cruise 6, an increase by a factor of 5.9. Drilling was completed before 
cruise 4, and one would expect that the maximum concentration of Ba would be 
found on the fourth cruise. There is no statistical difference in the Ba 
concentration between cruises 4 and 6 at the 95-percent level of confidence 
(a=0.05) because of the large within-station variability in the Ba 
distribution (fig. 5). 
The concentration decreases at the time of cruise 7, and except for 
cruise 11, remains at a fairly constant level of about 80 ppm from cruises 8 
through 12. The anomalously high value of 430 ppm (fig. 5) was excluded from 
calculation of the mean. The scatter in the data probably indicates that Ba 
is not distributed homogeneously over the sampling area. This heterogeneity 
is probably caused by the intermittent discharge of drilling fluids into a 
current field that continuously changes direction of flow throughout the tidal 
cycle. 
In agreement with the expected transport of drilling fluids to the west 
by the mean current flow, Ba concentrations were higher to the west than to 
the east. At station 18 (2 km to the west of the drill rig), maximum increase 
in Ba concentrations was about a factor of 2 as a result of drilling. The 
concentrations of Ba decreased to predrilling levels at the time of cruises 8 
and 9 and then increased again. At the time of cruise 12, Ba concentrations 
were 36 percent higher than predrilling levels and the difference between mean 
values of cruises 1 and 12 is statistically significant at the 99-percent 
level of confidence (a=0.01). In contrast, at station 17 (2 km to the east), 
the maximum increase was only about 1.3 times the background Ba 
concentration. A decrease in concentration was also seen at this station for 
cruises 8 and 9 followed by an apparent increase. However, the concentration 
measured on cruise-12 samples is not significantly different at the 95 percent 
level of confidence from the cruise-1l concentration. 
29 
