locations. Second, the subsurface maximum in concentration suggests either 
that new sediments, having a lower Ba concentration, have accumulated on top 
of the drilling mud components or that new sediments have been exchanged (no 
net accumulation) for the drilling mud components by a combination of 
sedimentation, sediment mixing, and erosion. 
A future follow-up of this study should be undertaken to determine the Ba 
concentration and the Ba/Al ratio in profiles using the bulk sample. 
Comparison of profiles of the bulk sample and the fine fraction is necessary 
to determine the amount of Ba which is missed by the standard field sampling 
technique of collecting the upper 2 cm of sediment. In addition, longer core 
samples (30-40 cm) should be taken at the drill sites to carefully determine 
whether the decrease in Ba concentration in the surface sediment is due to 
actual removal or to downward mixing. 
Barium inventory and decrease at block 312 
The high density of stations and the frequent sampling at the drill site 
in block 312 present the opportunity to estimate the inventory of barium in 
the sediments before, during, and after drilling. One objective of this 
exercise is to determine how much of the Ba actually discharged by the 
drilling rig was deposited within 6 km of the drill site at the time of well 
completion. Of particular interest is an estimation of the rate at which Ba 
concentrations decreased in the surface sediments after drilling was 
completed. The barium added by the drilling can be considered to be a tracer 
for sediment transport processes. Although barium sulfate has a greater 
density than the average sediment on the bank, the rates of removal determined 
for barium may provide some insight into the fate of future contaminants that 
reach the sediments on Georges Bank. 
a7 
