ever, one occurred at both stations at depths 

 somewhere between 12 and 18 meters (39 and 

 59 ft.). No thermocline was observed in 

 November. The earliest thermocline record- 

 in in 1931 was reported on June 29 at both 

 stations. It persisted on the subsequent 

 dates to October 9 but disappeared on Octo- 

 ber 21. It had gradually descended in both 

 waters with the advance of the season from 

 levels of about 10 to 20 meters (33 to 66 

 ft.) to 22 to 32 meters (72 to 105 ft,). A 

 double thermocline was recorded on July 10, 

 1931. The thermal gradients ranged from 

 2° to 13° (4° to 23° F.) with an average of 

 7.7° (13,9° F.) and covered depth intervals 

 of 2 to 8 meters (7 to 26 ft.) with an 

 average of 4.8 meters (15.8 ft.). 



STATIONS OFF 

 MILWAUKEE-PORT WASHINGTON-SHEBOYGAN 



Temperatures off the Milwaukee- 

 Sheboygan shore were obtained on 17 days 

 during June 23-August 9, 1930, and June 1- 

 September 23, 1931, at 7 shallow stations 

 with depths of 60 to 84 meters (197 to 276 

 ft,) and at 6 deep stations with depths of 

 102 to 146 meters (335 to 479 ft.) that 

 averaged 73 and 126 meters (240 and 413 

 ft.) (table 7). 



The 1930 surface temperature reached 

 a maximum of 19.6° (67.3° F.) on July 29 

 in the shallow water and 19.9° (67.8° F.) 

 on August 9 in the deep water, the last 

 dates of observation. Except for the 

 shallow-water records of July 1 and 2, the 

 temperatures tended to increase during the 

 period of observation. The waters warmed 

 at about the same rate at both groups of 

 stations, in contrast to other areas except 

 off Waukegan. In 1931 the surface tempera- 

 ture of both waters rose from about 8° 

 (46° F.) on June 1 and 2 to a maximum of 

 21,7° (71,1° F.) on July 24 at a deep sta- 

 tion and 19.4° (66.9° F.) on August 31 in 

 shallow water. The surface waters appeared 

 to have been warmer at the deep than at 

 the shallow stations in the fall and also 

 in 1931 than in 1930 during the summer. 



Temperatures of the subsurface shal- 

 low and deep waters followed the seasonal 

 trend of the 1930 and 1931 surface tempera- 

 tures down to depths that either extended 

 to the bottom or ranged from about 5 to 40 

 meters (16 to 131 ft.). The temperatures 

 below these upper layers did or did not 



shift again at different depths. Seldom 

 did the upper-level temperatures of any 

 region decline during midsummer as much as 

 they did (2.4° and 33.3° C. ; 4.3° and 5.9° 

 F.) in the shallow water on July 1 and 2, 



1930. On the first the water had cooled 

 near the surface but on the next day down 

 to a depth of at least 18 meters (59 ft.). 

 This reduction may have been caused by the 

 unusual cold air, its temperature having 

 been lowered from about 22° to 13° (72* 

 and 43° F.). 



Five-degree (41° F.) water descended 

 gradually at the shallow stations from about 

 25 (82 ft.) to 44 meters (144 ft.) with the 

 advance of the season during June-September. 

 At the deep stations, however, this degree 

 water fluctuated between 25 and 36 meters 

 (82 and 118 ft.) during June and July and 

 then descended in August and September to 

 a maximum of 43 meters (141 ft.). 



The recorded bottom temperatures 

 fluctuated from 4.0° to 4.5° (39.2° to 40.1° 

 F.) in the shallow waters and from 3.8° to 

 4.0° (38.8° to 39.2° F. ) in the deep waters. 

 On July 9, 1931, the bottom temperature of 

 3.9° (39.0° F.) had risen to as high as 65 

 meters (213 ft.) at a deep station and was 

 still recorded at 80 meters (262 ft. ) on 

 July 25 and August 13. An upwelling must 

 have taken place, 



A thermocline was recorded earlier in 

 1930 than in 1931, In 1930 it was present 

 at all stations from June 23 to August 9 

 except on July 1 when it had been obliter- 

 ated at the shallow station by warm water. 

 In 1931 no thermocline was reported in 

 June. The first one was recorded on July 9 

 and others were observed on all subsequent 

 dates except in the shallow water on Sep- 

 tember 23, The thermoclines had fluctuated 

 between depths of 10 and 25 meters (33 and 

 82 ft.) during the summer months except on 

 June 23, 1930, when a deep-station thermo- 

 cline had formed at depths of 4 to 7 meters 

 (13 to 23 ft,). In the fall the existing 

 thermoclines had been lowered to depths of 

 19 to 30 meters (62 to 98 ft,). A double 

 thermocline was recorded on August 13, 



1931, between 14 and 25 meters (46 and 82 

 ft.) at a deep station. The thermal gra- 

 dients varied from 4° to 13° (7° to 23° F.) 

 with an average of 7.3° (13.1° F. ) and 

 covered depth intervals of 2 to 9 meters 



(7 to 30 ft.) with an average of 4.6 meters 

 (15.1 ft,). 



17 



