Salinity Research Page

Background Information

Salt water from the ocean tends to be pushed into the Juan de Fuca Strait like a solid wedge, moving southeast from the mouth of the strait. At the same time, fresh water comes south and then west, from the Fraser River.  Since salt water is denser than fresh water, the two do not mix evenly when combined.  Salt water tends to sink and congregate at the bottom and the mouth of the Juan de Fuca strait, where it is closest to its source. Fresh water, on the other hand, tends to stay on the surface of the strait and nearer to the rivers from which is emanates.

Because Race Rocks is relatively shallow compared to the rest of the strait and is centrally located between the Fraser River and the Pacific Ocean, it is a unique environment in terms of salinity. Not only is there the meeting of the fresh and salt water, there is also the mixing of the two waters are forced together up and over Race Rocks. Surface salinity also tends to vary throughout the year due to the seasonal influx of fresh water from the Fraser River, run off from Glaciers and monthly tidal currents.

Part A

Go to the following websites and find out the following:

1)             Why is the ocean salty?

http://www.palomar.edu/oceanography/salty_ocean.htm

http://www.pausd.palo-alto.ca.us/k6science/water/w_q_a/saltyo.html

Average the Mean Annual Surface Salinity

Part B

In the following section, we will examine the average surface salinity at Race Rocks.

2)             Open an excel spreadsheet and label it RaceRockstemp.xls

3)             Go to the salinity information page.

4)             Highlight the salinity data and copy it

5)             Paste the information into the cells on the sheet. Each month should have its own column.

6)             Do an edit-replace and delete all the 99.9 numbers and replace them with a blank space.

7)             In the column to the right of the data, determine the average of all the mean surface salinities for each year.

8)             Graph the results.

9)             Answer the following questions:

a.    Which years had the maximum and minimum mean annual salinities?

b.    What is the range of the average mean salinity at Race Rocks?

c.    Why would the mean salinity change from year to year? (Think globally!)

Average the Mean Monthly Surface Salinity

Part C

10)         In the bottom row, beneath the columns of data, graph the monthly mean salinity measures for each month, since 1932.

11)         Graph the results.

12)         Answer the following questions:

a.    During what months was the salinity highest?

b.    During what months was the salinity lowest?

c.     What is the range of average salinity?

d.    Describe the graph and give reasons why you think surface salinity changes in a predictable manner over the course of the year.

When you have completed this page, go to Temperature Research Page