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16 The sulfur cycle in marine sediments. The cycle is energetically driven by deposited organic material and methane, both of which are used by sulfate reducing bacteria to produce H S. Much of the H S reacts chemically with 2 2 iron (oxyhydr)oxides to form FeS and a range of intermediate oxidation states including S 0 and FeS . The further 2 oxidation of these species back to sulfate is mediated by the vertical conveyer belt of bioturbation caused by burrowing macrofauna. Reoxidation of the solid phase sulfur species to sulfate at the sediment surface may be by oxygen, nitrate or manganese oxide. The same conveyer belt brings the oxidized iron back down towards the sulfide production zone where it reacts with further H S. A highly efficient recycling of sulfur is thereby achieved. (From 2 Jørgensen and Nelson 2004).
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This chapter deals with the biogeochemical transformations of sulfur and methane in marine sediments during early diagenesis. The term ‘early diagenesis’ refers to the whole range of postdepositional processes that take place in aquatic sediments and are coupled either directly or indirectly to the degradation of organic matter. We focus on the pro...
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... sediments, the production of H S may 2 exceed the availability of reactive metal oxides and H S accumulates in the pore water (see Fig. 8.6, 2 8.12, 8.13, and 8.17). The H S diffuses upwards 2 along a concentration gradient that generally reaches zero at the bottom of the suboxic zone. Concurrently, the H S reacts with buried iron 2 oxides to form FeS, FeS , S 0 and a number of other 2 solid or dissolved intermediate products. Once the reduced sulfur is bound in the solid phase, e.g. as pyrite, its further oxidation depends on a slow reaction with further Fe(III) species or its transport up to near-surface layers with oxidants of higher redox potential. Pyrite transport in near-surface sediments generally takes place through the conveyer belt of bioturbation whereby burrowing macrofauna mix the sediment or directly move sediment particles as part of their deposit feeding behavior (Fig. 8.16). As the pyrite reaches up into the suboxic zone it may react with oxidants such as oxygen or manganese oxide and be converted into sulfate and iron oxides (or iron (oxyhydr)oxides). The iron oxides are in turn transported downwards through the same conveyer belt and thereby become available for further binding of sulfide and pyrite formation. The pyrite oxidation by manganese oxide has been implied from chemical profiles (Canfield et al. 1993) and demonstrated directly through experiments (Schippers and Jørgensen 2001, 2002). The process is interesting in that it involves the reaction between two mineral phases in the sediment that must be in close proximity for the oxidation to proceed. The initial reaction is purely chemical and was proposed to occur by a Fe(II)/Fe(III)-shuttle in the pore fluid between the mineral surfaces of FeS and MnO . The immediate 2 2 products of the oxidation are thiosulfate and polythionates. These can be further oxidized to sulfate by manganese reducing bacteria, ...
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... reactions do not cause a net oxidation of the sulfur species, yet they have a key function in sulfide oxidation. Disproportionation provides a shunt in the sulfur cycle whereby the H S formed by this reaction may be 2 oxidized again to the same sulfur intermediate by metal oxides. Manganese oxide, for example, rapidly oxidizes H S to S 0 without participation of 2 bacteria, but does not oxidize the S 0 further to sulfate (Burdige 1993). The elemental sulfur may, however, be disproportionated (Eq. 8.19) whereby a fourth of it is oxidized completely to sulfate while the remaining three fourths return to the sulfide pool. Through repeated partial oxidation of sulfide to elemental sulfur with manganese oxide and subsequent disproportionation of the elemental sulfur to sulfate and sulfide a complete oxidation of sulfide to sulfate by manganese oxide may be achieved (Fig. 8.16; Thamdrup et al. 1993; Böttcher and Thamdrup ...
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... MOBs were consistently present within the top decimeter of surface sediments (i.e., the section that we could target at Norskebanken and Hinlopen Trough). However, O 2 in marine sediments is typically consumed within the upper millimeters of the sediment surface (Jørgensen and Kasten, 2006). Unless that bio−irrigation through larger marine benthic organisms introduces O 2 to deeper sediment layers (Kristensen, 2000;Dauwe et al., 2001;Niemann et al., 2006), or that some of the detected MOBs can utilize electron acceptors other than O 2 (Kits et al., 2015;Martinez-Cruz et al., 2017;Su et al., 2023), it seems likely that MOBs in subsurface sediments at Norskebanken and Hinlopen Trough are mostly dormant in situ. ...
Understanding methane flux dynamics in Arctic cold seep systems and the influence of oceanic currents on microbial methane-oxidizing bacteria (MOB) is crucial for assessing their impact on Arctic methane emissions. Here, we investigate methane dynamics and associated microbial communities at two cold seep areas, Norskebanken and Hinlopen Trough, North of Svalbard. Methane concentrations and methane oxidation rates (MOx) were measured in bottom and surface waters, with higher values observed in bottom waters, particularly at Hinlopen Trough. Dominant water column MOB clusters were Milano−WF1B−03 and Methyloprofundus. Methane availability drove MOx activity, as indicated by higher concentrations in bottom waters and sediments where MOx was elevated, too. Sediment MOB communities varied among locations, with Hinlopen featuring higher diversity and abundance. Similarities between sediments and water column MOBs suggest potential recruitment from sediments, possibly via a bubble shuttle mechanism. In addition, bottom water MOB community composition also showed similarities between the Norskebanken and Hinlopen seeps, implying an exchange of water column microbes between the two seep areas, which may likely be driven by the regional current regime. Together, our results show that bubble-mediated transport and translocation via currents are important processes shaping the community structure and efficiency of the microbial methane filter in the water column.
... The continental margin is the active terrestrial-ocean interface that serves as a primary location for the biochemical and sedimentary cycling of organic carbon (OC), nitrogen (N), and sulfur (S) (Berner, 1982;Jørgensen and Kasten, 2006;Hu et al., 2011;DeLaune and White, 2012;Hu et al., 2014;Jørgensen et al., 2019;Chen et al., 2021). Dynamic physicochemical reactions along continental margins create complex OC-N-S cycles that can be affected by local climate; however, the mechanistic link of climate change to the OC-N-S cycles is not well understood (Mcleod et al., 2011;Liu Q. et al., 2018;Liu X. T., et al., 2018;Sun et al., 2020;Liu X. T., et al., 2021;Wang et al., 2021;Zhao et al., 2021;Liu et al., 2023). ...
The correlation between the amount of organic carbon (OC) and sulfur (S) in sediments has been widely used as a paleosalinity indicator to distinguish between marine and freshwater environments. However, whether the ratio of total OC to total S (TOC/TS) can be used to identify unsteady or dynamic marine environments across sedimentary strata is still contended. An HZW1907 sediment core of 80 m in length was successfully collected in the middle of Hangzhou Bay (HZB), serving as one of the few boreholes that are crucial for the study of geologic and geo-environment changes in the coastal regions of eastern China since the Last Glacial Maximum (LGM). Total OC (TOC), stable carbon isotope, and TS of 82 subsamples from the HZW1907 core were analyzed to reconstruct the history of the shallow water biological pump and sulfur preservation record in the bay since the Late Pleistocene. Our results indicate that the samples had low concentrations of TOC (0.21%) and total nitrogen (TN) (0.02%), high mass ratio of TOC/TN (10.8), low δ¹³C (−24.9‰), low TS content (0.06%), and a high ratio of TOC/TS (9.1) from 33.6 ka BP to 12.3 ka BP, implying that freshwater organic matter (OM), algae, and C3 plant fragments were the main sources of OM in a relatively cold environment. The abundances of TOC, TN, and TS increased to 0.56%, 0.07%, and 0.4%, respectively, while δ¹³C (−23.9‰) increased and TOC/TS (2.7) decreased in the Holocene sediments, suggesting that seawater began to influence the composition of the sediments of HZB. Climate warming, which is likely to have impacted the results, was experienced from 12.3 ka BP. An OC isotope mixing model indicated that since the Mid-late Holocene, more than 70% of riverine OM accounted for the total OM. The TOC/TS ratio was identified as an effective indicator of seawater intrusion, with C/S ratios of 1–6 being considered to indicate a “sea–land transitional zone” sedimentary environment, a C/S >6 indicating freshwater, and a C/S<1 indicating normal marine facies. These findings provide crucial evidence for using TOC/TS to distinguish freshwater from marine environments and enhance our understanding of past climate changes. Therefore, these geochemical indicators can be used in conjunction with other sedimentary records to obtain accurate results about sedimentary evolution.
... This kind of behaviour was also seen in the KRE, where vertical profiles of dissolved Mn and Fe showed a sharp rise below the SWI across the estuary, but the intensity of mobilisation differed among the sites. In cores K2, K4, and K5, the increase of the dissolved Fe was at a lower depth (2-4 cm) than dissolved Mn (0-2 cm), which is consistent with the ideal redox sequence of the estuarine sediments [75]. At sites K1 and K3, however, the redox zones were more compressed, resulting in the Mn and Fe peaks in the same layer, just below the SWI (0-2 cm). ...
To study the processes that govern the post-depositional mobility of metals in the estuarine sediment, five sediment cores were sampled in the Krka River estuary (Croatia). The obtained concentration ranges in the pore water were 0.057–49.7 μM for Fe, 0.310–100 μM for Mn, 0.068–26.8 nM for Co, 0.126–153 nM for Cu, 11.5–2793 nM for Zn, 0.222–31.3 nM for Pb, 4.09–59.4 nM for U, 38.8–2228 nM for Mo, and 0.065–2.29 nM for As. The vertical distribution of metals in the dissolved and solid fraction of the sediment, coupled with other diagenetic tracers (e.g., dissolved sulphide), demonstrate the importance of early diagenetic reactions, in particular Fe and Mn oxyhydroxide and sulphate reduction, for the cycling of metals in the sediment. The redox zonation in the sediment was compressed, and the suboxic zone occurs immediately below the sediment–water interface. The estimated benthic fluxes in the estuary were 5220 kg y−1 for Fe, 27,100 kg y−1 for Mn, 6.00 kg y−1 for Co, 20.5 kg y−1 for Cu, 5.16 kg y−1 for Pb, 111 kg y−1 for Mo, and 87.3 kg y−1 for As. The riverine input was more important than the benthic flux, except in the case of Mn and Fe.
... Determining the redox conditions in the sediments is essential to reconstruct metal speciation and mobility as well as biogeochemical processes. The redox zonation of marine sediments is dictated by conditions in the bottom waters, the magnitude and rates of organic matter mineralization and biological activity reworking the surface sediment (Jørgensen and Kasten, 2006). In general, the uppermost sediment layer is rich in oxygen diffusing from the overlying water column. ...
... Microorganisms rapidly consume the oxygen as an electron acceptor in the process of organic matter oxidation. Below the oxic zone, less thermodynamically favourable compounds (yielding lower energy gain for the microbes) are consumed in the following order: nitrate (NO 3 − ), manganese (oxy)hydroxides, iron (oxy)hydroxides and sulfate (SO 4 2− ) (Jørgensen and Kasten, 2006). This succession corresponds to a steep decrease in redox potential and the pH, initially steeply decreasing within the oxic zone as a result of aerobic respiration and reoxidation of reduced species, tends to increase with depth due to anaerobic alkalinity production (Silburn et al., 2017). ...
... This is visible in Fig. 4, where Mn bulges are located immediately above the Fe ones. By definition, the suboxic zone is followed by the anoxic zone of sulfate reduction (Jørgensen and Kasten, 2006). Consistent with the expected zonation, in our cores, we observe sulfate starting to decline below the Mn and Fe reduction zones. ...
Historical copper mine tailings deposited in the Repparfjord, Northern Norway, provided new insight into the biogeochemical impact of submarine tailings disposals on high-latitude coastal ecosystems. The submarine tailings disposal in the Repparfjord represents a product of mining activities between 1972 and 1979. Their environmental impact has been extensively studied during the last decade, but geochemistry of the sediment pore water, which is crucial to assess and monitor the in-situ metal leaching and bioavailability, has never been analysed. The actual impact on the benthic fauna remains poorly known. Therefore, this study couples the pore water chemistry and the foraminiferal analysis obtained from selected sediment cores (gravity core, multicore, box cores) to examine metal stability and the past and current status of the foraminifera community. We measured down-core sulfate and trace metal concentrations and Eh-Ph and applied the Shannon index, the AZTI´s Marine Biotic Index (F-AMBI) index and the foraminiferal abnormality index. This study confirms the ongoing leaching of copper from the underlying mine tailings and release across the sediment-water interface. Leaching of Ni, Zn and Pb have been attributed to weathering of natural bedrock lithologies. The original benthic foraminiferal community disappeared almost entirely during the disposal period, and now it is dominated by stress-tolerant and opportunistic species like Bulimina marginata and Spiroplectammina biformis. Anyhow, against previous assumptions, the community composition changed, while the overall diversity and abnormalities (FAI) shell formation is unaffected by elevated copper concentrations.
... 931The surface sediments at these sites are composed of silty 932 clay, clayey silt, and sandy silt( Figure 1). Sediment com-933 position was different between the sites, but the TOC/TS 934 contents remained below the predicted Holocene satura-935 tion line( Figure 5 F), indicating sulfate mineralization pro-936 cesses( Berner, 1982 ;Jørgensen and Kasten, 2006 ). Most 937 sites showed Hg profiles with enhanced contents at 10 and 938 20 cmbsf, and thus a relatively continuous sedimentation 939 with little disturbance. ...
The present study aims to understand the impact of submarine groundwater discharge (SGD) on a coastal area with different lithology and degrees of SGD. Sampling cam- paigns took place in Puck Bay and the Gulf of Gdansk, southern Baltic Sea encompassing years between 2009 and 2021. The methodological approach combined geophysical characterization of the surface sediments with detailed spatial and temporal (isotope) biogeochemical investigations of pore and surface waters, and was supported by nearshore groundwater and river surveys. Acoustic investigations identified areas of disturbance that may indicate zones of preferential SGD release. The composition of porewater and the differences in the bay’s surface
waters disclosed SGD as common phenomenon in the study area. Regional SGD was estimated through a radium mass balance. Local estimation of SGD, based on porewater profiles, revealed
highest SGD fluxes at the sandy shoreline, but relatively low elemental fluxes. Though SGD was low at the muddy sites corresponding elemental fluxes of nutrients and dissolved carbon exceeded those determined at the sandy sites due to intense diagenesis in the top sediments. SGD appears to be sourced from different freshwater endmembers; however, diagenesis in surface
sediments substantially modified the composition of the mixed solutions that are finally discharged to coastal waters. Overall, this study provides a better understanding of the SGD dynamics
in the region by a multi-approach and emphasizes the need to understand the processes occurring at the sediment-water interface when estimating SGD.
... Goldhaber and Kaplan, 1975;Jørgensen, 1982;Canfield, 1991;Jørgensen et al., 2019). Dissimilatory sulfatereducing bacteria and archaea obtain energy from the reduction of sulfate (SO 4 2-) linked to the oxidation of electron donors such as molecular hydrogen, methane or organic acids such as acetate, lactate and pyruvate that are produced by biological degradation of organic matter (Jørgensen and Kasten, 2006). This metabolic coupling with carbon implies that microbial sulfate reduction plays an important role in the global carbon cycle, and estimates suggest that the annual global reduction of 11.3 teramoles of sulfate is responsible for the oxidation of 11-29% of the organic carbon flux to the seafloor (Bowles et al., 2014). ...
Microbial sulfate reduction is generally limited in the deep sea compared to shallower marine environments, but cold seeps and hydrothermal systems are considered an exception. Here, we report sulfate reduction rates and geochemical data from marine sediments and hydrothermal vent fields along the Arctic Mid Ocean Ridges (AMOR), to assess the significance of basalt-hosted hydrothermal activity on sulfate reduction in a distal deep marine setting. We find that cored marine sediments do not display evidence for sulfate reduction, apart from low rates in sediments from the Knipovich Ridge. This likely reflects the overall limited availability of reactive organic matter and low sedimentation rates along the AMOR, except for areas in the vicinity of Svalbard and Bear Island. In contrast, hydrothermal samples from the Seven Sisters, Jan Mayen and Loki’s Castle vent fields all demonstrate active microbial sulfate reduction. Rates increase from a few 10s to 100s of pmol SO4²⁻ cm⁻³ d⁻¹ in active high-temperature hydrothermal chimneys, to 10s of nmol SO4²⁻ cm⁻³ d⁻¹ in low-temperature barite chimneys and up to 110 nmol cm⁻³ d⁻¹ in diffuse venting hydrothermal sediments in the Barite field at Loki’s Castle. Pore fluid and sediment geochemical data suggest that these high rates are sustained by organic compounds from microbial mats and vent fauna as well as methane supplied by high-temperature hydrothermal fluids. However, significant variation was observed between replicate hydrothermal samples and observation of high rates in seemingly inactive barite chimneys suggests that other electron donors may be important as well. Sediment sulfur isotope signatures concur with measured rates in the Barite field and indicate that microbial sulfate reduction has occurred in the hydrothermal sediments since the recent geological past. Our findings indicate that basalt-hosted vent fields provide sufficient electron donors to support microbial sulfate reduction in high- and low-temperature hydrothermal areas in settings that otherwise show very low sulfate reduction rates.
... This S/C ratio can suggest that organic matter in the sediments comprises humic and lignin substances, which have low reactivity and are less used by sulfate-reducing bacteria (Berner, 1984;Sato et al., 2012). The high S/C ratios of "cold-seep" sediments, ranging from 0.19 to 3.14 and increasing significantly below 5-6 cm (Fig. 6), highlight the important role of AOM in sulfur behavior within sediments (Hensen et al., 2003), as well as the significant addition of chrome reducible sulfur to the sedimentary sulfur pool (Hu et al., 2020;Jorgensen and Kasten, 2006;Lin et al., 2016). This observation is also supported by the negative correlation between TS and TOC in cores from stations AMK-6027 and AMK-6948 (Table 5). ...
The East Siberian Arctic shelf is renowned for its active methane-rich fluid seeps, confirmed by numerous gas flares in the water column and direct observations of methane release from the seafloor. These cold-seep sites serve as natural laboratories for studying the impact of methane seepage on early diagenesis, authigenic mineral formation, and the geochemical cycles of carbon, sulfur, and other elements. This study examines the grain size and chemical composition of two sediment types from the Laptev Sea shelf: cold-seep sediments influenced by sulfate-driven anaerobic methane oxidation, and unaffected “seep-free” sediments (i.e., control site). High methane concentrations (up to 649 μM/L) in the surface layer of sediments indicate that the sulfate–methane transition zone is found close to the sediment–water interface approximately 5–6 cm below the seabed. At the
cold-seep site, thin layers containing up to 40% sand fraction were discovered among the fine-grained sediments.
We infer that upward-migrating fluids may contribute to the remobilization of the fine fraction, resulting in concentration of coarse particles. Cold-seep sediments are characterized by molybdenum (Mo) enrichment compared to the lithological background, although one “seep-free” core exhibits evidence of authigenic Mo deposition. The Mo concentration (up to 16.8 ppm) indicates that enrichment occurs under sulfidic conditions restricted to pore water, which are caused by anaerobic methane oxidation. The high Mo concentration in one “seep-free” core likely implies past cold-seep activity. A general Mo–U covariation indicates that the molybdenum enrichment in cold-seep sediments from the Laptev Sea outer shelf is controlled by a weak particulate shuttle process.
... The authors did not directly include information derived from 35 S-radiotracer measurements of sulfate reduction. They concluded that the earlier global estimate suggested by Jørgensen and Kasten (2006) of 75 Tmol SO 4 2yr − 1 was too high and was not realistic. ...
... This conclusion motivated us to re-evaluate these global numbers. The first, highly embarrassing observation was that the 75 Tmol SO 4 2yr − 1 published by Jørgensen and Kasten (2006) should read 65 Tmol SO 4 2yr − 1 , as it was taken directly from Canfield et al. (2005). In the Canfield et al. (2005) summary, sulfate reduction rates were taken from 35 S-radiotracer experiments on marine sediments derived from the literature. ...
... Rates were binned into regions (salt marshes, mangroves, etc.) and water depths, averaged, and then extrapolated to the global ocean based on the areas represented by these different regions. The global number of Canfield et al. (2005) and Jørgensen and Kasten (2006) included salt marshes, mangroves, seagrasses, macroalgae and coral reefs. The number by Bowles et al. (2014) did not, and the two global estimates are therefore not directly comparable. ...
... In this study, we aimed to enrich thermophilic UAH-degrading microorganisms in connection to the reduction of sulfate, one of the most abundant terminal electron acceptors in anoxic marine sediments, from GB sediment (Thamdrup, 2000; Frontiers in Microbiology 14 frontiersin.org Jørgensen and Kasten, 2006;Bowles et al., 2014). Previous cultivation efforts using GB sediment revealed UAH oxidation in mesophilic aerobic bacteria degrading naphthalene and phenanthrene (Bazylinski et al., 1989;Goetz and Jannasch, 1993), and anaerobic degradation of benzene by Desulfatiglans strains SB-21 and SB-30 at 28-30°C (Phelps et al., 1998). ...
Unsubstituted aromatic hydrocarbons (UAHs) are recalcitrant molecules abundant in crude oil, which is accumulated in subsurface reservoirs and occasionally enters the marine environment through natural seepage or human-caused spillage. The challenging anaerobic degradation of UAHs by microorganisms, in particular under thermophilic conditions, is poorly understood. Here, we established benzene- and naphthalene-degrading cultures under sulfate-reducing conditions at 50°C and 70°C from Guaymas Basin sediments. We investigated the microorganisms in the enrichment cultures and their potential for UAH oxidation through short-read metagenome sequencing and analysis. Dependent on the combination of UAH and temperature, different microorganisms became enriched. A Thermoplasmatota archaeon was abundant in the benzene-degrading culture at 50°C, but catabolic pathways remained elusive, because the archaeon lacked most known genes for benzene degradation. Two novel species of Desulfatiglandales bacteria were strongly enriched in the benzene-degrading culture at 70°C and in the naphthalene-degrading culture at 50°C. Both bacteria encode almost complete pathways for UAH degradation and for downstream degradation. They likely activate benzene via methylation, and naphthalene via direct carboxylation, respectively. The two species constitute the first thermophilic UAH degraders of the Desulfatiglandales. In the naphthalene-degrading culture incubated at 70°C, a Dehalococcoidia bacterium became enriched, which encoded a partial pathway for UAH degradation. Comparison of enriched bacteria with related genomes from environmental samples indicated that pathways for benzene degradation are widely distributed, while thermophily and capacity for naphthalene activation are rare. Our study highlights the capacities of uncultured thermophilic microbes for UAH degradation in petroleum reservoirs and in contaminated environments.
... In anoxic sediments, the carbon cycle is tightly coupled to sulfur/methane cycles (Jørgensen and Kasten 2006). The present dataset and model can be used to understand the impact of flood deposition on these coupled cycles. ...
At the land-sea interface, the benthic carbon cycle is strongly influenced by the export of terrigenous particulate material across the river-ocean continuum. Episodic flood events delivering massive sedimentary materials can occur, but their short-term impact on carbon cycling is poorly understood. In this paper, we use a coupled data-model approach to estimate the temporal variations of sediment-water fluxes, biogeochemical pathways and their reaction rates during these abrupt phenomena. We studied one episodic depositional event in the vicinity of the Rhône River mouth (NW Mediterranean Sea) during the fall-winter of 2021–2022. The distribution of dissolved inorganic carbon (DIC), sulfate (SO42−) and methane (CH4) were measured in sediment porewater collected every 2 weeks before and after the deposition of a 25 cm sediment layer during the main winter flood event. Significant changes in the distribution of DIC, SO42− and CH4, concentrations were observed in the sediment porewaters. The use of an early diagenetic model (FESDIA) to calculate biogeochemical reaction rates and fluxes revealed that this type of flooding event can increase the total organic carbon mineralization rate in the sediment by 75 % a few days after deposition, essentially by increasing the sulfate reduction contribution to total mineralization relative to non-flood depositional period. It predicts a short-term decrease of the DIC flux out of the sediment from 100 to 55 mmol m−2 d−1 after the deposition of the new sediment layer with a longer-term increase by 4 %, therefore implying an initial internal storage of DIC in the newly deposited layer and a slow release over relaxation of the system. Furthermore, examination of the stoichiometric ratios of DIC and SO42− as well as model output over this five-months window shows a decoupling between the two modes of sulfate reduction following the deposition – organoclastic sulfate reduction (OSR) intensified in the newly deposited layer below the sediment surface, whereas anaerobic oxidation of methane (AOM) intensified at depth below the former buried surface. This depth-wise bifurcation of both pathways of sulfate reduction in the sediment column is clearly related to the deepening of the sulfate-methane transition zone (SMTZ) by 25 cm after the flood deposition. Our findings highlight the significance of short-term transient biogeochemical processes at the seafloor and provide new insights on the benthic carbon cycle in the coastal ocean.
