District Engineers; and W. T. Laidly, Chief Tech- 

 nical Assistant. 



Constantine Ben assisted in integrating U. S. 

 Lake Survey data with U. S. Fish and Wildlife 

 Service data in this report. 



THERMOGRAPH RECORDS 



Thermograph data are from instruments in- 

 stalled by the U. S. Fish and Wildlife Service at: 

 the Lake Superior and Ishpeming Railroad ore dock, 

 Marquette, Michigan, in 1951; Stannard Rock light- 

 house in 1952; and the wellhouses of the Marquette 

 water plant (1955) and the Calumet andHecla water 

 plant (1953). All implements were standard Taylor 

 recording thermographs with 7-day spring-driven 

 clocks and stainless-steel thermal elements. 



Leo Erkkila, in charge of the sea lamprey con- 

 trol program of the U. S. Fish and Wildlife Service, 

 was responsible for making the installations and 

 supervised the collection of thermograph data. 



EXPLANATION OF DATA 



Temperature data 



Bathythermograph data of the Great Lakes are 

 well suited for presentation in tabular form. Almost 

 without exception the water is nearly homothermous 

 or there is a well-defined metalimnion (the stratum 

 in which the greatest change in the vertical temper- 

 ature gradient occurs). The temperature traces can 

 be represented with reasonable accuracy by the sur- 

 face and bottom temperatures under homothermous 

 conditions, and by temperatures at the surface, top 

 and bottom of tlie metalimnion, and at the bottom 

 when the water is stratified. Oceanographers have 

 not found it practical to present bathythermograph 

 temperatures in tabular form because of the usual 

 lack of well-defined temperature zones and die gen- 

 eral variability of temperature gradients. 



Temperatures from bathythermograph traces 

 were read from 3- by 5-inch photographic enlarge- 

 ments of the grid and superimposed trace. These 

 prints are on file at the Ann Arbor office of the Great 

 Lakes Fishery Investigations. Values for each bathy- 



thermograph were adjusted by the mean deviation 

 of the temperature from the comparable bucket (ot 

 sea chest intake) temperature so that values of dif- 

 ferent instruments and for different cruises would be 

 comparable. Bathythermographs used on the Cisco 

 were calibrated once during each cruise and at the 

 end of the operating season according to a procedure 

 given by U. S. Hydrographic Office Publication No. 

 607 (1955). The accuracy obtained by this procedure 

 is better than -f 0. 3" C. The reversing thermometers 

 were calibrated by the Engineering Research Institute, 

 University of Michigan. Corrections were only cal- 

 culated to 0. 1* C. Therefore, temperatures taken by 

 these instruments are recorded to the nearest 0. 1" C. 



Some discrepancy occasionally occurred among 

 reversing thermometer, bathythermograph, and bucket 

 temperatures. There are several explanations for these 

 disagreements: error in depth of reversing thermometers; 

 hysteresis of the bathythermograph; and human errors in 

 reading and recording data. Also, reversing thermom- 

 eter and bathythermograph lowerings usually were not 

 made simultaneously. 



Bathythermograph slides obtained from the U. S. 

 Lake Survey were studied in the same manner as those 

 from the Cisco . The depth range of the Survey bathy- 

 thermographs was 0-450 feet. Calibrations of the in- 

 struments were not made until the close of the 1957 

 season at which time it was discovered that the bathy- 

 thermograph used in 1957 functioned improperly below 

 2. 2° C. , consequently temperatures below this figure 

 have not been recorded for that year. A few other 

 slides were discarded because the traces had been 

 partially obliterated. The recorded temperatures are 

 probably accurate to + 0. 7° C. 



Thermograph temperatures at the four installations 

 were for the following depths: 



Lake Superior and Ishpeming Railroad ore dock 15 feel 



Stannard Rock lighthouse 16 feet 



Marquette water plant 55 feet 



Calumet and Hecla water plant 12 feet 



Daily maximum and minimum temperatures were 

 recorded to the nearest "F. These readings were con- 

 verted to the nearest 0. 1° C. in this report. The 

 temperatures given in tables 19-31 can be considered 

 accurate to+ 0.5* C. 



10 



