TJIE VOYAGE OF H.M.S. CHALLENGER. 
•»s 
At the 100 fathoms depth the temperature conditions have materially altered. As 
reganls the entrance to the Gulf, it is within the North Atlantic isothermal of 65°, but 
over the Gulf itself temperature, to the west of long. 90° W., falls below 60°, and over 
a small region between that line and the continent it falls to 55°. Here, then, 
observation gives no evidence that the dense surface waters descend to any great depth 
carr^’ing with them their high temperature downward. The evidence, on the contrary, 
goes to show that the strong surface current issuing through the Straits of Bernini, with 
the «leej)er current it generates, drains away, to a very large extent, the whole of the 
warm dense waters of the surface, thus bringing about an upwelling of colder water in 
the western part of the Gulf, so that the temperature there is 15° lower than it is 
immediately to the south-west of Cuba. Unfortunately, no specific gravities have 
been available at this and lower depths in the Gulf of Mexico, which would probably 
show a diminished specific gravity corresponding to the diminished temperature. 
Three specific gravities have, however, been observed in the western part of 
the Atlantic, viz., 1-0278, 1-0278 and 1-0274, which may be regarded as pointing to a 
mixing of the higher surface specific gravities of the Gulf of Mexico with the water 
of the Atlantic at this depth. 
The relation of the temperature of the west of the Gulf of Mexico to that of the 
.\tlantic continues to hold at greater depths till the temperature falls at 700 fathoms to 
.39°-5, at which depth the Gulf of Mexico becomes “ a closed sea,” and the temperature 
remains at this point down to the greatest depth, 2067 fathoms, of the Gulf of 
Me.xico. The following gives a comparison of the lowest temperature in the Gulf of 
.Mexico and the temperature at the entrance to the Gulf at the different depths : — 
I )eptli in 
Fathoms. 
Temperature at 
Entrance. 
Lowest Tempera- 
ture in Gulf. 
Difference. 
200 
.55“ 0 
46°0 
9°-0 
.300 
50° -0 
44°-0 
6°-0 
1 too 
43°-5 
41°0 
2° -5 
1 .000 
41°-5 
40°-0 
r-5 
600 
41°-0 
40°-0 
l°-0 
700 
40°0 
39®-5 
0°-5 
These far-Ls jw)int to a strong upwelling of the deej) waters in the western division 
of the Gulf of .Mr*xieo, ncce.s.sitated by the strong current which issues from it, and which 
''xtciul.H to a ronsidcrablc dej»th in the ocean. This view is borne out by the fact that 
the .\tlantif e.xstorly current i.s there embayed before starting to join the Atlantic north- 
ca.Hteni current on its way towards the Arctic Ocean, and southerly and south- 
wf->.tcrly wiii<ls bc« f>mc prevalent, thus inducing upwelling in the western part of the Gulf. 
It h.x*- ber-n cahail.'ited that, owing to the heaj)ing up of the waters driven by the 
