STATIONS OFF 

 LUDINGTON-FRANKFORT 



Temperatures were obtained on 26 days 

 off the Ludington-Frankf ort shore during 

 June 18-August 5, 1930, and May 15-Septem- 

 ber 18, 1931, at 6 shallow stations with 

 depths 47 to 63 meters (154 to 207 ft,) 

 averaging 56 meters (184 ft.) and at 11 

 deep stations with depths 89 to 250 meters 

 (292 to 820 ft.) averaging 144 meters (472 

 ft.) (table 4). 



The shallow-water surface temperature 

 rose from 8.7" (47.7° F.) after June 18, 

 1930, to temperatures that fluctuated from 

 12.2" to 14,2° (54.0° to 57,6° F. ) through 

 July and reached a peak of 19,9° (67.8° F.) 

 on August 5, the last date. In 1931 it 

 progressed from 4.1° (39.4° F.) on May 15 

 to 21.6° (70.9° F,) on July 30 and then 

 varied from 19,0° to 19,9° (66.2° to 67.8° 

 F.) except on August. 26 and 27 when the 

 temperature dropped to 13* (55° F.). 



At the deep stations the surface tem- 

 perature increased consistently from 7.4° 

 to 20.0° (45.3° to 68.0° F.) in 1,930 and 

 from 4.0° (39,2° F.) to a maximum of 21.5° 

 (70.7° F.) on August 18 in 1931 and then 

 fluctuated from 17.1° to 20.2° (62,8° to 

 68.4° F.) excluding the sudden decline to 

 14° (57° F.) on August 26. The surface 

 warmed more slowly at the deep stations in 

 both years but by late July and thereafter 

 their temperatures generally exceeded those 

 of the shallow stations. 



The reduction in surface temperature 

 of about 7° (13° F,) between August 18-19 

 and August 26-27, 1931, in both deep and 

 shallow stations was an unusual summer inci- 

 dent, although 2m upwelling had also dropped 

 the surface temperature to the same extent 

 on August 17 at a station between Grand 

 Haven and Muskegon. The decrease continued 

 in the subsurface waters down to the 8-meter 

 (26 ft.) level on August 26 at the shallow 

 station and to the bottom on the next day 

 and nearly to the bottom on the 26th at the 

 deep station. The reduction of the upper- 

 level temperatures resulted from the cold 

 air, cind the severe storm that started late 

 on August 19 and continued to the early 

 morning of the next day. This storm in- 

 creased the swell and current. Adverse 

 weather continued so that no hydrographic 

 data could be collected during August 20- 

 25. However, an upwelling of cold water 



may also have reduced the temperatures of 

 the lower levels at the deep station. 



The subsurface temperatures of both 

 years followed, with exceptions on only 

 three dates (July 8 and 23, 1930, and 

 August 18, 1931), the direction of changes 

 of the surface temperatures either to the 

 bottom or down to depths that ranged from 

 about 5 to 48 meters (16 to 158 ft.) in 

 1930 and 5 to 70 meters (16 to 230 ft.) in 

 1931, The temperatures below these upper 

 layers, if not reversed to the bottom, 

 were either changed again or fluctuated at 

 the greater depths, 



A late-winter temperature was still 

 evident on May 15 and 19, 1931, when a 

 degree of 3,8 (38.8° F. ) was recorded at 

 20 meters (66 ft.) at a shallow station 

 and at 10 meters (33 ft.) at a deep sta- 

 tion. No temperatures below 4° (39.2° F.) 

 were observed at any shallow station after 

 mid-June, except on July 30, 1931, when a 

 bottom temperature of 3.9° (39,0° F,) 

 occurred at a depth of only 47 meters (154 

 ft,), the result of an upwelling revealed 

 by the temperatures of July 22 and 30, 

 The rising of cold water also took place 

 on other dates. The temperature was de- 

 creased on July 8, 1930, up to at least 

 the 5-meter (16 ft.) level at both sta- 

 tions and on August 18, 1931, at the shal- 

 low station, 



A temperature of 3,9° (39,0° F,) was 

 recorded up to July 10 in 1930 but only at 

 the bottom of deep stations. In 1931 the 

 deep-station temperatures below 4° (39,2° 

 F.) gradually moved to greater depths with 

 the advance of the season until in certain 

 waters they had disappeared. The tempera- 

 ture of 3.9° (39.0° F.) had been lowered 

 to depths of 60 to 65 meters (197 to 213 

 ft.) during May 29-June 23 and 85 to 95 

 meters (279 to 312 ft.) on June 24. The 

 other records of 3.9° (39.0° F.) obtained 

 on July 20, 22, and September 4 at depths 

 of 75 to 100 meters (246 to 328 ft.) were 

 no doubt the results of the upwelling of 

 water from greater depths, as evidenced by 

 the fact that temperatures of the same 

 levels at other stations were higher dur- 

 ing the same period. In the deepest basin 

 of the lake with depths of 189 to 250 

 meters (620 to 820 ft.) the temperatures 

 ranged from 3.8° to 4.0° (38.8° to 39.2° 

 F.) at the level of 125 meters (410 ft.) 

 and from 3.6° to 3.8° (38.5° to 38.8° F.) 



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