Summer 1975 



The temperature structure of summer 1975 (Fig. 21 

 was characterized by four prominent features: the 

 development of a stroofj seasonal thermocline above 50 m 

 offshore of the 100-m isobath, vertical mixing and warm- 

 ing of coastal waters, breakdown of two temperature 

 minimum cells below the thermocline (50-150 ml. and 

 the minor fluctuation of temperatures in waters deeper 

 than 150 m. 



Summer solar warming developed a thermocline above 

 50 m in the central Gulf of Maine, with gradual down- 

 ward conduction of heat. Above the thermocline waters 

 warmed at a rate of about 2°C per month. The maximum 

 surface temperature, l.T.6°C, was reached in August, 

 with surface temperatures generally being l°to2°C 

 higher than in coastal waters (Fig. 2). 



Coastal waters (inshore of the 100-m isobath) warmed 

 throughout the water column, with weak thermocline 

 development off Maine and homogeneous conditions off 

 Nova Scotia. Bottom temperatures reflected the mixing 

 conditions off Nova Scotia, having a greater monthly rise 

 and higher maximum temperature than coastal Maine. 



During June and July two low temperature cells ex- 

 isted between ,50 and 150 m in central gulf waters, bound- 

 ed by the shallow thermocline and seaward progression of 

 warmer coastal waters. As the season progressed, these 



cold areas dissipated through warming influence from 

 surrounding layers. A temperature inversion of l''-2°C oc- 

 curred below 1.50 m during -June and .luly with upward 

 mixing that appeared to isolate the shallower cold cells. 

 By August this inversion disappeared and temperatures 

 nionotonicallv decreased to the bottom. 



Autumn 1975 



Autumn 1975 temperatures (Fig. .i) involved a change 

 from the warming to a cooling trend, with increased ver- 

 tical mixing. Coastal Maine and central gulf waters 

 began a steady cooling trend in September, while waters 

 off Nova Scotia reached a maximum temperature during 

 September and cooled through October and November. 

 The central gulfs thermocline mixed downward, with 

 continued warming of middepth waters into November. 

 Bottom waters (deeper than 150 m) warmed through 

 September and October, then cooled in November. 



Winter 1975-76 



The temperature for the winter of 1975-76 (Fig. 4) 

 showed an acceleration in the cooling trend as the largest 

 temperature decrease occurred between December and 

 January (>2°C above 50 m). Minimum temperatures 



JUNE 75 

 BAR HARBOR 



Figure 2. — Vertical temperature sections (°C) for the Gulf 

 of Maine between Bar Harbor, .Maine, and Yarmouth. 

 Nova .Scotia, summer 197.5. 



