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REGIONAL STATION NUMBER 
FIGURE 3.—Percent silt plus clay in samples collected at each regional station during years 1 (x), 2 (triangle), and 3 (circle). Sta- 
tions are listed in order of increasing water depth. 
four out of the last five cruises, but by cruise 12, 
the concentration of Ba in the fine fraction was still 
more than 10 times higher than in the predrilling 
sample. At station 17, 2 km upstream of the drill 
rig, the Ba concentrations increased less than at sta- 
tion 18, 2 km downstream of the drill rig. The effect 
of the mean westerly current flow, which would 
indicate preferential transport to the west, seems 
to be illustrated by these data. 
The concentration of Cr (fig. 7) increased slightly 
at station 16 in an apparent response to drilling, 
reached a maximum concentration of approximately 
2 times background levels by the third cruise, and 
then decreased to background concentrations again. 
No increases in Cr concentration were observed at 
BA, IN PPM 
CRUISE | 
es 
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2 
ON e U 
Shey 
RS 
FIGURE 4.—Concentrations of barium in bulk sediment at up- 
stream control stations on different sampling occasions. Drill- 
ing began after the first cruise and ended at all locations before 
the sixth cruise. Station locations are shown in figure 1A. 
13 
stations 17 or 18. The concentration of Al, Cu, and 
Hg in the fine fraction at station 16 also increased 
and decreased with similar magnitude and timing, 
as did that of Cr. We did not identify systematic 
increases of these metals at any other station. 
At block 312, the drilling began just after the se- 
cond cruise and was completed just before the fifth 
cruise. The Ba concentrations in the fine fraction 
of sediment clearly increased after drilling began 
and, at most stations, apparently decreased after 
the drilling ended (fig. 8). Concentrations of Cr did 
not increase during the drilling period. The other 
metals showed no changes attributable to drilling. 
The temporal change of Ba in the fine fraction at 
the site-specific survey suggests a westward trans- 
port of Ba-rich fine sediment during this monitoring 
period. At station 5-28, the easternmost station of 
this detailed survey, Ba concentrations reach a lower 
maximum than at most other stations and, with the 
exception of cruise 10, are at or near background 
levels for cruises 7-12. At station 5-2, located 0.5 
km east of the drill rig, Ba concentrations reach a 
maximum after the completion of drilling (cruises 
4 and 5) and decrease at the time of cruises 6 
through 10. Ba concentrations at station 5-29, 6 km 
to the west, continue to increase between the com- 
pletion of drilling and the time of cruise 8. This con- 
tinued postdrilling increase and maintenance of 
high concentrations through cruise 12 may be 
caused by the transport and deposition of Ba-rich 
fine sediment originally deposited closer to the rig. 
These results suggest that Ba was being dispersed 
from the immediate vicinity of the drilling rigs. 
To see how far the Ba from drilling mud could be 
traced, we analyzed the fine fraction of sediment at 
stations 10 and 12, approximately 65 km west of the 
block 312 drill site, and stations 2 and 3, approxi- 
mately 35 km to the east of the easternmost drill 
site. At stations 12 and 10 we measured maximums 
