Deposition of deep-sea manganese nodules

Details Deposition of deep-sea manganese nodules Deposition of deep-sea manganese nodules

Feb 1974

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974gecoa..38..279c&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 38, Issue 2, pp.279-300

Computer Science

9

Scientific paper

Manganese at equilibrium in seawater occurs dominantly as Mn 2+ and inorganic complexes at a concentration ratio of about 1:0.72; solubility decreases exponentially with increasing pH or Eh. However, the nodule oxides birnessite and todorokite are at least four orders of magnitude undersaturated relative to the Mn concentrations of seawater, and are metastable relative to hausmannite and manganite. This apparent lack of equilibrium is explicable by the mechanism of precipitation. Surfaces assist Mn precipitation by catalyzing equilibration between dissolved and reactive O 2 and simultaneously also by adsorbing ionic Mn species. The effective Eh at the surface becomes 200-400 mV above that of seawater; the oxidation rate of Mn increases about 10 8 ×, and the activation energies for Mn oxidation decrease ~ 11.5 kcal/mole. Consequently, marine Mn nodules and crusts form by adsorption and catalytic oxidation of Mn 2+ and ferrous ions at nucleating surfaces such as sea-floor silicates, oxyhydroxides, carbonates, phosphates and biogenic debris. The resulting ferromanganese surfaces autocatalyze further growth. In addition, Mn-fixing bacteria may also significantly accelerate accretion rates on these surfaces. Mn which accumulates in submarine sediments may be diagenetically recycled in response to steep solubility gradients causing upward migration from more acidic and reducing horizons toward the sea floor. In contrast, the concentrations of the predominant ferric complexes, Fe(OH) 3 0 and Fe(OH) 4 - , are relatively less sensitive to the Eh's and pH's found in this environment; Fe is therefore not as readily recycled within buried sediments. Consequently, Fe is not so effectively enriched on the sea floor, although it precipitates more readily than Mn because seawater is saturated in amorphous Fe(OH) 3 . The metastable, perhaps kinetically-related, Mn oxides of nodules have a characteristic distribution: birnessite predominates in oxidizing environments of low sedimentation rate and todorokite where sedimentation rates and diagenetic Mn mobility are higher. Surface adsorption and cation substitution within the disordered birnessite-todorokite structure account for the high trace element content of Mn nodules.

Affiliated with

Also associated with

No associations

Rating

Deposition of deep-sea manganese nodules does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Deposition of deep-sea manganese nodules, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Deposition of deep-sea manganese nodules will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1371335