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

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.

Compared to other ocean basins there are few reported Recent methane seep communities from the Indian Ocean, with records from offshore Indonesia and Pakistan, and, more recently the east coast of India, in the Krishna-Godavari and Mannar Basins in bathyal water depths. Also from the former area, Upper Pleistocene aged fossil methane seep assemblages have been recovered from sediment cores. Here we describe systematically bivalves, gastropods and scaphopods from a methane seep assemblage penetrated by two sediment cores, drilled in 1045 m and 1050 m water depth, at horizons dated to between 40 and 52 kyrBP. The fossil molluscs comprise 29 taxa: 15 gastropods, 12 bivalves and two scaphopods. Of these, nine are new species: six gastropods (Paralepetopsis bathyalus Hoffman & Little sp. nov., Mesopelex godavariensis Hoffman & Little sp. nov., Anatoma sahlingi Hoffman & Little sp. nov., Cirsonella aperta Hoffman & Little sp. nov., Dikoleps? magnarota Hoffman & Little sp. nov., and Alvania axistriata Hoffman & Little sp. nov.) and three bivalves (Ledella favus Hoffman & Little sp. nov., Yoldiella umbostriata Hoffman & Little sp. nov., and Vesicomya prashadi Hoffman & Little sp. nov.). Six of the molluscan taxa likely had chemosymbionts: (Acharax sp., Gigantidas cf. platifrons, Conchocele sp., Pliocardia cf. solidissima, Callogonia cf. leeana, and Archivesica cf. kawamurai), representing 21% of the diversity in the seep assemblage. Apart from Acharax sp., all these putative chemosymbiotic taxa were likely obligate to seeps, as was probably the case for Paralepetopsis bathyalus Hoffman & Little sp. nov. and Anatoma sahlingi Hoffman & Little sp. nov. The other bivalve, gastropod and scaphopod species in the assemblage have living relatives common in bathyal habitats and can thus be considered as facultative or ‘background’ fauna. The fossil seep assemblage shares some taxa with recent seep communities in the east coast of India and elsewhere in the Indian Ocean, although additional systematic work is needed on the living taxa for a full comparison to be made.

The overall aim of the CAGE 13-7 cruise was to study the gas release activity from gas hydrated sub-seabed environments at the continental margin off Svalbard towards the Norwegian-Greenland Sea and Arctic Ocean. Acoustic measurements in the water column, water sampling for gas analyses, seismic profiling, bathymetry mapping, and sediment coring allowed to reach this aim. Generally, the water column above gas flares may be rich in methane but methanotrophic microorganisms might hinder an escape of methane from the water to the atmosphere. At the Molloy transform and the Vestnesa ridge we collected seismic data and sediment cores for sampling gas hydrates. We also took sediment cores from a submarine slide complex at the continental margin of NW Svalbard. The age of this slide is of interest because it sits on gas hydrated sediments as indicated by a BSR. The timing of the slope failure is unknown. At the massive Hinlopen slide area we surveyed the eastern sidewall, the toe of the slope and a block within the major slide debris flow area to understand better a potential coupling between slide processes and gas hydrates. Seismic profiles show bottom simulating reflectors that are indicative for gas hydrate underneath the southeastern headwall of this slide complex. The cruise may be known as: CAGE13_JM

CAGE 14-5 cruise allowed to study the gas release from gas hydrated sub-seabed environments at the continental margin off NW and N-Svalbard and the transport and distribution of methane within the water column. We carried out acoustic profiling (18, 38 and 120 kHz) in the water column, CTD water sampling for gas analyses, seismic profiling (mini GI guns), bathymetry mapping (EM300), and sediment gravity coring (3m corer). Though water above gas flares may be enriched in methane, methanotrophic microbescan reduce the methane concentrations and thus the amount of methane that may escape from the seabed to the ocean, one of the topics investigated during this cruise The cruise may be known as: CAGE14_5_JM

All depth and thickness estimates in this section are approximate and assume a seismic velocity of 1500 m/s. BathymetryHoles M0094A and M0094B lie in the deepest part of the basin at 7469 m.The acquired bathymetry data do not capture the entire basin but are instead limited to the length of the subbottom profile.The western side of the basin is bound by a series of north-northwest-trending topographic terraces that cause topography to step up to the west, with a maximum slope gradient of 12%-15% at the steepest points.To the east, the topography has a lower slope gradient, rising gently at 6%-8%.Basin width, defined as the extent of the flat bottom basin between sharp topographic boundaries, is less than 1700 m for most of the basin, although it broadens toward the northern end of the profile line.

On continental margins, high saturation gas hydrate systems (>60% pore volume) are common in canyon and channel environments within the gas hydrate stability zone, where reservoirs are dominated by coarse-grained, high porosity sand deposits. Recent studies, including the results presented here, suggest that rapidly deposited, silt-dominated channel-levee environments can also host high saturation gas hydrate accumulations. Here we present several sedimentological data sets, including sediment composition, biostratigraphic age from calcareous nannofossils, grain size, total organic carbon (TOC), C/N elemental ratio, delta C-13-TOC CaCO3, total sulfur (TS), and delta S-34-TS from sediments collected with pressure cores from a gas hydrate rich, turbidite channel-levee system in the Gulf of Mexico during the 2017 UT-GOM2-1 Hydrate Pressure Coring Expedition. Our results indicate the reservoir is composed of three main lithofacies, which have distinct sediment grain size distributions (type A-silty clay to clayey silt, type B-clayey silt, and type C-sandy silt to silty sand) that are characteristic of variable turbidity current energy regimes within a Pleistocene (< 0.91 Ma) channel-levee environment. We document that the TOC in the sediments of the reservoir is terrestrial in origin and contained within the fine fraction of each lithofacies, while the CaCO3 fraction is composed of primarily reworked grains, including Cretaceous calcareous nannofossils, and part of the detrital load. The lack of biogenic grains within the finest grained sediment intervals throughout the reservoir suggests interevent hemipelagic sediments are not preserved, resulting in a reservoir sequence of silt dominated, stacked turbidites. We observe two zones of enhanced TS at the top and bottom of the reservoir that correspond with enriched bulk sediment delta S-34, indicating stalled or slowly advancing paleo-sulfate-methane transition zone (SMTZ) positions likely driven by relative decreases in sedimentation rate. Despite these two diagenetic zones, the low abundance of diagenetic precipitates throughout the reservoir allowed the primary porosity to remain largely intact, thus better preserving primary porosity for subsequent pore-filling gas hydrate. In canyon, channel, and levee environments, early diagenesis may be regulated via sedimentation rates, where high rates result in rapid progression through the SMTZ and minimal diagenetic mineralization and low rates result in the stalling of the SMTZ, enhancing diagenetic mineralization. Here, we observed some enhanced pyritization to implicate potential sedimentation rate changes, but not enough to consume primary porosity, resulting in a high saturation gas hydrate reservoir. These results emphasize the important implications of sedimentary processes, sedimentation rates, and early diagenesis on the distribution of gas hydrate in marine sediments along continental margins.

ADVERTISEMENT RETURN TO ARTICLES ASAPPREVHighlightNEXTEnergy Transition and Climate Mitigation Require Increased Effort on Methane Hydrate ResearchMiriam Kastner*Miriam KastnerScripps Institution of Oceanography, La Jolla, California 92093, United States*E-mail: [email protected]More by Miriam Kastner, Mark MyersMark MyersMyenergies, Anchorage, Alaska 99507, United StatesMore by Mark Myers, Carolyn A. KohCarolyn A. KohCenter for Hydrate Research, Colorado School of Mines, Golden, Colorado 80401, United StatesMore by Carolyn A. Kohhttps://orcid.org/0000-0003-3452-4032, George MoridisGeorge MoridisLawrence Berkeley National Laboratory, Berkeley, California 94720, United StatesTexas A&M University, Petroleum Engineering Dept., College Station, Texas, 77840, United StatesMore by George Moridis, Joel E. JohnsonJoel E. JohnsonUniversity of New Hampshire, Durham, New Hampshire 03824, United StatesMore by Joel E. Johnson, and John ThurmondJohn ThurmondHess Corporation, Houston, Texas 77010, United StatesMore by John ThurmondCite this: Energy Fuels 2022, XXXX, XXX, XXX-XXXPublication Date (Web):February 24, 2022Publication History Received3 February 2022Published online24 February 2022https://doi.org/10.1021/acs.energyfuels.2c00338Published 2022 by American Chemical SocietyRIGHTS & PERMISSIONSArticle Views324Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (402 KB) Get e-Alerts Get e-Alerts

Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH4) from sediments. Ebullitive CH4 flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH4 flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH4 emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH4 emissions was greater in lake middles-where methanogens were more abundant-than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH4-cycling microorganisms and syntrophs, were predictive of porewater CH4 concentrations. Results suggest that deeper lake regions, which currently emit less CH4 than shallower edges, could add substantially to CH4 emissions in a warmer Arctic and that CH4 emission predictions may be improved by accounting for spatial variations in sediment microbiota.