Cobalt in pore waters of marine sediments

Abstract

During early diagenesis on the sea floor, metal-recycling processes exert important controls on the preservation rates and distributions of metals in marine sediments. The elucidation of internal recycling processes, therefore, is important in understanding trace-metal mass balances in the oceans. Recent measurements of cobalt in seawater¹ suggest that cobalt is scavenged from the deep sea and hence follows biogeochemical pathways similar to manganese. We present here measurements of cobalt in pore waters of marine sediments and find that cobalt was released into pore waters in the sub-oxic sediment zone during dissolution of sedimentary manganese oxides (Table 1, Fig. 1). Solid-phase cobalt concentrations in surface (oxic) sediments, above the pore water remobilization horizon, are almost double those measured in the deep (anoxic) sediment zone (Table 2, Fig. 1). The sediment and pore water distributions indicate that a large fraction of sedimentary cobalt is recycled with manganese between oxic and sub-oxic pore waters and redeposited in surface (oxic) sediments.