542 BULLETIN OF THE BUREAU OF FISHERIES 



warming) ; and that while the inshore (Cape Sable) end of the profile was coldest, 

 as is usual at this season, the temperature was fractionally higher close in to the land 

 near the cape than a short distance out at sea. A differential of this same sort would 

 have been more apparent had the profile been located a few miles farther east, 

 because the whole column in 75 meters depth, close in to Shelburne (station 20073), 

 was fractionally warmer than 2° (p. 1000), while the water farther out on the shelf 

 (stations 20074 and 20075) was colder. 



BOTTOM 



The temperature of the bottom water, in depths greater than 200 meters, varied 

 in March from 4.02° off the northern slope of Georges Bank in 330 meters (sta- 

 tion 20064) to 6.84° in the Eastern Channel in 215 meters (station 20071), with 

 readings of 5.06° to 5.59° at depths of 225 to 250 meters elsewhere in the basin. 

 It is interesting to find the deepest water coldest just north of Georges Bank at the 

 location just mentioned, for this was also the case at 200 meters; whereas the north- 

 ern side of the basin, not the southern, was the coldest at 100 meters. 



For the biologist, the bottom temperature of the gulf at the coldest season is 

 .interesting as evidence of the greatest cold that bottom-dwelling animals of any sort 

 must endure in various regions. In general, a parallelism then obtains between 

 temperature and depth, the bottom being warmer the deeper the water. This rela- 

 tionship is complicated, however, by the increase in temperature from the shore 

 seaward (p. 525), independent of depth, illustrated by the charts for the 40-meter and 

 100-meter levels (figs. 12 and 13.) 



With more or less ice forming every winter in shoal bays and among the islands, 

 the littoral zone is chilled from time to time to the freezing point of salt water in 

 such situations. In Cape Cod Bay the Fish Hawk had a reading as low as —1.5° 

 in 17 meters and —0.4° on the bottom in 34 meters on February 6, 1925 (cruise 6, 

 station 6a, p. 1005) ; and while these readings are the lowest so far recorded for the 

 open gulf, the data for that year and for station 20062 show that in Alassachusetts 

 Bay generally the bottom may be expected to chill to about 0° out to about the 

 30 to 40 meter level at some time during most winters, perhaps every year. No 

 doubt this applies equally to the bays along the coast of Maine and to the tributaries 

 of the Bay of Fundy; biit along the open northern shores of the gulf, where strong 

 tides produce an interchange of water more active than in Massachusetts Bay, it is 

 not likely that the bottom temperature ever falls as low as 0° except within the 

 littoral zone. Our two March stations (200S3 and 20084) similarly show the bottom 

 slightly warmer at 50 metei's along western Nova Scotia at that season than in 

 Massachusetts Bay; but later in the spring, when the icy Nova Scotian water from 

 the east is flowing in greatest volume past Cape Sable, the bottom of the eastern 

 side of the gulf may also be chilled to 1° - 0° down to a depth of 50 meters — per- 

 haps still deeper, for a brief period, in some years. On the other hand, it seems 

 that the bottom temperature of the deep troughs of the gulf never falls below 4°, 

 except, perhaps, in very exceptional years. 



Thus, any animal dwelling on bottom in the inner part of Cape Cod Bay, or 

 anywhere among the islands of the coastal zone shoaler than 40 to 50 meters, is apt 

 to be subjected to a temperature close to zero or lower at the end of winter. There 



