No. 18 2km WEST 
10,000 
F 
1,000 
PPM 
TESS 5678 9 Ole 
No.16 at DRILL RIG 
I2S34O 6 7 8 © fo Il l2 
No. 17 2km EAST 
Needs & 7 8 © lo i) (2 
CRUISE 
FIGURE 7.—Concentrations of barium (circle) and chromium (x) in the fine fraction (less than 60 »m) on different sampling occa- 
sions near the drill site at block 410. Drilling began after the first cruise and ended prior to the fourth cruise. Error bars 
are one standard deviation among three individual replicates. ND=no data. 
classes for sediments collected on different cruises 
at these three locations. For cruise 4, all three sta- 
tions have similar modes and less than 1 percent 
silt plus clay. The size distributions are similar on 
both sampling dates, except that the sample at sta- 
tion 5-2 has a modal size in the 500-1,000 um range 
for cruise 10 and a modal size in the 210-510 pm 
range for cruise 4. 
At control station 2, the Ba inventory among the 
different size classes (fig. 11A) is distributed in the 
same pattern as the sediments are distributed (fig. 
10A, B). Most of the Ba (more than 80 percent) is 
contained in the modal size class of 210-500 um. 
However, the Ba concentrations of the fine fractions 
are higher than in the coarser fractions (fig. 11B), 
and only minor differences exist between samples 
from cruises 4 and 10 at this location. 
The inventory of Ba and the concentration of Ba 
among the different size classes at station 5-2 are 
considerably different on cruises 4 and 10 (figs. 12A 
B). The concentration of Ba in the finer sediments 
is much lower on cruise 10 than on cruise 4. The 
differences indicate that while the rig was operating 
(cruise 4), fine-grained sediments containing high 
levels of Ba were being deposited (accumulating) in 
the sediments and that since drilling has ended, the 
16 
processes of sediment transport have preferentially 
removed the fine material. In the time between 
cruises 4 and 10, the Ba contained in the 30-60 pm 
fraction decreases from about 50 percent to 10 per- 
cent (fig. 12A). The distribution of Ba is bimodal 
for each cruise, but the distribution changes from 
one in which the fines are carrying a large Ba inven- 
tory as a result of drilling mud accumulation (cruise 
4) to one which begins to resemble the distribution 
of Ba in the uncontaminated sediment (cruise 10). 
The interpretation of data collected at station 16 
is somewhat complicated because the net concen- 
tration of Ba in the sample collected during cruise 
4 was lower than that collected on cruise 10. This 
may be related to the high spatial variability of Ba 
in sediment adjacent to the drilling rigs as dis- 
cussed on page 12. The inventory at station 16 for 
cruise 4 has a strong peak in the 210-500 pm-modal 
size (fig. 13A), similar to the distribution at control 
station 2 (fig. 11A) and a small enrichment of Ba 
in the finer size fractions compared to the uncon- 
taminated control station. At station 16 on cruise 
10, we measured a higher total concentration of Ba, 
with higher concentrations distributed in the finer 
fraction of cruise 10 than of cruise 4 (fig. 13B). The 
distribution of the Ba inventory for station 16 on 
