Table 2.

Summer physical variables for the Great Lakes based on data collected during summer surveys from 1996 to 2017, including average site depth for all profiles analyzed, thermal structure (epilimnion, thermocline, and hypolimnion), maximum relative thermal resistance to mixing (RTRM), maximum thermal gradient, and the 1% PAR depth (daytime profiles only). Values shown are the mean ± one standard deviation.

	n profiles	Thermocline present (%)	Site depth (m)	Epilimnion depth (m)	Thermocline depth (m)	Hypolimnion depth (m)	RTRM	Thermal gradient (°C m−1)	1% PAR depth (m)
Superior	473	99	169 ± 54	12.5 ± 5.3	17.2 ± 8.6	33.7 ± 13.2	22.9 ± 21.8	−1.7 ± 1.1	35.6 ± 8.9
Huron	359	100	82 ± 27	11.9 ± 3.7	16.7 ± 5.7	35.1 ± 9.3	49.8 ± 33.2	−2.6 ± 1.2	39.8 ± 10.0
Michigan	388	100	109 ± 58	11.9 ± 4.5	16.5 ± 5.5	34.8 ± 9.2	54.7 ± 51.1	−2.6 ± 1.2	31.9 ± 8.2
Northern	226	100	116 ± 70	11.8 ± 4.8	16.8 ± 6.4	34.5 ± 10.3	47.4 ± 49.8	−2.3 ± 1.0	29.9 ± 6.4
Southern	162	100	99 ± 34	12.0 ± 4.1	16.0 ± 4.0	35.2 ± 7.7	60.9 ± 51.6	−3.0 ± 1.2	33.9 ± 9.3
Ontario	229	99	99 ± 47	11.5 ± 4.7	14.7 ± 5.5	33.1 ± 10.5	49.8 ± 33.2	−2.7 ± 1.3	20.8 ± 5.5
Western	112	100	102 ± 33	9.5 ± 3.7	11.9 ± 4.5	28.5 ± 7.2	56.4 ± 37.3	−2.9 ± 1.4	21.8 ± 6.1
Central	117	97	95 ± 57	12.9 ± 4.9	17.5 ± 4.9	38.1 ± 11.2	44.4 ± 28.4	−2.6 ± 1.3	20.0 ± 4.9
Erie	459	81	24 ± 13	12.7 ± 4.2	15.6 ± 4.7	20.7 ± 7.2	76.6 ± 62.9	−4.0 ± 3.0	16.1 ± 6.9
Western	135	35	10 ± 1	5.5 ± 1.7	5.9 ± 1.7	5.7 ± 1.1	17.0 ± 35.3	0.3 ± 0.5	7.5 ± 3.4
Central	217	100	23 ± 1	13.2 ± 3.1	16.0 ± 2.3	17.7 ± 2.1	110.0 ± 54.3	−6.2 ± 2.0	18.2 ± 3.8
Eastern	107	100	45 ± 9	14.4 ± 4.2	18.9 ± 3.6	29.0 ± 4.9	72.6 ± 51.4	−4.3 ± 1.9	22.1 ± 5.6