The concentration of Cr in these same samples (fig. 5) did not increase 
as a result of drilling even at the drill site. Similarly, we observed no 
changes in the concentrations of other metals in the bulk sediments during 
this period of monitoring. 
In block 312 (station 5), the location of the site-specific survey, 
increases in Ba were observable following the initiation of drilling on 
December 8, 1981 (fig. 6). The greatest increase (factor of 4.7 above 
background) was observed at the drill site (station 5-1). At this location, 
there is a large standard deviation among three individual replicates and a 
considerable amount of scatter in the data following cruise 5. These trends 
are similar to those observed at station 16, also adjacent to a drill rig, and 
are thought to reflect the heterogeneity of drilling mud distribution in the 
sediments near the rig-e At stations more than 0.5 km from the drill site, 
slightly higher increases were observed to the west than to the east, which is 
consistent with the preferential direction of transport. At all but station 
5-10, the maximum concentration was observed during cruise 5, which was 
conducted immediately after drilling was completed. At most stations, the 
concentrations decreased rapidly by cruises 6 and 7 and remained essentially 
constant through cruise 12. 
The concentration of Cr (fig. 6) or of other metals in bulk sediments at 
block 312 did not increase as a result of drilling. 
Trace metals in the fine fraction of sediment 
Within the sediment fraction finer than 60 um (appendix table 4B), the Ba 
concentration increased dramatically at stations near the drill rig at block 
410 (fig. 7). At station 16, adjacent to the rig, the average Ba 
concentrations reached 8,000 to 10,000 ppm between the third and seventh 
cruises. Lower concentrations were measured in four out of the last five 
30 
