The chemical composition of subducting sediment and its consequences for the crust and mantle

https://homepages.uc.edu/~algeot/Tribovillard-Algeo-etal-CG-2006.pdf

Trace metals as paleoredox and paleoproductivity proxies: An update

Dissimilatory Fe(III) and Mn(IV) reduction.

A dissimilatory Fe(III)- and Mn(IV)-reducing microorganism was isolated from freshwater sediments of the Potomac River, Maryland. The isolate, designated GS-15, grew in defined anaerobic medium with acetate as the sole electron donor and Fe(III), Mn(IV), or nitrate as the sole electron acceptor. GS-15 oxidized acetate to carbon dioxide with the concomitant reduction of amorphic Fe(III) oxide to magnetite (Fe(3)O(4)). When Fe(III) citrate replaced amorphic Fe(III) oxide as the electron acceptor, GS-15 grew faster and reduced all of the added Fe(III) to Fe(II). GS-15 reduced a natural amorphic Fe(III) oxide but did not significantly reduce highly crystalline Fe(III) forms. Fe(III) was reduced optimally at pH 6.7 to 7 and at 30 to 35 degrees C. Ethanol, butyrate, and propionate could also serve as electron donors for Fe(III) reduction. A variety of other organic compounds and hydrogen could not. MnO(2) was completely reduced to Mn(II), which precipitated as rhodochrosite (MnCO(3)). Nitrate was reduced to ammonia. Oxygen could not serve as an electron acceptor, and it inhibited growth with the other electron acceptors. This is the first demonstration that microorganisms can completely oxidize organic compounds with Fe(III) or Mn(IV) as the sole electron acceptor and that oxidation of organic matter coupled to dissimilatory Fe(III) or Mn(IV) reduction can yield energy for microbial growth. GS-15 provides a model for how enzymatically catalyzed reactions can be quantitatively significant mechanisms for the reduction of iron and manganese in anaerobic environments.

/pdf/novel-mode-of-microbial-energy-metabolism-organic-carbon-1x82bcmire.pdf

Novel mode of microbial energy metabolism: organic carbon oxidation coupled to dissimilatory reduction of iron or manganese.

The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

The concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor. Here we present vertical profiles of seawater manganese concentrations above the rift valley of the Mid-Atlantic Ridge (MAR). The values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley. These plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins. Differences between them suggest that there are at least five hydrothermal sources along this 1,700-km-long section of mid-ocean ridge.

Gary P. Klinkhammer

Papers

Hydrothermal manganese plumes in the Mid-Atlantic Ridge rift valley

Geochemical proxies of North American freshwater routing during the Younger Dryas

Composition of anoxic hypersaline brines in the Tyro and Bannock Basins, eastern Mediterranean

Helium-3 and manganese at the 21°N East Pacific Rise hydrothermal site

Determination of the rare earth elements in natural waters by isotope-dilution mass spectrometry