Geochemical Energy for Catabolism and Anabolism in Hydrothermal Systems
Abstract
Chemically reduced deep-sea vent fluids mixed with oxidized seawater can generate redox disequilibria that serve as energy sources for chemolithoautotrophic (catabolism) and biomass synthesis (anabolism) reactions. Numerical models can be used to evaluate Gibbs energies of such processes on the early Earth and in present-day systems. Here, geochemical data from compositionally diverse vent fluids (Lost City, Rainbow, Logatchev, TAG, 21 °N EPR) are combined with several seawater chemistries to yield a wide range of mixed hydrothermal solutions; this is the starting point for our thermodynamic calculations. In ultramafic-hosted hydrothermal systems, such as Rainbow or Lost City, aerobic chemolithotrophic catabolisms (oxidation of H2, FeII, CH4) are the most energy-yielding at low temperatures (<25 °C); at elevated temperatures, the anaerobic counterparts (e.g., sulfate reduction, methanogenesis) dominate. In basalt-hosed systems, such as TAG and 21 °N EPR, aerobic sulfide oxidation appears to dominate over much of the microbially-relevant temperature range. Such catabolic reaction energetics can then be used to put constraints on the amount of primary biomass production. Under putative early Earth conditions, for example, the net chemoautotrophic synthesis of cellular building blocks is thermodynamically most favorable at moderate temperatures (~50°C), where the energy contributions from HCO3- and H+ in cool seawater coupled to the reducing power in hot vent fluid are optimized. At these conditions, and counter to conventional wisdom, the synthesis of amino acids may even yield small amounts of energy.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B51D0424A
- Keywords:
-
- 0400 BIOGEOSCIENCES;
- 0450 Hydrothermal systems (1034;
- 3017;
- 3616;
- 4832;
- 8135;
- 8424);
- 0456 Life in extreme environments;
- 0466 Modeling;
- 0471 Oxidation/reduction reactions (4851)