joint USGS and MMS program designed to measure currents and sediment transport 
on the Continental Shelf and in the major submarine canyons that cut into the 
southern flank of Georges Bank (Butman and others, 1982b; Butman, 1984). 
Because the sediment traps used here were no further than 50 m above the 
bottom and because of the high current velocities at all the mooring 
locations, the traps primarily collected sediments which were resuspended from 
the bottom. However, particles 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 vicinity of block 312, the 
concentration of Ba is clearly higher in postdrilling samples than in 
predrilling samples (table 3A, B). 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 is expected because 
the discharge of Ba was not constant, nor was the current field that 
transports the drilling mud during and after discharge. 
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 predrilling 
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. 
47 
