Diagenetic Processes in Deep-Sea Sediments

Within red clays, the diffusive flux of Mn is small (23 pg cm ka ) and corresponds to about 7% of the total sedimentation flux of Mn (Glasby 1991). Mnis therefore largely immobilized in red clays. By contrast, 96% of the Cu in red clays is regenerated from the sediment into the bottom water as a result of the diagenetic flux across the sediment/water interface. Red clays therefore provide a relatively low flux of Mn and transition elements to the sediment surface and this is not an impoPant source of metals for manganese nodule formation in red clay areas. 

In a comparison of pore water profiles of red clays and hemipelagic sediments, Sawlan and Murray (1983) showed that Mn and Fe are below the detection limit in the pore waters of red clays, Ni is present in the same concentation as in ocean bottom water and Cu shows a pronounced maximum at the sediment-water interface. In hemipelagic clays, denitrification becomes important and remobilization of Mn and Fe takes place. Ni correlates with Mn in the pore waters suggesting that it is associated with the Mn oxides in the solid phase. Cu is regenerated very rapidly at the sediment-water interface. The diffusive flux of Mn in hemipelagic sediments was determined to be in the range 2,200- 

000 pg cm ka . More detailed studies of pore water profiles in five different areas of the Californian Borderland confirmed the importance of Mn recycling in the surface sediments when the oxygen content of the bottom waters exceeds 0.1 ml C (Shawetal. 1990). Co and Ni appeared to be scavenged by Mn oxides and trapped in the surface sediments whereas the accumulation of Cu appeared to be more closely related to the flux of biogenic material to the sediment. 

---