The Georges Bank monitoring program 1983; analysis of trace metals in bottom sediments

Circular 915

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From July 1981, when drilling began on Georges Bank, to May 1982, the concentration of barium, a major element in drilling mud, has increased by a factor of 3.5 in bulk sediments 200 m from the drill site in block 410 and by a factor of 2.3 at the drill site in block 312. The postdrilling barium concentrations are within the range of predriiling concentrations measured at other locations on Georges Bank. We estimate that no more than 21 percent of the barite (principal barium-bearing mineral) discharged during drilling remains within 6 km of the drill site in block 312. No drilling-related changes in the concentration of chromium or other metals have been observed in bulk sediments from blocks 410 or 312. The chemical signal of drilling mud in surficial sediments has been enhanced by separating and analyzing the sediment fraction finer than 60 ?m. Barium concentrations in the fine fraction have increased by factors of 36 and 22 at the drill sites in blocks 410 and 312, respectively. At the drill site in block 410, aluminum, chromium, copper, and mercury concentrations in this fraction temporarily increased by approximately a factor of 2 and then decreased to background. The concentrations of aluminum, barium, cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, organic carbon, vanadium, and zinc in surface sediments of Georges Bank both before and after drilling are low compared to concentrations in average crustal rocks and are characteristic of unpolluted, coarse-grained sediments as found in other Continental Shelf areas.

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The Georges Bank monitoring program 1983; analysis of trace metals in bottom sediments
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U.S. Geological Survey
iii, 36 p. :ill., 1 map ;27 cm.