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CRUISE | QS WAS ROU anor OE iaulOpiusl IliMl2 
FIGURE 9A. AND 9B—Concentrations of barium (9A) and the 
barium-to-aluminum ratio (9B) in the fine fraction of sediment 
blends on different sampling occasions at station 2 (X), 3 (¢), 
10 (QO), and 12 (9). 
Sediment traps also were deployed 6 km east of 
the drilling rig in block 312 while drilling was in 
progress (ST426) and after drilling was completed 
in this block (ST513 and ST515). The Ba concen- 
trations of these sediments are also higher than 
those of predrilling samples. Some of the material 
contributing to the elevated Ba concentrations 
measured in these samples may have originated 
from the four drilling rigs operating between 5 and 
45 km to the south or to the east of these trap loca- 
tions. Alternatively, storm and tidal currents 
could have transported material eastward. 
There is a weak but positive indication that drill- 
ing mud was transported in measurable concen- 
trations to the expected depositional site at the 
head of Lydonia Canyon (fig. 14, table 3). Drilling 
began during the second period in which sediment 
traps were used to collect suspended sediment 
(fig. 14). The concentration of Ba in the fine frac- 
tion of trap sediments from the head of Lydonia 
Canyon increases slightly from the first deploy- 
ment until the fourth deployment and then 
appears to increase more dramatically at the time 
of the fifth deployment, which includes the period 
when four wells were finishing drilling activity 
on the bank (fig. 14). On the basis of these 
increases in Ba concentration, which were 
measured in traps at two levels in the water col- 
umn (10 m and 20 m above bottom), we suggest 
that a small drilling mud signal was present in the 
suspended matter in Lydonia Canyon. No such 
indication is apparent from the analysis of the bulk 
sediment-trap material—for which the Ba concen- 
trations during the period of drilling are generally 
within one standard deviation of the concentra- 
tions determined in predrilling trap samples 
(table 3). 
TRACE-METAL VARIATIONS WITH DEPTH IN SEDIMENT 
During the second and third year of monitoring, 
sediment cores and grab samples (appendix table 
4D; Bothner and others, 1984b) were subsampled 
as a function of sediment depth to determine the 
depth profiles of metal concentrations. A gradient 
in the depth profile of a metal concentration can 
indicate the introduction or removal of the metal. 
Our first objective was to extend our search for 
drilling-related Ba to locations on the bank where 
data from seasonal cruises may not be available. 
Second, we hoped to make some inferences about 
the extent and rate of downward mixing of newly 
introduced Ba by benthic organisms and (or) cur- 
rents by examining profiles at stations adjacent 
to drilling operations. 
We examined the profiles of Ba and Ba/A1 in four 
areas where the introduction of drilling mud was 
not expected (fig. 154-D; location of samples 
shown in fig. 1). Although there is some scatter 
in the Ba values, particularly in sample M11- 
03- 00-AX, the Ba/Al ratio is constant with 
depth at all four locations. This observation is 
particularly important because it argues against 
the possibility that the naturally occurring Ba 
dissolves in response to reducing conditions in 
18 
