Surface Temperature and Salinity 



Surface temperatures and salinities varied 

 seasonally among the coastal areas; the sea- 

 sonal trends within each area were sinnilar, 

 however. Mean temperatures in 1965 and 

 1966 generally increased from an annual low 

 in winter to a summer high and declined in 

 the fall (fig. 5). The single exception was in 

 the eastern area in 1966; mean temperatures 

 increased slightly from sumn-ier (8.7° C.) 

 to fall (9.0° C). Temperatures in winter were 

 low in each of the areas (0.0° C.). Tem- 

 peratures decreased from west to east in 

 spring, summer, and fall. The range in tem- 

 perature fronn winter to summer was greatest 

 in the western area--about 5° C. greater 

 than the difference in the eastern region. 



Seasonal changes in salinity (measured in 

 parts per thousand) were similar in both 

 years (fig. 5). In the western and central 

 areas mean salinities decreased fronn an 

 annual high in winter to a low in spring, 

 and subsequently rose in summer and fall. 

 Salinities in the east decreased from winter 

 to a low in spring, and increased progressively 

 to the annual high in the fall. Spring and 

 sumnner salinities were lower in the western 

 and central areas in 1966 than in 1965; in 

 the eastern area values were higher in 1965. 



Areal differences in temperature and sa- 

 linity along the Gulf coast result from local 

 environmental conditions rather than from 

 large-scale advection of waters. The low 

 temperatures and high salinities of the eastern 

 area fronn spring through fall are the products 

 of vertical mixing through the water column 

 induced by tidal stirring, and minimal river 

 drainage; higher temperatures and lower sa- 

 linities of the western region result from 

 increased stability of the water column, re- 

 duced tidal mixing, and large-scale runoff 

 from rivers (Bigelow, 1914, 1915, 1917, 1927; 

 Sherman, 1966). Profiles of tennperature and 

 salinity based on observations made in 1966 

 corroborate earlier reports of vertical nnixing 

 in the eastern Gulf and stratification of water 

 in the western area during the warmer months 

 (fig. 6); inshore to offshore observations of 

 temperature and salinity were made from 

 the nnouths of three rivers--the Merrinnack, 

 Penobscot, and Machias--to approximately 

 28 km. offshore. The relatively low tem- 

 peratures and high salinities in the western 

 and central areas in winter result from wind- 

 induced mixing of the water column, and the 

 movement of cold air over the Gulf from 

 the adjacent land mass by the prevailing north- 

 west winds of the season (Bigelow, 1927). 



WEST 



CENTRAL 



EAST 



16 



14 



12 



uj 10 



3 

 f- 



2 8 



4 - 



2 - 







33.0 



8 



6 



4 



2 



e 32.0 



S« 8 



>- 6 



i ^ 



D 2 

 m 31.0 



8 

 6 

 4 

 2 

 30.0 



: 1 



J I I L 



J I L 



1965 



1966 





J I I L 



j^VV'"^ .♦^VV'^^ ^<j^>>^'' 



<^^ 



Figure 5. — Mean seasonal surface temperature and salinity 

 for the western, central, and eastern areas of the coastal 

 Gulf of Maine in 1965 and 1966. 



Areal Distribution of Zooplankton and 

 Hydrography 



The general decrease in zooplankton volumes 

 from west to east along the coast is similar 

 to the areal decline in abundance observed 

 in earlier investigations (Bigelow, 1926; Fish 

 and Johnson, 1937; Sherman, 1966). This de- 

 crease appears to be caused by dissimilar 

 hydrography in the different areas. In the 

 eastern Gulf the unstable water column, low 



