Cape Sable, although for only a few weeks dur- parallel with the isopycnals. McLellan (1957) 



ing the spring, it can act to retard vernal warm- presents a detailed discussion of "isopycnic 



ing in the Gulf of Maine. mixing" and stirring as determined from T-S 



Hayes (in press) identifies Gulf of Maine diagrams. 



Bottom Water (below 150 m.) as Slope Water, "The distinction between 'stirring' and 'mixing' 



which, on entering the Gulf of Maine through as brought out by Eckart (1948) is important, 



the Eastern Channel, is slightly modified. How- Stirring obviously can, and probably always 



ever, for the purposes of the present discussion, does, take place on surfaces of equal density, 



this Bottom Water will be considered to be in since low internal friction in the fluid makes 



the realm of Slope Water. hydrostatic equilibrium (or quasi-equilibrium) 



_, ^ ,. ,. i. J J! J i- „u the only state admissible. The very nature of 



T-S diagrams were constructed from data ob- . . ■' , • ,• , • ^ 



1 1 ■ T/-CXT * T- ■ na 1 J CO 1 ^!^„ mixmg, however, implies a change in entropy. 



served during ICNAF cruises 68-1 and 69-1 for ^' \ i • i ^ t L 



, ^ , ^, ^ ^- ,c o - J o\ T*. ;o At the same time, the physical nature of sea 



selected offshore stations (figs. 6, (, and 8). It is . , ^, ', • • j; . * „ ,.„i 



^ , ■ .■ e c " water is such that the mixing of waters of equal 



readily apparent from examination oi ngures ( ... • j , • • j -i. 



1 o .1 i. ^1 ir>.,r. T. o f 11 fu., density is accompanied by an increase in density 



and 8 that the 1969 T-S curves fall within . ^, •' ^ ^ , ^ jt ^-^ . • ■ ^ i 



-,-.,,,, , . » o ij. Oi. ITT * in the product (except for the trivial case where 



McLellan's boundaries for Gulf Stream Water • • , ... ^ -j .- i ^ t. 



.,,.,.,...- ^ , , „r . the original constituents are identical as to tem- 



as well as within his limits for Coastal Water » t-.n i.-. .u 



1 C11 iiT . r^^ rr a A t perature and salinity) . . . but it must be remem- 



and Slope Water. The T-S curves drawn for ^ i .i. . ^i j ^ <■ a \ 



,-.„ J / J . J- 11 -.1 • .1 1 A ■ * bered that the products are represented by a 



1968 data do not fall within the boundaries for .■,.,• \, t. a i . i ^ \ \\. 



„ ,. o. ^TT . TT -i. 1 ij u ^ A straight line on the T-S plot and not by the 



Gulf Stream Water. However, it should be noted ^ i • . „ 



i.1. . .1 ,r,/.o . .• 1 .• J i. * J curve ot equal sigma-t. 



that the 1968 station locations do not extend ' " 



quite as far seaward as those for 1969. This is When points at like depths for several stations 



not to say that a Gulf Stream intrusion did occur within the narrow band are joined, a straight 



in 1968, for as previously noted water tempera- line relationship is apparent. This strengthens 



tures of this region in this year were signifi- the above inference to horizontal mixing. 



cantly lower than those of 1969. It should be tx-ij <■ ^ ^ ^„of 



/ . , , , T^^x.T^ • T Dissolved oxygen measurements were made at 



emphasized that the ICNAF cruise data were . -"^ . \, ^ . . ^. ^z-ixt * t^ 



, J. -J-. /T T-u \ most stations occupied during both iCJNAl^ 



observed in midwinter (January-iebruary), ' ■■, -c. ^ r~, 



whereas McLellan's data were collected during ^^^i^es. Water types can be identified as Coastal, 



June when vernal warming is well in progress. Slope, or Gulf Stream according to their char- 



„, „ „ - ,„„n 1 ^r.nr. Ti x Ecteristic dissolved oxygen values (McLellan, 



The T-S curves for 1968 and 1969 did not re- „ ^, r,, , , ^ . • i i- , j 



„„i ., ^ J! J- i.- . u A A ■ 1957). Table 2 compares typical dissolved oxy- 



veal the presence of distinct bounded regions ' ^ ■'^ • t , j 



with blank areas between them, thus indicating g^n values observed by McLellan with dissolved 



thorough horizontal mixing throughout the re- oxygen data from selected ICNAF stations. It 



gion. In both years the distribution of T-S is evident that Gulf Stream Water was present 



points for the surface layer (0-150 meters) was at the 1969 stations, while the 1968 data indi- 



confined to a relatively narrow band nearly cated only Slope and Coastal Water. 



Table 2 — Dissolved oxygen values for selected ICNAF stations, 1968 and 1969. 



McLellan's Stations ICNAF 68-1 Stations ICNAF 69-1 Stations 



Depth (m) (ml/1) (ml/1) (ml/1) 



Gulf Slope Coast 1 2 24 25 1 2 15 16 



n T. 7- 6^6 7^0 Ya 5?r It It 5.0 5.0 



50 ______ 6.0 5.8 6.8 5.4 4.T 4.8 4.T 4.7 



100 4.9 4.4 6.3 5.5 4.6 5.2 5.3 4.T 4.8 4.6 4.5 



150 5.0 4.8 6.5 3.9 4.0 3.5 5.2 4.6 4.5 4.T 4.8 



200 4.7 4.1 5.5 5.3 3.8 3.6 5.2 4.6 4.5 5.4 4.3 



250 ______ 4.0 4.0 3.7 3.9 4.8 __ 5.2 5.0 



300 4.7 3.9 5.7 



400 __ 3.3 6.1 



500 __ 3.9 6.1 



