The carbon cycle is one of the most important elemental cycles on our planet because, via the cycling of carbon between the lithosphere, hydrosphere, atmosphere and biosphere, the carbon cycle controls climate and thus the habitability of our world. There are several aspects of the carbon cycle that must be better understood in order to shed light on how our planet became habitable and how our activities are shaping habitability into the future, but one in particular concerns the cycling of organic carbon (OC) in the oceans. The cycling of OC in the oceanic environment is of fundamental importance to the Earth system on both the vastly long timescales that have created the planet we see today, and the much shorter timescales that we now rely on for our socioeconomic wellbeing. On multi-million year timescales the balance between the degradation and preservation of OC in sediments has played a fundamentally important role in controlling atmospheric carbon dioxide and oxygen. On decadal to centennial timescales the balance between the degradation and preservation of OC in seawater plays a pivotal role in controlling atmospheric carbon dioxide today, and thus in regulating modern climate and potentially mitigating against the effects of climate change.
Over these two different timescales the cycling of OC in the oceans is of vital importance to the Earth system, but despite many years of research, we still do not fully understand how OC escapes degradation and becomes preserved. All OC is derived from living organisms, which are essentially quite easily broken down by microbes living in sediments and seawater, so the fact that any OC is preserved is actually profoundly puzzling. To date several factors are known to be important for OC preservation, including the amount of time that organic molecules are exposed to oxygen, but the correlations between these factors and OC burial on a global scale are rather weak and it is clear that there must be one or more other processes responsible for preservation. In this regard recent work increasingly highlights the potential importance of minerals for OC protection and preservation. In particular iron and manganese minerals have been shown to lock up OC and protect it from degradation, with perhaps as much as 20% of all OC in marine sediments associated with reactive iron phases, creating a so-called 'rusty sink' that might preserve OC over thousands of years.
MinOrg investigated the role of minerals in the preservation of OC in sediments and seawater in fine detail, through combined experiments and modelling, using cutting-edge molecular-level techniques to determine the exact mechanisms of OC association with minerals and their preservation potential. Through careful experimentation and molecular to global modelling approaches the project addressed one overarching hypothesis, that minerals play a major role in the preservation of OC in marine sediments and the production of long-lived OC in seawater. There were four broad objectives to determine 1) the mechanisms of OC association with minerals; 2) whether OC associated with minerals is protected from degradation in sediments; 3) whether OC associated with minerals helps produce long-lived OC in seawater; 4) the contribution of mineral OC to carbon preservation and the impact of mineral OC on the oceanic carbon cycle.
MinOrg has generated a new understanding of OC preservation that can be used to better evaluate feedbacks between the oceanic carbon cycle and climate, over timescales relevant to both the evolution of our planet and the habitability of the Earth's surface over the coming centuries. This is of significant societal benefit as we strive to understand Earth history and the links between the biological and chemical components of our planet, and our role in a rapidly changing environment. In particular with respect to O1 and 2, MinOrg has identified that carboxyl-rich OC is especially associated with minerals and protected from degradation, and together with amino-rich OC, can become polymerised at mineral surfaces to form large macromolecules that may be preserved in sediments over hundreds of thousands of years. With respect to O3 and 4, MinOrg has discovered that this so-called geopolymerisation and resultant long term OC preservation plays an important role in the global carbon and oxygen cycles and may have helped regulate climate and oxygenation over geological time. The culmination of these discoveries are published in several high profile papers, including in Communications Earth & Environment, Nature Communications, Nature Geoscience and Nature. To encapsulate the findings of this project MinOrg has developed a new concept called the Mineral Carbon Pump, which describes how OC becomes associated with minerals, protected from degradation, and impacts the carbon cycle. This work is under review with Nature Geoscience.
