STATIONS OFF 

 GRAND HAVEN-MUSKEGON 



Temperatures were collected on 15 days 

 off the Grand Haven-Muskegon shore (table 3 ) 

 during June 19-August 18, 1930, and May 14- 

 Septeinber 29, 1931, at 5 shallow stations 

 with depths 40-74 meters (131-243 ft.) and 

 at 5 deep stations with depths 94-108 meters 

 (308-354 ft.). These depths averaged 53 

 and 101 meters (174 and 331 ft.). 



The surface temperatures of the waters 

 during both years rose progressively from 

 the first dates of observation throughout 

 the summer usually reaching the maximum dur- 

 ing the first week of August. The temper- 

 atures reached 20° (68° F.) in 1930 and 

 nearly 23° (73° F. ) in 1931. Although the 

 surface temperatures were at first lower at 

 the deep than at the shallow stations, they 

 rose higher in deep water late July or early 

 August. However, an upwelling had reduced 

 the shallow-water temperature sharply to 

 14.5° (58.1° F.) on August 17, 1931, 6.8° 

 (12.2° F.) below the deep-water temperature. 

 The surface waters were warmer in 1931 than 

 in 1930 during the summer months. 



In both years the subsurface tempera- 

 tures of the shallow stations followed the 

 trend of the surface temperatures either to 

 the bottom or down to levels that fluctu- 

 ated between 3 and Eibout 25 meters (10 and 

 82 ft.). The reversal of the temperatures 

 below these different levels had continued 

 to the bottom. In deep water the subsurface 

 temperatures had also followed the direc- 

 tions of change of the surface temperatures, 

 except on September 3, 1931, either to the 

 bottom or down to at least 50 meters (164 

 ft.) in 1930 and to 10-25 meters (33-82 ft.) 

 in 1931, below which the reversed tempera- 

 tures either remained constant or increased 

 and decreased at the different levels. 



The subsurface temperatures of the 

 deep stations gradually approached those 

 of the shallow stations and as the season 

 advanced the former at times exceeded the 

 latter at various levels. Upwellings had 

 shifted the relationship when in 1931 cold 

 water had risen to at least a 12-meter (39 

 ft.) level on July 18 at the deep station 

 and to the surface on August 17 at the 

 shallow station, an unusual occurrence. 



Five-degree (41° F.) water was still 

 found above the 5-meter (16 ft.) level on 



May 14, 1931, at both stations. During the 

 period from the middle of June to the end 

 of September this temperature had been low- 

 ered in both years to depths that usually 

 varied from about 25 to 35 meters (82 to 

 115 ft.) in the shallow water and 30 to 45 

 meters (98 to 148 ft.) in the deep water. 

 Temperatures below 4.0° (39.2° F.) were 

 recorded in May and June but only at the 

 deep-water stations. On May 14, 1931, a 

 temperature of 3.8° (38.8° F.) was recorded 

 from the 6-meter (20 ft.) level to the bot- 

 tom. Bottom temperatures of 3.9° (39.0* F. ) 

 were recorded on June 20, 1930, and 22, 

 1931, but thereafter they varied from 4..0° 

 (39.2° F.) to 4.2° (39.6° F. ) in deep water 

 reaching the mjiximum in August 1930 and 

 early September 1931. The shallow-water 

 bottom temperatures fluctuated from 4.0° 

 (39.2° F.) to 4.6° (40.3° F.) in 1930 and 

 5.2° (41.4° F.) in 1931 during May-Septem- 

 ber, reaching the maximum in August of both 

 years. 



The earliest recorded thermocline 

 appeared in 1930 on June 20 but only at the 

 shallow station at depths of 24 to 27 meters 

 (79 to 89 ft.). Later it was eliminated but 

 then again recorded on July 25 in depths of 

 only 10-16 meters (33-52 ft.). Technically 

 no thermocline formed at the deep station 

 on this date but the difference of the tem- 

 peratures at 15 and 18 meters (49 and 59 

 ft.) was 2.9* (5.2° F.). In August a ther- 

 mocline occurred in both waters at nearly 

 the same level between depths of 15 and 22 

 meters (49 and 72 ft.). 



In 1931 the thermocline was first 

 recorded on July 2 at two levels of a deep- 

 water station. It persisted thereafter in 

 both waters on all dates of observations 

 to September 29. During the summer it had 

 fluctuated between depths of 10 and 20 

 meters (33 and 66 ft.) in the shallow water 

 and between depths of 5 and 17 meters 

 (16 and 56 ft.) in the deep water. In the 

 fall the thermoclines of both waters had 

 descended to depths between 18 suid 27 

 meters (59 and 89 ft.). 



The depth intervals covered by the 

 thermoclines generally ranged from 3 to 8 

 meters (10 to 26 ft.) and averaged 4 meters 

 (13 ft.) in each year. The thermocline 

 thermal gradients averaged 7° (13° F.) in 

 the shallow waters in 1930 and in both 

 waters in 1931 but averaged only 4° (7* F. ) 

 in the deep waters in 1930. 



