CLIMATE AND THE DISTRIBUTION OF MARINE ANIMALS 



303 



for a comparison between the temperatures of the 

 water of the Gulf in recent j-ears and during the 

 period 1912-26. It seems appropriate, then, to 

 commence tliis survey with a brief summary of 

 the temperatures of the Gulf for the earlier period. 



Depths to 150 meters 



Ijile mnter minimum. — The chief cause for the 

 winter chilling that is so conspicuous a phase of 

 the seasonal temperature cycle in the Gulf — reach- 

 ing its clima.x some time in February — is the loss 

 of heat by radiation from the surface of the sea 

 during tlie part of the year when the overlaying 

 air is colder than the water. Since the coldest 

 winds in winter blow out over the Gulf from the 

 quarter between west and north, surface tempera- 

 tures fall as much as 4° to 5° lower along the 

 western and northern margins of the Gulf than 

 over the central basin or Georges Bank offshore 

 (Bigelow 1927, p. 523, fig. 1). This is equally true 

 whether the season is severe or mild. A few days 

 of near-zero weather, with high west-to-north 

 winds, at any time in late December, January, or 

 February are enough to chill the water in enclosed 

 situations all around the coastline of the Gulf to 

 the freezing point of salt water, i. e., to about 

 28.9° F. at a sahnity of 32°/oo. This is about the 

 lowest temperature to be expected around the 

 shoreline of the Gulf, except close to the mouths 

 of rivers. How much ice actually forms under 

 these conditions varies greatly from place to place, 

 depending on local topography, on strength of 

 tidal currents, on rapidity of interchange with the 

 waters outside, and on the thoroughness with 

 which the channels are kept open by passing 

 vessels. For details in this respect concerning 

 harbors, bays, and rivermouths along the coast 

 from Provincetown, Mass., at the tip of Cape 

 Cod, to tlie mouth of Passamaquoddy Bay, the 

 reader is referred to the Coast Pilot, Atlantic 

 Coast, section A (l^. S. Coast and Geodetic Survey, 

 1918). 



Ice has never been known to mass in any 

 amount outside the outer islands and headlands 

 north of Boston. But cases are on record of ice 

 from neighboring harbors and from the shallower 

 parts of Cape Cod Bay massing in heavy fields or 

 windrows, sometimes as mucli as 10 feet tliick, 

 out in Cape Cod Bay (U. S. Coast and Geodetic 

 Survey, 1918; p. 277). It was not unusual in 

 Februarv for the surface to chill below 30° F. 



there, and along the coast as far north as the 

 offing of Boston. 



Two such areas with negative temperatures 

 developed in February 1925: one area off the 

 Scituate-Marshficld shore (31°-32° F.), the other 

 in the central part of Cape Cod Bay (30.9° at the 

 surface on the 9th, and 29.2° at 17 meters) doubt- 

 less resulted from the ice that had extended a mile 

 or more offshore south of Wellfleet on December 

 29, 1924 (Bigelow 1927: p. 655). The area occu- 

 pied by water colder than 32° may have been 

 more extensive still in Massachusetts Bay in 1934. 

 That year the mean water temperature in Boston 

 Harbor was onh' 29.8° for February, and a photo- 

 graph taken from the open Cohasset coast on 

 February 10 shows the pack ice reaching at least 

 1)2 miles seaward. The severe winter of 1920 was 

 of this same general type in the Gulf — to judge 

 from readings of 33.4° at the surface and 32.6° at 

 50 meters off Boston as late as March 5 — also the 

 winter of 1923, when a mean water temperature 

 of only about 30.2° in Boston Harbor for February 

 was followed by vernal warming so tardj- that the 

 water off the Scituate shore was still only about 

 37° at the surface and 32.6° at 80 meters on the 

 18th of April. 



In short, winters of the general order of severity 

 represented by 1925 were not exceptional during 

 the 2d to 4th decades of the 20th century, though 

 they did not recur regularly. But the available 

 record makes it most unlikely that the surface 

 temperature ever falls below 32° to 33° F. for more 

 than a few hundred yards out from tide line off 

 the open coast of the Gulf anywhere to the north 

 of Boston, even during the most severe wnnters. 

 On February 7, 1925, for example, when the sur- 

 face temperature was 31° inside Gloucester Har- 

 bor, it was 35° only 1 mile outside. 



Readings of 32.9° to 34.8° F. taken in March 

 1920 (a tardy spring) at the 40-meter level — to 

 which vernal warming had not yet penetrated — 

 in the trough between Jeffrey's Ledge and the New 

 Hampshire coast, and near Wood Island, Seguin 

 Island, Great Duck Island, and Petit Manan Is- 

 land off the Maine coast, point to a seasonal mini- 

 mum of 32° to 35° all around the periphery of 

 tlie Gulf northward and eastward from Cape Ann. 

 In the more severe winters, this minimum includes 

 the outer part of the open Bay of Fundy to judge 

 from Mavor's (1923, p. 375) record of 34.6° at the 

 surface and 34.2° at 10 metei-s, on February 7. 



