Description: The occurrence of microbially induced smectite-to-illite (S-I) reaction has challenged both the notions of solely inorganic chemical control for this reaction and the conventional concept of a semiquantitative illite geothermometer for the reconstruction of the thermal and tectonic histories of sedimentary basins. Here, we present evidence for a naturally occurring microbially induced S-I transition, via biotic reduction of phyllosilicate structural Fe(III), in mudstones buried at the Nankai Trough, offshore Japan (International Ocean Discovery Program Site C0023). Biotic S-I reaction is a consequence of a bacterial survival and growth strategy at diagenetic temperatures up to 80 °C within the Nankai Trough mudstones. These results have considerable implications for petroleum exploration, modification of fault behavior, and the understanding of microbial communities in the deep biosphere.

Description: This dataset comprises leached contents of different manganese and iron mineral phases from sediment cores, which were retrieved by a multiple corer (MUC) during RV SONNE expedition SO239 in 2015. During this cruise, different European contract areas for the exploration of polymetallic nodules in the area of the Clarion-Clipperton Zone (CCZ) were visited (BGR, IOM, GSR, IFREMER), which are currently being explored in light of potential future deep-sea mining. Furthermore, one of the protected Areas of Particular Environmental Interest (APEI), more precisely the APEI3 north of the CCZ, was visited. For the extraction of various manganese and iron minerals, the extraction schemes after Koschinsky et al. (2001) and Poulton and Canfield (2005) were combined. The leached mineral phases comprise (1) carbonate-associated Mn and Fe (Mncarb; Fecarb), (2) easily reducible/mobilizable Mn- and Fe(oxyhydr)oxides (Mnmobil; Femobil), (3) easily reducible Fe oxides, such as ferrihydrite and lepidocrocite (Feox1) and associated Mn oxides (Mnox1), (4) reducible Fe oxides, such as goethite and hematite (Feox2) and associated Mn oxides (Mnox2) and (5) magnetite (Femag) and associated Mn oxides (Mnmag). The dataset was produced in the laboratories of the Alfred Wegener Institute (AWI) Bremerhaven, Germany.

Description: This dataset comprises solid-phase bulk sediment manganese, iron and aluminum contents from sediment cores, which were retrieved by a multiple corer (MUC) during RV SONNE expedition SO239 in 2015. During this cruise, different European contract areas for the exploration of polymetallic nodules in the area of the Clarion-Clipperton Zone (CCZ) were visited (BGR, IOM, GSR, IFREMER), which are currently being explored in light of potential future deep-sea mining. Furthermore, one of the protected Areas of Particular Environmental Interest (APEI), more precisely the APEI3 north of the CCZ, was visited. The dataset was produced in the laboratories of the Alfred Wegener Institute (AWI) Bremerhaven, Germany.

Description: The occurrence of microbially induced smectite-to-illite (S-I) reaction has challenged both the notions of solely inorganic chemical control for this reaction and the conventional concept of a semiquantitative illite geothermometer for the reconstruction of the thermal and tectonic histories of sedimentary basins. Here, we present evidence for a naturally occurring microbially induced S-I transition, via biotic reduction of phyllosilicate structural Fe(III), in mudstones buried at the Nankai Trough, offshore Japan (International Ocean Discovery Program Site C0023). Biotic S-I reaction is a consequence of a bacterial survival and growth strategy at diagenetic temperatures up to 80 °C within the Nankai Trough mudstones. These results have considerable implications for petroleum exploration, modification of fault behavior, and the understanding of microbial communities in the deep biosphere.

Description: IODP Expedition 370 (Temperature Limit of the Deep Biosphere off Muroto) established Site C0023 down to 1180 mbsf in the Nankai Trough off Shikoku Island, Japan, to explore the upper temperature limit of microbial life in deep subseafloor sediments. Part of the scientific program is to investigate the availability of nutrients and energy substrates and to identify unique geochemical and microbial signatures that differentiate the biotic and abiotic realms and/or their transitions (Heuer et al., 2017). Iron (Fe) reduction is considered one of the most ancient forms of microbial respiration (Vargas et al., 1998). In addition, Fe reducers can grow under high temperature and pressure conditions (Kashefi and Lovley, 2003), suggesting that microbes that use Fe oxides as energy substrates are potential candidates to survive close to the temperature limit of the deep biosphere. In this study, we aim at assessing the role of Fe oxides for microbial respiration and the related diagenetic alterations in deep sediments of Site C0023 by applying sequential extractions of Fe oxide and sulfide minerals. Volcanic ash layers, which are ubiquitous in sediments of Site C0023, are of particular interest as they have been identified earlier as hotspots for microbial life (e.g., Inagaki et al., 2003). Torres et al. (2015) further showed that ash layers at a different site in the Nankai Trough are typically rich in Fe and Mn oxides. Their results support the findings of Treude et al. (2014) who postulate a coupling of microbial processes to mineralogy. In addition, on-board measurements show a release of dissolved Fe into the pore water in the depth interval associated with volcanic ash layers (Heuer et al., 2017), suggesting that the observed liberation of dissolved Fe is related to an alteration of Fe phases in these ash layers. Our results show that the total Fe content in sediments of Site C0023 is relatively constant at ~4.2 wt%. The reactive Fe oxide content represents 25% of the total Fe. Based on sequential extractions, the fraction associated with amorphous Fe oxide such as ferrihydrite and lepidocrocite is the dominant Fe fraction with ~0.7 wt%. Mineralogical analyses are currently conducted in order to determine specific Fe mineral phases within this fraction. The total Fe contents in the ash layer samples strongly vary between 1.4 and 6.8 wt%. However, most samples generally contain less total Fe than the surrounding sediments. Similarly, the contents of the reactive Fe oxides are significantly lower. Thus, reactive Fe oxides in ash layers at Site C0023 do not seem to represent the energy substrate for microbial Fe reduction. As one of the next steps, stable Fe isotope (δ56Fe) analyses will be performed on (1) pore-water samples, the (2) different Fe oxide phases and (3) sediment residues remaining after sequential extractions in order to trace the source and reaction pathway for the observed release of dissolved Fe into the pore water. Diagenetic Fe cycling, in particular the reductive dissolution of Fe oxides driven by the reaction with hydrogen sulfide, may lead to the transformation of reactive Fe oxides to Fe sulfides such as pyrite (e.g., Berner 1970). Fe monosulfide contents are below detection limit in sediments of Site C0023. Pyrite, in contrast, occurs over the whole core interval with strongly varying contents. Three significant peaks with contents up to 0.5 wt% could be observed at 552, 707 and 1033 mbsf. The pyrite profile generally mimics the total sulfur profile, which suggests that most of bulk sulfur is present as pyrite. Fe bound in pyrite (Fepyrite), however, only represents less than 5% of the total Fe pool, except for the interval with elevated pyrite contents where Fepyrite accounts for ~10% of bulk Fe. This indicates that sulfidation does not affect the whole Fe oxide pool in sediments of Site C0023. The reductive dissolution of primary ferrimagnetic Fe oxides and the formation of secondary paramagnetic pyrite is generally known to modify rock magnetic properties such as magnetic susceptibility (e.g., Berner, 1970). Thus, our geochemical results are presented in combination with post-cruise generated magnetic susceptibility data. By combining the geochemical methods, including sequential Fe oxide and sulfide extractions and subsequent δ56Fe analyses, with rock magnetic measurements, we intend to decipher the role of Fe mineral phases in maintaining deep subsurface life at Site C0023. Acknowledgements - This research used samples and data provided by the International Ocean Discovery Program (IODP). We would like to thank all personnel involved in the operations aboard the DV Chikyu during Expedition 370 and the support team at the Kochi Core Center. We further would like to thank the German Research Foundation (DFG) for funding this project (project number: 388260220) in the framework of the priority program 527 (Bereich Infrastruktur – International Ocean Discovery Program). References: Berner, R.A., 1970. Sedimentary pyrite formation. AJS 268: 1-23. Heuer, V.B., Inagaki, F., Morono, Y., Kubo, Y., Maeda, L., and the Expedition 370 Scientists, 2017. Expedition 370 Preliminary Report: Temperature Limit of the Deep Biosphere off Muroto. International Ocean Discovery Program. Inagaki, F., Suzuki, M., Takai, K., Oida, H., Sakamoto, T., Aoki, K., Nealson K.H., Horikoshi, K., 2003. Microbial communities associated with geological horizons in coastal subseafloor sediments from the Sea of Okhotsk. AEM 69: 7224-7235. Kashefi, K., Lovley, D.R., 2003. Extending the upper temperature limit of life. Science 301: 934. Torres, M.E., Cox, T., Hong, W.-L., McManus, J., Sample, J.C., Destrigneville, C., Gan, H.M., Gan, H.Y., Moreau J.W., 2015. Crustal fluid and ash alteration impacts on the biosphere of Shikoku Basin sediments, Nankai Trough, Japan. Geobiology 13: 562-580. Treude, T., Krause, S., Maltby, S., Dale, A.W., Coffin, R., Hamdan, L.J., 2014. Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: Implications for deep sulfur cycling. GCA 144: 217-237. Vargas, M., Kashefi, K., Blunt-Harris, E.L., Lovley, D.E., 1998. Microbiological evidence for Fe(III) reduction on early Earth. Nature 395: 65-67.

Description: IODP Expedition 370 established Site C0023 down to 1180 mbsf in the Nankai Trough, Japan, to explore the upper temperature limit of microbial life in deep subseafloor sediments. The area is characterized by strongly changing sedimentation rates. The diagenetic iron (Fe) cycling is an important process within the deep biosphere. However, microbial and abiotic alterations of Fe phases in deep subseafloor sediments are poorly understood. Fe (oxyhydr)oxides are important carriers of sedimentary magnetic signals. Diagenetic cycling, especially the reductive dissolution of Fe (oxyhydr)oxides driven by microbial degradation of organic matter and/or by reactions with hydrogen sulfide, may lead to transformations of primary ferrimagnetic Fe (oxyhydr)oxides to secondary Fe sulfides, and thus, to modification of rock magnetic properties. In this study, we aim at assessing the alteration of the primary sedimentary record at Site C0023, including authigenic formation of secondary minerals, pyritization as well as effects on rock magnetic properties. To investigate the Fe mineralogy, sequential extractions of Fe (oxyhydr)oxides and sulfides are combined with rock magnetic analyses and SEM-EDS observations. The reactive Fe pool includes Fe carbonates and Fe (oxyhydr)oxides. Amorphous Fe oxides are the dominant reactive Fe fraction at Site C0023. Fe sulfides, mainly pyrite, are present in all investigated intervals. However, pyritization only affects 5 to 15% of the reactive Fe pool. Rock magnetic properties also show the presence of metastable Fe sulfides in the upper interval between 200 and 450 mbsf. Their preservation might be caused by limited hydrogen sulfide availability, an increase in sedimentation rates, which prevents a complete pyritization by decreasing the time the interval was located in the sulfidic zone, or by recent authigenesis. Combining our geochemical and rock magnetic data improves the understanding of iron cycling in subseafloor sediments and the role of iron minerals in maintaining life in the deep biosphere.

Description: Trace metals such as Mo, U, and V are useful paleo-redox proxies because of their sensitivity to redox conditions and unique incorporation pathways into marine sediments. However, microbial processes can change the primary signal of specific trace metals that can record the environment at the time of deposition. To investigate the impact of microbial activity on trace metals during early diagenesis, geochemical analysis was performed via bag-incubations on samples collected from two giant box corers during RV SONNE Expedition SO260, funded by the MARUM-Center for Marine Environmental Sciences at the University of Bremen. The first core was taken at the head of the Mar del Plata Canyon, consists of mud to fine sand, and was sampled at five depths. The second core was taken on a coral mound, contains larger grains and abundant coral fragments, and was sampled at four depths. Four splits were taken at each depth; the first split was processed on-board, while splits 2-4 were stored in argon flushed aluminum bags at 4°C for processing and analysis every 4 months on-shore. Our data show strong changes in the pore-water trace metal concentrations in the first box core samples, with Mo increasing more than 5000 nM within 8 months. In samples from the second box core, pore-water Mo increases by more than 1000 nM in the first 4 months before decreasing likely due to the onset of sulfate reduction and, consequently, the formation of hydrogen sulfide leading to the (co-)precipitation of Mo. Our data indicate that the dissolution of iron and manganese oxides leads to the release of associated trace metals at different time points for each site. With comparable amounts of organic carbon at both sites, the observed changes are likely related to sediment composition and physical properties. The sediments sampled at the coral mound have a higher overall porosity and thus provide more space for fluid circulation and host microbial communities. This could explain the faster cycling of iron minerals, potential onset of sulfate reduction, and thus changes in the concentration of relevant trace metals. Therefore, our data suggest that trace metal cycling is not only related to the overall sediment composition, but also to physical properties including pore space, permeability, and grain size which affect how much area is available for microbial communities.

Description: Detailed temperature reconstructions over the past 2000 years are important for contextualising modern climate change. The mid‐latitude SE Pacific is a key region in this regard in terms of understanding the climatic linkages between the tropics and southern high latitudes. Multi‐centennial timescale temperature variability remains, however, poorly understood, due to a lack of long, high‐temporal‐resolution temperature records from this region and from the southern high latitudes in general. We present a unique alkenone sea surface temperature (SST) record from 44°S on the southern Chilean margin in the SE Pacific spanning the last 2300 years at decadal resolution. The record displays relatively large changes including a cooling transition from 14°C to 12.5°C between 1100 and 600 cal yrs BP, in line with other Chile margin SST records and coeval with Antarctic cooling. This cooling is attributable to reduced Southern Ocean deep convection, driven by a late Holocene sea‐ice increase in the Weddell Sea associated with increased El‐Niño Southern Oscillation (ENSO) variability. Superimposed on the late Holocene cooling we observe multi‐centennial timescale SST variability, including relatively cool SSTs (12.5°C) from 950 to 500 cal yrs BP, corresponding to the Medieval Climate Anomaly, and warmer SSTs (13°C) from 500 to 200 cal yrs BP, corresponding to the Little Ice Age. These oscillations may reflect either multi‐centennial internal variability of the Southern Ocean deep convection and/or multi‐centennial variability in the phasing of ENSO and Southern Annular Mode (SAM) events.