Chemical Composition of Sediments and Interstitial Brines from the Atlantis II, Discovery and Chain Deeps

Abstract

A total of 110 sediment samples and 58 interstitial water samples have been analyzed by wet chemical and optical spectrographic methods. Sample handling and storage procedures included the use of inert atmosphere and refrigeration to inhibit any changes in the samples prior to analysis. Most of the interstitial waters are essentially saturated with respect to sodium chloride and are enriched in iron, copper, zinc and other heavy metals, as reported by other workers. The interstitial waters obtained from sediments around the edges of the deeps show more similarity to normal sea water.

The sediment samples show a wide variation in physical appearance and in chemical composition, from oxidized red muds to dark sulfide-rich muds and a few light-colored carbonate-rich samples. Extreme variations in composition are found between adjacent sample sites, and considerable variation is found even within different splits from the same core. Vertical variations in the cores are also extreme, sometimes within a few centimeters of depth. The moisture content of the sediment samples, as received, varied widely with an average of about 55 per cent by weight. The in situ water content was higher. The water soluble salt portion of the sediment was not determined separately, but it made up more than half of the solid sediment in many cases. Some of the sulfide-rich parts of this deposit contain high concentrations of zinc, copper and other heavy metals, but the average metal content of the deposits is much lower than would be indicated by these few high values.