The Negev Lab

A comprehensive understanding of biogeochemical cycles is of great importance as these play a major role in the biogeochemical transformation, remineralisation and recycling of carbon and other nutrients in subsurface sediments. The scale and kinetics of these biogeochemical reactions are not entirely dependent on the chemical species participating in the reaction but are also significantly affected by bioturbation; catalysing the biogeochemical reactions. Bioturbation is an umbrella term for all the physical and chemical changes brought to the stratified layers of sediments by the routine activities of flora and fauna living in there. Bioturbation increases the transport flux of freshwater rich in oxygen to the anoxic deeper layers, changing the chemical environment and providing favourable conditions for the oxidation of reduced elements like Fe2+, Mn2+, and S2-. Once these elements are oxidised, either these precipitate to the bottom layers or are reduced by the microbe in anoxic/hypoxic environments to generate the energy required for their growth and survival. These microbes facilitate the redox conditions in the sub-surface and surface sediments by catalyzing the electron transfer between electron donors and the terminal-electron acceptors. In marine sediments, the primary source of electrons is often the organic matter (OM) present in the sediments, and this continuous uptake of electrons leads to its progressive oxidation. However, microbes sequentially deliver the electrons to terminal-electron acceptors, in order of their decreasing Gibbs free energy (O2, NO3–, Mn4+, Fe3+, SO2-4 ) hence harnessing maximum energy for their growth through these metabolic pathways.  This sequential utilization of these elements by microbes creates a characteristic distribution of redox conditions subsequently establishing an electrochemical gradient, which is classically leading to redox zonation in the sediments, hence shaping the modern-day ocean chemistry profile of various essential biogeochemical elements. In this project we aim to understand the evolution of redox zonation and temporal periodicities of Fe, S and Mn coupled to C under the influence of Bioturbation. Further, the larger aim of this research is to elucidate new pathways in the cycling of major biogeochemical elements like Fe, S and C that could be applicable to the global oceans, further establishing the oceanic mass balance of redox-sensitive elements. Additionally, the findings of this research could be used for reconstructing the paleo-ocean chemistry profile of our planet before the onset of the great oxidation event.