71 



surrounded on all sides by water 5° to 6° colder except south- 

 westward where warmer water lay. The first half of the month 

 the influence of the 3o°-38° water mass spread outward on all sides, 

 as shown by the increase in white area over the Banks when we 

 compare charts F and G. The Atlantic water lying off the eastern 

 face of the Banks continued to press shoreward as shown by the 

 convexity of isotherms 45, 38, 34, on chart G. The arctic water 

 between these two classified types of water m'asses, viz, local, or 

 Bank, on the west and the Atlantic on the east, was squeezed into a 

 narroAv strijD barely 10 miles in width. The latter half of the month 

 the Banks water spread northeastAvard on the surface in a promi- 

 nent manner, displacing 'arctic water on the surface as far northeast- 

 ward as 46° 45' north, 49° 20' west, as shown on chart H. The 

 phenomenon of Banks water to expand over the central Banks region 

 and spread to the northeastward was previously recorded in 1913, 

 a year which in many respects, as to absence of normal masses of 

 arctic water in the Grand Bank vicinity, corresponds with this 

 spring.® 



A comparison between charts G and H for the month of April and 

 chart F for March brings out the fact that the northern edge of the 

 warm Atlantic water, as indicated by the 55° isotherm, began reced- 

 ing southward between the forty-third and forty-fifth parallel early 

 in April, a movement which continued the latter half of the month. 

 This is entirely in accord with previous observations in this locality 

 at this time of the year and which has been pointed out in pre- 

 vious discussions.'' (See March report, p. 10.) The recession is 

 due, it is believed, to a slackening in the intensity of circulation 

 which prevails at a maximum during the winter months. 



The " cold wall " changed position southeastward of the Tail and 

 assumed a wedgelike form the latter part of the month, Avhich is a 

 characteristic shape that has often been charted and discussed here- 

 tofore. The bottom configuration, a rise in the ocean floor which ex- 

 tends southwestward from the Tail over 150 miles, is an important 

 factor in determining the course of the easterly moving water 

 masses, and its reflection is seen even in the surface water isotherms 

 55 and 60 on chart H. 



Compared with previous years, the position of the " cold wall " 

 between the forty-first and forty-second parallels is normal, and its 

 behavior during the month was quite similar to its behavior during 

 the same period of 1922.^ Surface temperatures over the conti- 



^ Mathews, D. J. : " Report on the work carried out by the steamship Scotia, 1913," 

 1914. 



■f Smith, Edward H. : Ice Observation and Ice Patrol Service, U. S. C. G. Bull. No. 11. 

 pp. 139-140. 



s Smith, Edward H. : International Ice Observation and Ice Patrol Service, U. S. C. G. 

 Bull. No. 10, 1923. Charts J and K. 



