220
IIILAEtY B. MOORE
coastal values. If we restrict our tropical data more rigorously to
latitudes between 10"N and 1O"S, the ratios remain very similar at
1*9:1 and 4.0:1 respectively. There is, then, a definite seasonal
temperature range in the tropics, and, judging from the American
coasts, about a fourfold difference between tropical coastal waters and
those in mid-latitudes.
B. Salinity
Raymont (1963) quotes average surface salinities in relation to
latitude for all oceans (Fig. 2). These show a maximum salinity between
latitudes 20" and 25", a slight drop towards the equator, and a more
36
35
34
33
J 32
I
A
c
.- -
-
; 31
30
29
28
27
salinity range
\ /
1 0
20
30
40
50
60
'
Latitude
FIG. 2. Relation of salinity and seasonal salinity range to latitude.
marked drop in high latitudes. It is unfortunate that good data are
scarce for coastal waters, but again we have long term observations for
the tide stations on the American coasts in the Coast and Geodetic
survey data. In using these we have omitted those estuarine stations
where the salinity did not rise above 25%, at some time in the year.
These data show a similar pattern to that found in the oceanic values
except for a generally lower salinity and a greater range.
As with temperature, we may be more concerned with the seasonal