1. Light in the Sea: Secchi Disc Activity
The Secchi disc is a simple device for measuring water transparency. To use the disc lower it into water until it just vanishes. Note the depth by using the markings on the rope used to lower the disc. The rope is marked off in 1.0 m increments. Raise the disc back up and note the depth at which it reappears. The average of the two depths is the limit of visibility, or the index of transparency. The index of transparency depends on several factors including productivity, state of the sea, time of day, cloud cover, and currents.
The Secchi disc is used to estimate the depth that can be considered the limit of primary production. One general rule is that photosynthesis can take place at a depth shallower than three times the Secchi disc depth. At three times the Secchi depth light is about 1% of that at the surface.
The extinction coefficient can be calculated from the Secchi disc depth using the equation:
k = 1.7/Z sd
where Zsd is the Secchi disc depth.
Once the extinction coefficient is known the ratio of light at depth to light at the surface can be calculated with the equation:
I/Io = e-kL
where I is light at depth, Io is light at the surface, and L is depth in meters.
Use the Secchi disc to obtain values for Zsd at 0800, 1200, and 1600 at the same location. Note any differences in conditions. Use the values to obtain the extinction coefficient at each time. Use the extinction coefficients to plot I/Io versus depth on the same graph. Use depths of 10m, 20m, 30m, 40m, 50m, 60m, 70m, 80m, 90m, and 100m for your graph. The easiest way to do this is enter the depths in a list on the TI and then create another list using the enter values.
2. Method to Determine the Calcium Carbonate Content of Sand
The amount of calcium carbonate content of sand can be determine by using hydrochloric acid, HCl, to dissolve the calcium carbonate, CaCO3, present in sand. The reaction is represented by:
CaCO3(s) + 2HCl(aq) -----> CO2(g) + H2O + CaCl2(aq))
As the chemical reaction shows, carbon dioxide will be liberated when the calcium carbonate reacts with the hydrochloric acid. By weighing a sample before and after reaction with acid, the amount of calcium carbonate in the sample can be determined. This is used to classify the sand.
3. Light and dark Bottle Method for Determining Gross Primary Production
To examine the energy flow in an ecosystem an accurate estimate of the amount of solar energy fixed by green plants has to be known. This fixed solar energy forms the basis of the food chain and dictates the amount of life an area can support. The light and dark bottle method uses the relationship between oxygen production and carbon fixation to predict the amount of energy stored as carbon compounds in a marine ecosystem.
It is essential that all atmospheric oxygen be eliminated from the sample bottles during the experiment. Collect approximately two liters of sample water from the appropriate depth to be studied. As soon as the sample is collected, measure its oxygen content with the oxygen meter. Rinse one clear and one dark bottle with the sample water, then fill bottles with as little aeration as possible. Return the bottles to the depth collected. Make sure the bottles are secure and will not clash with wave action. the two bottles should remain at depth for a minimum of two hours, but preferably 4-6 hours. At the end of the period, the bottles are brought back to the surface and the oxygen measured in each bottle.
4. Diurnal Variations of Oceanic Conditions
The sea is constantly changing. Organisms must adapt to these changes if they are to survive. For example, many zooplanktons migrate daily from several hundred meters depth to near the surface. Night migrations enable zooplankton to feed during the night and return to deeper waters for protection during the day. In this activity, we will examine how the sea changes over a twenty-four period with respect to several parameters.
In teams of two, you will take the following measurement every two hours: water temperature, air temperature, oxygen at 1 m, salinity (with hydrometer), wind speed, wind direction, wave height, pH
Once data are collected, plot the air temperature, water temperature, oxygen, salinity and pH on one graph. Use different colors to distinguish the different variables.