PERCENT OF TONAL Ba 
50 
>1000 1000-500 500-210 2I0-I05 
105-60 
STATION I6 
lO-| < 
60-30 30-10 
SEDIMENT -SIZE CLASSES, IN um 
FIGURE 13A.—Relative amount percent of total barium in different size fractions of bottom sediment collected on cruises 4 
and 10 at regional station 16 on Georges Bank. 
4. 
no adverse chemical stress to bottom-dwelling 
organisms is expected from these measured 
increases in barium concentrations. This 
prediction is being tested by the biological 
studies conducted within the monitoring pro- 
gram (Battelle-WHOI, 1984). No drilling- 
related changes in the concentrations of 
chromium or of other metals have been 
observed in bulk sediments from any of the 
locations sampled in this program. 
. Of the barite discharged to the ocean waters 
while drilling in block 312, we estimate that 25 
percent was present in the sediments within 
6 km of the well at the time of the fifth moni- 
toring cruise, which was conducted 4 weeks 
after drilling was completed. 
. The inventory of barite, which accumulated as 
a result of drilling in block 312, has decreased 
steadily for almost a year during the period 
following drilling with a half-life of 0.34 year. 
A much slower rate (half-life 3.4 years) is esti- 
mated for the period between cruises 8 and 12. 
At the time of cruise 12, the Ba inventory be- 
tween 0.5 and 2 km from the well site was 
approximately 12 percent higher than the pre- 
drilling value. 
The barite from drilling mud is associated with 
the fine-sediment fraction in low concentration 
and is widely distributed. The fate of this barite 
is closely linked to the energetic sediment- 
transport processes characteristic of this 
region. We found evidence for Ba transport and 
deposition to the west of the drilling activity. 
The Ba accumulated at stations 10 and 12 
along transect III, at new coring stations 
50 km west of transect III, in sediment-trap 
material and sediments from the head of 
Lydonia Canyon, and in sediments near the 
head of Oceanographer Canyon. In addition, we 
found peaks in the concentration of Ba with 
time at upstream control stations 2 and 3, 
located 35 km northeast of the nearest drilling 
activity. The data from sediment-trap analyses 
suggest that barite that is originally deposited 
near a drill site in this area can be resuspended 
to at least 25 m above the sea floor. 
RECOMMENDATIONS FOR FUTURE WORK 
In this 3-year study we have shown that Ba 
introduced to Georges Bank during the 
exploratory phase of drilling is distributed over 
