be mentioned that the few records indicate 

 that midsummer temperatures of the upper 

 waters not beyond 30 meters (98 ft.) were 

 lower in 1930 than in 1932. 



STATIONS IN GREEN BAY 



Eight series of temperatures were 

 taken in Green Bay on 8 days at 5 stations 

 during September 21-October 4, 1930, and 31 

 on 24 days at 24 stations during April 19- 

 June 13, 1932 (table 10) . The depths 

 ranged from 30 to 43 meters (98 to 141 ft.) 

 in the midsection in 1930, except at sta- 

 tion 46 where the water was only 19 meters 

 (62 ft.) deep. They averaged 32 meters 

 (105 ft.). In 1932 the depths varied from 

 24 to 35 meters (79 to 115 ft.) with an 

 average of 29 meters (95 ft.) in the cen- 

 tral section and from 31 to 46 meters (102 

 to 151 ft.) in the upper region with an 

 average of 38 meters (125 ft.). 



Surface temperatures tciken on the 

 same day or two consecutive days showed no 

 greater differences between the northern 

 and southern areas than in either one of 

 these sections during the same time of year. 

 All of Green Bay waters were, therefore, 

 treated as a unit, although the northern 

 waters did not seem to warm as fast as the 

 southern waters as indicated, for example, 

 by the records of May 9 and 10 and 12 and 

 13. Although the generally greater depths 

 of the northern stations may have accounted 

 for the slower rise of temperatures, this 

 factor was not responsible for the differ- 

 ences of the temperatures on May 12 and 13 

 because the depths of both stations were 

 identical. Perhaps the location of a sta- 

 tion may have been the dominant factor. 

 The 1932 records will be considered first. 



The temperatures of April 19, 1932, 

 ranged from 1.0" (33.8° F.) at the bottom, 

 the lowest recorded, to 1.2" (34.2° F.) at 

 the surface. The temperatures in general 

 increased gradually with the advance of the 

 season to June 13, 1932, the last day. It 

 is noticed that they did not consistently 

 change gradually from the bottom to the 

 surface until May 13. The irregular sub- 

 surface temperatures probably resulted 

 from the inflow at different levels of the 

 several tributary waters. 



None of the temperatures exceeded 

 2.0° (35.6° F.) until April 27, 3.0° (37.4° 



F.) until May 3, and 4.0° (39.2° F.) until 

 May 10. The differences between the bottom 

 and surface temperatures of this period 

 averaged 0.2° (0.36° F.), only once exceed- 

 ing 0.3° (0.54° F.). As the temperatures 

 above 4.0° (39.2° F.) started to rise the 

 differences between those of the bottom sind 

 surface also increased due to the changes 

 at the upper levels. Five-degree (41° F.) 

 water appeared first on May 11 in central 

 Green Bay between depths of 5 and 10 meters 

 (16 and 33 ft.) and below 15 meters (49 

 ft.), but by May 17 it had already been 

 exceeded at all depths. 



The surface temperature rose quite 

 regularly from 1.2° (34.2° F.) on April 19 

 to the maximum of 17.6° (63.7° F.) on 

 June 13. The subsurface temperatures fol- 

 lowed with only three exceptions the direc- 

 tion of change of the surface temperatures. 

 At almost all stations the shifting took 

 place down to the bottom. Virtually all 

 of the decreases involved the records of 

 the upper region. However, when compari- 

 sons were confined to this region then the 

 data show that most of the temperatures 

 had risen with the advance of the season. 

 The bottom temperature also increased quite 

 regularly from 1.0° (33.8° F.) on April 19 

 until it reached 6.6° (43.9° F.) on May 23 

 when it was not exceeded thereafter. 



A thermocline did not develop until 

 June 8 in northern Green Bay at the deeper 

 of two stations when the temperature dropped 

 from 11.3° (52.3° F.) to 8.2° (46.8° F.) 

 at depths of 9 to 10 meters (30 to 33 ft.). 

 However, in the same area the thermocline 

 apparently had been eliminated on June 9 

 but reappeared on June 13 nearer the sur- 

 face at depths of 2 to 8 meters (7 to 26 

 ft.) and at higher temperatures that ranged 

 from 10.6° to 16.8° (51.1° to 62.2° F.). 



It may be mentioned incidentally 

 that the surface waters of Green Bay warmed 

 much more rapidly than those of Upper Lake 

 Michigan as indicated by the difference 

 of 4.1° (7.4° F.) between their averziges 

 of the period June 6-14. 



The 1930 autumn records of Green Bay 

 showed that the surface temperatures of 

 October had decreased to the same level of 

 those of early June in 1932. The average 

 declined from 16.2° (61.2° F.) during 

 September 21-25 to 13.0° (55.4° F.) during 

 September 30-October 4. The fall subsurface 



29 



