Microbial processes in marine sediments drive changes in redox conditions, ultimately controlling the cycling of elements between the dissolved and solid phases. The microbial community driving these cycles depends on trace metals, but it can also be inhibited at elevated metal concentrations. During diagenesis, many trace elements are released from iron (Fe) and manganese (Mn) (oxyhydr)oxides, potentially affecting microbial metabolisms. Here we present results from geochemical and microbiological analyses of samples collected during R/V Polarstern Expedition PS119 to the East Scotia Ridge. The sediments are dominantly diatomaceous ooze with high contents of reactive Fe and Mn (oxyhydr)oxides and increased trace metal contents from nearby hydrothermal vents. Two multi-corer cores were sampled immediately after collection at five specific sediment depths (three splits each), sealed anaerobically in incubation bags, and analyzed in 4-month intervals post collection for major, minor, and trace metals and 16S rRNA gene sequencing. By isolating the sediment from overlying seawater during the incubation process, we simulated the in situ diagenetic processes of Fe and Mn oxide reduction. Our data show that Mn and trace metals, especially Mo, Ni, Tl, and Cu, are mobilized during early diagenesis. Analysis of 16S rRNA genes revealed shifts in the microbial community from Nitrososphaera and Nanoarchaeia to Bacteroidia and Bacilli alongside a marked decrease in richness, Pielou's evenness, and Shannon alpha diversity during the eight-month incubations. We statistically correlate the microbial community shift with the changes in porewater trace metal concentrations, revealing that Mn, Co, Ag, and Tl are driving the microbial compositions in these samples. In this organic matter limited but Fe and Mn (oxyhydr)oxide rich system, we simulate deeper diagenesis to peer into the role of changing Fe, Mn, and trace metal cycles and highlight the role of Fe and Mn (oxyhdyr)oxides as shuttles for trace metals to the deep biosphere. By identifying key metals that are diagenetically cycled and affect the in situ microbial community, we reveal feedbacks between metals and microbial communities that play important roles in biogeochemical cycles on Earth, provide insight into the origin and potential evolution of metabolic pathways in the deep biosphere, and offer clues that may aid in our understanding of Earth's history and potentially beyond.

We investigated sediment core records from the Cascadia Margin (Ocean Drilling Program Sites 1249 and 1252 at Hydrate Ridge; Integrated Ocean Drilling Program Site U1325 offshore Vancouver Island) using a Zr/Rb heavy mineral proxy from X-ray fluorescence (XRF) core scanning to identify intervals of primary detrital magnetic susceptibility (kappa) and predict intervals where diagenesis caused magnetite dissolution by hydrogen sulfide. We also measured total sulfur (TS) content, grain size distributions, total organic carbon (TOC) content, and the magnetic mineral assemblage to further constrain the role of diagenesis on kappa. Understanding how kappa can be used to better characterize the varied effects of detrital and diagenetic signals in marine settings is important for understanding biogeochemical cycling and records of paleoenvironmental change. The upper 100 m of slope basin Site 1252 contains multiple intervals (> 90 m total) of decreased kappa correlated with elevated TS content, consistent with dissolution of magnetite and precipitation of pyrite, iron monosulfides, and/or elemental sulfur. Similarly at the other slope basin site, Site U1325, kappa is lower and TS is elevated in the interval between 24 and 51 mbsf, due to sulfide formation. At both slope basin sites, these low kappa intervals correspond with high TOC, suggesting the possibility that organoclastic sulfate reduction (OSR) is likely a major driver of diagenetic alteration of kappa at these sites. High TS:TOC ratios at Site U1325 suggests anaerobic oxidation of methane (AOM) during sulfate-methane transition zone (SMTZ) migration may have contributed to alteration of kappa. In contrast, within the upper 90 m of Site 1249, a methane seep site at the summit of Hydrate Ridge, kappa is almost entirely altered by diagenetic processes, with much of the low kappa explained by a high degree of iron sulfide formation, while some intervals are affected by precipitation of magnetic iron sulfides that maintain or even increase kappa. The presence of abundant methane seepage and gas hydrate as well as chemosynthetic seafloor fauna at this site, suggests that sulfide is released to the water column and AOM, rather than OSR, drives diagenetic alteration of kappa at this site. Overall, the slope basin sites show episodic variation of kappa that is influenced by TOC content, likely driven by changes in marine primary productivity and sedimentation rate, while the seep site shows consistently altered kappa with lower TS content and no correlation with TOC. Methane seep environments likely experience loss of hydrogen sulfide to the water column and oxidation of hydrogen sulfide by seafloor seep fauna, which limits the amount of solid phase sulfur (pyrite, iron monosulfides, elemental sulfur) that can be precipitated within the sediments. In contrast, the migration of a buried SMTZ at slope basin sites results in enhanced sulfur precipitation within the sediments. This integrated magnetic and geochemical approach reveals the diagenetic production pathway and residence time of sulfide with the sediment column ultimately controls the style and degree of

Despite the growing recognition of in-situ silicate alteration (dissolution and formation) in marine sediments, its global significance and controlling factors are still poorly understood. By compiling information from scientific ocean drilling programs and applying numerical modelling, we aim to 1) provide constraints on the environmental parameters of silicate dissolution in marine sediments, 2) identify silicate phases responsible for the hyper porewater alkalinity (>56 meq/L) commonly observed from productive continental margin sediments, and 3) investigate the interplay between silicate dissolution, clay formation, and carbonate authigenesis as well as their effect on marine carbon cycling. Through numerical modelling, we show that alkaline conditions resulting from combined iron and sulfate reduction favour formation of smectite group clay minerals, while the acidic conditions arising from organic matter fermentation promote dissolution of saponite and several mica-group silicates. This result resonates with previous observations of reverse weathering (i.e. clay formation) in shallow iron- and/or sulfate reducing sediments, while silicate weathering (i.e. silicate dissolution) has been reported deeper in methanogenic sediment columns. Using pore fluid composition data, we show that marine silicate weathering is primarily driven by dissolution of K- and Mg-containing silicate minerals. Especially, higher-than-seawater Mg concentrations were observed in almost all sites that have hyper alkalinity and the weathering process contribute more than one-third of the measured alkalinity. No apparent difference was observed for porewater Ca concentrations when comparing sites with and without hyper alkalinity, which hints for complicated feedbacks through authigenic carbonate formation. The global dataset analysed revealed that sites with high alkalinity correspond to locations with a medium distance from shore. While such a pattern cannot be easily explained by supply of organic matter nor by silicate phases alone, we interpret this observation to be the result of sediment maturity. Our inference is further strengthened by observations of higher alkalinity at sites with greater thermal history within the methanogenesis zone, a factor that measures how much time and temperature a sediment parcel has experienced under subsurface conditions. Collectively, we conclude that substantial dissolution of marine silicate phases occurs when the sediments have been transported some distance offshore and buried below sulfate reduction zone for a prolonged period and/or experience sufficiently high geothermal heating.We simulated alteration of silicate and carbonate phases within a complete early diagenetic sequence to understand how dissolved carbon is converted to alkalinity under variable organic matter degradation rates. We show that authigenic carbonate formation is effective in control downcore DIC/alkalinity level with a moderate organic matter degradation rate. Only a very limited amount of carbonic acid produced by reverse weathering can diffuse away from sediments. Under a scenario with fast organic matter fermentation, dissolution of silicates (such as phlogopite) becomes the only buffer for porewater pH that converts most of the dissolved inorganic carbon produced from organic matter fermentation to carbonate alkalinity. Consequently, marine weathering sustained by silicate mineral dissolution increases the alkalinity production by as much as 16%, with most of the alkalinity leaking to surface oxic sediments instead of being sequestrated as carbonate minerals.

Hadal trenches (>6000 m water depth) have been revealed as hotspots of organic carbon burial and microbial respiration in the ultradeep ocean environment. However, understanding of the anaerobic metabolic pathways and rates, as well as carbon-silicon cycling, in the hadal trench sediments remains very fragmentary because of the shallow nature of traditional coring penetration. Using materials collected during International Ocean Discovery Program (IODP) Expedition 386 in the Japan Trench and a reaction-transport model, we provide a regional quantitative assessment of organic carbon turnover by sulfate reduction, anaerobic oxidation of methane, and methanogenesis in addition to silicate weathering and authigenic carbonate and clay formation. We show that rapid burial of relatively labile organic carbon resulting from subduction earthquakes triggers organic carbon and methane turnover at rates comparable to those in continental margin sediments, thereby stimulating active silicate weathering and authigenic carbonate formation. Despite vigorous organic carbon turnover, the vast majority of organic carbon is buried, implying an important role of tectonic-associated events in translocating and preserving organic carbon in the deepest part of the ocean. These results quantitatively demonstrate, for the first time, active coupled carbon-silicon cycling in hadal trench sediments and have implications for the subduction zone carbon budget.

In the past decade, thousands of previously unknown methane seeps have been identified on continental margins around the world. As we have come to appreciate methane seep habitats to be abundant components of marine ecosystems, we have also realized they are highly dynamic in nature. With a focus on discrete depth ranges across the Cascadia Margin, we work to further unravel the drivers of seep-associated microbial community structure. We found highly heterogenous environments, with depth as a deterministic factor in community structure. This was associated with multiple variables that covaried with depth, including surface production, prevailing oxygen minimum zones (OMZs), and geologic and hydrographic context. Development of megafaunal seep communities appeared limited in shallow depth zones (similar to 200 m). However, this effect did not extend to the structure or function of microbial communities. Siboglinid tubeworms were restricted to water depths > 1000 m, and we posit this deep distribution is driven by the prevailing OMZ limiting dispersal. Microbial community composition and distribution covaried most significantly with depth, but variables including oxygen concentration, habitat type, and organic matter, as well as iron and methane concentration, also explained the distribution of the microbial seep taxa. While members of the core seep microbiome were seen across sites, there was a high abundance of microbial taxa not previously considered within the seep microbiome as well. Our work highlights the multifaceted aspects that drive community composition beyond localized methane flux and depth, where environmental diversity adds to margin biodiversity in seep systems.

Volcanic ash alteration is deemed a crucial diagenetic process that can impact element budgets in the ocean. In this study, we aim to evaluate the role of volcanic ash alteration in controlling sedimentary lithium (Li) cycling through Li isotope analyses of pore fluids and sequentially leached fractions of bulk sediments (i.e., exchangeable Li, carbonate-bound Li, and silicate-bound Li) of three sites drilled along a transect from the incoming to the upper plates of the Hikurangi margin, New Zealand, during IODP Expedition 375. The downcore trends of Li concentration and isotopes in the Quaternary hemipelagic sediments of the three study sites reflect multiple concurrent diagenetic processes, including Li desorption via ion exchange with ammonium, volcanic ash dissolution, and authigenic clay formation. Reaction-transport modeling results yield higher rates of Li release by ion exchange and volcanic ash dissolution than those of Li consumption by authigenic clay formation at both Sites U1518 and U1520, leading to a net increase of Li concentration up to 252 mu M and lower delta Li-7 (10.4-23.5 parts per thousand) than seawater. At Site U1519, authigenic clay formation exerts a larger role in regulating sedimentary Li budget than ion exchange and ash dissolution. Notably, the drastic increase in Li concentrations and the decrease in delta Li-7 values at the boundary of Units III/IV of Site U1520 are attributed to the extensive autochthonous volcanic ash alteration, rather than Li transport by fluid flow. Similar Li geochemical profiles have also been observed in other ash-bearing sediments worldwide, e.g., Site 918 drilled in the Irminger Basin, southeast Greenland, Site 1040 in the Costa Rica subduction zone, and Site 808 in the Nankai Trough. Additional reaction-transport simulations of Li data show that volcanic ash dissolution rates outcompete clay authigenesis rates at sites that have experienced rapid sediment deposition (0.05-0.14 cm yr(-1)); in contrast, clay authigenesis dominated the pore-fluid Li budget at Site 919 where a low sedimentation rate (7.1 x 10(-3) cm yr(-1)) was estimated. Based on these observations, we surmise that the rapid depositional system with sufficient volcanic ash supply can act as a source of isotopically light Li, in contrast to the general perception that volcanic ash alteration represents a major sink for oceanic Li. This previously unrecognized Li source may be important in the marine Li cycle.

Alteration of volcanogenic aluminosilicates (VAs) in marine sediments is recognized as critical in regulating geochemical cycles and sustaining the oceanic deep biosphere, but rates of VA alteration and its associated authigenic mineral formation are not commonly reported. Here we present results on analyses of sediments and pore water recovered from the upper 150 mbsf of four sites drilled on the northern Hikurangi margin during IODP Expeditions 372 and 375. Petrographic analyses show that volcanogenic materials (glass shards, feldspar, volcanic lithoclasts) constitute important components (15-45 wt%) of the hemipelagic mud, and reveal ongoing glass alteration with accompanying authigenic phase formation. A reaction-transport model constrained by pore water Sr, Sr-87/Sr-86, Ca, Mg, and Si was applied to simulate VA diagenetic reactions. Our model results yield VA alteration rates of 0.047-0.64 mmol Sr m(-2) yr(-1), with substantially higher values at Sites U1517 and U1520 that experienced rapid sediment emplacement. In addition, our simulations show that >99% of the dissolved Si generated by VA alteration is fixed in silica cement and authigenic clay, and that similar to 50% of Ca incorporated in the authigenic carbonate is supplied by VA alteration. First-order estimates suggest that, in addition to authigenic carbonate precipitation, authigenic clay formation may represent an important sink for dissolved Mg. This study quantitatively examines the linkage between VA alteration and formation of authigenic phases, highlights its role in subsurface geochemical cycles, and indicates that slope instability may play an important role in promoting VA diagenesis.

Marine sediment is a critical reservoir for global Si cycle since it receives biogenic and lithogenic Si phases through ocean.Moreover, the subsurface Si phase alterations have been shown that are linked to the C cycle of marine sediment and ocean through producing or sequestering CO 2 over geological time.In order to assess the impact of early Si alterations on the C cycle, we study Si isotopic signatures from sediment and porewater retrieved from Ulleung Basin, offshore Korea.UBGH2-1_1 sampled the upper 217 meters below seafloor (mbsf) and has a maximum of porewater alkalinity of 128 mM; UBGH 2-6 reached 227 mbsf with the highest alkalinity of 70 mM.The various Si phases (biogenic silica, reactive silicate and neoformed Si phase) in the sediments are separated through a sequential leaching protocol with Si isotopic signatures analyzed from the leachate and mineral composition determined from the residual materials.We identify three different diagenetic zones from both cores based on geochemical results.In the shallowest first zone, d 30 Si of porewater (d 30 Si porewater ; 0.2 to 0.3 ‰ for 2-1_1 and 0.2 to 0.4 ‰ for 2-6) and d 30 Si of neoformed Si phase (d 30 Si neoformed ; -2.4 to -0.9 ‰ for 2-1_1 and -0.8 to -0.2 ‰ for 2-6) increase with decreases in dissolved Si, K and Mg concentrations.The following second zone is the interval where the porewater alkalinity increase sharply.The decreases of d 30 Si porewater (0.4 to -0.6 ‰ for 2-1_1 and 0.4 to -0.1 ‰ for 2-6) and d 30 Si neoformed (-0.9 to -1.5 ‰ for 2-1_1 and -0.2 to -0.6 ‰ for 2-6) are accompanied by the increase of dissolved Si and K concentrations and in the second zone.The deepest third zone features increasing values of d 30 Si porewater (-0.6 to 1.2 ‰ for 2-1_1 and -0.1 to 0.7 ‰ for 2-6) and dissolved Si concentration and decreasing and dissolved Si and K concentrations.We hypothesized that phase neoformation, silicate (d 30 Si values: -0.8 ‰ for 2-1_1 and 2-6) dissolution and biogenic silica (d 30 Si values: 1.5 ‰ for 2-1_1 and 1.6 ‰ for 2-6) dissolution are the main processes in the first, second and three zones, respectively.

The main goal of CAGE 15-­2 cruise was to study the gas hydrate system and methane emissions off western Svalbard and in Storfjordrenna. We addressed this through a comprehensive scientific program comprising dives with the MISO-­‐Tow Cam adapted to the multicorer frame from UiT-­‐NPI (TowCam/Multicorer, TCM), methane measurements in sediments and water column, sediment coring (multicorer + gravitycorer), water column and sediment biogeochemistry, microbiology, micropaleontology, macrobiology, and bathymetric mapping. In addition, during the ecosounder and TCM surveys we collected data for selecting the locations for the CAGE observatories to be deployed during the cruise. The areas investigated were: W Prins Karls Forland (two sites at ca 90 m and 240 m water depth),An area located at the coordinate 78N 08E called “site 7808” (ca 90 m water depth; marker CAGE 882),Vestnesa Ridge (ca 1200 m water depth; markers CAGE 888 and 895),Storfjordrenna (two sites at ca 350, benthic station SR1, and 390 m water depth, Pingos site; marker CAGE 933),Craters area (ca 350 m water depth). We planned the following activities during the CAGE 15-­2 cruise: EM 300 Simrad swath bathymetry mapping to identify seabed morphologyMapping of flare distributionsCTD stations at different water depths and in different areas for measurements ofocean water masses characteristics, andwater sampling for water/gas chemistry and microbiology investigations across methane seeps.TCM surveys (video-­‐camera) to image seabed fluid flow expressions, sites of bacteria mats and gas bubbles. These results were used to define sampling stations and collect data for the future deployment of CAGE observatories (cruise CAGE15-­‐3)Repeated deployments with TCM to sample surficial and shallow sediments with respect to microbiology, geochemistry, biogeochemistry, and micropalentology.Gravity corer for studying sediment biogeochemistry, biomarkers, microbiology, and foraminifera.Van Veen grabs sampling for studying macrofauna.Scrape sampling to collect fauna communities and possible carbonate blocks. The cruise may be known as: CAGE15_2

We use geochemical and petrographic data from anoxic sequences of the Nicobar Fan to document extensive marine silicate weathering (MSiW) in the input sediment of the Sumatra subduction zone and the conditions that result in authigenic minerals originating from this reaction: precipitation of authigenic carbonate—which sequesters carbon—and formation of authigenic clay—which releases CO2. Increase in 87Sr/86Sr in pore fluids from International Ocean Discovery Program Expedition 362 (Site U1480 to 0.71376 and Site U1481 to 0.71296) reveals a radiogenic strontium contribution from alteration of the Himalayan continental sediment that dominates the Nicobar Fan. Peaks in the dissolved strontium isotope data coincide with zones of methane presence, consistent with MSiW reactions driven by CO2 generation during methanogenesis. Later‐stage fan sequences from 24 to 400 mbsf (meters below seafloor) contain only minor carbonate with 87Sr/86Sr ratios that deviate only slightly from the co‐eval seawater values (0.70920–0.70930); geochemical data in this zone point to a contribution of authigenic clay formation. In contrast, microscopy and elemental mapping of the carbonate‐cemented zones in the earliest fan deposits (>780 mbsf) show replacement of feldspars and dense minerals by carbonate, which ranges in volume from a few percent of the grain to near total grain obliteration. This deeper authigenic carbonate is significantly enriched in radiogenic 87Sr (0.71136–0.71328). Thus, MSiW leads to distinct products, likely in response to a weathering‐derived supply of silica in the younger setting versus calcium enrichment via diffusion from oceanic basement in the older sequence.

During International Ocean Discovery Program (IODP) Expedition 385, sediments from Guaymas Basin were sampled with the goal of understanding the role of sill emplacement and fluid flow, as well as its associated temperature and fluid circulation regimes, on subsurface carbon mobilization and preservation of organic-rich sediments.We report on the concentration and isotopic composition of dissolved inorganic carbon (DIC) in pore fluids from Sites U1545 and U1546, which were drilled in the northern basin; Sites U1547 and U1548, which sampled an active hydrothermal vent site; Sites U1549 and U1552, which targeted cold seeps; and Site U1550, which was drilled in the axial trough.There is large variability in the DIC concentrations.The highest values were recorded at Sites U1549, U1550 (up to ~75 mM), and U1552 (~169 mM).The isotopic composition of the DIC (δ 13 C DIC ) ranges -23.50‰ to 22.64‰ referenced to Vienna Peedee belemnite.At all locations outside Ringvent Site U1547, depletions in δ 13 C DIC values typically coincide with the sulfate-methane transition zone (SMTZ).Enrichment in δ 13 C DIC above seawater values, indicative of ongoing microbial methanogenesis, was recorded below the SMTZ at all locations except Ringvent.

Abstract The response of Arctic Ocean biogeochemistry to subsurface flow driven by permafrost thaw is poorly understood. We present dissolved chloride and water isotopic data from the Chukchi Sea Shelf sediments that reveal the presence of a meteoric subsurface flow enriched in cations with a radiogenic Sr fingerprint. This subsurface fluid is also enriched in dissolved inorganic carbon and methane that bear isotopic compositions indicative of a carbon reservoir modified by reactions in a closed system. Such fluid characteristics are in stark contrast with those from other sites in the Chukchi Sea where the pore water composition shows no sign of meteoric input, but reflect typical biogeochemical reactions associated with early diagenetic sequences in marine sediment. The most likely source of the observed subsurface flow at the Chukchi Sea Shelf is from the degradation of permafrost that had extended to the shelf region during the Last Glacial Maximum. Our data suggest that the permafrost‐driven subsurface flow most likely took place during the 2–3°C warming in the Early Holocene Thermal Maximum. This time scale is supported by numerical simulation of pore water profiles, which indicate that a minimum of several thousand years must have passed since the cessation of the subsurface methane‐bearing fluid flow.

Archaea mediating anaerobic methane oxidation are key in preventing methane produced in marine sediments from reaching the hydrosphere; however, a complete understanding of how microbial communities in natural settings respond to changes in the flux of methane remains largely uncharacterized. We investigate microbial communities in gas hydrate-bearing seafloor mounds at Storfjordrenna, offshore Svalbard in the high Arctic, where we identify distinct methane concentration profiles that include steady-state, recently-increasing subsurface diffusive flux, and active gas seepage. Populations of anaerobic methanotrophs and sulfate-reducing bacteria were highest at the seep site, while decreased community diversity was associated with a recent increase in methane influx. Despite high methane fluxes and methanotroph doubling times estimated at 5-9 months, microbial community responses were largely synchronous with the advancement of methane into shallower sediment horizons. Together, these provide a framework for interpreting subseafloor microbial responses to methane escape in a warming Arctic Ocean.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

We report the trace element composition of solid-phase and pore water samples recovered from sediments above the framework wedge of the upper plate of the Costa Rica subduction zone at Sites U1378 and U1379 drilled during Expedition 334 of the Integrated Ocean Drilling Program. This expedition was part of the Costa Rica Seismogenesis Project (CRISP), which sampled sediments, fluids, and crustal rocks to characterize the chemical and physical properties of the eroding material in the upper plate before subduction because these sediment properties influence the seismogenic behavior of the plate interface. Molybdenum (Mo), vanadium (V), uranium (U), arsenic (As), nickel (Ni), and rubidium (Rb) concentrations were measured on pore fluids and sediments using an inductively coupled plasma–mass spectrometer at the University of California, Riverside (USA). At Site U1378, pore water concentrations of the redox-sensitive elements Mo, V, and U, as well as As, show maximum values at or just above the contact between Lithostratigraphic Units I and II, whereas at Site U1379, these trace elements show distinct maxima in Unit II. At Site U1379, a sharp decrease in Unit III in solid-phase Mo, U, and Ni also occurs. In these cases, the concentration trends indicate the release of elements into the pore water in sediments dominated by clay and silty clay. The overall analyzed trace metal content in the sediments point to terrigenous material as the main input source.