It remains unclear what controls carbon burial in marine sediments. Thus, we combined model and data analyses to identify patterns of organic matter reactivity at the seafloor on a large-scale. We found large spatial variability on organic matter reactivity, which results from complex regional environmental factors. Based on that, we estimated rates of carbon and nutrient recycling within sediments. Our results are essential to improve predictions of future changes on carbon cycling and climate.
It remains unclear what controls carbon burial in marine sediments. Thus, we combined model and...
Review status: this preprint is currently under review for the journal BG.
Advancing on large-scale trends of apparent organic matter reactivity in marine sediments and patterns of benthic carbon transformation
Felipe S. Freitas1,3,a,Philip A. Pika2,4,b,Sabine Kasten5,6,7,Bo B. Jørgensen8,Jens Rassmann9,Christophe Rabouille9,Shaun Thomas10,c,Henrik Sass10,Richard D. Pancost1,3,and Sandra Arndt4Felipe S. Freitas et al.Felipe S. Freitas1,3,a,Philip A. Pika2,4,b,Sabine Kasten5,6,7,Bo B. Jørgensen8,Jens Rassmann9,Christophe Rabouille9,Shaun Thomas10,c,Henrik Sass10,Richard D. Pancost1,3,and Sandra Arndt4
1Organic Geochemistry Unit, School of Earth Sciences & School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom
2BRIDGE, School of Geographical Sciences, University of Bristol, Bristol, BS8 1RL, United Kingdom
3Cabot Institute for the Environment, University of Bristol, Bristol, BS8 1UH, United Kingdom
4Biogeochemistry and Earth System Modeling, Geosciences, Environment and Society Department, Université Libre de Bruxelles, Brussels, CP160/03 1050, Belgium
5Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
6Faculty of Geosciences, University of Bremen, 28359 Bremen, Germany
7MARUM – Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
8Section for Microbiology, Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
9Laboratoiredes Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ-Université Paris Saclay, 91198 Gif-sur-Yvette, France
10School of Earth and Ocean Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom
acurrent address: School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom
bcurrent address: Department of Earth Sciences, VU University of Amsterdam, 1081 HV Amsterdam, the Netherlands
ccurrent address: RSR Ltd, Parc Ty Glas, Llanishen, Cardiff, CF14 5DU, United Kingdom
1Organic Geochemistry Unit, School of Earth Sciences & School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom
2BRIDGE, School of Geographical Sciences, University of Bristol, Bristol, BS8 1RL, United Kingdom
3Cabot Institute for the Environment, University of Bristol, Bristol, BS8 1UH, United Kingdom
4Biogeochemistry and Earth System Modeling, Geosciences, Environment and Society Department, Université Libre de Bruxelles, Brussels, CP160/03 1050, Belgium
5Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27570, Germany
6Faculty of Geosciences, University of Bremen, 28359 Bremen, Germany
7MARUM – Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
8Section for Microbiology, Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
9Laboratoiredes Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ-Université Paris Saclay, 91198 Gif-sur-Yvette, France
10School of Earth and Ocean Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom
acurrent address: School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom
bcurrent address: Department of Earth Sciences, VU University of Amsterdam, 1081 HV Amsterdam, the Netherlands
ccurrent address: RSR Ltd, Parc Ty Glas, Llanishen, Cardiff, CF14 5DU, United Kingdom
Received: 20 Nov 2020 – Accepted for review: 15 Dec 2020 – Discussion started: 06 Jan 2021
Abstract. Constraining the mechanisms that control organic matter (OM) reactivity and, thus, degradation, preservation and burial in marine sediments across spatial and temporal scales is key to understanding carbon cycling in the past, present, and future. However, we still lack a quantitative understanding of what controls OM reactivity in marine sediments and, as a result, how to constrain it in global models. To fill this gap, we quantify apparent OM reactivity (i.e., model-derived estimates) by extracting reactive continuum model parameters (a and v) from observed benthic organic carbon and sulfate dynamics across 14 contrasting depositional settings distributed over five distinct benthic provinces. Our analysis shows that the large-scale range in apparent OM reactivity is largely driven by the wide variability in parameter a (10−3 < a < 107) with a high frequency of values in the range 100 < a < 104 years. In contrast, inversely determined v-values fall within a narrow range (0.1 < v < 0.2). Results also show that the variability in parameter a and, thus, in apparent OM reactivity is a function of the whole depositional environment, rather than the traditionally proposed, single environmental controls (e.g., water depth, sedimentation rate, OM fluxes). Thus, we caution against the simplifying use of a single environmental predictor for apparent OM reactivity beyond a specific local environmental context. In addition, diagenetic model results also indicate that, while OM fluxes exert a dominant control on depth-integrated OM degradation rates across most depositional environments, apparent OM reactivity becomes a dominant control in depositional environments that receive exceptionally reactive OM. Model results also show that apparent OM reactivity largely controls the relative significance of OM degradation pathways, and thus the redox zonation of the sediment, as well as depth of the sulfate-methane transition zone and rates of anaerobic oxidation of methane. Consequently, apparent OM reactivity also determines uptake and consumption of benthic terminal electron acceptors and nutrient recycling fluxes across a wide range of different depositional environments. In summary, our large-scale assessment not only further support the notion of apparent OM reactivity as a dynamic ecosystem property and highlights its crucial role for benthic biogeochemical cycling and exchange, but it also provides the first quantitative constraint on the most plausible range of reactivity parameters a and v. It thus represents an important advance for model parameterization as it largely alleviates the difficulty of determining OM reactivity in such models by constraining it to only one variable, i.e. the parameter a.
It remains unclear what controls carbon burial in marine sediments. Thus, we combined model and data analyses to identify patterns of organic matter reactivity at the seafloor on a large-scale. We found large spatial variability on organic matter reactivity, which results from complex regional environmental factors. Based on that, we estimated rates of carbon and nutrient recycling within sediments. Our results are essential to improve predictions of future changes on carbon cycling and climate.
It remains unclear what controls carbon burial in marine sediments. Thus, we combined model and...