Full page fax print - International Seabed Authority

Figure 2. Profiles of dissolved manganese and phosphate compared to oxygen
content of seawater over a seamount; low-oxygen seawater (the oxygen
minimum zone, OMZ) is a reservoir for high manganese contents
1.3. Historical Background and Research Investment
The first major advance in the study of oceanic Fe-Mn deposits occurred with the
discovery of deep-ocean nodules and crusts by the Challenger Expedition of 1873-6 16.
Dredge hauls collected black Fe-Mn nodules from abyssal depths (4500-6000 m) and
coatings, layers, and crusts of iron-manganese oxides from depths as shallow as 370 m.
Those samples contained significant minor concentrations of copper, nickel, cobalt,
thorium, and thallium 17.
After World War II, it was established that metal scavenging on active catalytic
surfaces concentrated metals in manganese oxides in the oceans 18. Most nodules studied
were from abyssal depths with 0.30% cobalt or less, whereas a few samples, from ocean
spreading axes, had as little as 0.03% cobalt, and samples from seamounts had cobalt
contents as high as 0.70%. During the escalation of interest in abyssal Fe-Mn nodules in
the 1960s and 1970s, Mero 19 and others 20 noted that topographic highs (seamounts and
ridges) in the central Pacific had deposits with the highest mean cobalt contents (1.2%) of
any region of the global ocean. During that time, Cronan 21 showed that there is an
inverse correlation between water depth and cobalt content of nodules (Fe-Mn crusts)
International Seabed Authority 45