No.5-29 6 km WEST 
No.5-28 6km EAST 
FE 
No. 5-18 2 km WEST No. 5-2 O5 km EAST 
10,000 F F 
E E om 
° Ba ia 
x Cr ' 
AR ' be N-o-- pre 
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° ‘o--0--0 ea ‘° f [ f \ 
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ee © i 2 o- no-° om 0 H \ ra 
Lp ore ic) CES i % 
4 aS 
x = 
ha ca ND Seay x oe E 
XIX ND HX Se Nae xe oe x x eX ND XA be XX 
[ e x % x x 
D> eh dV MQ’ kB? GH? qh gh ee ane » 
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OT 2345678 9012 234567 8 9101/12 Iipe 34) Se G8) SHON pe seae non er8. SRlONlin2 
CRUISE 
FIGURE 8.—Concentrations of barium (circle) and chromium (x) in the fine fraction (less than 60 ym) on different sampling 
occasions near the drill site at block 312. Drilling began after the second cruise and ended just prior to the fifth cruise. 
ND=no data. 
cruise 10 (fig. 13A) is similar to the distribution at 
station 5-2 on cruise 10 (fig. 12A). We are planning 
to analyze a third sample from each station col- 
lected on cruise 12 and to resample a blend from 
cruise 4 at station 16 if sufficient archived material 
remains. 
Among the other metals analyzed in the size- 
separated samples (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, 
V, and Zn), only Al and Pb concentrations (and V 
for cruise 10) in the fractions finer than 30 um at 
the drill sites are higher than those at the control 
station (Bothner and others, 1984b; and appendix 
table 4C). Concentrations of the remaining metals 
are distributed similarly at the three stations. 
TRACE-METAL CONCENTRATIONS OF 
SEDIMENT-TRAP SAMPLES 
The objective of the sediment-trap experiment was 
to measure the concentration of drilling mud com- 
ponents in suspended matter and to determine if 
drilling mud was transported to the head of Lydonia 
Canyon. Sediment traps were deployed at various 
heights above the sea floor in the vicinity of block 
312 and in Lydonia Canyon (appendix table 1C). This 
experiment was part of a joint USGS and Minerals 
Management Service (MMS) program designed to 
measure currents and sediment transport on the 
Continental Shelf and in the major submarine can- 
yons that cut into the southern flank of Georges 
Bank (Butman and others, 1982b; Butman, 1984). 
Because the sediment traps used here were no fur- 
ther than 50 m above the bottom and because of 
17 
the high current velocities at all the mooring loca- 
tions, the traps primarily collected sediments that 
were resuspended from the bottom. However, parti- 
cles falling from surface waters (such as discharged 
drilling mud), biological material produced in the 
water column, and particles introduced from the 
atmosphere also were collected by the traps. 
Among the trap samples from locations in the vi- 
cinity of block 312, the concentration of Ba is clearly 
higher in postdrilling samples than in predrilling 
samples (table 3). The highest concentration of Ba 
(1,900 ppm) was measured in sediment trap ST424, 
which was positioned 1 km west of the drill rig in 
block 312 while drilling was underway. The sediment 
in this trap was collected in a long tube that was 
later sectioned into length intervals that represent 
different time intervals of the deployment. The last 
material to enter the trap was deposited at the top 
of the tube. The variation in Ba concentration from 
interval to interval suggests that the flux of Ba to 
these traps was not constant. A variable flux was ex- 
pected because the rate of Ba discharge and the cur- 
rent field around the drilling rig were not constant. 
The trap-sample material that was collected at the 
drill site in block 312 and 1 km to the west of the 
drill site after drilling was completed contained Ba 
concentrations five times higher than the predrill- 
ing concentrations. The increase in concentration 
suggests that the barium sulfate deposited in the 
sediments was periodically resuspended to at least 
25 m above the sea floor (the depth of our shallowest 
trap near the drilling sites) and transported with the 
prevailing currents. 
