Hydrothermal Production of Organic molecules: carbon transformation and Decomposition in ocean crust fluids

The global mid-ocean ridge is dotted with deep-sea hot springs fueling a 'deep biosphere' of ancient microorganisms, likely the first to emerge on Earth. The ocean is thus considered the 'cradle of life', yet the nexus of this thinking - the potential for dissolved organic molecules to spontaneously form in these hot spring fluids - is a process we do not fully understand. Through the recently completed HyPOD experimental and field program examining the origins of diverse organic molecules forming in hot, reducing fluids emanating from these aquifers, we can now confirm that many molecules form by multiple pathways including thermal breakdown of crustal microbial carbon, sedimentary organic matter and marine dissolved organic matter (DOM), in addition to non-biological carbon dioxide reduction (generating abiotic molecules from which life can emerge). Thus, many separate processes have been shown to contribute to a diverse organic 'menu' for life at the seafloor, forming as a function of differing thermal stresses on the precursor materials. This key result can, through further analyses of fluids help identify subsurface conditions of carbon transformation in seafloor hydrothermal systems. Both abiotic synthesis of origin-of-life relevant molecules, and pyrolysis of pre-existing organic matter have, until now, been poorly studied phenomena at conditions of deep-sea hot springs, leaving huge gaps in our understanding of carbon transformation in ocean crust fluids. Understanding hydrothermal production of the small organic molecules now detectable is critical for assessing energy sources for biotech-relevant microbes, and a potential hydrothermal origin of life on Earth and other ocean worlds in our Solar System (e.g. Enceladus). HyPOD has demonstrated the generation of diverse hydrocarbons, sulfur-, nitrogen- and oxygen-rich small organic molecules from multiple pre-existing carbon sources in hot springs, using state-of-the-art high temperature-pressure experiments, cutting-edge analytical methods and theoretical models to illuminate the diversity, differences & isotope signatures of organic products formed. The project has also resulted in a submitted publication for novel trace organic analyses, that should benefit the scientific communities studying vent biogeochemistry. The HyPOD team has completed analyzing a large portfolio of seafloor hydrothermal fluids sampled either immediately before or during the project from diverse Arctic, Mid-Atlantic and Caribbean mid-ocean ridge hydrothermal systems. We have measured both carboxylic acids as well as methanol - a key origin-of-life relevant compound - in our organic analyses of real hot spring fluids, and our results are critical for our understanding of carbon cycling in volcanic ocean crust. We have completed over ten long-term (weeks to months) experiments to reveal the high-temperature fate of microbial deep biosphere carbon, marine dissolved organic matter and sedimentary carbon, in addition to experiments on the formation of prebiotic hydrothermal organic ingredients for the origin of life. Experiments have already been conducted on Bacteria, Archaea, Arctic and Pacific marine sediments, and deep ocean dissolved organic matter, showing that these materials all generate a wide diversity of molecules, and a 'menu' that changes markedly with temperature. All of these results have been presented at international conference in late 2022 and mid 2023, and publications will be submitted in 2024-2025. Already published results have indicated that timescales of hydrothermal fluid circulation are vitally important for organic molecule stability, and first glimpses at key fluids sampled as part of this project and project HACON. In addition, recent publications in 2024 show that minerals are not required (or likely not effective) in catalyzing the formation of methane and other single carbon species. In total, the HyPOD project has resulted in at least 12 published or publishable (planned) works in major Tier 1 journals, 4 of which are already in publication since 2022. The remainder are currently in preparation for submission throughout 2024 and 2025.

From the original proposal, expected outcomes included the ability to assess the inventory of origin-of-life-relevant primordial organics in hot spring fluids, & the products & impacts of microbial, marine dissolved and sedimentary carbon pyrolysis, and how they yielding life-supporting organics & signatures of subsurface life. As outlined in the results report (Section 4), we are delivering on all these outcomes as the resulting scientific publications from the project are disseminated during 2024-2025. Our experiments show that many of the molecules considered to be essential for a hydrothermal origin of life (e.g. formic acid, methanethiol) can be produced from multiple deep sea sources, including abiotic synthesis and thermal alteration of all known preexisting organic matter forms (marine dissolved organic matter, sedimentary organic matter, vent microbial biomass). While this may confound the scientific community diligently trying to ascertain which molecules are strictly abiotic and which are derived from organic matter, it highlights the enormous potential for hydrothermal fluids to generate small, microbially metabolizable or primordial biochemistry relevant organics by multiple means, by simple application of heat to precursor carbon forms over several months. The insights from the experiments promise to help guide future sampling efforts for organics in hydrothermal fluids, as well as biotechnology prospecting, by providing a clear 'first assessment' of what types of organics can be generated from what (in terms of precursors/conditions). This will be the legacy of HyPOD to the scientific community, and is best summarized by a quote from a leading senior Professor in the field from the USA serving as PhD opponent for one of the HyPOD PhD fellows - "these pioneering results indicate that experiments of this type can be done and .. products can be followed as functions of time using the .. gold bag approach. By jump-starting this type of work, these results bode well for further investigations." HyPODs secondary objective was to improve analytical methods for quantifying low-molecular-weight nitrogen-, sulfur- and oxygen-bearing organics in natural hot spring fluids, & use this knowledge to further understand carbon cycling by hydrothermal microorganisms of much interest for biotechnology prospecting. In this endeavor, we have also had successful outcomes that will impact the future of the field. Our novel High-Pressure Ion Chromatography method for determining trace concentrations of oxygen-bearing organics (carboxylic acids) is being submitted to the reputable ASLO journal Limnology & Oceanography: Methods, home to all widely respected analytical methods in biogeochemistry. We expect our advancements in trace nitrogen- (amino acid) and sulfur-bearing (thiols) analyses to be published as novel methods included in the experimental studies. These methods are already contributing to bioprospecting efforts (e.g. NFR project DeepSeaQuence).

The global mid-ocean ridge is dotted with deep-sea hot springs fueling a 'deep biosphere' of ancient microorganisms, likely the first to emerge on Earth. The ocean is thus considered the 'cradle of life', yet the nexus of this thinking - the potential for dissolved organic molecules to spontaneously form in these hot spring fluids - is a process we do not fully understand. Emerging evidence of diverse organic molecules in hot, reducing fluids emanating from these aquifers suggests they form by multiple pathways, including non-biological CO2 reduction (generating abiotic molecules from which life can emerge), and thermal breakdown of crustal microbial carbon or dissolved organic matter (DOM) - perhaps signifying life's presence beneath the seafloor. Both abiotic synthesis of origin-of-life relevant molecules, and pyrolysis of pre-existing organic matter are poorly studied phenomena at conditions of deep-sea hot springs, leaving huge gaps in our understanding of carbon transformation in ocean crust fluids. Understanding hydrothermal production of the small organic molecules now detectable is critical for assessing energy sources for biotech-relevant microbes, and a potential hydrothermal origin of life on Earth and other ocean worlds in our Solar System (e.g. Enceladus). HyPOD will rigorously examine generation of diverse hydrocarbons, sulfur-, nitrogen- and oxygen-rich organic molecules from multiple carbon sources (CO2, microbial carbon, DOM, sedimentary kerogen) in hot springs, using state-of-the-art high temperature-pressure experiments and theoretical models to illuminate the diversity, differences & isotope signatures of organic products formed. Validating these findings through organic analyses from real hot spring fluids as part of HyPOD will transform our understanding of carbon cycling in volcanic ocean crust, revealing the high-temperature fate of microbial deep biosphere carbon, and the prebiotic hydrothermal organic ingredients for the origin of life.