A global assessment of the mixed layer in coastal sediments and implications for carbon storage

Song, Shasha; Santos, Isaac R.; Yu, Han‐Qing; Wang, Faming; Burnett, William C.; Bianchi, Thomas S.; Dong, Junyu; Lian, Ergang; Zhao, Bin; Mayer, Lawrence M.; Yao, Qingzhen; Yu, Zhigang; Xu, Bochao

doi:10.1038/s41467-022-32650-0

Cited by 36 publications

(23 citation statements)

References 82 publications

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“…Hence, the use of core-based profiles to derive OC respiration rates can underestimate the actual OC respiration rate substantially in unbioturbated settings such as in anoxic environments. Since around 15% of the coastal ocean has a negligible mixed layer [54], we propose that the reactive surface layer is an important feature in the global coastal seafloor. The predominant use of core-based methods when estimating OC respiration rates in sediments underlying anoxic bottom waters [5,17] has led to the global impact of bottom-water anoxia on OC burial efficiencies being overestimated.…”

Section: Discussionmentioning

confidence: 97%

“…By not accounting for the presence of this reactive surface layer, the OC burial efficiency can be overestimated by a factor of 10. Around 15% of the modern coastal seafloor does not have a mixed layer [54]. In these regions, respiration rates, and thus OC rain rates, are likely underestimated.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

et al. 2023

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Organic carbon (OC) burial efficiency, which relates the OC burial rate to respiration in the seafloor, is a critical parameter in the reconstruction of past marine primary productivities. The current accepted theory is that sediments underlying oxygen-deficient (anoxic) bottom waters have low respiration rates and high OC burial efficiencies. By combining novel in situ measurements in anoxic basins with reaction-transport modelling, we demonstrate that sediments underlying anoxic bottom waters have much higher respiration rates than commonly assumed. A major proportion of the carbon respiration is concentrated in the top millimeter—the so-called ‘reactive surface layer’—which is likely a feature in approximately 15% of the coastal seafloor. When re-evaluating previously published data in light of our results, we conclude that the impact of bottom-water anoxia on OC burial efficiencies in marine sediments is small. Consequently, reconstructions of past marine primary productivity in a predominantly anoxic ocean based on OC burial rates might be underestimated by up to an order of magnitude.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

et al. 2023

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“…However, in the last decade, the deposition rate increased sharply to 2.82 g cm -2 a -1 . It can be seen that near surface sediment mixing had occurred, which indicated that attributed to mixing from sediment resuspension or reworking in recent years (Song et al 2022).…”

Section: Chronologymentioning

confidence: 97%

Responses of burial characteristics of n-alkanes and polycyclic aromatic hydrocarbons in Poyang Lake, China to changes in organic matter inputs from 1886 to 2019

Tian

Chen

Zhao

et al. 2022

Preprint

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The potential influences of the increased anthropogenic stress during the Anthropocene have led to a focus on the sedimentary record in lake and estuary environments. In this study, the spatio-temporal occurrence of 16 polycyclic aromatic hydrocarbons (PAHs) and the n-alkanes from nC12–nC37 associated with organic groups (i.e., organic nitrogen (ON), organic carbon (OC), organic hydrogen (OH), and organic sulfur (OS)) in the 210Pb-dated estuary sediments of Poyang Lake were investigated and their sources and impacts were traced. The ON, OC, OS, and OH contents in the sediment cores ranged between 0.12 − 0.65%, 1 − 7.95%, 0.01 − 0.82%, and 0.03 − 1%, respectively. The age of estuarine sediment cores in Poyang Lake was measured to be 1885–2019 by the 210Pb-dating method. The 133-year sediment deposition occurred over different stages, each with its own characteristics. The PAH fluxes were in the range of 787.65–11269.18 ng cm− 2 a− 1. The high-ring PAHs were dominant, accounting for 74.02% of the total, and the main sources were biomass combustion and automobile exhaust emissions from 1885–2019 without marked change. On a centennial scale, the main n-alkane peaks were nC15, nC31, and nC33, which had an obvious odd-even predominance. The deposition flux of Σn-alkanes varied within the range of 10.33 − 213.86 µg cm− 2 a− 1. The long-chain monomers were dominant, and were found to originate from herbs. The environmental indicator analysis revealed that the restoration of forests and eutrophication of water bodies caused by human activities and a climate change from wet to drought conditions contributed to the relative contribution of autochthonous organisms and vascular plants during 1886–2019.

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“…Here, solute transport is driven by diffusion along concentration gradients, and solid-phase electron acceptors and Corg are deposited to the sediment surface. In contrast, vertical particle transport in muds only occurs by macrofaunal activity or by strong physical forcing, for example in mobile deltaic muds (Aller, 1998;Song, et al, 2022).…”

Section: Particle and Solute Transport In Sandy Advective Sedimentsmentioning

confidence: 99%

Ideas and perspectives: The benthic iron flux from sandy advective bioturbated sediments

Wehrmann

Perger

Dwyer

et al. 2023

Preprint

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Abstract. Multiple investigators have suggested that the benthic flux of dissolved iron (Fed) from continental shelf sediments represents an important source of this micronutrient to ocean waters. The magnitude, biogeochemical controls, and seasonal dynamics of Fed fluxes to date, however, have mostly been studied for muddy cohesive sediments dominated by molecular diffusion. Data from these studies have been included in global biogeochemical models to determine the contribution of this Fe source to the ocean. Fed fluxes from sandy advective sediments have received little consideration, although these sediments cover 50–60 % of the continental shelves. Sandy permeable deposits function as dynamic catalytic filters characterized by the rapid exchange of solutes and infiltration of particles —including labile Corg and reactive metal oxides— and high biogeochemical reaction rates. In this article, we discuss how the fundamentally different modes of solute and particle transport in sands affect the sedimentary Fe cycle and Fed flux. We present a case study in which we simulate bioirrigation in sands in summer and winter. In our experiments, Fed fluxes from non-irrigated sediments under diffusive conditions did not exceed 6 and 13 μmol Fe m-2 d-1 in winter and summer, respectively. Fluxes from irrigated cores reached values of 150 μmol Fe m-2 d-1 (winter) and 115 μmol Fe m-2 d-1 (summer). The results indicate that the pumping activity of the benthic macrofauna plays a key role in controlling the extent of the benthic Fed flux from permeable sediments, and that both biogenic and physical advection enhance fluxes. We argue that bioturbated sandy advective sediments constitute an important benthic Fe source to coastal waters and advocate for a more differentiated treatment of sediment type (muddy diffusive vs. sandy advective) and macrofaunal activity -reflecting different functional groups of the macrobenthos- in global biogeochemical Fe models. A better understanding of the benthic Fe cycle in sandy advective sediments is particularly important to help predict how anthropogenic effects such as changes in the deposition patterns of Corg and metals, the expansion of oxygen minimum zones, and changes in benthic biodiversity will affect the tightly coupled benthic-pelagic ecosystem along continental shelves.

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A global assessment of the mixed layer in coastal sediments and implications for carbon storage

Cited by 36 publications

References 82 publications

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

Responses of burial characteristics of n-alkanes and polycyclic aromatic hydrocarbons in Poyang Lake, China to changes in organic matter inputs from 1886 to 2019

Ideas and perspectives: The benthic iron flux from sandy advective bioturbated sediments

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