Periodic Reporting for period 4 - MINORG (The role of minerals in the oceanic carbon cycle)
Periodo di rendicontazione: 2021-12-01 al 2023-08-31
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.
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.
For O1 we determined the mechanism of association of simple OC molecules with sediment iron minerals. We found that carboxyl groups control OC uptake and that OC with increasing carboxyl-richness is more strongly attached to minerals, and thus, less readily degraded during chemical attack. We discovered a novel preservation mechanism, namely iron and manganese catalysed geopolymerisation, that might account for a significant fraction of OC preservation in the oceanic environment. These discoveries are published in several high profile papers, including in Communications Earth & Environment, Nature Communications, Nature Geoscience and Nature, and there are several manuscripts under revision with and in prep for similar dissemination.
For O2 we especially concentrated on whether our mineral associated OC was less readily degraded during microbial attack. In particular we found that iron and manganese catalysed geopolymerised OC is significantly longer lived than its component parts with a degradation behaviour more similar to humic substances, which are one of the most recalcitrant forms of OC in the environment. These discoveries are published in Nature Communications with two further manuscripts in prep for similar dissemination.
For O3 and 4 we developed two new biogeochemical models, one for quantifying the role of minerals in carbon cycling between sediments and seawater, and another for predicting the role of mineral-associated OC in carbon preservation, climate and oxygenation over geological time. Some of this work is published in Nature Geoscience, while some is under review with Nature Geoscience. Three further manuscripts are in prep for similar dissemination.
In addition to the publications above, results have been disseminated at scientific meetings and conferences, and via popularised publications, press releases and social media.
For O2 we especially concentrated on whether our mineral associated OC was less readily degraded during microbial attack. In particular we found that iron and manganese catalysed geopolymerised OC is significantly longer lived than its component parts with a degradation behaviour more similar to humic substances, which are one of the most recalcitrant forms of OC in the environment. These discoveries are published in Nature Communications with two further manuscripts in prep for similar dissemination.
For O3 and 4 we developed two new biogeochemical models, one for quantifying the role of minerals in carbon cycling between sediments and seawater, and another for predicting the role of mineral-associated OC in carbon preservation, climate and oxygenation over geological time. Some of this work is published in Nature Geoscience, while some is under review with Nature Geoscience. Three further manuscripts are in prep for similar dissemination.
In addition to the publications above, results have been disseminated at scientific meetings and conferences, and via popularised publications, press releases and social media.
In O1 our experiments using new synchrotron spectroscopy tools represented a step change for investigating OC-mineral interactions, and demonstrated that the carboxyl group is especially important for OC preservation.
In O2 our microbial incubation experiments allowed us to work with a much greater range of OC and explain observations of sediment biogeochemistry as a function of mineralogical and microbial processes.
In O3 and 4 our conceptual model for OC cycling represented a paradigm shift for degradation and preservation concepts. Our biogeochemical model showed that geopolymerised OC is a previously overlooked route to OC preservation and planetary homeostasis.
In O2 our microbial incubation experiments allowed us to work with a much greater range of OC and explain observations of sediment biogeochemistry as a function of mineralogical and microbial processes.
In O3 and 4 our conceptual model for OC cycling represented a paradigm shift for degradation and preservation concepts. Our biogeochemical model showed that geopolymerised OC is a previously overlooked route to OC preservation and planetary homeostasis.