Influences on the Oceanic Biogeochemical Cycling of the Hybrid-Type Metals: Cobalt, Iron, and Mangaese

Abigail Noble, Ph.D., 2012
Mak Saito, Advisor

Cobalt, iron, and manganese are important redox active trace metal micronutrients with oceanic distributions that are influenced by biological and abiotic sources and sinks. Understanding the biogeochemical cycling of these hybrid-type metals was investigated by studying the distributions of these metals in different oceanic regions.

A large subsurface plume of dissolved cobalt, iron, and manganese was found in the Eastern South Atlantic, caused by a combination of reductive dissolution in coastal sediments, upwelling, advection, biological uptake, and remineralization.  Isopycnal uplift within eddies, ice melt, and winter mixing are also discussed as processes that deliver metals to the regions studied during this thesis.  The biological influence on surface distributions of cobalt was apparent by the observation of linear relationships with phosphate. Speciation studies suggest that there may be two classes of cobalt binding ligands, and that organic complexation plays an important role in preventing cobalt scavenging in the ocean.

The relative rates of scavenging for cobalt, iron, and manganese show environmental variability: in the South Atlantic, these metals were scavenged at very different rates, but in the Ross Sea, mixing and circulation over the shallow sea was fast, scavenging played a minor role, and the cycles of all three were coupled.