15 
Fig. 4. Contours of HgSiOg along 45.86°/oo and 45.83°/oo isopyenal horizons based on TTO data 
and corresponding values at the GEOSECS stations. 
Along a traverse southward from the Denmark Straits the following relationships are seen. 
At 60°N, 56°N, and 54°N(Fig. 2), the TTO salinities are distinctly lower than the GEOSECS 
values but no significant differences in the chemical signatures are found. At 47°N (Fig. 3, 
upper panel) both a salinity difference and dissolved silica and oxygen differences are seen bet- 
ween the surveys. The TTO waters are lower in silica and in oxygen (i.e. they have a smaller 
component of Antarctic derived water) than the GEOSECS waters. At 42°N (Fig. 3, middle panel) 
the GEOSECS-TT™ salinity difference is gone. However, the TTO stations have less silica and 
higher oxygen. In Figure 4 contours of HgSiOg content along the 45.86°/oo and 
45.83°/oo isopyenal horizons are shown based on the TTO data set. Also shown are the 
H4SiO4g values obtained for these densities at the GEOSECS stations. As can be seen, the 
GEOSECS values for station 1 (45°N) are considerably higher (i.e., = ym/kg) than expected from 
the TTO contours. The results along this traverse can be best explained by calling upon inten- 
sified overflow of water across the Denmark Straits into the western basin. This intensification 
results in a push back of the intruding high silica-low oxygen southern water. 
The situation at station 24 in the Gibbs Fracture Zone is quite different. The relatively 
warm, saline and low silica content water found in the bottom of the fracture zone during the 
GEOSECS survey has been displaced by relatively cold, fresh and high silica content water. 
This water can only have originated in the open Atlantic to the south of the fracture zone. Our 
interpretation is that as the pulse of new water from the Denmark Straits pushed southward 
along the western margin of the basin, old water moved northward along the eastern margin of 
the basin and entered the western end of the Gibbs Fracture Zone. It appears that the inten- 
sification of production of deep water at the head of the western basin was accompanied by the 
weakening of the production of deep water at the head of the eastern basin! 
