Portland Lightship (Figure 3, Table 3) 



The Portland lightship region experi- 

 enced winter temperatures which were slightly 

 above normal in February and March, followed 

 by rapid warming in April with readings well 

 above the mean. Beginning in mid-April, 

 when the thermocline was taking form, there 

 was a sharp drop in salinities, both surface 

 and bottom, and lower than usual salinities 

 persisted till early June; during this time 

 there appeared an intrusion of cold water, 

 apparent throughout the water column, but 

 most pronounced near the bottom, where mini- 

 mum readings were conparable to those that 

 had been found in late March. It is likely 



that this colder water came from the north- 

 east, moved by the cynamic gradient which 

 resulted from spring runoff and augmented 

 by northerly jind easterly winds which were 

 dominant in late March £ind early April. 



Summer surface values average slightly 

 below the mean and below those for the 

 previous year. Cooling was a little in 

 advance of the mean throughout the autumn 

 £ind early winter. 



Salinity values were uniformly below 

 those for 1957, a dry year, up until Decem- 

 ber, but closely pairalleled those for 1956. 

 The minimum values in May were below siny 

 recorded during the previous two years. 



Figure 3. Portland Lightship, 1958, (Dashed line in upper diagram, mean 

 for period 1947-1956) 



