Justification of the alternative methods is presented 
in Bothner and others (1982). 
ANALYTICAL ACCURACY AND PRECISION 
Analytical accuracy was determined by analyzing 
rock standard MESS-1. All of the metals are within 
one or, at most, two standard deviations of the “best 
values” established for this standard (table 2). 
Excellent agreement also exists among aliquots of 
samples submitted as blind replicates (appendix 
table 2). 
Analytical precision was determined by peri- 
odically analyzing replicate aliquots taken from a 
single sample. Coefficients of variation shown in 
table 2 indicate that the standard deviation is 
typically less than 10 percent of the mean value, 
except for concentrations at or near the detection 
limit of the method. 
To maintain our internal quality control and to 
provide typical sample material for interlaboratory 
comparisons, four sediment standards representing 
different textural types were prepared from large 
samples of Georges Bank sediment. The levels of 
trace metals are being established by several analyt- 
ical methods. Splits of these materials are available 
to those interested in cross-calibration studies. 
RESULTS AND DISCUSSION 
SEDIMENT TEXTURE 
The texture of the surface sediments sampled in 
the third year of monitoring (appendix table 3A, 
textural data of other samples in appendix tables 
3B and 3C) is very similar to the texture measured 
in the first two years (fig. 2) as defined by the 
average mean ¢ values at each station for a given 
year. Low yearly variability of the mean ¢ grain 
sizes occurs, as demonstrated by the close match 
of the data patterns. Mean ¢ values range from 
about 1 ¢ (coarse sand) at station 5-1 (fig. 1B) to 
about 6.3 ¢ (medium silt) at station 13A, located 
south of Martha’s Vineyard. The error bars (stand- 
ard deviation about the mean of samples from each 
of four seasons) indicate that the within-station 
variability is much smaller than the between-station 
variability. 
The sediments on Georges Bank are typically 
greater than 95 percent sand and contain minor 
amounts of gravel, silts, and clays. The sand is 
primarily medium to coarse grained, ranges in 
8 
coloration from a clear or translucent yellow to a tan 
iron-oxide stain, and has an angular to subrounded 
grain shape. The minerals making up the sand frac- 
tion are primarily quartz with minor amounts of 
feldspar and trace amounts of heavy minerals. 
Authigenic minerals such as framboidal pyrite and 
ferromanganese micronodules have been found at 
various locations on the bank in very low concen- 
trations (Poppe and others, 1984). 
The concentrations of silts and clays in the 
regional samples are generally less than 4 percent 
(fig. 3), and the mean station values for year 3 are 
similar to those of years 1 and 2. The relative 
paucity of silts and clays reflects the strong 
winnowing processes associated with tidal and 
storm-generated currents on Georges Bank 
(Butman and Folger, 1979; Butman and Moody, 
1983; Butman and others, 1982a; Parmenter and 
others, 1984). We sampled transects I, II, and III 
(fig. LA), and found that the content of sediment 
finer than 63 pm (silt plus clay) increases slightly 
toward the shelf edge, perhaps in response to 
increasing water depth. 
Areas that showed a significant concentration of 
fine sediments (finer than 63 ym) during each sam- 
pling cruise were located at regional station 14A 
(80-90 percent fines) in the Gulf of Maine, regional 
station 7A (22-30 percent fines) at the head of 
Lydonia Canyon, and regional stations 13 and 138A 
(34-50 and 92-97 percent fines, respectively) located 
south of Nantucket Island. This last area, known 
as the Mud Patch, is thought to be one of the 
depositional sites for sediments from upstream 
areas on Georges Bank (Bothner and others, 1981; 
Twichell and others, 1981). The close correlation bet- 
ween the concentrations of fine sediment, organic 
carbon, and trace metals was discussed in the report 
for year 1 (Bothner and others, 1984a). 
Determination of the major minerals in the clay 
fraction of the sediments by X-ray diffraction indi- 
cates that illite is predominant, with moderate 
amounts of chlorite and small concentrations of 
kaolinite present (Bothner and others, 1979). Mont- 
morillonite is present only in trace amounts, or it is 
absent. The origin of the illite and chlorite in the 
clay fraction is thought to be unweathered material 
eroded from Paleozoic and older rocks in the north- 
ern Appalachian region and transported to the Con- 
tinental Shelf during glacial periods (Hathaway, 
1972). 
The concentration of gravel is variable and ranges 
from 0 to almost 16 percent (appendix table 3A). 
The gravel is composed of rock fragments or shell 
hash or a mixture of both. Drill cuttings were 
