Description: Numerous studies have provided compelling evidence that the Pacific Ocean has experienced substantial glacial/interglacial changes in bottom-water oxygenation associated with enhanced carbon dioxide storage in the glacial deep ocean. Under postulated low glacial bottom-water oxygen concentrations (O), redox zonation, biogeochemical processes and element fluxes in the sediments must have been distinctively different during the last glacial period (LGP) compared to current well-oxygenated conditions. In this study, we have investigated six sites situated in various European contract areas for the exploration of polymetallic nodules within the Clarion-Clipperton Zone (CCZ) in the NE Pacific and one site located in a protected Area of Particular Environmental Interest (APEI3) north of the CCZ. We found bulk sediment Mn maxima of up to 1 wt% in the upper oxic 10 cm of the sediments at all sites except for the APEI3 site. The application of a combined leaching protocol for the extraction of sedimentary Mn and Fe minerals revealed that mobilizable Mn(IV) represents the dominant Mn(oxyhydr)oxide phase with more than 70% of bulk solid-phase Mn. Steady state transport-reaction modeling showed that at postulated glacial O of 35 μM, the oxic zone in the sediments was much more compressed than today where upward diffusing pore-water Mn2+ was oxidized and precipitated as authigenic Mn(IV) at the oxic-suboxic redox boundary in the upper 5 cm of the sediments. Transient transport-reaction modeling demonstrated that with increasing O during the last glacial termination to current levels of ∼ 150 μM, (1) the oxic-suboxic redox boundary migrated deeper into the sediments and (2) the authigenic Mn(IV) peak was continuously mixed into subsequently deposited sediments by bioturbation causing the observed mobilizable Mn(IV) enrichment in the surface sediments. Such a distinct mobilizable Mn(IV) maximum was not found in the surface sediments of the APEI3 site, which indicates that the oxic zone was not as condensed during the LGP at this site due to two- to threefold lower organic carbon burial rates. Leaching data for sedimentary Fe minerals suggest that Fe(III) has not been diagenetically redistributed during the LGP at any of the investigated sites. Our results demonstrate that the basin-wide deoxygenation in the NE Pacific during the LGP was associated with (1) a much more compressed oxic zone at sites with carbon burial fluxes higher than 1.5 mg Corg m−2 d−1, (2) the authigenic formation of a sub-surface mobilizable Mn(IV) maximum in the upper 5 cm of the sediments and (3) a possibly intensified suboxic-diagenetic growth of polymetallic nodules. As our study provides evidence that authigenic Mn(IV) precipitated in the surface sediments under postulated low glacial O, it contributes to resolving a long-standing controversy concerning the origin of widely observed Mn-rich layers in glacial/deglacial deep-sea sediments.

Description: Rare earth elements and yttrium (REY) are often used as proxies for (paleo)environmental conditions and for the reconstruction of element sources and transport pathways. Many geological systems are well described with respect to the behavior of REY but deep-sea sediments with their manifold processes impacting the sediment during early diagenesis leave some questions about the origin and development of the shale-normalized REY (REYSN) patterns unanswered. Here we report REY data for sediment solid phase and pore water from the upper 10 m of deep-sea sediments from the Clarion Clipperton Zone (CCZ) in the central equatorial Pacific. The solid-phase REY profiles show highest concentrations at depth below 5–8 m. The REYSN patterns show an enrichment in middle REY (MREY) (LaSN/GdSN between 0.35 and 0.60; GdSN/YbSN between 1.19 and 1.47) and either no or negative CeSN and YSN anomalies (i.e. chondritic to sub-chondritic Y/Ho ratios between 24.7 and 28.7). Based on correlation analyses of bulk sediment element concentrations and sequential extractions, we suggest that a Ca phosphate phase controls the distribution and the patterns of REY in these silty clay pelagic sediments rich in siliceous ooze. The MREY enrichment develops at the sediment-water interface and intensifies systematically with depth. The negative CeSN anomaly intensifies with depth possibly because Ce is mostly bound to Mn- and Fe-(oxyhydr)oxides. Therefore, Ce concentrations remain relatively constant throughout the sediment core, while its trivalent REY neighbors are mostly hosted by the Ca phosphate phase that continuously incorporates REY from ambient pore waters. The non-redox-sensitive trivalent REY concentrations increase with depth, producing or enhancing a negative CeSN anomaly through coupled substitution of REY3+ and Na+ for Ca2+. The solid-phase REYSN pattern is therefore determined by the pore-water REYSN pattern and not suitable for paleoceanographic interpretation. The similarity of the pore-water and solid-phase REYSN patterns suggests, however, that only minor fractionation occurs during REY incorporation into the Ca phosphate crystal structure.

Description: The dataset includes solid-phase geochemistry data of sediment cores from Site C0023 (Hole A) that was recovered during International Ocean Discovery Program (IODP) Expedition 370 in the Nankai Trough offshore Japan in the Pacific Ocean (Drilling vessel Chikyu). Site C0023 was established on 17 September 2016. Coring terminated on 3 November 2016. Stable carbon isotopes of total organic carbon measurement occurred on an EA-IRMS system after complete decalcification of homogenized sediment samples with 10% HCl. The δ13C-TOC values are expressed relative to VPDB (Vienna Pee Dee Belemnite).

Description: Hemipelagic sediments contained in 7 cc plastic cubes were analyzed for paleomagnetic and rock magnetic properties. Samples were collected from Hole C0023A drilled during International Ocean Discovery Program (IODP) Expedition 370, off Cape Muroto, Shikoku Island, Japan, which took place in 2016 (Heuer et al., 2017, https://doi.org/10.14379/iodp.proc.370.2017). A series of magnetic measurements were carried out at the Center for Advanced Marine Core Research, Kochi University, Japan. These analyses include magnetic susceptibility, natural remanent magnetization and its alternating field demagnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization. Detailed rock magnetic measurements, which include hysteresis parameters, characterize magnetic mineral assemblages in terms of abundance, grain size, and composition. For further information on the methodology, please refer to “Read Me” document.

Description: The dataset includes rock magnetic end-member unmixing data of sediment cores from Site C0023 (Hole A) that was recovered during International Ocean Discovery Program (IODP) Expedition 370 in the Nankai Trough offshore Japan in the Pacific Ocean (Drilling vessel Chikyu). Site C0023 was established on 17 September 2016. Coring terminated on 3 November 2016. End-member modelling of isothermal remanent magnetization (IRM) acquisition curves were performed to characterize the iron mineralogy. IRM acquisition curves were measured using a Princeton Measurements Corporation Vibrating Sample Magnetometer (VSM). IRM was imparted stepwise (non-linearly) up to a maximum field of 1 T with an averaging time of 200 ms. Unmixing of IRM acquisition curves were performed using the web application MAX UnMix by Maxbauer et al. (2016). Mean coervity (Bh) is given in log10 B mT and dispersion parameter (DP) in log. EC is the extrapolated contribution to the total IRM.

Description: The dataset includes solid-phase geochemistry data of sediment cores from Site C0023 (Hole A) that was recovered during International Ocean Discovery Program (IODP) Expedition 370 in the Nankai Trough offshore Japan in the Pacific Ocean (Drilling vessel Chikyu). Site C0023 was established on 17 September 2016. Coring terminated on 3 November 2016. Algal lipid biomarker analysis was performed after Sturt et al. (2004) and HPLC-MS analyses after Becker et al. (2015). Biomarker concentrations are reported as the integrated peak area of the sum of all detected diols normalized to kg extracted sediment (PA/kg).

Description: The dataset includes solid-phase and porewater trace elements data of sediment cores from Site C0023 (Hole A) that was recovered during International Ocean Discovery Program (IODP) Expedition 370 in the Nankai Trough offshore Japan in the Pacific Ocean (Drilling vessel Chikyu). Site C0023 was established on 17 September 2016. Coring terminated on 3 November 2016. Solid-phase trace elements data include bulk molybdenum (Mo), uranium (U), vanadium (V), and rare earth elements (REEs) contents, and Mo isotopes. Trace element analyses were performed using a Thermo Fisher iCAPQ ICP-MS equipped with a ASX560 AutoSampler. Approximately 50 mg of each dry sediment powder was dissolved in Teflon bomb with the double-distilled concentrated HNO3-HF (1:1) mixture. The dissolution was maintained in an oven at 185°C for 3 days and then dried down to evaporate HF. The residues were re-dissolved with double-distilled concentrated HNO3 followed by the HNO3-H2O (1:1) mixture, and dried again. After that, the sample was dissolved in the final 3ml 2N HNO3 stock solution. Finally, the sample solution is diluted by 1000 times with 2.5% HNO3 and 10ppb Rh internal spikes. The standard GBW07316 was used as a reference. Internal spikes and external monitors were used to correct instrument drift mass bios. The ICP-MS procedure for trace element analyses is based on the protocol developed by Eggins et al. (1997, doi:10.1016/S0009-2541(96)00100-3). The Mo-isotope composition were analyzed by a Thermo-Fisher Scientific Neptune-Plus multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) using the double-spike method. About 0.02-0.05g whole-rock powders were weighed and combined with appropriate amounts of a 97Mo-100Mo double spike within a pre-cleaned 15 mL PFA beaker. The sample was then dissolved using 1 mL HNO3 and 2 mL HF at 140 ℃ for 2 days before being dried at 120 ℃ and re-dissolved in 4 mL of a 1 M HCl-0.3 M HF mixture for column separation. Molybdenum was separated and purified using an N-benzoyl-N-phenyl hydroxylamine extraction chromatographic resin with the approaches outlined in Li et al. (2014, doi:10.1111/j.1751-908X.2013.00279.x). Pore water trace elements data include Mo, U, V, and nickel (Ni). The pore water was collected during IODP Expedition 370 as described in the Expedition 370 Methods by Heuer et al. (2017;doi:10.14379/iodp.proc.370.103.201). The trace elements were measured in untreated (original) in acidified pore-water samples. The inductively coupled plasma-mass spectrometry (ICP-MS, Element2, Thermo Fisher Scientific Inc.) is equipped with an ESI Apex-Q desolvating system to increase the sensitivity.