Water Temperature 

 Introduction 



With the exception of the detailed data collected by Parmenter (1929) 

 in Lake Erie, our knowledge of temperatures in the deeper parts of the Great 

 Lakes is limited to a few occasional records, some of which are obviously 

 erroneous. Coleman (1922) reviewed many of the early records. Wright (1931) 

 cited other records, and called attention to the fact that bottom tempera- 

 tures below U* C. in summer have been found in all of the five Great Lakes 

 except Lake Erie. A large number of surface temperatures are recorded by 

 Norton and Grunsky (1927). 



In the present investigation all temperature readings were taken 

 with a Richter & Wiese reversing thermometer. The instrument used was 

 graduated in degrees and tenths of degrees centigrade, and readings were 

 made to the nearest 0.05 degree. 



The temperature conditions in Western Lake Erie are extremely simple 

 and are normally quite uniform over a large area. The simplicity and uni- 

 formity result from the nature of the basin; it is not only shallow, but it 

 is unusually uniform in depth over large expanses. For that reason, the 

 records of almost any station will be fi? und typical of a large area sur- 

 rounding it, although the records at different stations may vary in minor 

 details. However, a record of temperatures at one station taken intermittent- 

 ly over a long period may not show the same characteristics as the record of 

 another nearby station taken intermittently on different dates. This i6 true 

 because a therrnocline may be established and destroyed in a short time, and 

 thus not appear on a record taken at one or two week intervals. 



The record of Station 1^8 (Stone's Cove) has been selected for presen- 

 tation because it is more complete than any other and because it appears to 

 be tj'pical of the offshore area. It is close to the shore of South Bass 

 Island, but the w ater deepens so rapidly at that point that the temperature 

 seems to be unaffected by the island's presence. Data from other stations 

 will be given in order to make up the deficiencies in the record at Station 

 l58 and to show conditions at special points in the lake. 



Theriral Stratification 



Western Lake Erie is characterized by almost total absence of thermal 

 stratification. The record of Station l58 for 1929, given in Table 8 shows 

 this fact very well. On only one of the l6 dates for which temperature data 

 are aveilable was there any evidence of stratification. The date was June 27, 

 when there was a gradient of 1.25* C. in the stratum between 8 and 9 meters. 



