National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 1979

Chemical composition, size distribution, and particle morphology of suspended particulate matter at DOMES sites A, B, & C: Relationships with local sediment composition

Baker, E.T., R.A. Feely, and K. Takahashi

In Marine Geology and Oceanography of the Pacific Manganese Nodule Province, J.L. Bischoff and D.Z. Piper (eds.), Plenum Pub. Corp., New York, 163–202 (1979)

Detailed measurements of the concentration, composition, size, and morphology of suspended particulate matter (SPM) in the eastern equatorial Pacific Ocean were made during separate cruises in 1975 and 1976. SPM concentrations in the surface waters (0-300 m) were highly variable (~30 ± 18 µg/1) and primarily dependent on the concentration of biogenic material which accounted for >90% of the total SPM. Mean Si/Al, K/Al, Ti/Al ratios were significantly higher than the corresponding values for the underlying sediments, indicating probable concentration of these elements in biogenic matter and other nonaluminosilicate phases. Mn/Al ratios, however, were close to or even less than the sediment values. Particle concentrations, mean size, and Si/Al, K/Al, Ti/Al, and Fe/Al ratios all decreased from the surface waters to the top of the bottom nepheloid layer (BNL), indicating progressive dissolution and a concomitant remineralization of associated elements. However, nonaluminosilicate phases still accounted for more than 40-70% of the Si, K, Ti, and Fe in the deep water zone. After deposition, most of this nonaluminosilicate phase is either transformed into authigenic smectites or dissolved and released back into the water column. Within the BNL (approximately the bottom 400 m of the water column), concentration increases of Al, Si, K, Ti, Mn, and Fe averaged 201%, 74%, 46%, 78%, 200%, and 119%, respectively, greater than the overlying waters, whereas total SPM increased only 20-40%. Chemical mass-balance calculations suggest that this BNL concentration increase is due to resuspension of aluminosilicates and hydrogenous Mn from the 1 µm fraction of the local bottom sediments.

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