MS20 Laboratory: Physical and Biological Factors Affecting Oxygen ...

MS20 Laboratory: Physical and Biological Factors Affecting 

Oxygen in Sea Water 

Objectives 

• Understand the relationship between oxygen concentration and temperature 

• Understand the relationship between oxygen concentration and salinity 

• Use The Winkler titration method to determine oxygen concentration in a water sample 

• Investigate the relationship of latitude and longitude on oxygen concentration 

• Investigate the effect of de[p[th on oxygen concentration 

Introduction 

The amount of a gas in seawater is a function of both biological and physical factors. In the case 

of a gas like oxygen, the biological processes of plant photosynthesis and plant and animal 

respiration strongly affect the oxygen concentration. This biological process is shown in Figure 

One. 

Figure One. Chemistry of photosynthesis and respiration 

In this process, carbon dioxide and water combine in the presence of light to produce additional 

plant material (glucose, cellulose) and oxygen. To accurately predict oxygen concentration, 

several biologically related factors must be considered, such as the number of organisms 

producing oxygen, the amount of respiration taking place, the amount of light available to the 

organisms, the nutrients available, and the turbidity of the water. In addition, there are also several 

physical factors that affect the amount of oxygen dissolved in seawater. These include salinity, 

temperature, and pressure, as well as mixing resulting from wind or currents. The concentration of 

oxygen can also indicate the "health" of the water, especially in regard to pollution. 

Procedure 1: Winkler Method for Determination of Oxygen Concentration in a Sea Water 

Sample 

General Chemical Reactions That Occur During Analysis for Oxygen in Seawater 

(The first three steps of this procedure have been carried out by your instructor) 

MS20 Lab Oxygen rev.3/27/2005 Page 1 of 16

1. To a carefully collected se water sample, add a manganous sulfate solution and a alkaline 

potassium hydroxide-iodide solution to the seawater. This forms manganous hydroxide-which is a 

precipitate. 

2. The newly formed manganous hydroxide Mn(OH) 2 reacts with the dissolved oxygen in the 

seawater to form a hydrated tetravalent oxide of manganese. 

3. Next add sulfuric acid to the solution in the presence of iodide to release free iodine. 

4. The free iodine released from this reaction is equivalent to the dissolved oxygen present in the 

seawater. In the presence of a starch solution this free iodine has an intense blue color. 

5. Using the titration method, determine the amount of I 2 present (and therefore the oxygen 

content) by adding a standardized sodium thiosulfate solution until the blue color disappears. This 

takes place when all the free iodine is gone. 

Sampling for Oxygen Analysis 

Because this experiment requires that the samples react with the chemical solution for a given 

period of time, all the samples will be collected and chemically “fixed” collections by the instructor 

before the lab period begins. The following samples have been collected (see Figure Two). The 

model lake samples are collected from the surface first, then sequentially down into the "lake". 

1. 0 o / oo salinity, room temperature aquarium (standard) 

2. 35 o / oo salinity, room temperature aquarium 

3. 0 o / oo salinity, polluted room temperature aquarium 

4. Model lake-surface 

5. Model lake-75 cm down 

6. Model lake-near bottom 

Figure Two. Water sampling procedure 


The water samples have been collected and the oxygen “fixed” in the following manner: 

1. Each BOD (biological oxygen demand) bottle was filled right to the brim with the water sample. 

BOD bottles (as shown in Figure Three, step 1) were filled with the rubber tubing resting on the 

bottom of the bottle so that "extra" oxygen was not added by splashing or agitation. 

2. Using the automatic pipettes, 1 ml of prepared manganous sulfate solution (step 2) was 

added to each BOD bottle followed immediately by 1 ml of the alkaline potassium iodide 

solution (step 3). After adding the potassium iodide solution, the water in most of the BOD bottles 

turns a straw yellow. However, those samples with little or no oxygen (polluted environment and 

lake bottom) will have a very weak yellow color or even a pale gray. 

3. The bottles were stoppered then shaken (step 4); the contents were allowed to settle for 15 

minutes, and then the bottles were shaken again. 

4. To each bottle 1 ml of concentrated sulfuric acid (step 5) was added. The bottles were restoppered 

and shaken until the precipitate dissolved. The solution turns slightly darker. 

5. The sample has now been "fixed" and can be analyzed any time during the lab period. The 

"fixing" process means that free iodine has been released in exact proportion to the oxygen that 

was in the sample at the time of “fixing”. The addition of oxygen to the sample after “fixing” will not 

affect the amount of free iodine now in the sample and so will not alter the titration results. 

Figure Three. Oxygen analysis flow chart 


Standardizing the Thiosulfate Solution 

If we know the oxygen content of a given water sample, we can use this as our standard and 

calibrate the thiosulfate solution to it. This assumes, of course, that we know the exact condition of 

our water sample, its salinity, temperature, and degree of oxygen saturation. If we use aerated 

fresh water at room temperature, we can closely approximate the actual oxygen content of the 

water by consulting the proper oceanographic tables. 

Table One shows the theoretical saturations of oxygen at 0 o / oo salinity and at the temperature 

ranges typically encountered in nature. 

Table One. Theoretical Oxygen Saturation at Various Temperatures 

TEMPERATURE 0 2 TEMPERATURE 0 2 TEMPERATURE 0 2 

(ºC) mL/L (ºC) mL/L (ºC) mL/L 

0 10.22 9 8.07 18 6.61 

1 9.94 10 7.88 19 6.48 

2 9.66 11 7.71 20 6.36 

3 9.39 12 7.54 21 6.23 

4 9.14 13 7.37 22 6.11 

5 8.90 14 7.21 23 6.00 

6 8.68 15 7.05 24 5.89 

7 8.47 16 6.90 25 5.77 

8 8.27 17 6.75 

Sample 1, from the open aquarium at 0 o / oo salinity, will represent your standard. In order to 

calibrate your thiosulfate solution, you will need to know how many milliliters of thiosulfate are 

needed to titrate the standard. 

Procedure 

1. Transfer exactly 50 mLof the known sample into a 125 mLErlenmeyer flask, using a 50 mL 

volumetric flask for the transfer (Figure Three, steps 6 and 7). 

2. Fill a 50 mL buret with thiosulfate solution (step 8). Record the buret level in Table Two below. 

3. Add approximately 5 mL of the starch solution (step 9) to your sample in the flask. The solution 

in the flask becomes dark blue. Slowly titrate (add thiosulfate from the buret) until the solution 

becomes colorless (step 10). You might hold a sheet of white paper behind the flask to help 

determine when the solution becomes colorless. At this point, you may still observe a few blue 

particles- don't worry about them. You have reached the end point! Record the final amount in 

the buret in Table Two. After calculating the difference between the starting and ending points on 

the buret, you will know the number of milliliters of thiosulfate required to render the solution 

colorless. 


4. Calibrate the thiosulfate solution by noting the number of milliliters of solution required to titrate 

a standard volume (50 ml) of fresh water ( 0 o / oo ), room temperature. 

Run the standard twice, taking the second 50 mL aliquots from the same BOD bottle as you took 

the first. Average your results from the two runs. Find the theoretical oxygen content from Table 

One. 

For the remaining samples (the unknowns), complete steps 6 through 10 on Figure Three for 

each analysis. Titrate each unknown once, unless you miss the end point. 

To calculate the concentration of each unknown, you will use the following formula 

unknown O 2 concentration = known O 2 concentration x mL thiosulfate used for unknown / ml thiosulfate for known 

where the known O 2 concentration is the one you determined from the standard. 

Record your results on your answer sheet. 

Procedure 2. Dissolved Oxygen (DO) in the Sea: Oceanographic Data Tables 

The following tables contain actual hydrographic data taken by oceanographic vessels 

throughout the world’s oceans. Hydrocasts always include the temperature, salinity and depth. 

Dissolved oxygen and phosphate data are often included. The exact location of the hydrocast is 

given by the latitude and longitude. 

1. Mark on Map A all the stations given in the data tables. 

2. Graph dissolved oxygen versus depth. 

Answer the following questions. 

A. How do surface values compare from place to place? 

B. How does dissolved oxygen vary with depth per locale? From locale to locale? 

C. What factors affect oxygen concentration? 

D. Are there any subsurface maximums? Minimums? If so, explain what causes them. 


Charles H. Gilbert; August 21; 21º11’N, 158º18’W;wind 090º,14kt; weather, cloudy 

Depth (m) T (ºC) S (º/ ºº 

) O 2 (mL/L) PO 4 -P (µg-at/L) σ t (g/mL) 

0 26.15 34.96 4.79 0.20 22.98 

24 26.16 34.96 4.78 0.10 22.97 

50 25.70 35.01 4.87 0.10 23.16 

73 23.86 35.01 5.02 0.06 23.17 

99 22.00 35.12 5.04 0.12 24.33 

147 20.08 35.14 4.77 0.17 24.87 

200 17.22 34.74 4.63 0.43 25.28 

250 13.94 34.38 4.48 0.48 25.74 

274 11.27 34.16 4.23 0.51 26.09 

300 9.78 34.13 4.19 0.61 26.33 

Charles H. Gilbert; August 20; 21º09’N, 158º20’W; wind 030º,11kt; weather, cloudy 



0 26.15 34.96 4.78 0.22 22.98 

23 26.09 34.96 4.82 0.17 23.00 

43 26.08 34.99 4.77 0.08 23.02 

63 25.48 34.99 4.84 0.03 23.21 

85 22.66 35.03 4.99 0.07 24.07 

122 21.30 35.12 4.98 0.05 24.52 

176 20.20 34.83 4.84 0.06 24.60 

219 17.68 34.58 4.48 0.40 25.05 

242 15.92 34.36 4.51 0.21 25.29 

265 14.85 35.07 4.54 0.28 26.08 

Hugh M. Smith; September 17; 21º14’N, 158º19’W; wind 050º, 8kt; weather, partly cloudy 



0 26.07 35.07 0.13 23.09 

26 25.88 35.05 0.17 23.13 

51 25.50 35.10 0.12 23.28 

77 23.11 35.10 0.06 24.00 

105 21.50 35.10 0.12 24.45 

156 19.68 35.05 0.26 24.90 

208 17.10 34.74 4.32 0.36 25.31 

258 14.12 34.38 4.32 0.70 25.70 

284 13.08 34.33 4.00 0.90 25.88 

310 11.33 34.22 3.89 1.13 26.13 

409 8.26 34.18 2.44 0.86 26.61 

506 6.37 34.20 1.48 1.22 26.89 

605 5.67 34.34 1.36 1.21 27.09 

803 4.64 34.45 0.91 1.29 27.30 

1001 4.09 34.51 1.11 1.30 27.41 

1511 2.62 34.61 1.70 1.59 27.63 

2037 1.98 34.63 2.20 2.98 27.70 

2557 1.68 34.67 2.58 2.71 27.75 

2570 1.72 34.69 2.64 1.10 27.77 


Crawford; Station 441; 24º 16'S 07º 43'W; Date: 9/19 


) O 2 (mL/L) PO 4 -P (µg-at/L) Total P (µg-at/L) 

0 20.07 36.265 4.98 0.32 0.71 

50 19.59 36.194 5.14 0.35 0.56 

100 19.00 36.129 5.09 0.34 0.52 

195 15.18 35.474 4.81 0.50 0.79 

295 13.09 35.203 4.81 0.72 0.86 

390 11.09 34.938 4.53 1.13 1.25 

490 8.90 34.692 4.26 1.45 1.51 

590 6.74 34.488 4.25 1.83 1.89 

685 4.97 34.359 4.47 2.15 2.14 

785 4.22 34.354 4.30 2.17 2.29 

980 3.42 34.447 4.10 2.28 2.25 

1130 3.22 34.556 4.12 2.23 2.16 

1285 3.22 34.664 4.13 2.08 1.94 

1430 3.16 34.738 4.44 1.88 1.85 

1755 2.91 34.827 4.79 1.71 1.65 

2050 2.68 34.854 5.06 1.67 1.60 

2345 2.60 34.873 5.19 1.61 1.61 

2640 2.52 34.883 5.23 1.61 1.56 

2935 2.46 34.884 5.24 1.53 1.54 

3235 2.42 34.886 5.19 1.61 1.60 

3530 2.39 34.888 5.14 1.62 1.57 

3830 2.40 34.890 5.08 1.59 1.59 

4125 2.41 34.891 5.07 1.66 1.59 

4425 2.44 34.890 5.08 1.69 1.67 

4575 2.47 34.891 5.14 1.64 1.56 


Crawford; Station 440; 24º 16'S 09º 11'W; Date: 9/18 


) O 2 (mL/L) PO 4 -P (µg-at/L) Total P (µg-at/L) 

0 20.21 36.320 4.94 0.30 0.47 

50 19.75 36.303 5.02 0.41 0.41 

100 19.45 36.263 4.94 0.41 0.54 

200 15.26 35.489 4.81 0.45 0.72 

295 12.86 35.148 4.50 0.80 1.04 

395 10.74 34.889 4.36 1.16 1.28 

495 8.56 34.667 4.01 1.58 1.70 

595 6.66 34.484 4.13 1.85 1.93 

695 5.27 34.382 4.32 2.01 2.03 

790 4.34 34.356 4.32 2.17 2.12 

990 3.49 34.421 4.11 2.22 2.21 

1190 3.22 34.571 4.00 2.16 2.15 

1385 3.18 34.723 4.34 1.96 1.97 

1585 3.03 34.802 4.68 1.82 1.75 

1725 2.90 34.816 4.76 1.67 1.71 

1925 2.70 34.834 4.90 1.61 1.63 

2125 2.59 34.852 5.07 1.61 1.64 

2420 2.52 34.871 5.26 1.57 1.62 

2720 2.49 34.880 5.32 1.60 1.60 

3020 2.44 34.883 5.26 1.48 1.69? 

3315 2.40 34.882 5.29 1.46 1.48 

3615 2.39 34.887 5.18 1.56 1.59 

3915 2.40 34.888 5.15 1.67 1.65 

4215 2.44 34.889 5.11 1.76 1.77 

4515 2.47 34.889 5.14 1.79 1.80 

Thor; August 10, 41º32’N 29º24’E 


) σ t (g/mL) O 2 (mL/L) H 2 S (mL/L) 

0 24.1 17.59 10.56 5.14 

10 24.1 17.59 10.56 5.14 

25 12.73 18.22 13.54 7.40 

50 8.22 18.30 13.22 6.71 

75 7.44 18.69 14.62 5.51 

100 7.61 19.65 15.33 2.33 

150 8.31 20.75 16.12 0.17 

200 8.54 21.29 16.51 0.90 

300 8.68 21.71 16.82 2.34 

400 8.72 21.91 16.97 4.17 

600 8.76 22.16 17.16 4.96 

800 8.80 22.21 17.19 6.06 

1000 8.85 22.27 17.24 6.04 


Horizon; November 23; 24º57’S 145º01’W; wind 180º, force 2; weather, missing; sea, slight. 


) O 2 (mL/L) PO 4 -P SiO 3 -Si pH 

(µg-at/L) (µg-at/L) 

σ t 

0 23.52 34.83 4.94 0.20 1 8.14 23.67 

8 23.53 34.88 4.95 0.12 2 8.35 23.71 

79 20.98 35.38 5.15 0.15 2 8.37 24.81 

157 19.58 35.36 5.03 0.23 0 8.30 25.16 

310 15.40 35.17 4.62 0.47 3 8.24 26.03 

462 10.87 34.71 4.64 1.06 4 8.16 26.59 

615 6.72 34.35 5.09 1.65 11 7.99 26.97 

766 5.58 34.29 5.23 1.78 17 8.00 27.07 

923 4.66 34.32 4.46 2.24 35 8.02 27.20 

1081 3.87 34.42 3.68 2.44 58 7.91 27.36 

1243 3.24 34.47 3.54 2.53 79 7.92 27.46 

1411 2.76 34.52 3.60 2.47 93 7.93 27.55 

1582 2.46 34.54 3.65 2.49 105 7.94 27.59 

1756 2.30 34.59 3.65 2.55 109 7.93 27.64 

1935 2.16 34.60 3.52 2.48 123 7.98 27.66 

2115 2.04 34.61 3.53 2.49 128 7.98 27.68 

2289 1.94 34.61 3.58 2.48 129 7.95 27.69 

2628 1.82 34.61 3.67 2.56 126 8.03 27.70 

2815 1.76 34.66 - 2.40 107u 8.08 27.74 

3013 1.70 34.64 3.79 2.54 130 8.04 27.73 

3212 1.64 34.63 3.94 2.55 134 8.04 27.72 

3608 1.54 34.65 4.05 2.42 130 8.06 27.75 

3806 1.52 34.67 4.15 2.45 132 8.07 27.77 

4006 1.52 34.68 4.16 2.47 131 8.05 27.77 

4205 1.52 34.68 4.17 2.49 130 8.07 27.77 

4406 1.50 34.69 4.30 2.48 129 8.10 27.78 


Atlantis Cruise 242; Station 5636; June 17; 19º01’N 39º21’E 

µg-at/L 


) O 2 (mL/L) PO 4 -P Total P 

1 30.49 38.04 3.92 0.18 0.46 

22 30.36 38.17 3.92 0.20 0.57 

44 29.13 38.49 4.08 0.18 0.62 

66 26.74 38.82 3.76 0.20 0.46 

87 25.41 39.45 3.34 0.23 0.71 

131 23.22 40.36 2.52 0.49 0.52 

175* 22.16 40.50 2.13 0.65 0.86 

262* 21.78 40.55 0.54 1.00 1.62 

350 21.69 40.57 1.08 0.95 1.36 

437 21.67 40.57 1.00 0.86 1.07 

Atlantis Cruise 242; Station 5637; June 17; 19º05’N 39º28’E 

µg-at/L 



1 30.47 38.48 3.85 0.19 0.54 

25 30.23 38.43 3.91 0.21 0.40 

49 28.44 38.49 4.08 0.21 0.58 

74 26.29 39.04 3.85 0.19 0.55 

99 24.74 39.94 3.38 0.23 0.51 

148 22.43 40.50 2.80 0.44 0.81 

197* 21.93 40.53 0.79 0.93 1.33 

296 22.04? 40.54 0.37 1.14 1.40 

394 21.71 40.61 0.52 1.14 1.33 

493* 21.69 40.60 0.88 1.04 1.29 

399 21.76 40.59 0.48 --- --- 

597 21.69 40.57 1.16 0.84 --- 

794 21.69 40.61 1.73 0.65 1.00 

989 21.74 40.60 2.11 0.53 0.84 

1180* 21.88? 40.62 2.27 0.52 --- 

1359* 21.79 40.59 2.32 0.55 0.81 

1419 21.84 40.57 2.34 0.44 0.77 

1440 21.79 40.60 2.34 0.49 0.93 

1456 21.82 40.61 2.34 0.68 0.55 

1471* 21.83 40.61 2.30 0.72 0.79 


Atlantis Cruise 242; Station 5608; May 16; 25º21.9’N 36º07.9’E 


) O 2 (mL/L) PO 4 -P (µgat/L) 

Total P (µgat/L) 

3 25.44 39.83 4.06 --- 0.39 

25 25.14 39.90 4.09 --- 0.21 

71 22.15 40.35 4.07 --- 0.17 

116* 21.94 40.47 3.41 --- 0.40 

161 21.94 40.45 2.80 --- 0.49 

207* 21.81 40.47 2.22 --- 0.77 

78 22.97 40.36 3.96 --- 0.48 

158 21.95 40.48 2.75 --- 0.71 

238 21.72 40.55 1.60 --- 1.22 

567* 21.67 40.58 1.64 --- 1.51? 

910 21.71 40.58 2.22 --- 0.62 

1266 21.79 40.62 2.46 --- 0.56 

1636* 21.81 40.62 2.59 --- 0.58 

1730 21.84 40.62 2.55 --- 0.52 

1825* 21.84 40.57 2.54 --- 0.59 

1875 21.87 40.58 2.59 --- 0.59 

1923* 21.88 40.58 2.59 --- 0.61 

1971 21.86 40.58 2.60 --- 0.66 

1991 21.92 40.59 2.48 --- 0.62 

2008* 21.96 40.58 2.41 --- 0.64 

2019 --- 40.59 2.43 --- 0.60 

Atlantis Cruise 242; Station 5609; May28; 07º59.0’N 58º59.0’E 

µg-at/L 



1 29.50 35.39 3.91 0.24 0.43 

10 29.49 35.40 3.91 0.39 0.35 

19 29.49 35.39 3.93 0.29 0.37 

48 28.98 35.44 4.08 0.27 0.44 

96 25.12 35.62 3.18 0.52 0.76 

144 19.20 35.40 1.54 1.18 1.16 

192* 16.37 35.34 1.05 1.07 1.30 

288 12.66 35.19 1.31 1.73? 1.60 

385 11.76 35.18 1.02 1.61 2.02 

578 10.41 35.26 0.53 1.88 2.33 

771 9.43 35.29 0.42 2.03 2.67 

966* 8.35 35.23 0.55 2.52? 2.67 

1162 6.66 35.06 0.89 2.09 2.78 

1455* 4.87 34.91 1.43 1.96 2.41 

1582* 4.14 34.80 1.74 --- --- 

1978 2.83 34.75 2.43 1.62 2.28 

2374* 2.19 34.75 2.84 --- 2.27 

2769 1.88 34.75 3.02 1.91 2.48 

3020 --- --- --- --- --- 


R/V Anton Bruun; Station 80; 15º43’N 90º 

µg-at/L 


) O 2 (mL/L) PO 4 -P NO 3 -N NO 2 -N SiO 3 -Si 

1 29.37 32.469 4.63 0.06 u 0.02 17.3 

25 27.33 32.974 4.79 0.15 0.5 0.04 10.2 

50 26.09 33.282 4.73 0.17 u 0.02 8.8 

75 25.96 33.858 3.95 0.33 1.1 0.21 0.4 

100 22.94 34.624 0.61 1.72 17.9 0.06 13.3 

125 19.35 34.752 0.28 2.08 24.0 0.08 26.4 

149 16.75 34.881 0.15 2.33 25.5 0.06 26.9 

199 13.91 34.955 0.24 2.55 29.6 0.01 32.9 

299 11.45 35.022 0.33 2.69 30.6 0.03 39.9 

398 10.47 35.027 0.40 2.83 32.0 0.04 44.2 

498 9.76 35.017 0.36 2.91 32.0 0.05 53.6 

598 8.99 35.012 0.46 2.97 30.3 0.03 60.6 

697 8.36 34.996 0.51 3.04 31.9 0.04 69.8 

797 7.72 34.978 0.64 3.14 33.5 0.07 75.8 

896 7.09 34.952 0.81 3.16 34.0 0.03 82.9 

996 6.55 34.939 0.96 3.22 34.1 0.03 89.7 

995 6.62 34.943 0.90 3.22 33.5 0.02 89.4 

1195 5.64 34.901 1.33 3.19 33.6 0.02 101 

1496 4.40 34.858 1.82 3.14 32.3 0.03 116 

1780 3.20 34.804 2.53 3.14 35.7 0.04 132 

2073 2.56 34.766 2.97 3.08 35.8 0.03 136 

2371 2.20 34.762 3.18 3.03 34.7 0.03 140 

R/V Anton Bruun; Station 80; 15º43’N 90º 

µg-at/L 


) O 2 (mL/L) PO 4 -P NO 3 -N NO 2 -N SiO 3 -Si 

1 28.84 34.121 4.48 --- --- --- --- 

39 28.73 34.107 4.50 0.14 1.6 0.06 2.9 

58 28.28 34.275 4.90 0.14 u 0.04 3.5 

87 27.37 34.316 4.48 0.22 0.4 0.03 2.1 

111 26.86 34.491 4.09 --- --- --- --- 

130 25.38 34.732 2.61 0.24 11.3 0.17 7.6 

159 21.67 34.799 0.56 1.72 25.3 0.08 15.9 

207 16.73 34.877 0.14 2.10 33.0 0.13 28.6 

304 12.11 35.006 0.19 2.41 33.7 0.14 85.4? 

400 10.84 35.023 0.12 2.58 41.3 0.14 44.8 

497 10.08 35.028 0.17 --- --- --- --- 

593 9.32 35.016 0.31 2.60 38.8 0.08 56.9 

690 8.61 34.995 0.35 2.64 35.5 0.05 63.3 

786 8.06 34.984 0.54 2.69 36.4 0.07 66.6 

883 7.46 34.961 0.58 2.90 37.8 0.04 73.5 

979 6.87 34.948 0.83 

970 6.88 34.948 0.76 

1164 5.82 34.903 1.21 

1456 4.45 34.855 1.69 

1751 3.18 34.797 2.29 

2046 2.51 34.764 3.27 


Meteor; March 9; 56º37’N 44º54.5’W 


) σ t O 2 (mL/L) O 2 (%) 

0 2.82 34.87 27.80 7.24 96 

50 3.01 34.90 27.81 7.26 97 

100 3.09 34.92 27.82 7.24 97 

200 3.17 34.93 27.82 6.70 90 

800 3.26 34.96 27.83 6.98 94 

1000 3.20 34.95 27.83 6.96 93 

1500 3.17 34.93 27.82 6.99 94 

2000 3.23 34.93 27.82 --- --- 

Meteor; March 30; 59º38’N 40º42.5’W 


) σ t O 2 (mL/L) O 2 (%) 

0 4.07 34.96 27.76 6.92 95 

50 4.07 34.97 27.77 6.99 96 

100 4.06 34.96 27.77 6.81 94 

200 3.98 34.97 27.77 6.84 94 

800 3.76 34.95 27.77 6.60 90 

1000 3.33 34.89 27.77 6.64 89 

1500 3.28 34.94 27.82 6.39 86 

2000 2.84 34.96 27.88 6.37 87 


Name__________________ Lab Section_______________ Date________ 

ANSWER SHEET Oxygen Lab 

Table Two 

Calibration water temp theoretical oxygen starting point ending point mLs of 

thiosulfate used 

1 st run 

2 nd run 

Average = 

Calculate your unknown concentrations using the average mls of thiosulfate from Table Two and 

the known oxygen concentration from Table One in this equation: 

unknown O 2 concentration = known O 2 concentration x mL thiosulfate used for unknown / ml thiosulfate for known 

6. Determine the oxygen content of sample 2: 35 o / oo salinity water, room temperature. 

milliliters of thiosulfate solution calculate 0 2 

7. Determine the oxygen content of sample 3: polluted lake environment. 


8. Determine the oxygen content of sample 4: model lake – surface sample. 


9. Determine the oxygen content of sample 5: model lake - 75 cm down. 


10. Determine the oxygen content of sample 6: model lake - bottom. 


Answer the following questions: 

1. Assume you misread your buret end point and added too much thiosulfate solution for your 

standard. How would this affect all of your other results? 


2. What if someone mixed up the numbers of the water bottles in the laboratory "lake" so that the 

surface sample was the "polluted environment" sample? At what stage in the experiment could 

you first recognize the mix-up? Explain! 

3. In winter, some fresh water lakes have the same temperature from top to bottom (isothermal). 

Would the oxygen values also be the same from top to bottom? Explain! 

4. Consider the oxygen values listed in One. Also compare the measured oxygen values for the 

water at 0 o / oo and 35 o / oo salinity. In the open ocean, which factor, temperature or salinity, would 

have a more important effect on oxygen concentration? (hint: consider the 

range of temperatures and salinities that might occur going from the equator to the polar regions) 

5. Graph the distribution of oxygen in the model lake that you observed. Would this be typical of 

an actual lake environment? Why or why not? 


6. The percentage of saturation of a gas in seawater can be calculated from the physical 

properties of the water (temperature, salinity, and atmospheric pressure). Sometimes, however, in 

the case of oxygen we have super saturation occurring in the surface layers. Why? (hint: 

consider the coastal ocean and processes that add O 2 to the water) 

7. Oxygen is a non-conservative gas- that is, it is affected by biological processes. Assume for the 

moment, however, that no biological processes are taking place. Sketch in the oxygen curve 

(below right) to indicate the theoretical oxygen concentrations with depth. Consider that the 

oxygen gets into the seawater through the air/sea interface only, and its concentration is 

controlled by the physical factors of temperature and salinity (ignore pressure effects and 

biological effects). (hint: consider what salinity and temperature are doing in each zone before 

plotting the oxygen curve!)

MS20 Laboratory: Physical and Biological Factors Affecting Oxygen ...

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