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Deep-water sedimentary processes and organic carbon burial effects
SU Ming, MA Wenbin, LUO Kunwen, GAO Ya, OU Hejie
Journal of Marine Sciences ›› 2025, Vol. 43 ›› Issue (4) : 21-40.
PDF(2290 KB)
PDF(2290 KB)
Deep-water sedimentary processes and organic carbon burial effects
Deep-water sedimentary processes are key drivers that shape seafloor topography and actively participate in marine material cycles, thereby playing a crucial role in the formation of depositional systems and material cycling along continental margins and within deep-sea basins. The transport and transformation of carbon elements and carbon-containing substances are essential for sustaining organic life and maintaining climate stability. As an important end-member reservoir in this cycle, deep-sea sediments act as efficient sinks for atmospheric greenhouse gases, exerting significant regulatory effects on climate evolution over geological timescales. This study aims to elucidate the coupling mechanisms between distinctive deep-water sedimentary processes and organic carbon burial, providing a theoretical basis for establishing the “Shelf edge-slope-deep sea basin organic matter continuous transport system” and the “Deep-water organic carbon burial pyramid model”. By comprehensively analyzing representative deep-water organic carbon burial systems in global ocean basins, this research demonstrates that turbidity currents and bottom currents are the main dynamic mechanisms enabling the continuous transport of deep-water organic matter. The (micro)biological carbon pump, turbidity current carbon pump, bottom current carbon pump, and deep stratigraphic carbon pump together form the core framework for deep-water sedimentary carbon burial. Furthermore, the factors influencing deep-water organic carbon burial outcomes exhibit hierarchical characteristics. However, current research on deep-water organic carbon burial is still in its early stages, with limited case studies and mechanistic understanding, underscoring the urgent need to strengthen research on carbon burial processes in deep-water environments.
deep-water sedimentation / organic carbon burial / turbidity current / bottom current / carbon pump / submarine canyon / pyramid model
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. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.
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| [121] |
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| [122] |
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| [123] |
\n Nitrogen and phosphorus are the two macro-nutrients that limit biological productivity in the ocean. While the supply of P depends on geological processes, N is biologically supplied from an inexhaustible atmospheric source, but can be limited by micro-nutrients, especially iron. Here we present a record of N and C isotopes over the past 165 Ma in marine sediments to address feedbacks between the N-cycle and productivity. Over most of the last 165 Myr, the fixed N averaged +3.2‰, (−2 and +9‰), but higher in distal areas of the ocean due to limited vertical mixing. Using an isotope box model and a coupled climate model we show that this is caused by winds that induce upwelling changing due to continental meander. Upwelling along low latitude east-west orientated Tethyan coastlines results in low δ\n 15\n N, while upwelling along narrow N-S coastlines as it does today, results in high δ\n 15\n N due to denitrification.\n
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| [124] |
A recent paradigm explains that the downward pumping of biogenic carbon in the ocean is performed by the combined action of six different biological carbon pumps (BCPs): the biological gravitational pump, the physically driven pumps (Mixed Layer Pump, Eddy Subduction Pump and Large-scale Subduction Pump), and the animal-driven pumps (diurnal and seasonal vertical migrations of zooplankton and larger animals). Here, we propose a research community approach to implement the new paradigm through the integrated study of these BCPs in the World Ocean. The framework to investigate the BCPs combines measurements from different observational platforms, i.e., oceanographic ships, satellites, moorings, and robots (gliders, floats, and robotic surface vehicles such as wavegliders and saildrones). We describe the following aspects of the proposed research framework: variables and processes to be measured in both the euphotic and twilight zones for the different BCPs; spatial and temporal scales of occurrence of the various BCPs; selection of key regions for integrated studies of the BCPs; multi-platform observational strategies; and upscaling of results from regional observations to the global ocean using deterministic models combined with data assimilation and machine learning to make the most of the wealth of unique measurements. The proposed approach has the potential not only to bring together a large multidisciplinary community of researchers, but also to usher the community toward a new era of discoveries in ocean sciences.
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| [125] |
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| [126] |
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| [127] |
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| [128] |
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| [129] |
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| [130] |
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| [131] |
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| [132] |
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| [133] |
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| [134] |
Photosynthesis produces molecular oxygen, but it is the burial of organic carbon in sediments that has allowed this O2 to accumulate in Earth’s atmosphere. Yet many direct controls on the preservation and burial of organic carbon have not been explored in detail. For modern Earth, it is known that reactive iron phases are important for organic carbon preservation, suggesting that the availability of particulate iron could be an important factor for the oxygenation of the oceans and atmosphere over Earth history. Here we develop a theoretical model to investigate the effect of mineral–organic preservation on the oxygenation of the Earth, supported by a proxy compilation for terrigenous inputs and the burial of reactive iron phases, and find that changes to the rate of iron input to the global ocean constitute an independent control on atmosphere–ocean O2 and marine sulfate levels. We therefore suggest that increasing continental exposure and denudation may have helped fuel the rise in atmospheric O2 and other oxidants over Earth history. Finally, we show that inclusion of mineral–organic preservation makes the global marine O2 reservoir more resilient to changes in nutrient levels by breaking the link between productivity and organic carbon burial. We conclude that mineral–organic preservation is an important missing process in current assessments of Earth’s long-term carbon cycle.
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| [135] |
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| [136] |
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| [137] |
Vast regions of the dark ocean have ultra-slow rates of organic matter sedimentation, and their sediments are oxygenated to great depths yet have low levels of organic matter and cells. Primary production in the oxic seabed is supported by ammonia-oxidizing archaea, whereas in anoxic sediments, novel, uncultivated groups have the potential to produce H and CH, which fuel anaerobic carbon fixation. Subseafloor bacteria have very low mutation rates, and their evolution is likely dominated by selection of different pre-adapted subseafloor taxa under oxic and anoxic conditions. In addition, the abundance and activity of viruses indicate that they affect the size, structure and selection of subseafloor communities. This Review highlights how microbial communities survive in the unique, nutrient-poor and energy-starved environment of the seabed, where they have the potential to influence global biochemical cycles.
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| [138] |
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