is a chart for specific conductivity) On the following page, you will see a graph of the data for the past 24 hours Under the graph, next to “add another perimeter to this graph” select “Sal (Salinity)”. Click “add Data” 13. What is causing the graph to rise and dip during the day? (Hint think about where the station is located) 15. Look at graphs of each of the other measured characteristics in this location. How do they Change over the course of a day. (List them below or on another sheet and explain what trend you see for each during a 24 hour period). 14. What challenges do habitats similar to Pellicur Creek and Pine Island present to aquatic life that live in that area? Explain.