cruises, but by cruise 12, the concentration of Ba in the fine fraction was 
still more than ten times higher than in the predrilling sample. At station 
17, 2 km upstream of the drill rig, the Ba concentrations increased less than 
at station 18, 2 km downstream of the drill rig. The effect of the mean 
westerly current flow, which would predict 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 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 second 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 transport of Ba-rich fine sediment during this 
monitoring period. At station 5-28, the easternmost station of this detailed 
survey, the Ba concentration 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 
concentration reaches the maximum after the completion of drilling (cruises 4 
33 
