548 



BULLETIN OF THE BUREAU OF FISHEEIES 



It is probable that vernal warming followed a similar course, at first, in the 

 coastal zone in 1921, with the indraft of warmer and salter water from offshore main- 

 taining the winter status of cold surface stratum and warmer bottom water into the 

 first week of March. In 1 925, however (p. 1004) , warming from above and from below 

 raised the temperature of the whole column in Massachusetts Bay at a more nearly 

 equal rate from the middle of February until late in March, whereas in Ipswich Bay the 

 surface warmed the more rapidly from the beginning. In 1920, however, the surface 

 was already fractionally warmer than the 20 to 40 meter stratum as early as March 

 4 (p. 524), and it may be that in any year when an extremely severe winter chills the 

 upper 100 meters or so of the guK to an abnormal degree the surface at once com- 

 mences to warm after the grip of winter is released, whereas in more normal years 

 the surface temperature may be expected to remain almost stationary for a brief 

 period during late February and early March. In 1924, when a foot or so of snow 

 fell on March 11 and 12, followed by several days of freezing weather, the surface 

 had warmed to only 2.2° at a station 8 miles off Gloucester {Halcyon stsition 10652) 

 by March 19, with about 1.8° at depths of 40 and 70 meters. 



The progressive warming of Massachusetts Bay is illustrated for a warm April 

 by the FisTi Hawk stations for 1925, when the mean surface temperature rose from 

 2° on March 10 to about 4.6° on April 4 to 8. A definite regional differentiation 

 also had developed, with the surface warmest (5° to 5.4°) in Cape Cod Bay, where it 

 had been coldest during the preceding months. Thus, the relationship characteristic 

 of winter (coldest next the land) was now definitely reversed, so to continue through 

 the spring (fig. 22) and summer. At the 40-meter level, however, the bay still con- 

 tinued slightly warmer at its mouth (3.2° to 3.9°, Fish HawJc stations 30 to 33 and 

 84) than in Cape Cod Bay or near the Plymouth shore (2.9° and 2.6°, stations 6a 

 and 10), evidence that the indraft of offshore water continued to exert more influence 

 on the temperature of the deeper strata (up to the 7th or 8th of April in that year) 

 than did solar warming from above. This was not the case in Ipswich Bay, how- 

 ever, where the 40-meter temperature was almost precisely the same on April 7 (2.4° 

 to 2.8°) as it had been on March 10 (2.5° to 2.7°), though the surface had warmed 

 from 3.35°-3.6° to 4.2°-4.9° during the interval. 



By April 21 to 23 the mean temperature of the surface of Massachusetts Bay 

 had risen to 5.2° (4° to 6.8° at the individual stations, fig. 22) and the 40-meter 

 temperature to a mean value of about 3.8°, but virtually no change had yet taken 

 place in the temperature of the bottom water at depths greater than 60 meters, a 

 constancy illustrated by the following table. In 1920, also, the inner part of the bay 

 was actually slightly colder at 40 meters on April 20 (1.58°) than it had been on 

 April 6 to 9 (2.2°-2.4° at stations 20089 and 20090), evidence of some up welling of 

 the colder water from below. 



