what is actually being observed. From the volume 

 flow calculations, the flow during the first survey 

 is minimal. This leads to the postiilation that 

 late winter steady state conditions are described. 

 That is to say that the cold water input at the 

 head of the system is being advected south and 

 warmed sufficiently such that steady conditions 

 of tlie conveyor belt form exist. On the other 

 hand, the beginning of cold water intrusion into 

 a background of existing winter water conditions 

 might be a better conclusion. 



The arguments for steady state are few indeed 

 since 1 week after the first survey, a vast increase 

 of water along with profound property changes 

 occurred in the Labrador Current. If steady 

 state conditions existed on the first survey, great 

 mixing would be required to warm the prow of 

 cold water moving south. The warming would 

 result from the warmer water on all sides of the 

 tongue including in front of the intruding prow. 

 The anomalous point is that the salinity along the 

 core of the Labrador during the first survey grades 

 lower to the south. This was quite difi^erent from 

 the expected situation of the Labrador Current 

 grading more saline to the south. Figures 27A 

 and 2SA are plots of salinity at the center stations 

 along the Labrador Current during the first and 

 third surveys. It shows that the salinity graded 

 lower from north to south during the first 

 survey and then higher from north to south on the 

 third siu'vey. The lateral salt distribution grades 

 higher to the east and slightly less to the west. 

 On the Banks the salinity grades liigher to the 

 south during the first survey, as expected. If 

 mixing and warming are occurring with resulting 

 steady state conditions as envisioned above, then 

 the contribution from the east would cause higher 

 salinities as the water moved south rather than 

 the lower salinities actually observed. Water 

 from the west would tend to lower the salinity 

 slightly, but this effect woidd be masked by the 

 much greater salt content of the water from the 

 east. A more reasonable explanation is that we 

 are observing the intrusion of new water from the 

 north, the initial arrival of more severe properties 

 resulting from the spring freshening of the 

 Labrador Curi'ent. 



The higher salinity to the north observed on the 

 first survey can be attributed to the winter in- 

 crease in salinity and off-shore mixing further 

 tiorth due to a reduced flow rate. This would not 

 be observed later in the season because of the 

 increased flow and contribution of sea ice melt 



water. In this situation the intruding cold water 

 could account for the great slopes of the sigma-t 

 surfaces which would also tend to isolate these 

 tongues from any lateral influence. This colder 

 water mass seems to be invading a more imiform 

 environment and a leveling adjustment towards 

 some form of equilibrium has not had time to 

 take place. Horizontal mixing, across sigma-t 

 surfaces, would be minimal initially, but would 

 eventually become dominate and alter the property 

 distribution to that found on the third survey. 

 This theory is also compatible with the great 

 freshening of flow observed only 1 week after the 

 first survey. Water velocities of only 0.5 knots 

 would be required to move the intruding cold 

 water from the north, found on the first survey, 

 down to section U of the check siu'vey. Velocities 

 of this magnitude were found in the Labrador 

 Current during the first and check survey periods. 

 It could also be expected that some indication of a 

 change of this niagnitude would be observed in the 

 first survey results. Again a relation is seen with 

 the speculation from the previous section in that 

 there is a salinity flow control on the Banks and 

 slope and that this initial flow is tied in with new 

 water arriving on the Banks and slope. This 

 causes a change in the dynamics of the regime and 

 requires a supply of water to fill the continuity 

 conditions of flow, thus explaining the warmer 

 temperatures observed during the check survey 

 of section U where warmer water is drawn in to 

 meet increased mass continuity requirements. 



Some surface influence is also shown in the 

 sigma-t presentation. This is indicated by the 

 crowding of the isotherms as the sigma-t surface 

 approached the sea surface and is particularly 

 apparent in the southeastern regions of the Banks 

 nearer to the Atlantic Current. Montgomery 

 (1938) cited the sea surface intersection with the 

 sigma-t surfaces as the fonuation region of the 

 water found on or slightly below the particular 

 intersecting sigma-t surface. No doubt some sur- 

 face mixing and sinking is taking place, however, 

 the water on the sigma-t surfaces flowing along 

 the Banks' slope has its source outside of the 

 immediate area of interest. 



Isentropir and Geostrophic Comparison 



The fact that these isentropic presentations 

 disclose flow tendencies independent of geostrophic 

 computations provides a useful tool for comparison 

 with the dyiuunic calculations. Certain areas of 

 uncertainty in the calculated surface circulation 



10 



