The use of nickel (Ni) and its isotope system as biogeochemical tracers of past ocean environments requires a sound understanding of the oceanic mass balance and the sinks that control output fluxes. Recent efforts have focused in particular on quantifying and understanding the size and Ni isotope composition of the most complicated and largest sink of Ni from the dissolved oceanic pool, the output to oxic Mn-rich sediments. The precise processes controlling Ni and its isotopes during early diagenesis in oxic sediments are not yet fully understood, but could impact estimates of the net oxic sink used in oceanic mass balance calculations. To address this issue, we present Ni concentration and isotope data from fully oxic Mn-rich sediments and corresponding porewater samples from 3 stations in the Equatorial North Pacific, south of Hawai'i. As in other abyssal Mn-rich sediments, Ni is well correlated with Mn in the solid phase, suggesting that Mn oxides are the dominant vector by which Ni is supplied to these sediments. Authigenic Ni isotope compositions in the solid phase are isotopically lighter than global deep seawater Ni (similar to 1.33 parts per thousand) and range from 0.52 to 1.06 parts per thousand, within the range of other abyssal Mn-rich sediments (0.26 to 1.08 parts per thousand). At all three stations, the porewater results indicate the presence of a reactive Ni pool that is mobilised into the aqueous phase near the top of the cores. Nickel concentrations in the porewaters are significantly higher at the core top (30-63 nM) than in seawater (similar to 8 nM), decrease to seawater concentrations downcore, and correlate with porewater DOC concentrations. Additionally, porewater Ni isotopes are heaviest (similar to 1.8 parts per thousand) near the sediment-water interface, where DOC levels are highest, and decrease monotonically to values that are close to, but slightly lower than, the deep ocean Ni isotope composition (similar to 1.3 parts per thousand) further down in the cores. The relationship between Ni concentration, isotopes and DOC in the porewater suggests that Ni is remobilised into porewater from Mn oxides due to lowering of pH as a result of the remineralisation of organic matter. The heavy isotope composition of porewater Ni is likely controlled by isotope fractionation between residual solid Mn oxide Ni (light) and organically-complexed heavy aqueous Ni. This isotopically heavy pore fluid Ni leaves the sediment via a diffusive benthic flux. Despite this reactive zone very close to the sediment-water interface, these diagenetic processes barely impact sediment geochemistry, suggesting that the buried sink of Ni to Mn oxide-rich sediments is accessible via analysis of solid sediment in the upper few 10 s of cm at such sites.

Since the discovery of cable bacteria more than a decade ago, these multicellular, filamentous sulfur-oxidizing bacteria have been found in a range of sedimentary environments. However, their abundance, diversity, and activity in continental margin sediments overlain by oxygen-deficient waters at water depths of > 100 m remain poorly known. Here we address this by studying five basins along the coasts of California and Mexico. All sediments are organic carbon rich (2.5 wt %-7.5 wt %) and characterized by active iron and sulfur cycling. Nitrate is present in the bottom water at all sites. Results of fluorescence in situ hybridization (FISH) indicate a low areal abundance of cable bacteria (0.2 to 19 m cm-2) in sediments of the hypoxic San Clemente, Catalina, and San Pedro basins and the anoxic San Blas basin. In the anoxic Soledad basin, in contrast, we found abundant cable bacteria near the sediment surface (129 m cm-2). DNA amplicon sequencing detected cable bacteria reads in sediments of the hypoxic San Pedro basin and the anoxic Soledad and San Blas basins. Phylogenetic analysis indicated that the diversity of the amplicon sequence variants (ASVs) was spread across the Candidatus Electrothrix lineage, including multiple ASVs closely related to Electrothrix gigas, a recently discovered species of giant cable bacteria. Additionally, multiple sequences retrieved from the Soledad and San Blas basins revealed affiliation with a clade sister to Electrothrix, hypothesized as a novel genus, suggesting possible relic or novel adaptations of cable bacteria to these anoxic and nitrogenous environments. The areal abundance of cable bacteria was negatively related to sediment Fe / S ratios, suggesting a control by sulfide availability. However, free sulfide in the porewater was only detected at the anoxic Soledad site. Micro-profiling of pH and electric potential points toward a lack of cable bacteria activity at the time of sampling, possibly due to a limitation by a suitable electron donor and/or acceptor. Periodically enhanced organic matter input and associated sulfate reduction and/or inflows of oxic water could alleviate the deficiency, creating the observed niche for diverse cable bacteria.

Trace elements and isotopes (TEIs) are important to marine life and are essential tools for studying ocean processes 1 . Two different frameworks have arisen regarding marine TEI cycling: reversible scavenging favours water-column control on TEI distributions 2–5 , and seafloor boundary exchange emphasizes sedimentary imprints on water-column biogeochemistry 6,7 . These two views lead to disparate interpretations of TEI behaviours 8–10 . Here we use rare earth elements and neodymium isotopes as exemplar tracers of particle scavenging 11 and boundary exchange 6,7,12 . We integrate these data with models of particle cycling and sediment diagenesis to propose a general framework for marine TEI cycling. We show that, for elements with greater affinity for manganese oxide than biogenic particles, scavenging is a net sink throughout the water column, contrary to a common assumption for reversible scavenging 3,13 . In this case, a benthic flux supports increasing elemental concentrations with water depth. This sedimentary source consists of two components: one recycled from elements scavenged by water-column particles, and another newly introduced to the water column through marine silicate weathering inside sediment 8,14,15 . Abyssal oxic diagenesis drives this benthic source, and exerts a strong influence on water-column biogeochemistry through seafloor geometry and bottom-intensified turbulent mixing 16,17 . Our findings affirm the role of authigenic minerals, often overshadowed by biogenic particles, in water-column cycling 18 , and suggest that the abyssal seafloor, often regarded as inactive, is a focus of biogeochemical transformation 19,20 .

Cerium (Ce) stable isotopes, combined with Ce anomalies, serve as potential proxies for reconstructing Earth's past redox conditions. However, the behavior of Ce isotopes and Ce anomalies across different oceanic redox environments remains underexplored. This study presents a Ce anomaly and Ce isotope dataset of marine sediments from a range of modern oceanographic regimes, including anoxic continental margins and oxic Equatorial Pacific environments. By integrating bulk sediment geochemistry, sequential extraction, and X-ray absorption spectroscopy data, we reveal the decoupling between Ce stable isotope values (delta 142Ce) and Ce anomalies (Ce/ Ce*). Margin sediments exhibit negative Ce anomalies (0.48 to 0.96) that display a negative correlation with delta 142Ce (-0.05 to 0.12 %o), which are close to or higher than the upper continental crust value (-0.03 +/- 0.06 %o). This relationship results from the influence of seawater-derived REEs through authigenic phosphates and organic matter, as well as clastic inputs. In contrast, Equatorial Pacific sediments exhibit positive Ce anomalies (1.05 to 1.23) that are positively correlated to their delta 142Ce values (0.08 to 0.16 %o), which exceed the upper crust baseline. This pattern is attributed to Mn(IV)-oxide-driven oxidative adsorption of Ce. Here, we purpose a first-order estimate for the delta 142Ce value in bottom seawater of the Equatorial Pacific (about 0.3 to 0.4 %o). These findings enhance our understanding of marine Ce geochemistry and underscore the importance of integrating Ce anomalies with Ce isotope signatures for paleoceanographic redox reconstructions.

Thallium (Tl) isotopic values (epsilon 205Tl) appear to track changes in marine manganese oxide deposition, with these isotope signatures having been utilized as a proxy for rapid oceanic seafloor (de-)oxygenation events. With a residence time longer than ocean mixing time and the ability to track the deposition of manganese oxides, epsilon 205Tl may effectively record the earliest global transitions in the extent of ocean oxygenation. However, some uncertainty remains for the minor Tl sinks in degree of fractionation from seawater values, if any, with the limited data currently available suggesting at least a 6 epsilon unit range in fractionation from seawater values in low oxygen environments. This study provides Tl data for sediment cores from a range of low-oxygen marine environments. With these data, we identify potential processes that impact the range of Tl isotope variations within the sediments, which are not all due to local Mn oxide cycling. Previous work indicates that euxinic (anoxic and sulfidic water column) conditions and early diagenetic pyrite formed under consistently anoxic sediments record seawater values with no (or not measurable) fractionation during absorption to pyrite. Our new data provide downcore confirmation. Meanwhile, only limited data from 'suboxic' environments (those with low oxygen but likely not permanently anoxic conditions) has been analyzed. Thus, isotopic data for suboxic systems is needed to refine the current mass balance. Several sites off the California, Mexico, and Peru coasts with a range of redox states from oxic to perennially anoxic were selected to allow for a comparison across a range of open ocean bottom water conditions. The locations with oxic sediments tend to document more positive values compared to seawater, as expected due to local manganese oxide incorporation. Sediments from more 'suboxic' (manganous to ferruginous) sites tend to have invariable downcore geochemical signatures that are between marine inputs (-2) and modern seawater (-6) values, indicating a mixing of epsilon 205Tl signatures from different authigenic phases; however, these are not primarily due to the incorporation of Mn oxides as the concentrations are low and uncorrelated. The anoxic sites record Tl isotope compositions near seawater values, confirming that early diagenetically formed pyrite (and precursor minerals) record seawater epsilon 205Tl signatures under permanent anoxia. Importantly, these permanently anoxic localities have minor Mn contents, which suggest no local Mn oxide Tl isotope signatures. Therefore, unlike the anoxic sediments, the 'suboxic' sediments have a Tl isotope value that is slightly offset from seawater without significant Mn oxide deposition, thus suggesting there could be a fractionation for this process. Our observations provide improved constraints on the Tl isotope system, especially on a poorly constrained aspect of the mass balance, which will be important for deep-time applications.

The rubidium (Rb) isotope system has the potential for tracing water-silicate interactions and providing information on the global Rb cycling. However, the Rb isotope compositions of modern seawater and its major inputs and outputs remain poorly understood. Here we measured Rb isotope compositions of seawaters, pelagic clay sediments and porewaters from the western and central equatorial Pacific Ocean. Our results show that the delta Rb-87 of modern seawater is homogeneous (0.13 +/- 0.04 parts per thousand; 2SD, n = 13) and higher than both the local sediments (-0.17 parts per thousand to 0.03 parts per thousand) and the bulk lithosphere (Delta Rb-87(seawater-UCC) = 0.27 parts per thousand). The Rb in pelagic clay sediments is primarily associated with silicates (> 90%) and partially with exchangeable fractions (similar to 4%). The exchangeable fractions display relatively lower delta Rb-87 (-0.07 +/- 0.05 parts per thousand; 2SD, n = 6). Meanwhile, the correlation between K/Rb and delta Rb-87 of bulk sediments, along with investigations on the clay sized particles (delta Rb-87 = -0.06 parts per thousand), represents that lithogenic silicates have relatively low K/Rb and delta Rb-87 close to the UCC while formation of authigenic phillipsite or clays can result in higher bulk K/Rb (up to 930) and delta Rb-87 (up to 0.03 parts per thousand). The delta Rb-87 of both authigenic silicates and absorbed fractions in deep-sea sediments are lower than seawater, which can partially contribute to the removal of isotopically light Rb from seawater. The delta Rb-87 of the measured marine porewaters are approximately homogeneous (0.08 parts per thousand to 0.14 parts per thousand) and similar to seawater. The result consistent with previous K isotope investigation in this region with limited impact of authigenic silicates. Using a mass balance estimation in a steady state with isotope data, the flux of sediment removal for Rb in the ocean is about 2.2 - 12.0 x 10(7) kg/year.

The deposition of volcanic ash into the ocean initiates a range of chemical and biological reactions. During diagenesis, these reactions may enhance the preservation of organic carbon (OC) in marine sediments, which ultimately promotes CO2 sequestration from the ocean-atmosphere system. However, this interpretation is reliant on a small number of studies that make a link between tephra and OC burial. Here, we compare organic and inorganic geochemical data from tephra-bearing marine sediments from three sites that differ widely in their location, age, and composition. We show that OC is buried in, and proximal to, tephra layers, in proportions higher than would be expected via simple admixture of surrounding sediment. Our data indicate that this OC is preserved primarily through interactions with reactive iron phases, which act to physically protect the carbon from oxidation. Analysis of the composition of the OC associated with reactive iron indicates it is isotopically (consistently more negative δ13C than sediment) and chemically (comprised of compounds not found in the sediment) distinct from OC in the background sediments. We interpret this signal as indicating a microbial source of OC, with autochthonous OC production resulting from autotrophic microbial exploitation of nutrients supplied from tephra. This finding has implications for our understanding of carbon cycling on Earth, and possibly for the emergence of life in terrestrial and perhaps even extra-terrestrial environments.

In the marine environment, nickel distributions are linked to the biogeochemical cycling of both organic matter and manganese. Thus, Ni and its isotopes have the potential to be used to reconstruct changes of bioproductivity and oxygenation in paleoenvironments. However, their utility relies on an understanding of the behaviour of Ni in modern marine environments. Here we investigate the distribution of Ni under a range of oxidation-reduction conditions, with organic carbon (Corg) burial rates that range from approximately 0.08 to 8.4 mmol m−2 d−1, none of the sites show deep (> 5 cm) penetration of dissolved oxygen into the sediment. We present Ni concentrations for sediments and pore fluids, as well as Ni isotope compositions from pore fluids, from the California and Mexico continental margins. The sites are sufficiently reducing that solid-phase Mn concentrations are typically <1000 ppm, but two of the stations, where oxygenated bottom water bathes the underlying sediment, have near-surface sediment Mn concentrations that reach up to 2.3%.Dissolved Ni is lower in pore fluids for stations with high solid phase Corg compared to those stations with oxygenated bottom water and high solid phase Mn concentrations. The calculated benthic fluxes of Ni at all stations are small relative to their burial rates, which implies a high Ni burial efficiency (> 85%). Pore fluid δ60Ni values range from approximately −0.39 to +2.36 ‰, with the higher δ60Ni values occurring at the Corg-rich station, and the lower values at the Mn-rich stations. At the station with the highest Corg content, the distribution of solid-phase Ni as a function of Corg content is consistent with the strong association of Ni with Corg seen at open-ocean upwelling margins globally. In contrast, the other stations investigated here clearly do not show such an association. Our data offer support for the notion that Ni accumulation within sediments is linked to organic matter accumulation in regions of high photic zone productivity and where the sediments are reducing. However, at the sites in our study where Mn oxidation-reduction reactions occur near the sediment-water boundary, any simple relationship between Ni and Corg burial is obfuscated. With a sufficiently deep oxygen penetration depth and the formation of a solid-phase Mn oxide layer, Ni burial within the sediment can be highly efficient. Importantly, Ni is well preserved in sediments deposited under the full range of conditions studied here. This observation of high Ni preservation is an important constraint if Ni is to be used as a proxy to reconstruct paleoenvironmental conditions.

Report includes detailed drilling data: BHA length, bit parameters, and primary depth measurements.

This composite report returns data from two different gas chromatograph configurations (GC3 and NGA). Each row combines data from several measurements made on the same sample at the same time for a particular headspace or vacutainer sample. If data do not exist for a particular expedition, the column does not appear. Gas samples were measured by gas chromatography and either flame ionization detection (GC-FID) or thermal conductivity detection (GC-TCD). Reported analytes may include methane, ethane, ethene, propane, propene, n-butane, i-butane, n-pentane, i-pentane, n-hexane, i-hexane, n-heptane, i-heptane, nitrogen, oxygen, carbon monoxide, carbon dioxide, and hydrogen sulfide. When data are available, methane to (ethane + ethene) ratio (C1/C2�ratio) is reported. To identify individual samples and tests, see each separate analysis (GC3, NGAFID, and/or NGATCD).

Color reflectance data were measured on section halves using an integration sphere and a UV-VIS spectrophotometer mounted on the Section Half Multisensor Logger (SHMSL). Spectral counts are recorded in the range of 380 to 700 nm, covering the visible spectrum, and binned in ~2 nm bins. Spectral data are reduced from spectra and recorded in tristimulus XYZ values, CieLAB L*a*b* values, and other units.

The micronutrient iron (Fe) plays a fundamental role controlling primary productivity in the upper ocean, with volcanic eruptions and deposition of airborne volcanic material (termed tephra) a potential source of Fe. Here, we investigate the geochemical and Fe isotopic (δ56Fe) composition of tephra layers, sediments, and mixed tephra-sediment samples from the Integrated Ocean Drilling Program (IODP) Hole 1396C, located offshore the volcanically active island of Montserrat in the Lesser Antilles, Caribbean Sea. We find that buried tephras, which have experienced diagenesis, exhibit lighter δ56Fe (relative to standard IRMM-524a) compositions (down to −0.26 ± 0.04‰, 2SD) than fresh tephra deposited in Montserrat (δ56Fe = 0.02 ± 0.02‰, 2SD). Such negative values suggest that isotopically heavier Fe has been lost from the originally deposited material. Using multivariate statistical modelling and mass balance constraints, we identify the outward Fe flux (with calculated δ56Fe of 0.21 ± 0.31‰, 2SD, n = 12) during non-reductive dissolution of tephra as the likely cause of the retention of these light δ56Fe compositions. Due to the widespread nature of tephra deposition, tephra diagenesis may provide an important source of isotopically heavy dissolved Fe (dFe) to the oceans. This process contrasts with more commonly considered reductive dissolution processes, which provide a source of dFe enriched in light isotopes to the oceans.

Close-up images taken by digital cameras as requested by the science party, typically when the section-half image is not sufficient. Close-up photographs of the areas of interest may be taken from whole-round sections, pieces, or section halves in sediments and rock.

Alkalinity was determined by Gran titration with an autotitrator (Metrohm 794 basic Titrino) using 0.1 M HCl at 20 degrees C. Report includes alkalinity, correction factor (if applicable), and pH.

The development of nickel isotopes as a chemical tracer of past ocean environments requires a sound understanding of the modern oceanic budget. Our current understanding of this budget implies a large elemental and isotope imbalance between inputs to and outputs from the dissolved pool of the ocean. This imbalance is mainly caused by the dominant oxic sink of Ni to Mn oxide-rich sediments. Though the Ni isotope composition of Fe-Mn crusts has previously been used as proxy for the Ni isotope composition of these sediments, crusts and nodules represent a very small part of the total Mn oxide output. Instead, Mn oxide microparticle supply to pelagic and hemi-pelagic sediments dominates the removal of Mn to sediments, but there are very few isotope data for such samples. Here we present the first extensive Ni concentration and isotope dataset from fully oxic Mn-rich pelagic sediments, from 6 different sites across the open Pacific and 10 closely-spaced sites in the Indian Ocean. We also present data for one hemi-pelagic site representing a suboxic setting on the California Margin. Abyssal Pacific and Indian Ocean sediments have a Ni/Mn ratio of 0.02 (similar to Fe-Mn crusts) and their authigenic Ni is isotopically lighter (860Ni = +0.26 to +1.08%o) than seawater (+1.33%o) and crusts (+1.55 & PLUSMN;0.38%o). Data presented here for organic carbon-rich suboxic sediments of the Californian margin have lower Ni/Mn ratios (0.004 to 0.014 for the oxic top of the core, where Mn oxide is present in abundance) and even lighter authigenic Ni isotope compositions (860Ni =-0.08 & PLUSMN;0.11%o).We show that the Ni isotopes of nearly all Mn-rich sediments and deposits analysed to date, including the new data presented here, are correlated with Co/Mn ratios, suggesting that both are controlled by accumulation rate, progressive incorporation of Ni into the metal oxide structure and isotopic re-equilibration between the solid and aqueous phase. At sites where sediments are diagenetically processed, such as the California Margin, differential diagenetic remobilisation of Mn, Ni and Co cause deviations from this correlation. We present a new mass balance calculation that recognises the importance of scavenging of oceanic Ni to Mn oxide-rich proximal hydrothermal sediments, with low Ni/Mn and light isotope compositions. The mass balance produces a budget that can be simultaneously balanced for both amounts and isotope compositions of Ni. This result provides a strong basis for the application of Ni isotopes as records of the evolution of the metal sink from the oxic oceans through Earth history.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/).

Fundamental elemental component (total carbon, hydrogen, nitrogen, and sulfur) fluctuations help define the origin, depositional environment, and diagenetic alteration of source materials. To determine C, H, N, and S, solid samples are reacted with a catalyst, separated by chromatography, and detected by thermal conductivity on a FlashEA 1112 CHNS elemental analyzer. Organic carbon can be directly measured on the elemental analyzer by acidification of the sample to drive off carbonate as carbon dioxide before analyzing. Total organic carbon on this report is measured rather than calculated.

On 10 February, the pilot boarded at 0942 h.The vessel began the transit to the first site (U1579) with the first line away at 1024 h.The pilot was away at 1045 h, and the start of the sea passage was recorded as 1048 h.Within minutes of the vessel reaching full throttle, the newly commissioned UPS began rejecting the ship's power and started to run off the batteries.The vessel was throttled back to half speed at 1116 h.The UPS returned to normal operating mode.This reaction was verified several more times to diagnose the problem, and it was decided to take the UPS offline.Beginning at 1245 h, JRSO IT services were taken offline.The UPS was bypassed, and regulated power was restored at 1445 h.The vessel returned to full throttle at 1448 h, and the sea voyage continued at full speed.JRSO IT services were fully restored at 1715 h.During the transit, daily COVID-19 antigen testing was conducted in the conference room for the science party and JRSO staff and in the ship's medical office for the crew.The testing continued daily for 8 days out of port and every other day after that until the end of the 2 week mitigation period.

Digital section images were taken of the flat face of split cores on the Section Half Imaging Logger (SHIL) using a linescan camera at a resolution of 20 lines/mm (50 micron pixels). Cores were imaged as soon as possible after splitting to minimize color changes that occur through oxidation and drying. The SHIL produces TIF files as well as reduced-size JPG files. The TIF files are not kept online but users may request them from the IODP-JRSO Data Librarian.