ANAMMARKS: ANaerobic AMmonium oxidiation bioMARKers in paleoenvironmentS

In modern marine environment, 30-50% of nitrogen lost from the ocean is due to anaerobic ammonium oxidation (anammox). This bacterial process removes an important nutrient, nitrogen, from the marine phytoplankton system. Thus, anammox has a direct consequence on global marine primary production, the uptake of carbon dioxide, and the carbon cycle. Anammox bacteria performing this process are only active in low-oxygen to anoxic settings, included oxygen minimum zones (OMZs) in the water column. OMZs are expanding in our current changing climate and it is important to understand how this expansion will affect anammox activity and in turn the carbon cycle. Reconstructing paleoclimate in analogs for modern and future climate allows us to study how future changes will affect elements like the anammox processes. There are several instances in Earth's climate history when expanding OMZ has led to full-scale oceanic anoxia. Anammox bacteria are members of a deep-branching phylum, and the process has been hypothesised to have played an important role in creating and maintaining oceanic anoxia during crucial periods of Earth's history (e.g. Jurassic and Cretaceous Oceanic Anoxic Events (OAEs)). Determining how anammox was involved in these past scenarios will help better predict what likely outcomes we can expect in our future.

Organic geochemistry uses molecular fossils, called biomarkers, to study the impact microbial processes have had on the environment. Currently, tracing anammox bacteria using biomarkers is done using ladderane lipids. However, the applicability of a biomarker has temporal limitations. For example, the inability to withstand degradative processes, which occur during and after deposition, restricts how far back in time these biomarkers can be applied. Although ladderane lipids are excellent biomarkers for modern environments, they are highly labile and not well suited for tracing past anammox activity. Thus, in order to clarify the role anammox has played during these past extreme climate events, lipids must first be identified that can be used as biomarkers in more mature sediments.

Two distinct lipid classes have shown potential as biomarkers for past anammox, and will be assessed in this project. These lipids will be evaluated and will be implemented to trace anammox in past oceanic settings. The first class (bacteriohopanepolyols, specifically BHT isomer) seem suitable for sediments deposited within the last 50 Ma, and that have not been exposed to thermal stresses after burial. For example, we will apply these biomarkers to a 2 Myr sediment record underlying the Peru OMZ to explore the hypothesis that anammox influences the expansion of OMZs by contributing to nitrogen removal during increased OMZ.

The second class (unusual cyclic and branched long-chain alkanes) extends the time window of detection into thermally mature sediments. These biomarkers will be investigated in OAE events to determine how anammox influenced a shift towards nitrogen-fixation being the dominate pathway of nutrient uptake during OAEs. Additionally, these alkanes will be economically benefit project partners in the petroleum industry, where biomarkers for anoxia would indirectly indicate preservation potential of organic matter and petroleum.

We will create a simplified method for anammox detection that we will disseminate to other geochemistry laboratories for their studies of the anammox process. Combined, these findings and those specifically from our system studies will help understand past nitrogen cycling by using our established biomarkers to trace past anammox activity. Finally, the results of our studies of paleo-anammox will be incorporated into the biogeochemical model GENIE. This will improve our understanding of the role anammox played in past nitrogen cycling. Subsequently, model results will help to better predict the implications of anammox on future nitrogen and carbon cycling under our changing climate.

The work carried out in this project has economical, societal, and academic benefactors. It will directly benefit organic geochemists, biogeochemical modellers, and the energy industry, as well as indirectly benefit natural resource management, and policy makers. The outputs of this project will create an accessible method for anammox detection, enhance our knowledge of the mechanisms underpinning the carbon and nitrogen cycles, further our understanding of how the anammox process affects marine oxygen minimum zones, and create a more environmentally favourable and economical way of petroleum exploration:

The research done in collaboration with industry partners in the Netherlands is of economic interest to the petroleum industry. This project proposes to investigate and validate biomarker lipids for anaerobic oxidation of ammonium (anammox). The detection of these biomarkers in oil and source rock samples would indicate anoxia. Lack of oxygen during sediment deposition leads to increased organic matter preservation, and to higher quality source rocks. Biomarker evidence of anammox in elements of a petroleum system (e.g. source rock and oil) would indicate anoxia, and provide insight into the depositional setting and petroleum generation potential of the source rock.

This project will contribute to the understanding of past fluctuations in marine oxygen minimum zones (OMZ), and marine nitrogen cycling. Present-day OMZs are expanding due to increased nutrient consumption and rising ocean temperature in the oceans. OMZ increase will affect marine geochemical cycles, potentially decreasing global fish stocks. Results from this project will indirectly contribute to the NERC Research Strategy of responsible management of natural resource by contributing to the predictions on how the expansion of modern OMZs will affect local and international fishing industries. Additionally, our research on past changes to the nitrogen cycle during expanded OMZs will provide new and critical insights into the fluctuations in the nitrogen cycle with climate change. As such, our project falls broadly into the Newcastle University's Scheme and the School of Agriculture and Engineering's Societal Challenge Research Theme of Sustainability.
We will work alongside Newcastle Institute for Sustainability (IfS) to better our understanding of the effect of our footprint on the global nitrogen cycle (e.g. run-off from agricultural fertilisation into water systems, increased oceanic anoxia). The services available through the IfS will help disseminate our research to a broader social and academic audience, such as through contact with their partner organisations in policy and energy and through the organisation of seminars to wide-ranging audiences. Additionally, the peer-reviewed publications from this research will be available to modelling communities which aim to simulate modern and past nitrogen and carbon cycling.

A related aspect of this projected impact is the development of a Gas Chromatography method that would make anammox biomarker analyses accessible to a broader geochemical audience. Currently, the methodology for the detection of anammox lipids requires instrumentations that not all geochemical laboratories have. This new method would be more distributable within already established laboratories, and increase the relevance of anammox research. Additionally, this method will be of use to small-scale petroleum companies wishing to explore past anoxic events, but which do not possess sophisticated instruments to do so. We will host a workshop to help promote the use of our method to both academic and industry beneficiaries.

We will also continue to be involved with local school-based activities (Big BANG UK, Yorkshire Fossil Festival) where we will integrate the basic project findings (e.g. ocean circulation, where petroleum comes from) into these events to stimulate student and public interest in in British science research.