No. 18 2000 m WEST No.I6 at DRILL RIG No. [7 2000 m EAST 
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FIGURE 5.—Concentrations of barium (circle) and chromium (x) in bulk sediment on different sampling occasions 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 devia- 
tion among three individual replicates. Anomalous value of 430 ppm in one of the three replicates at station 16 was omitted 
from calculation of the mean. ND = no data. 
in the Ba concentrations at the time of cruises 8 flows. We plan to examine meteorological data and 
and 10, respectively (fig. 9A). We were surprised to any available current records to determine if a 
find that maximums in the Ba concentrations, strong easterly current flow occurred sometime 
although of lower magnitude, were also recorded at _ before cruise 8. It is also possible that the Ba par- 
similar times at stations 2 and 3. The maximum _ ticles carried in the Georges Bank gyre could have 
value at station 3 on cruise 7 is statistically higher been transported from drilling locations in a clock- 
than the mean of the first 6 cruises at the 99.5- wise circular motion to stations 2 and 3. 
percent level of confidence (t test). 
The Ba/AI ratio (fig. 9B) that was plotted for each TRACE METALS IN DIFFERENT 
sampling period is also used to show relative SIZE FRACTIONS OF SEDIMENT 
changes in the Ba levels. Typically Al is highly cor- 
related with the percent of clay minerals in marine As a special study initiated during this program, 
sediments. As a result, Al is used in the ratio to we used nylon sieves to separate bulk sediment from 
remove the variability introduced by different Georges Bank into various grain-size classes and an- 
amounts of clay in the fine fraction on different alyzed the material in each size class for trace 
sampling dates. The Ba/AI ratio also eliminates the metals. We used this approach to determine how 
small error introduced in making the chloride cor- those trace metals (notably Ba) whose concentra- 
rection necessary to determine metal concentrations _ tions are elevated by drilling are distributed within 
of the fine fraction in mass units. The Ba/Al ratio the sediment-size fractions. This information may 
is at a maximum value at stations 2, 3, and 12 0n__ be useful in predicting the transport and dispersion 
cruises 7 or 8. The value for the relatively small of metals carried by various sediment-size classes. 
maximum at station 3 is statistically higher (t test) Judging on the basis of the textural analyses of 
at the 99.5-percent level of confidence than the mean standard barite by the American Petroleum Insti- 
of cruises 1-6. No Al data are available for samples _ tute, only about 4 percent of the barite used in well 
from station 10. drilling is in the 60-150 ym fraction, and the 
These findings are significant because they sug- remaining 96 percent is finer than 60 pm. Drilling 
gest that Ba in the finest fraction of drilling mud mud is known to adhere to drill cuttings, however, 
may be transported over very wide areas of the which are often greater than 1,000 um in size. 
bank, to the east as well as to the west. Butman Samples were collected on cruises 4 and 10 from 
and others (1982a) have stated that the mean the 0- to 2-cm interval at stations 16 and 5-2 adja- 
westerly flow can reverse on the southern flank of cent to drilling sites. To determine the natural dis- 
Georges Bank in response to strong winds from the tribution of metals in different size classes, sedi- 
southwest. Transport of sediment to stations on ment was collected on the same cruises from 
transect I from the easternmost drilling locations control station 2. 
(blocks 410 and 145), approximately 35 km, could Figures 10A and 10B show the distribution of 
have taken place during these eastward current sediment in weight percent among various size 
14 
