Carbon cycling: The role of Methane and Copper in an early ocean analogue Lake Matano

Abstract

This dissertation examines the carbon cycle of a modern ferruginous environment (Lake Matano, Indonesia), with a primary focus on the critical role of methane in carbon redistribution in this system. In addition, the mobility and availability of copper (Cu) (an essential component of microbial enzymatic systems related to methane oxidation) was evaluated in this iron-dominated, aquatic ecosystem. Fieldwork was conducted over several years to acquire the necessary samples and measurements that were used for constraining and modeling the lakes water budget, carbon cycle and copper mobility. It was determined that microbial methane oxidation was unusually high in the water column of this lake, providing possibly the highest anaerobic oxidation rates for this important greenhouse gas reported in freshwater or marine settings. Furthermore because of the nutrient limitations of the lake and its minimal photosynthetic activity it was shown that methane plays a key role in this carbon cycle and as a substrate for organic matter production, which in turn can be used as an energy source, and for cell growth. Ultimately some of this organic matter produced from methane will be buried and subsequently lithified. The availability of copper is intimately tied to this carbon cycle by its link to methanotrophy, as copper is a central part of the pMMO enzyme, which regulates enzyme expression and increases methanotrophic efficiency, and is therefore of paramount importance for the rates of methanotrophy occurring. Unexpectedly Cu is not entirely removed through sorption and co-precipitation by Fe and Mn oxides as often presumed in ferruginous and manganous environments where a lot of Fe(oxy)hydroxides and Mn oxides are present. It was found instead to be largely associated with organic matter and undergoing significant redistribution under microbial respiration between a variety of solid phases, including sulfide minerals. These discoveries deliver important insights into both the bioenergetics and microbial enzymatic evolution in the ferruginous basins of Precambrian Eons, through the continued study of one of their best modern analogue systems.