PHYSICAL OCEANOGEAPHY OF THE GULF OF MAINE 



575 



succession illustrated by these two stations is characteristic of that side of the basin 

 in general. 



No observations have been taken in the western side of the gulf in June, or on 

 Nantucket Shoals, on the cruises of the Bureau of Fisheries' vessels, except those 

 just mentioned; but the dailydata tabulated by Rathbun(1887) for several lighthouses 

 and lightships partially fill the gap for the coast sector between Cape Ann and the 

 Mount Desert region, and are consistent with the serials taken of late years in the 

 northeastern part of the gulf, in the Bay of Fundy, and in Massachusetts Bay. 



Approximate temperatures (°C) at the surface on June IS, from Rathbun's {1887) tables^ 



' Given only to nearest 0.1 °. 



The 10-day averages for Gloucester and Boothbay for 1920 (figs. 29 and 30) 

 show that the water warms only slightly faster in inclosed locations of this sort than 

 off the open coast (compare 13° at Gloucester and about 12° at Boothbay on June 

 15 with Rathbun's record of 12° to 13° at Thatchers Island, off Cape Ann, and of 9° 

 to 11° at Seguin Island. A temperature about 3 degrees lower at Matinicus Rock, 

 at the mouth of Penobscot Bay, than at Seguin Island, some 34 miles along the 

 coast to the westward, probably reflects some local retardation of vernal warming 

 by the spring freshets from the Penobscot River. Conversely, the comparatively 

 high temperature at Petit Manan suggests that readings as warm as 10° are to be 

 expected by June 15 after a few days of warm weather, in sheltered locations along 

 shore in shallow water, to the east as well as west of Mount Desert. In fact. Doctor 

 McMurrich records almost as high surface temperatures (9° to 9.5°) at St. Andrews 

 by June 15 in 1916. Lubec Narrows, however, open to the Grand Manan Channel 

 and with a great volume of water rushing through on every tide, had warmed to 

 only about 6° by this date in 1920 (fig. 31). 



Earlier in the season, and up to mid May, the vertical distribution of tempera- 

 ture in the upper 150 meters or so is of one type throughout the inner waters of the 

 gulf, though the actual values differ slightly from station to station. During late 

 May and June, however, very important differences develop between the state just 

 described for the western side of the gulf (where the rapid warming of the upper 

 stratum by the sun, coupled with the sudden estabhshment of a high degree of 

 vertical stability, causes the development of a steep temperature gradient in the 

 upper 40 to 50 meters, overlying water more nearly homogeneous) and the north- 

 eastern part of the gulf, where more active stirring by the tides spreads the warmth 

 received from the sun through a thicker stratum of water. Furthermore, we find 

 the rate of warming decreasing from west to east as we follow around the coast line 

 of the gulf, even after this regional difference in the downward dispersal of the heat 

 received has been allowed for. Thus, the surface had warmed only from 5° on May 



