Periodic Reporting for period 1 - SedTraceFlux (The critical role of sedimentary trace element fluxes in ocean biogeochemistry)
Période du rapport: 2021-09-01 au 2023-08-31
Understanding the ocean's biogeochemical cycles of trace elements has significant scientific and societal implications. First, many trace elements are vital nutrients for marine organisms. As a result, they can drive evolutionary processes, influence surface climate and environmental conditions by participating in global biogeochemical cycles of carbon and oxygen, and play a key role in maintaining the health of marine ecosystems. Second, trace elements serve as essential tools for investigating the ocean system and tracking its interactions with the biosphere, atmosphere, and lithosphere. Importantly, the isotopic compositions of many trace elements often provide scientists with the only means to reconstruct past ocean environmental conditions, enabling us to study how historical ocean changes have affected the origin and evolution of life on Earth.
Consequently, there is a growing effort to incorporate marine trace elements into state-of-the-art global models, aiming to enhance our ability to predict future changes in ocean chemistry and climate. However, these efforts have faced challenges due to our limited understanding of the sources and sinks of dissolved trace elements in the ocean. Recent findings specifically indicate that sedimentary source and sink fluxes may play significantly larger roles in shaping the distributions of marine trace elements than previously assumed. Yet, our knowledge of these fluxes and the relevant sediment biogeochemical processes remains insufficient, resulting in substantial uncertainties in the modern and paleo-applications of trace elements in the field of ocean biogeochemistry. The project aims to characterize the sedimentary processes and fluxes of these trace elements and isotopes, develop new modeling tools to study their biogeochemical cycling in marine sediments and understand the role of sedimentary processes in their global ocean cycles. The project is focused on the rare earth elements and transition metals.
The project has concluded that the sedimentary fluxes of trace elements and isotopes are regulated by diagenetic processes including organic matter remineralization, redox cycling, authigenesis, marine silicate weathering and reverse weathering; the sedimentary fluxes contribute significantly to the elemental and isotopic budgets of trace elements and isotopes; including sedimentary processes and fluxes in ocean models is needed to fully explain the distributions of trace elements and isotopes in the ocean.
Consequently, there is a growing effort to incorporate marine trace elements into state-of-the-art global models, aiming to enhance our ability to predict future changes in ocean chemistry and climate. However, these efforts have faced challenges due to our limited understanding of the sources and sinks of dissolved trace elements in the ocean. Recent findings specifically indicate that sedimentary source and sink fluxes may play significantly larger roles in shaping the distributions of marine trace elements than previously assumed. Yet, our knowledge of these fluxes and the relevant sediment biogeochemical processes remains insufficient, resulting in substantial uncertainties in the modern and paleo-applications of trace elements in the field of ocean biogeochemistry. The project aims to characterize the sedimentary processes and fluxes of these trace elements and isotopes, develop new modeling tools to study their biogeochemical cycling in marine sediments and understand the role of sedimentary processes in their global ocean cycles. The project is focused on the rare earth elements and transition metals.
The project has concluded that the sedimentary fluxes of trace elements and isotopes are regulated by diagenetic processes including organic matter remineralization, redox cycling, authigenesis, marine silicate weathering and reverse weathering; the sedimentary fluxes contribute significantly to the elemental and isotopic budgets of trace elements and isotopes; including sedimentary processes and fluxes in ocean models is needed to fully explain the distributions of trace elements and isotopes in the ocean.
This project created SedTrace, an open-source modeling framework for generating custom diagenetic models of trace elements and isotopes. SedTrace was designed to lower the coding barrier for the user. It only requires the user to supply an Excel sheet, which will be used to automatically generate computer code in Julia language. It also provides advanced computational tools to help the user carry out model simulations.
The project has modeled trace element speciation and diagenesis on the continental margin and abyssal seafloor, and the impact on the sedimentary fluxes. The speciation model considered both inorganic and organic ligands, as well as adsorption/desorption onto sediment particles including Fe-Mn oxides. A complex biogeochemical reaction network was included. The results showed that in continental margin sediments, Fe-Mn reduction and authigenic phosphate formation are the main drivers of rare earth element biogeochemistry and thus control their pore water profiles and fluxes. However, the pore water and authigenic Nd isotope data require input from silicate-sourced Nd, which is the result of the weathering of volcanic materials coupled with reverse weathering. In oxic sediment, in contrast, trace element cycling is mainly driven by organic matter remineralization and adsorption onto Fe-Mn oxide.
The project has tested and developed the procedure of measuring transition metals, Fe and Nd isotopes from the same pore water or sediment samples. The project has measured the pore water and sediment Fe, Nd, and transition metal concentration and isotope composition from a variety of environmental settings. This project has produced a large collection of pore water trace element isotope data.
In collaboration with colleagues, this project constrained the impacts of ocean circulation and internal cycling on the distribution of Ni concentration and isotope composition using ocean biogeochemical models. The results showed that marine Ni cycling is strongly tied to the phytoplankton community composition. The project has also created an ocean model of Nd cycling, including benthic flux and processes. The model demonstrates that to successfully simulate the distributions of both Nd concentration and isotope composition, sedimentary flux is needed in addition to the top-down processes.
Five peer-reviewed research articles have been published as a result of SedTraceFlux. An open-source software package SedTrace has been produced, and a website has been created to describe this software and other SedTraceFlux results. The results have also been presented at international conferences.
The project has modeled trace element speciation and diagenesis on the continental margin and abyssal seafloor, and the impact on the sedimentary fluxes. The speciation model considered both inorganic and organic ligands, as well as adsorption/desorption onto sediment particles including Fe-Mn oxides. A complex biogeochemical reaction network was included. The results showed that in continental margin sediments, Fe-Mn reduction and authigenic phosphate formation are the main drivers of rare earth element biogeochemistry and thus control their pore water profiles and fluxes. However, the pore water and authigenic Nd isotope data require input from silicate-sourced Nd, which is the result of the weathering of volcanic materials coupled with reverse weathering. In oxic sediment, in contrast, trace element cycling is mainly driven by organic matter remineralization and adsorption onto Fe-Mn oxide.
The project has tested and developed the procedure of measuring transition metals, Fe and Nd isotopes from the same pore water or sediment samples. The project has measured the pore water and sediment Fe, Nd, and transition metal concentration and isotope composition from a variety of environmental settings. This project has produced a large collection of pore water trace element isotope data.
In collaboration with colleagues, this project constrained the impacts of ocean circulation and internal cycling on the distribution of Ni concentration and isotope composition using ocean biogeochemical models. The results showed that marine Ni cycling is strongly tied to the phytoplankton community composition. The project has also created an ocean model of Nd cycling, including benthic flux and processes. The model demonstrates that to successfully simulate the distributions of both Nd concentration and isotope composition, sedimentary flux is needed in addition to the top-down processes.
Five peer-reviewed research articles have been published as a result of SedTraceFlux. An open-source software package SedTrace has been produced, and a website has been created to describe this software and other SedTraceFlux results. The results have also been presented at international conferences.
SedTraceFlux has improved our understanding of the sediment biogeochemical processes and thus contributes to the resolution of the global oceanic budgets of trace elements and isotopes and their application in paleoceanography. The pore water trace element and isotope data produced by this project are amongst the first such datasets which is a significant contribution to literature and allows mechanistic study of the sedimentary cycling of trace elements and isotopes. The open-source software SedTrace produced by this project is amongst the few tools dedicated to the modeling of the sedimentary cycling of trace elements and isotopes. It lowers the coding barrier, making it possible for users not skilled in computer programming to generate and run sediment diagenetic models. The project has also provided systematic observational and modeling evidence that supports the key role of benthic processes in ocean biogeochemistry, contributing to a comprehensive understanding of the water column to sediment transformation of trace elements and isotopes.