INTERACTIONS BETWEEN THE IRON, MANGANESE, AND OXYGEN CYCLES IN THE MARINE ENVIRONMENT
Date
2018-05
Authors
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Publisher
University of Delaware
Abstract
The speciation of dissolved Mn (dMnT) in oxygenated systems has typically
been assumed to be dominated by soluble Mn(II) in addition to Mn(IV) existing as
solid MnO2. Work in the last few decades has shown that the intermediate state,
Mn(III), is stabilized by organic ligands (L) in oxygen depleted waters, making up to
78% of dMnT in the oceanic-type surface waters of the Delaware Bay and up to 99%
of dMnT in surface waters of salt marsh creeks feeding the Broadkill River in
Delaware. These values were obtained using a known method involving
spectrophotometric determination of the kinetics of Mn(II) complexation with
porphyrin (POR). The higher percentage of Mn(III) in creek waters as opposed to the
bay was attributed to greater influence of the salt marsh in the form of an influx of
humic material as unknown ligands. The complexation of Mn(III) and humic materials
to form Mn(III)-L allows for increased transport of Mn and organic material to the
oceans or, in this case, the Delaware Bay. Unexpected oxidation of environmental
samples was observed, prompting laboratory experiments that uncovered a strong
interaction between iron, manganese, and oxygen in a somewhat saline matrix (S = 14
ppt). The interaction observed was due to a series of reactions, beginning with the
oxidation of Fe(II) producing superoxide. This superoxide was then able to react with
Mn(II) to generate MnOx. This previously unconsidered reaction series implies an
interaction between iron, manganese, and oxygen cycling in the environment with
relevance in not only surface water systems but also in hydrothermal vent systems and
banded iron formations. More work is needed to determine the extent to which this
interaction is occurring in natural systems.
Description
Keywords
Marine Science, iron, manganese, oxygen, marine environment