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The structure of the lithosphere and the associated magmatic systems found in different locations along slow‐spreading ridges can vary dramatically, from melt‐starved to magmatically robust segments. A growing number of studies suggest that the evolution of the magmatic crust being governed solely by fractional crystallization is too simplistic. Reactions between migrating melts and their surroundings play a key role during accretion, yet the full extent of their impact is still to be resolved. We present here the results of a petrological, microstructural, and in situ geochemical study of two drilled sequences from the Kane Megamullion and Atlantis Massif oceanic core complexes. We show that melt‐mush reactions generate locally strong textural and/or geochemical heterogeneity at the cm‐scale, but their impact can also be identified at the 100 m‐scale. We found evidence for assimilation at various degrees of primitive lithologies of potential mantle origin within the gabbroic sequence at both locations, in addition to typical melt‐mush reactions previously described in other slow‐spread magmatic systems. Observations and numerical modeling confirm the similarity of the reactions impacting both sequences. However, the regime of the reactions (ranges of assimilation to crystallization ratios) seems to vary between Kane Megamullion and Atlantis Massif, variations which likely result from differences in melt fractions present during melt‐mush reactions. We infer relying on our observations and previous studies that the regime of the reactions is most likely controlled by the melt flux during the formation of the two sections. Key Points: Kane Megamullion and Atlantis Massif oceanic core complexes record widespread melt‐mush reactions at different scalesIn addition to typical melt‐mush reactions, assimilation of primitive (mantle?) lithologies is observed within gabbro sequencesDiscrepancies in the melt‐mush reaction signatures of the two sequences reveal variable melt dynamics during accretion [ABSTRACT FROM AUTHOR]

Abstract The structure of the lithosphere and the associated magmatic systems found in different locations along slow‐spreading ridges can vary dramatically, from melt‐starved to magmatically robust segments. A growing number of studies suggest that the evolution of the magmatic crust being governed solely by fractional crystallization is too simplistic. Reactions between migrating melts and their surroundings play a key role during accretion, yet the full extent of their impact is still to be resolved. We present here the results of a petrological, microstructural, and in situ geochemical study of two drilled sequences from the Kane Megamullion and Atlantis Massif oceanic core complexes. We show that melt‐mush reactions generate locally strong textural and/or geochemical heterogeneity at the cm‐scale, but their impact can also be identified at the 100 m‐scale. We found evidence for assimilation at various degrees of primitive lithologies of potential mantle origin within the gabbroic sequence at both locations, in addition to typical melt‐mush reactions previously described in other slow‐spread magmatic systems. Observations and numerical modeling confirm the similarity of the reactions impacting both sequences. However, the regime of the reactions (ranges of assimilation to crystallization ratios) seems to vary between Kane Megamullion and Atlantis Massif, variations which likely result from differences in melt fractions present during melt‐mush reactions. We infer relying on our observations and previous studies that the regime of the reactions is most likely controlled by the melt flux during the formation of the two sections.

Seafloor hydrothermal systems play a significant role in the oceanic Mg cycle due to ubiquitous deposits of secondary Mg-rich clays during the strong fluid-rock reactions. However, the magnitude of net Mg enrichment and Mg isotopic fractionation, particularly within the medium-high temperature hydrothermal systems in felsic-hosted settings, are not well studied yet. Here we report elemental and isotopic compositions of Mg in hydrothermal chlorite-rich sediments, volcanic materials, and terrigenous sediments collected during the IODP Expedition 331 drilled to the thick sediment-covered and felsic-hosted middle Okinawa Trough (Iheya North Knoll) in the West Pacific. We investigate the sources of Mg in chlorite and Mg isotopic behavior at medium-high temperature hydrothermal alteration. After 1 mol/L HCl leaching, Mg isotopic compositions of chlorite-rich sediments present overall similar values in the residual fractions and bulk samples albeit with slightly higher values in the leachates. Mineralogical differentiation primarily determines the Mg isotopic compositions, showing that siliciclastic residues have slightly higher δ26Mg values than the leachates dominated by carbonates and oxides/hydroxides. Significant Mg isotopic fractionation happened in the medium-high temperature (∼150°C to 260°C) felsic-hosted hydrothermal system, with Δ26MgChl-SW ranging from 0.15‰ to 0.71‰ and yielding a negative correlation with temperature. This observation suggests the preferential incorporation of heavy Mg isotopes by the secondary chlorite precipitation. We infer that the medium-high temperature hydrothermal systems can take up about 8–14% of riverine input of Mg in the arc and back-arc regions. Incomplete removal of aqueous Mg in porewater and vent fluids by the medium-high temperature hydrothermal alterations in the arc and back-arc basins provides constraints on the Mg budget and isotopic composition of seawater. [ABSTRACT FROM AUTHOR]

Mission-Specific Platforms (MSPs) have been important members of the scientific ocean drilling family for two decades, operating alongside their impressive siblings JOIDES Resolution and D/V Chikyu. Over this time, 10 MSP expeditions were implemented in 7 different oceans and seas. These MSPs capitalised on alternative platforms and methods, and enabled the scientific community to access new geographical areas and new geological targets that could not be drilled by the JOIDES Resolution or Chikyu. Offshore heave-compensated wireline coring, onshore-mining-style wireline coring, remote seafloor drilling and giant piston coring have all featured on MSP expeditions. Equally diverse were the environments in which these technologies were deployed, from the ice-covered Arctic Ocean to the tropical seas of the Great Barrier Reef, and from the shallow waters of the Yucatan shelf to the ultra-deep hadal depths of the Japan Trench. In this paper we reflect on the diverse technologies of MSPs, how they increased scientific ocean drilling capability in the Integrated Ocean Drilling Program (2003−2013) and International Ocean Discovery Program (2013–2024), and the scientific achievements that they enabled. • MSPs enabled scientific ocean drilling in new geographical areas and reached new geological targets. • MSPs featured a diverse range of vessel- and seafloor-based coring systems. • MSPs operated in a wide range of marine environments, water depths and seabed penetrations. • MSPs have recovered just over 7.9 km of core from 230 boreholes in hard rock and soft sediment. [ABSTRACT FROM AUTHOR]

Basement formation pressures and temperatures were recorded from 1997 to 2017 in four sealed‐hole observatories in North Pond, an isolated ∼8 × 15 km sediment pond surrounded by thinly sedimented basement highs in 7–8 Ma crust west of the Mid‐Atlantic Ridge at ∼23°N. Two observatories are located ∼1 km from the southeastern edge of North Pond where sediment thickness is ∼90 m; the other two are ∼1 km from the northeastern edge where sediment thickness is 40–50 m. Sediments are up to 200 m thicker in the more central part of the pond. The borehole observations, along with upper basement temperatures estimated from seafloor heat flux measurements, provide constraints on the nature of low‐temperature ridge‐flank hydrothermal circulation in a setting that may be typical of sparsely sedimented crust formed at slow spreading ridges. Relative to seafloor pressures, basement formation pressures are modestly positive and increase with depth, except for a slight negative differential pressure in the shallowest 30–40 m in one northeastern hole. Although the observatory pairs are ∼6 km apart, the lateral pressure gradient in basement between them is very small. Formation pressure responses to seafloor tidal loading are consistent with high basement permeability that allows for vigorous low‐temperature circulation with low lateral pressure gradients. In contrast, there is significant lateral variability in upper basement temperatures, with highest values of ∼12.5°C beneath the thickly sedimented southwest section, lower values near the edges, and lowest values near the southeast edge. The results are key to assessing past and recent models for the circulation system. Plain Language Summary: Low temperature hydrothermal systems in young oceanic seafloor have important integrated thermal and chemical effects, but flow patterns are weakly constrained by direct observations and are poorly understood, especially in sparsely sedimented settings that are characteristic of much of the world's seafloor. We present 20 years of observations of seafloor and formation pressures and temperatures recorded by sealed borehole observatories beneath a North Atlantic ridge‐flank sedimented basin ("North Pond") surrounded by sparsely sedimented basement highs—the first such long‐term data from this common type of setting. The observations indicate that there is a vigorous low‐temperature hydrothermal flow system beneath the sediments of North Pond as previously concluded, but lateral pressure gradients in uppermost basement are very low; these observations require the permeability of uppermost basement to be very high. Our determinations of uppermost basement temperatures show greater variations than previously inferred, with the highest temperatures beneath the most thickly sedimented section. This is inconsistent with prior conceptual models of unidirectional hydrothermal flow in uppermost basement beneath the sediment pond, but more supportive of recent models with upflow beneath the most thickly sedimented section of the pond, accompanied by lateral flow toward the pond perimeter where mixing with seawater occurs. Key Points: Formation pressures in igneous basement beneath North Pond sediments are positive except in the upper few tens of meters near the pond edgeLateral pressure gradients in upper igneous basement are very low, implying very high permeabilities (∼10−10 m2) and vigorous flowBasement temperatures are highest beneath the thickest sediments, unsupportive of prior models for unidirectional flow in igneous basement [ABSTRACT FROM AUTHOR]

Abstract Basement formation pressures and temperatures were recorded from 1997 to 2017 in four sealed‐hole observatories in North Pond, an isolated ∼8 × 15 km sediment pond surrounded by thinly sedimented basement highs in 7–8 Ma crust west of the Mid‐Atlantic Ridge at ∼23°N. Two observatories are located ∼1 km from the southeastern edge of North Pond where sediment thickness is ∼90 m; the other two are ∼1 km from the northeastern edge where sediment thickness is 40–50 m. Sediments are up to 200 m thicker in the more central part of the pond. The borehole observations, along with upper basement temperatures estimated from seafloor heat flux measurements, provide constraints on the nature of low‐temperature ridge‐flank hydrothermal circulation in a setting that may be typical of sparsely sedimented crust formed at slow spreading ridges. Relative to seafloor pressures, basement formation pressures are modestly positive and increase with depth, except for a slight negative differential pressure in the shallowest 30–40 m in one northeastern hole. Although the observatory pairs are ∼6 km apart, the lateral pressure gradient in basement between them is very small. Formation pressure responses to seafloor tidal loading are consistent with high basement permeability that allows for vigorous low‐temperature circulation with low lateral pressure gradients. In contrast, there is significant lateral variability in upper basement temperatures, with highest values of ∼12.5°C beneath the thickly sedimented southwest section, lower values near the edges, and lowest values near the southeast edge. The results are key to assessing past and recent models for the circulation system.

Understanding sedimentary routing systems at continental margins can be challenging in tectonically active regions such as forearc basins. Here, we combine sand modal composition and detrital zircon U‐Pb data from the Kumano Basin and surrounding Nankai Trough region of Japan to explore sedimentation in an active forearc and its linkages to the regional tectonic history. Our analyses are on Miocene‐to‐Pleistocene samples collected by the Integrated Ocean Drilling Program (IODP) at inner and outer forearc basin sites C0009 and C0002, river samples from onshore Honshu, and published results from other Nankai IODP sites. Results show the sediments of many IODP samples are similar to that of the modern rivers. Data from C0009 demonstrate that the early accretionary prism already contained slope basins fed by sediments similar to those in the modern Kumano River by 7.1 Ma. The more distal C0002 section was predominantly fed by a system similar to the modern Yodo River, located to the west‐southwest. We conclude that the section was therefore tectonically transported, in agreement with the 'mobile model' of oblique tectonic convergence across SW Japan during late Miocene time. Deposition resumed after a ca. 5.6–3.8 Ma hiatus, with sediments primarily fed from the paleo‐Kumano River, with some input from the paleo‐Tenryu and Kiso/Nagara rivers located to the northeast. Input from the paleo‐Tenryu and Kiso/Nagara rivers was likely re‐routed towards the trench by ca. 1.3 Ma. Sediments similar to those of the distal Yodo River also make up part of the Kumano basin fill and are best explained by erosion of uplifted older accretionary prism sediments along the Megasplay Fault that bounds the forearc basin. Despite the temporal variability in sedimentation routed to the basin, basin‐fill dynamics appear to have been governed primarily by the critical‐wedge style dynamics driven by variations in frontal accretion and in‐ or out‐of‐sequence thrusting response. [ABSTRACT FROM AUTHOR]

Abstract The consolidation behavior of mudstone is controlled by the clay fraction and affects a wide range of deformation and fluid transport processes in accretionary wedge systems. I analyze the compression and permeability behavior of six sediment mixtures based on uniaxial resedimentation and constant rate of strain consolidation data. The sediment mixtures are composed of varying proportions of hemipelagic mudstone and silt‐size silica resulting in clay fractions ranging from 56% to 32% by mass. The hemipelagic mudstone is from Site C0011 drilled seaward of the Nankai Trough, offshore Japan, during Integrated Ocean Drilling Program Expedition 322. I show that porosity and compression index consistently decrease and permeability consistently increases with decreasing clay fraction over vertical effective stresses ranging from 0 to 21 MPa. Backscattered electron microscope images reveal that matrix porosity declines and large, jagged pore throats are being preserved in compaction shadows between silt grains as the clay fraction decreases. I compare the behavior of reconstituted samples with that of intact core and field measurements and interpret that increasing creep with depth and different mudstone fabrics explain differences in their compression curves. Finally, I provide empirical compression and permeability models that describe the evolution of porosity (void ratio) and permeability with vertical effective stress and as a function of grain size. Characterizing the in situ hydromechanical properties of subduction inputs is critical in order to relate input sediments to those at frontal thrust regions and predict pore fluid pressures and compaction‐driven fluid sources within the outer part of the accretionary prism.

Continuous sedimentary records of paleomagnetic directional variability and relative paleointensity (RPI) provide valuable information on the evolution of the geodynamo while also facilitating stratigraphic correlation and age control. While the Quaternary RPI record has received much attention, Pliocene records are relatively rare. Here, a u‐channel paleomagnetic study from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea refines the shipboard‐derived polarity stratigraphy and generates an RPI and directional record extending back 4.5 Ma. Rock magnetic data reveal changes in magnetic coercivity around 2.1 Ma that influences the quality of the paleomagnetic record; while the older record is well‐resolved and passes RPI quality criteria, much of the younger section does not. To facilitate the development of the RPI record, spike noise associated with discrete intervals of volcanogenic sediments are filtered from the data set. The resulting record passes RPI reliability criteria between 0–0.6 Ma and 2.1–4.5 Ma and represents the highest resolution RPI record extending into the early Pliocene. We use this record to refine the existing benthic δ18O chronology and open the door to high‐resolution RPI chronostratigraphies during the Pliocene. Although we find no evidence for a previously observed increase in magnetic field intensity after ∼4 million years ago, we do observe an asymmetrical form to RPI in the normal polarity intervals of the Gauss chron. We also find a polarity bias in inclination that cannot be simply explained by a drill string overprint, suggesting polarity‐driven field asymmetries that are particularly pronounced during the Pliocene. Plain Language Summary: As sediments slowly accumulate on the ocean floor past variations in magnetic field intensity and direction are recorded. While we have a relatively good record of intensity variations over the last 2–3 million years, we know little about earlier time intervals. Here, we reconstruct past magnetic (or paleomagnetic) variations over parts of the last 4.5 million years using a sediment core from the Caribbean Sea collected by the Integrated Ocean Drilling Program. A deterioration in the quality of the paleomagnetic signal occurred about 2.1 million years ago, however, prior to that time, the sediments preserve a high fidelity paleomagnetic record at a temporal resolution higher than any previously obtained. Good agreement to existing data from 2.1 to 3 million years ago builds confidence in the quality of our new observations. Although we find no evidence for a previously observed change in magnetic field intensity at around 4 million years ago, differences in mean inclination during normal as compared to reverse polarity intervals are observed, suggesting field asymmetries during this time interval. The unparalleled quality and length of our new record means we can now begin to define characteristic geomagnetic field behavior during times rarely observed. Key Points: Rock and paleomagnetic filtering provide a more robust estimate of relative paleointensity (RPI) that is used to refine the Integrated Ocean Drilling Program Site (IODP) U1396 δ18O chronostratigraphyIODP Site U1396 provides the longest, highest‐resolution, independently dated record of RPI to establish characteristic Pliocene behaviorPlio‐Pleistocene inclination anomaly contains a strong polarity bias and RPI asymmetry may be a characteristic feature of the Gauss chron [ABSTRACT FROM AUTHOR]

Abstract Noble gas abundance and isotope data from 12 drilling mud gas samples obtained during IODP Expeditions 338 and 348 provide new insights on fluid origin and fluid migration in the inner accretionary prism below the Kumano forearc basin offshore SE Japan. The samples originate from three adjoining boreholes (C0002F, C0002N and C0002P) spanning depths between 950 and 3050 meters below sea floor (mbsf) and are composed of air and variable contributions of mantle-derived and crustal fluids. Air-corrected 3He/4He ratios of samples from Exp. 338 fall between 0.44 ± 0.24 Ra and 3.26 ± 0.28 Ra. Samples #1400 and #1800 (sample number denotes depth in mbsf) are more influenced by radiogenic helium (1.33 ± 0.34 Ra resp. 0.44 ± 0.24 Ra), whereas the air-free helium isotopic composition of sample #950 is clearly higher (3.26 ± 0.28 Ra). Enhanced radon activity around 950 mbsf, 1100 mbsf, 1400 mbsf, and 1800 mbsf suggests active flow of fluids at these depths. The helium isotopic composition of two other samples (#1700 and #1850) collected during Exp. 338 and of all samples obtained during the 1-year-later Exp. 348 are less variable (1.74–2.46 Ra with a mean 3He/4He ratio of ~ 2.4 Ra) and no radon anomalies were observed during sampling. For these samples, we assume migration by diffusive flow of helium-bearing fluids through sediments of the accretionary prism. In contrast, elevated radon activities and the more variable helium isotopic composition of fluids from 950, 1400, and 1800 mbsf from Exp. 338 are better explained by channelized and active fluid flow through temporarily permeable strata, maybe as a short-term episodic flow event caused by reactivation of buried trust faults. The helium isotopic composition of #950 is in good agreement with estimated helium isotope values of the subducting Philippine Sea Plate (PSP) at present (~ 3.4 Ra), whereas fluids from 1400 and 1800 mbsf demonstrate the input of radiogenic helium from a crustal, probably terrestrial source.

Abstract Previous studies showed that the evolution of the Japan Sea paleoceanography since the Miocene has been influenced by the regional tectonism (e.g., opening/closing of the connecting seaways) and regional/global climate. In the Japan Sea, Expedition 346 of the Integrated Ocean Drilling Program (IODP) retrieved core sediments dating back to the Miocene at two sites (U1425 and U1430). In this study, we reconstruct shallow-to-deep-water hydrography of the Japan Sea during the Mio-Pliocene based on radiolarian assemblages at Sites U1425 and U1430 considering the local tectonism and changes in global/regional climate. Our data suggest that glacioeustatic sea-level changes have probably had an influence on the local paleoceanography between 9.5 and 7.0 Ma. Indeed, warm water probably flowed from the North Pacific into the Japan Sea when sea level was high via shallow central and eastern seaways. In addition, the sill depth of the northern seaway was probably close to 1000 m between 9.5 and 7.8 Ma and had probably allowed inflow of oxygen minimum zone water from the North Pacific to the Japan Sea when sea level was high. In contrast, our data imply that Cycladophora nakasekoi, an endemic species to the Japan Sea, dominated between 9.5 and 7.3 Ma when sea level was low. Our data also suggest a progressive shoaling of the sill for the period since 7.8 Ma and that global climatic events such as such the late Miocene cooling (7.5–5.5 Ma) and the early Pliocene warmth have had a sustained influence on the Japan Sea. During the mid-Pliocene, a deep cooling of the subsurface to intermediate water of the Japan Sea likely occurred because species related to subarctic subsurface to intermediate waters were dominant between 5 and 3.8 Ma. The Northern Hemisphere Glaciation (ca. 3.0–2.7 Ma) and Mid-Pleistocene Transition (1.2–0.8 Ma) have both likely intensified the cooling of the Japan Sea.

Abstract Integrated Ocean Drilling Program Expedition 346 “Asian Monsoon” obtained sediment successions at seven sites in the Japan Sea (Sites U1422–U1427 and U1430) and at two closely located sites in the northern East China Sea (Sites U1428 and U1429). The Quaternary sediments of the Japan Sea are characterized by centimeter- to decimeter-scale dark–light alternations at all sites deeper than 500 m water depth. The sedimentary records from these sites allow an investigation of the regional environmental response to global climate change, including changes in the Asian Monsoon and eustatic sea level. However, the discontinuous occurrence of calcareous microfossils in the deep-sea sediments and their distinct isotope signature that deviates from standard marine δ18O records do not permit the development of a detailed stable isotope stratigraphy for Japan Sea sediments. Here, we present the tephrostratigraphy for the two southernmost sites drilled in the Japan Sea (Sites U1426 and U1427) and for one site drilled in the East China Sea (Site U1429) along with the benthic δ18O isotope stratigraphy for the shallower Site U1427 and the East China Sea Site U1429. Eighteen tephra layers can be correlated between sites using the major-element composition and morphology of volcanic glass shards, and the compositions of grains and heavy minerals. Tephra correlations show that negative δ18O peaks in the Japan Sea correspond to positive glacial maxima peaks in the East China Sea. Using this integrated stratigraphic approach, we establish an orbital-scale age model at Site U1427 for the past 1.1 Myr. The correlation of tephra layers between the shallower Site U1427 (330 m below sea level: mbsl) and the deeper Site U1426 (903 mbsl) in the southern Japan Sea provides the opportunity for further age constraints. Our results show that alternations in sediment color at Sites U1426 and U1427 can be correlated for the past 1.1 Myr with minor exceptions. Thus, the stable isotope stratigraphy established at the shallower Site U1427 can be correlated to Site U1426, and in turn to all sites drilled during Expedition 346, based on correlations of dark–light layering.

Basin models can simulate geological, geochemical and geophysical processes and potentially also the deep biosphere, starting from a burial curve, assuming a thermal history and utilizing other experimentally obtained data. Here, we apply basin modelling techniques to model cell abundances within the deep coalbed biosphere off Shimokita Peninsula, Japan, drilled during Integrated Ocean Drilling Program Expedition 337. Two approaches were used to simulate the deep coalbed biosphere: (a) In the first approach, the deep biosphere was modelled using a material balance approach that treats the deep biosphere as a carbon reservoir, in which fluxes are governed by temperature‐controlled metabolic processes that retain carbon via cell‐growth and cell‐repair and pass it back via cell‐damaging reactions. (b) In the second approach, the deep biosphere was modelled as a microbial community with a temperature‐controlled growth ratio and carrying capacity (a limit on the size of the deep biosphere) modulated by diagenetic‐processes. In all cases, the biosphere in the coalbeds and adjacent habitat are best modelled as a carbon‐limited community undergoing starvation because labile sedimentary organic matter is no longer present and petroleum generation is yet to occur. This state of starvation was represented by the conversion of organic carbon to authigenic carbonate and the formation of kerogen. The potential for the biosphere to be stimulated by the generation of carbon‐dioxide from the coal during its transition from brown to sub‐bituminous coal was evaluated and a net thickness of 20 m of lignite was found sufficient to support an order of magnitude greater number of cells within a low‐total organic carbon (TOC) horizon. By comparison, the stimulation of microbial populations in a coalbed or high‐TOC horizon would be harder to detect because the increase in population size would be proportionally very small. [ABSTRACT FROM AUTHOR]

We present new meteoric 10Be concentration data from marine sediment cores recovered during Integrated Ocean Drilling Program Expedition 343 (JFAST) that help constrain the age, origin, and internal structure of the frontal prism at the Japan trench in the vicinity of the 2011 Tohoku‐oki M9 earthquake rupture. 10Be sediment ages from the lower portion of the frontal prism range from ~0–10 Ma, with >60% of analyzed samples above the décollement yielding young ages <2 Ma. Repetition and inversion of high‐over‐low 10Be‐concentration sediments indicate the presence of stratigraphic inversions that correspond to faulting and imbrication of late Miocene and Quaternary sediments. The density of faults inferred indicates that the frontal prism has a fault spacing on the order of 10 s of meters, and the identification of faults in the underthrust section suggests that the plate boundary décollement may be a zone with multiple slip surfaces. Comparison of 10Be concentrations in the frontal prism with those of the incoming and forearc slope sediments indicates that the majority of the prism is sourced from accretion of Pacific Plate sediments, rather than from reworked frontal prism or slope sediments. These data suggest that over at least the past ~1–2 Ma, the décollement preferentially has localized at or near the base of the incoming sediment section, with relatively efficient sediment accretion occurring even in the presence of subducted horst‐and‐graben topography. Plain Language Summary: We help constrain the physical and mechanical properties of the materials near the trench that hosted the 2011 Tohoku M9 earthquake and tsunami and test whether sediments from the Pacific Plate are scraped off or subducted as they enter the subduction zone. We use sediments from cores recovered during the Integrated Ocean Drilling Program Expedition 343. Because traditional sedimentologic and biostratigraphic techniques alone are not sufficient to determine sediment source region, we apply a new approach using the radioactive decay of the 10Be isotope. We use 10Be to date sediments, to identify sediments that have been faulted out of chronologic order, and to correlate sediments between sites. Our results show numerous faults in the system, likely resulting from multiple stages of deformation during slip over rough seafloor topography. Our data also indicate that 50–90% of the sediments on the incoming Pacific Plate are scraped off and 10–50% of the incoming sediments are subducted. The subducted sediments consist of muds and frictionally weak clays that might promote slip during subduction earthquakes. Similar approaches may provide insight on the composition and evolution of faults that host large earthquakes and tsunami at other plate boundaries. Key Points: Meteoric 10Be provides high‐resolution age control in the frontal prism of the Japan trench at IODP Exp 343 (JFAST) Site C0019The frontal prism and plate boundary contain faults at decameter scale spacing, possibly due to subduction of horst‐and‐graben topographyThe majority of incoming sediments at this location have been accreted to the overriding plate during at least the Quaternary period [ABSTRACT FROM AUTHOR]

The strength of accretionary prisms is important for understanding their formation and the generation of earthquakes along the underlying plate boundary faults. We establish a continuous depth profile of rock strength and possible ranges of the minimum and maximum horizontal stresses (Shmin and SHmax) based on indentation tests on cuttings samples at the Integrated Ocean Drilling Program (IODP) Site C0002 in the Nankai accretionary prism. The rock strength (i.e., differential stress) increases with depth from 5.1 and 11.0 MPa at 975 meters below the seafloor (mbsf) to 22.8 and 59.6 MPa at 3005 mbsf in normal and reverse faulting regimes, respectively. The minimum value of Shmin and the maximum value of SHmax range from 33.2 and 49.4 MPa at 975 mbsf to 57.1 and 139.6 MPa at 3005 mbsf, respectively. Our estimated strength, in combination with Coulomb wedge model, may improve understanding of the evolution of accretionary prisms. Key Points: Strength of the inner Nankai accretionary prism is estimated from indentation tests on cuttingsOur estimation constrains the ranges of possible maximum and minimum principal stresses, which are limited by rock strength and loading stress regimesDifferential stress reaches 57.1 and 139.6 MPa at ~3 km below seafloor for the normal and reverse faulting stress regimes, respectively [ABSTRACT FROM AUTHOR]

Volatile fatty acids (VFA) are key intermediates in the degradation pathway of organic matter (OM) in marine sediments. They are products of fermentation and are utilized as substrates in the terminal steps of microbial OM mineralization, such as sulfate reduction and methanogenesis. We studied the distribution of formate, acetate, propionate and butyrate concentrations in the pore water throughout 100-m deep sedimentary sequences in the Baltic Sea. The sediments included both sulfate and methane zones and were retrieved during the Integrated Ocean Drilling Program Expedition 347. VFA concentrations were consistently low throughout the sulfate and methane zones, ranging from few hundred nanomolar to about hundred micromolar, thus pointing to efficient microbial utilization in the terminal OM mineralization steps in both zones. Concentrations of formate followed a different depth trend than the other three VFAs suggesting a different mechanistical control of the formate turnover. Calculations of the Gibbs energy reveal that acetoclastic methanogenesis is exergonic (up to −30 kJ (mol CH 4)−1) throughout the sulfate zone and suggest that methanogens can potentially coexist with sulfate reducers in the sulfate zone while sharing acetate as a substrate. In the deeper methane-rich sediments, the energy yield of acetoclastic methanogenesis is generally very low (less negative than −10 kJ (mol CH 4)−1). The uniformly low acetate concentrations in the methane zone suggest its active microbial turnover but the pathway from acetate to methane still remains unclear. Interestingly, acetoclastic sulfate reduction still yields at least −20 kJ (mol sulfate)−1 in the methane zone and, thus, sulfate reducers may utilize acetate as electron donor in the methane zone, which is in agreement with the earlier findings of sulfate reducers in methanogenic sediments. [ABSTRACT FROM AUTHOR]

The Louisville Seamounts display age progressive volcanism and are thought to have formed as the Pacific Plate moved over a long‐lived primary hot spot. Here we present 70 new 40Ar/39Ar age results from the Integrated Ocean Drilling Program (IODP) Sites U1372, U1375, U1376, and U1377 drilled and cored during Expedition 330 to the northern, older end of the Louisville Seamounts. The five seamounts drilled are flat‐topped guyots with ages ranging from ∼74 Ma (Canopus Guyot) to ∼51 Ma (Hadar Guyot) recovering up to ∼510 m of basaltic material beneath thin sediment interfaces. Our 40Ar/39Ar measurements reveal that throughout each drill hole, most dates are constant within ∼500‐900 kyr at the 2σ confidence interval. In this study we use the new Louisville age information to compare against the Hawaiian‐Emperor trail on the Pacific Plate. The Louisville hot spot trail is low volume, dominantly alkali basalt, and seamounts have a relatively short lifespan up to ∼4 Myr, whereas the Hawaiian hot spot trail is high volume, has a tholeiitic shield‐building stage capped by an alkalic post‐shield stage, and has a lifespan up to ∼6‐7 Myr. Here we show a new approach to estimating a seamount's inception age based on the known cumulative age distributions for seamounts in the Louisville Seamount and Hawaii‐Emperor Seamount trails. Based on our new 40Ar/39Ar analyses, we conclude that existing absolute plate motion models misrepresent the age progression of Louisville Seamounts and that the timing of the Hawaiian‐Emperor Bend and the 169°W bend in the Louisville Seamounts are asynchronous by ~3.7 Myr. Key Points: The timing of the Hawaiian‐Emperor Bend and the 169°W bend in the Louisville Seamounts are asynchronous by ~3.7 MyrThe Louisville lava flows analyzed are successfully corrected for the presence of trapped 40Ar* with initial 40Ar/36Ar ratios up to 8,700Previously assigned seamount ages in absolute plate motion modeling misrepresent the inception ages of hot spot seamounts [ABSTRACT FROM AUTHOR]

To help understand volcanic facies in the subsurface, data sets that enable detailed comparisons between down-hole geophysical data and cored volcanic intervals are critical. However, in many cases, the collection of extended core intervals within volcanic sequences is rare and often incomplete due to challenging coring conditions. In this contribution we outline and provide initial results from borehole logging operations within two fully cored lava-dominated borehole sequences, PTA2 and KMA1, on the Big Island of Hawai'i. Data for spectral gamma, magnetic susceptibility, dipmeter resistivity, sonic, total magnetic field, temperature and televiewer wireline logs were successfully acquired for the open hole interval ca. 889 m to 1567 m within the PTA2 borehole. Spectral gamma was also collected from inside the casing of both wells, extending the coverage for PTA2 to the surface and covering the interval from ca. 300 to 1200 m for KMA1. High-quality core material was available for both boreholes with almost complete recovery which enabled high-resolution core-to-log integration. Gamma data are generally low commonly in the range ca. 7–20 gAPI but are shown to increase up to API of ca. 60 with some intrusions and with increases in hawaiite compositions in the upper part of PTA2. Velocity data are more variable due to alteration within porous volcanic facies than with burial depth, with a general degrease down-hole. The high-resolution televiewer data have been compared directly to the core, enabling a comprehensive analysis of the variations in the televiewer responses. This has enabled the identification of key features including individual vesicles, vesicle segregations, strained vesicles, chilled margins, rubble zones, intrusive contacts and pāhoehoe lobe morphologies, which can be confidently matched between the televiewer data and the full diameter core. The data set and results of this study include findings which should enable improved borehole facies analysis through volcanic sequences in the future, especially where down-borehole data and images but no core are available. [ABSTRACT FROM AUTHOR]

Abstract Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG 01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora , Acropora gr. humilis , Dipsastraea gr. pallida , Porites , and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora , including A. gr. humilis , and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales. Highlights • IODP 325 cores record history of GBR reef communities during past 30,000 years. • The GBR during the LGM is comprised coral taxa that are major reef-builders today. • LGM corals along the shelf edge may have been important to reseed reef upslope. • 13 ka transition to barrier reef occurs with shift to robust branching acroporids. • Sea-level, shelf morphology and sedimentation controlled reef community changes. [ABSTRACT FROM AUTHOR]

Abstract Olivine-rich troctolites (>70% olivine) reveal that extensive melt impregnation of pre-existing olivine-rich lithologies participate to the building of slow spread oceanic crust. To constrain their origin and their impact on the structure and geochemistry of oceanic crust, we realized a multi-scale petro-structural, geochemical, and numerical modeling study of olivine-rich troctolites drilled at IODP Hole U1309D (Atlantis Massif, Mid-Atlantic Ridge 30°N). Discrete intervals of olivine-rich troctolites display sharp to diffuse contacts with neighboring troctolites or gabbros. Their texture is characterized by plastically deformed (high temperature imprint), corroded coarse-grained to undeformed fine-grained olivine embayed in poikilitic clinopyroxene and plagioclase. Olivine crystallographic preferred orientations show weak [001] clusters. Olivine has variable major and minor element compositions, but similar fractionated REE (Dy N /Yb N = 0.04–0.11). We distinguished three types of olivine-rich troctolites based on microstructure, texture and mineral composition. Olivine-rich troctolites 1 and 2 display sharp contacts with adjacent lithologies. Type 1 has modal olivine <75%, occurring mainly as single rounded grains with primitive compositions (Mg# = 85–86), and associated with high Mg# clinopyroxene. Type 2 has higher olivine modes (>75%), dominantly forming aggregates, showing more evolved compositions (Mg# = 83–84) and associated with slightly lower Mg# clinopyroxene. These variations of olivine modes and compositions are in contrast to common trends of magmatic crystallization that predicts decreasing modal olivine with melt differentiation towards evolved compositions. Type 3 has diffuse contacts with gabbroic veins and modal olivine overlapping those of types 1 and 2. Chemical traverses along principal crystallographic axes of olivine are flat, suggesting local equilibrium between olivine and neighboring phases. Mineral modes and compositions, together with textures and microstructures, suggest that olivine-rich troctolites formed after melt-rock interactions in a reactive porous flow process. Their compositions are best modeled by percolation of primitive MORBs into Hole U1309D impregnated and compositionally heterogeneous harzburgites, triggering orthopyroxene dissolution, followed by olivine assimilation and concomitant crystallization of clinopyroxene and plagioclase. Modeling shows that Ni variations in olivine at constant Mg# are mantle inherited. Compositions of olivine-rich troctolite 1 are fitted assuming higher olivine assimilation (M a = 0.06–0.13) in contrast to olivine-rich troctolites 2 and 3 (M a = 0.01–0.02). Olivine-rich troctolite 3 was 'buffered' by crystallizing reacted melts, progressively more evolved as temperature decreased during a late stage process. We interpret olivine-rich troctolites from the Atlantis Massif as marking local assimilation of harzburgitic mantle into the gabbroic sequence during a period of enhanced magmatism at depth. Our study shows that the distribution and variable compositions of olivine-rich troctolites result from the incipient stages of this process when local spatial variations in mantle rock permeability, probably related to pyroxene distribution, controlled in turn melt transport and mantle-melt interactions. Highlights • Multi-scale, petro-structural and geochemical study, and numerical modeling of olivine-rich troctolites from Atlantis Massif. • Clinopyroxene-olivine geochemical profiles suggest local melt-rock interactions and re-equilibration processes. • Modeling shows that olivine in reactive olivine-rich troctolites is mantle inherited. • Formation of reactive olivine-rich troctolites is controlled by mantle permeability. • This study provide the principle microstructural and petro-geochemical characteristics of reactive olivine-rich troctolites. [ABSTRACT FROM AUTHOR]

Abstract Continuous and high-resolution records of the content, mass accumulation rate (MAR) and δ 13 C values of black carbon obtained from Integrated Ocean Drilling Program (IODP) Site U1430 in the southwestern Japan Sea have been established and combined with previous results obtained from Central Asia. The main objective of this work is to reconstruct the historical changes in vegetation types (C3–C4), and to constrain the driving force of C4 plant expansion over the last 13 Ma. The stable carbon isotope value of black carbon (δ 13 C BC) shows a major shift since the Miocene–Pliocene boundary (∼5.3 Ma), suggesting significant expansion of C4 plants in broad areas of Central Asia, including the inland basins of northwestern China and the Loess Plateau. However, a decline in the content and MAR of black carbon reveals the absence of any link between fire and C4 plant expansion in Central Asia, due to the dramatic decrease in biomass under a drying regime. On a global scale, asynchronous expansion of C4 plants suggests that regional hydroclimatic change, rather than decline in CO 2 concentration, was the most important factor to influence C4 expansion. We propose that the increased seasonality and the enhanced long-term aridity driven by the concurrent decline in winter westerly vapor, and increase in East Asian summer monsoon precipitation, were the main driving forces of C4 plant expansion in broad areas of Central Asia. Variations in winter westerly moisture have played a significant role in changes of regional climate and vegetation in Central Asia since the late Miocene. Highlights • We reconstruct an evolutionary history of Asian C4 plants since the middle Miocene. • C4 plant expansion in Central Asia occurred at the Miocene–Pliocene boundary. • Increased seasonality and aridity drove C4 expansion in Central Asia at 5.3 Ma. [ABSTRACT FROM AUTHOR]

The 11 March 2011 (Mw 9.0) Tohoku-Oki earthquake ruptured through the shallowest part of the subduction zone plate-boundary fault, producing tens of meters of displacement at the seafloor and a devastating tsunami. Because elastic and mechanical properties of faults and wall rocks are controlling factors in earthquake generation and propagation, information on these properties is essential to understanding and accurately modeling earthquake rupture and tsunami generation. Laboratory ultrasonic velocity measurements of samples of rock surrounding the Tohoku earthquake principal fault zone recovered by drilling during IODP Expedition 343 (JFAST) show that, under in situ conditions, materials in the frontal accretionary prism are slow and compliant, with P-wave velocities of 2.0-2.4 km/s, S-wave velocities of 0.8-1.0 km/s, and shear modulus of 1.0-2.3 GPa. In order to better understand the elastic properties of shallow subduction zone sediments, we compare our measurements from the Japan Trench to values from analogous shallow subduction zone drill core samples from other locations. We find that shallow subduction zone accretionary prism sediments in general have shear modulus values an order of magnitude lower than what is commonly used in earthquake rupture simulation models. We present a model of the shear modulus of the Japan Trench outer forearc based on laboratory and field measurements that can be adapted for use at other subduction zones and used in dynamic rupture models to improve seismic and tsunami hazard estimates. [ABSTRACT FROM AUTHOR]

We examine the importance of dispersed volcanic ash as a critical component of the aluminosilicate sediment entering the Nankai Trough, located south of Japan's island of Honshu, via the subducting Philippine Sea plate. Multivariate statistical analyses of an extensive major, trace, and rare earth element data set from bulk sediment and discrete ash layers at Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 quantitatively determine the abundance and accumulation of multiple aluminosilicate inputs to the Nankai subduction zone. We identify the eolian input of continental material to both sites, and we further find that there are an additional three ash sources from Kyushu and Honshu, Japan and other regions. Some of these ash sources may themselves represent mixtures of ash inputs, although the final compositions appear statistically distinct. The dispersed ash comprises 38 ± 7 weight percent (wt%) of the bulk sediment at Site C0011, and 34 ± 4 wt% at Site C0012. When considering the entire sediment thickness at Site C0011, the dispersed ash component supplies 38000 ± 7000 g/cm2 of material to the Nankai subduction system, whereas Site C0012 supplies 20000 ± 3000 g/cm2. These values are enormous compared to the ~2500 g/cm2 (C0011) and ~1200 g/cm2 (C0012) of ash in the discrete ash layers. Therefore, the mass of volcanic ash and chemically equivalent alteration products (e.g., smectite) that are dispersed throughout the stratigraphic succession of bulk sediment appears to be up to 15-17 times greater than the mass of discrete ash layers. The composition of the dispersed ash component at Site C0011 appears linked to that of the discrete layers, and the mass accumulation rate for dispersed ash correlates best with discrete ash layer thickness. In contrast, at Site C0012 the mass accumulation rate for dispersed ash correlates better with the number of ash layers. Together, the discrete ash layers, dispersed ash, and clay-mineral assemblages present a complete record of volcanism and erosion of volcanic sources; and indicate that mass balances and subduction factory budgets should include the mass of dispersed ash for a more accurate assessment of volcanic contributions to large-scale geochemical cycling. [ABSTRACT FROM AUTHOR]

Integrated Ocean Drilling Program (IODP) Expedition 318 recovered a ∼170 m long Holocene organic-rich sedimentary sequence at Site U1357. Located within the narrow but deep Adélie Basin close to the Antarctic margin, the site accumulated sediments at exceptionally high sedimentation rates, which resulted in extraordinary preservation of the organic sedimentary component. Here, we present an overview of 74 different mainly marine microfossil taxa and/or types found within the organic component of the sediment, which include the remains of unicellular and higher organisms from three eukaryotic kingdoms (Chromista, Plantae, and Animalia). These remains include phytoplanktonic (phototrophic dinoflagellates and prasinophytes) and very diverse zooplanktonic (heterotrophic dinoflagellates, tintinnids, copepods) organisms. We illustrate each marine microfossil taxon or type identified by providing morphological details and photographic images, which will help with their identification in future studies. We also review their ecological preferences to aid future (palaeo)ecological and (palaeo)environmental studies. The planktonic assemblage shows a high degree of endemism related to the strong influence of the sea-ice system over Site U1357. In addition, we found the remains of various species of detritus feeders and bottom-dwelling scavengers (benthic foraminifers and annelid worms) indicative of high export productivity at Site U1357. This study shows the potential of organic microfossil remains for reconstructing past environmental conditions, such as sea-ice cover and (export) productivity. [ABSTRACT FROM AUTHOR]

Guyots are large seamounts with a flat summit that is generally believed to form due to constructional biogenic and/or erosional processes during the formation of volcanic islands. However, despite their large abundance in the oceans, there are still very few direct constraints on the nature and formation of guyots, in particular those formed at high latitude that lack a thick cap of shallow-marine carbonate rocks. It is largely accepted based on geophysical constraints and surficial observations/sampling that the summit platform of these guyots is shaped by wave abrasion during post-volcanic subsidence of volcanic islands. Here we provide novel constraints on this hypothesis and the summit geology of guyots with a lithostratigraphic analysis of cores from three Louisville seamounts (South Pacific) collected during Expedition 330 of the Integrated Ocean Drilling Program (IODP). Thirteen lithofacies of sedimentary and volcanic deposits are described, which include facies not previously recognized on the top of guyots, and offer a new insight into the formation of high-latitude oceanic islands on a fast-moving plate. Our results reveal that the lithostratigraphy of Louisville seamounts preserves a very consistent record of the formation and drowning of volcanic islands, with from bottom to top: (i) volcaniclastic sequences with abundant lava-fed delta deposits, (ii) submarine to subaerial shield lava flows, (iii) post-volcanic shallow to deeper marine sedimentary rocks lacking thick reef deposits, (iv) post-erosional rejuvenated volcanic rocks, and (v) pelagic sediments. Recognition of erosional boundaries between subaerial lava flows and shallow-marine sedimentary rocks provides novel support for post-volcanic wave planation of guyots. However, the summit geology of Louisville seamounts is dissimilar to that of high-latitude Hawaiian-Emperor guyots that have emplaced in a similar tectonic and environmental setting and that include thicker lava stacks with apparently little lava-fed delta deposits. To explain observed lithostratigraphic discrepancy we propose that Louisville seamounts represent a distinct type of intraplate ocean volcano characterized by formation of a smaller island, with a central shield volcano surrounded by extended shallow-marine shelves formed by lava-fed deltas. In this interpretation the summit platform of Louisville-type guyots results from early (syn-volcanic) subaerial to shallow-marine constructional volcanic processes and marine erosion, enhanced by later (post-volcanic) wave planation. This contrasts with larger Hawaiian edifices that are capped by thicker shield volcanoes, and that develop an extended wave planation surface during post-volcanic subsidence (in the absence of efficient coral growth). The difference between Hawaiian- and Louisville-type volcanic islands and guyots can be explained by contrasted dynamic disequilibrium between magmatic growth, erosion, and subsidence during the island-building stage. Unlike Hawaiian-type volcanoes, Louisville seamounts are characterized by alkaline magmatism that extends from the late seamount to island stages. This supports more limited magmatic growth during the formation of Louisville islands, and we hypothesize that this promotes the formation of ephemeral shallow-marine platforms and extended lava-fed deltas. Hawaiian-type volcanoes and guyots are unusually large in the population of intraplate ocean volcanoes. Louisville-type guyots as defined in this study could therefore represent a very common but yet poorly documented mode of oceanic island formation in the Pacific Ocean and other similar fast-moving plate settings. [ABSTRACT FROM AUTHOR]

A high-resolution potassium content record of sediments from Integrated Ocean Drilling Program (IODP) Site U1422 drilled in the northern Sea of Japan was employed to yield an astronomical timescale for this ∼205 m thick sedimentary archive. The K content was quantified using the natural gamma radiation (NGR) data routinely measured on DV JOIDES Resolution . The U1422 K (wt.%) series shows an increasing trend with time, which parallels the growth of North Hemisphere ice sheets since ∼4 Ma, as revealed by the global benthic foraminifer's oxygen isotope stack (LR04). We propose that K content variations reflect changes in the relative contributions of Asian eolian dust and volcanic weathering products, in response to changes in global ice volume. Using the shipboard age model, constrained by palaeomagnetism and nanofossils datums, we tuned the U1422 K content variations to the LR04 stack. Our tuned age model for site U1422 goes back to 3.9 Ma. The studied record indicates that Asian dust generation is enhanced during periods of global cooling. The synchronous variations between the U1422 K record and the LR04 stack also suggest that global cooling played a dominant role in promoting the central Asian aridification since ∼3.9 Ma, while the uplift of Tibetan Plateau plays a secondary role, considering many disagreements still exists between the timing and amplitude of the Qinghai-Tibetan uplift and the evolution of central Asian aridity since the early Pliocene. [ABSTRACT FROM AUTHOR]

The Subtropical Front (STF) is one of the major ocean fronts in the south-west Pacific. The STF migration has a distinct but varying impact on the temperature change throughout the region. To improve our understanding on the history of the STF migration and the relationship between STF migration and global climate change, we have generated a 450-kyr record of sea surface temperature (SST) change at IODP Site U1352 located in the Canterbury Basin off New Zealand. Planktonic foraminiferal assemblages from the site were used to derive SST estimates. Comparisons of the planktonic foraminiferal assemblage and SST record of IODP Site U1352 with those of ODP Site 1119, DSDP Site 594 and core MD06-2986 allow us to reconstruct the spatial change of the STF over the last 450 kyr by locating the positions of its Southland Front (SF) section, which runs nearly parallel to the South Island's shoreline. The percentage of Neogloboquadrina pachyderma in the sum of Nq. pachyderma and Nq. incompta was below 40% at Sites IODP U1352, ODP 1119 and DSDP 594 during Marine Isotope Stage (MIS) 11c, MIS 7a–c and MIS 5e. Moreover, the SSTs of the three sites during these periods were similar and close to that of the present-day. This indicates that the three sites were covered by a Subtropical Water–Subantarctic Water (STW–SAW) mixture during these interglacials. IODP Site U1352 recorded a similar scenario during MIS 7e. In comparison with previous studies, the higher resolution record of IODP Site U1352 showed the influence of an STW–SAW mixture was limited to MIS 11c, MIS 7e, MIS 7a–c and MIS 5e at this site. The SSTs of Sites IODP U1352, ODP 1119 and DSDP 594 were similar during MIS 11a–b and MIS 9a–d. At the same time, the temperature differences among the three sites and core MD06-2986 (west of New Zealand) during MIS 11a–b and MIS 9a–d were larger than during interglacials MIS 11c, MIS 7a–c, and MIS 5e. These indicate that the Subantarctic Water (SAW) influenced Sites IODP U1352, ODP 1119 and DSDP 594 during MIS 11a–b and MIS 9a–d. The ~3–4 °C warmer SSTs at Sites IODP U1352 and ODP 1119 than at DSDP Site 594 suggest that the SF is situated between DSDP Site 594 and Sites IODP U1352, ODP 1119 during MIS 7d and glacial periods of MIS 10, MIS 8, and MIS 6. Hence, unlike previous studies in the region, MIS 7d is identified as a glacial period. [ABSTRACT FROM AUTHOR]

Pelagic sediments accumulated atop Shatsky Rise since Early Cretaceous time provide a valuable record of Pacific paleoceanography. The accepted sedimentation model invokes relatively continuous pelagic sediment accumulation punctuated by four regional hiatuses caused by changes in oceanic chemistry. That framework was proposed more than two decades in the past and based on low-quality single channel seismic profiles. It was developed at the center of Tamu Massif, the main topographic high of Shatsky Rise, and extended to other highs with uncertainty owing to sparse data. The availability of high-quality seismic data and additional coring by the Ocean Drilling Program and Integrated Ocean Drilling Program allows a re-examination. Seismic and core data indicate that sedimentation atop Shatsky Rise has been complex, with regional and local variability. Four major hiatuses were previously defined and tentatively correlated to nearby topographic highs. These breaks occurred approximately during the Aptian-Barremian and Cenomanian-Coniacian ages of the Cretaceous and during the Paleocene and Oligocene epochs of the Cenozoic. They are of variable length and tend to be of shorter duration at the summit of Tamu Massif, but of longer durations elsewhere. All produced erosional unconformities that may be related to mass wasting of the sediment cap edges. Each hiatus is approximately correlated with global falls of sea level, suggesting a connection, perhaps to intensified bottom currents at those times. Local variability is observed in the form of discontinuous layering, non-uniform sedimentation, thinning of the sediment caps at their edges, and local erosion near topographic highs. These variations are likely the result of shifting bottom currents, possibly resulting from interactions of internal tides with topography. Shatsky Rise sedimentation is inherently punctuated and non-uniform and the sedimentary record includes significant lateral variability. Other large oceanic plateaus are likely to exhibit similar sedimentary cap complexities. [ABSTRACT FROM AUTHOR]

The Oligocene–Miocene transition (OMT; ~ 23.1 Ma) terminates the late Oligocene warming trend and is marked by a transient, large-amplitude expansion of Antarctic ice sheets. The associated glacial maximum, which is expressed by a ~ 1‰ positive shift in benthic foraminiferal oxygen-isotope values, is commonly referred to as the ‘Mi-1 isotope event’. Whereas the causes for the glacial maximum at the OMT are intrinsically connected to Southern Hemisphere ice-sheet dynamics, the behavior of the surface ocean in the Northern Hemisphere during this time is poorly known. To contribute to a better understanding of the paleoceanographic evolution during the OMT in the higher-latitude North Atlantic, we have analysed both marine and terrestrial palynomorphs from Integrated Ocean Drilling Program (IODP) Site U1406 offshore Newfoundland; this site has yielded a complete OMT section and exhibits a high-quality magnetostratigraphy that provides precise age control and allows reliable correlation to other records beyond Newfoundland. Our palynological data, which span the interval from 23.3 to 22.5 Ma and have a mean temporal resolution of 11.9 kyrs, show strong ~ 110-kyr eccentricity-paced oscillations during the earliest Miocene; these oscillations are in phase with similar cyclicity identified in previously published benthic foraminiferal oxygen-isotope records. More specifically, a pronounced sea-level variability is documented by the abundances of neritic dinoflagellate cysts (dinocysts) and terrigenous palynomorphs, which both reach maxima during peak glacial intervals as inferred from previously published South Atlantic benthic oxygen-isotope data. A decline in the abundance of warmer-water dinocysts suggests a surface-water cooling offshore Newfoundland from the latest Oligocene onwards. Surface-water productivity (as derived from the ratio between heterotrophic and autotrophic dinocysts) remained generally low throughout the studied interval. Notably, this ratio does not exhibit any correlation with changes in surface-water temperature, which is estimated from the ratio of warm-water over cold-water dinocysts. Together with the consistently low surface-water productivity, the lack of a correlation between surface-water productivity and temperature makes it highly unlikely that the observed paleoceanographic change was caused by a southward migration of the Arctic Front. Instead, we argue that our data may document an enhanced influence of the (Proto-) Labrador Current on surface waters offshore Newfoundland during the earliest Miocene that suppressed the influence of the Gulf Stream in this region of the Northwest Atlantic. We speculate that the enhanced influence of the (Proto-) Labrador Current was triggered by cooling of the northern hemisphere and possibly modulated by high-latitude sea-ice expansion. [ABSTRACT FROM AUTHOR]

Astronomical tuning of sediment sequences requires both unambiguous cycle pattern recognition in climate proxy records and astronomical solutions, as well as independent information about the phase relationship between these two. Here we present two different astronomically tuned age models for the Oligocene-Miocene transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning has on astronomically calibrated ages and the geologic timescale. These alternative age models (roughly from ~ 22 to ~ 24 Ma) are based on different tunings between proxy records and eccentricity: the first age model is based on an aligning CaCO3 weight (wt%) to Earth's orbital eccentricity, and the second age model is based on a direct age calibration of benthic foraminiferal stable carbon isotope ratios (δ13C) to eccentricity. To independently test which tuned age model and associated tuning assumptions are in best agreement with independent ages based on tectonic plate-pair spreading rates, we assign the tuned ages to magnetostratigraphic reversals identified in deep-marine magnetic anomaly profiles. Subsequently, we compute tectonic plate-pair spreading rates based on the tuned ages. The resultant alternative spreading-rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant, or linearly changing, spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n-C7n.1r, which are not based on astronomical tuning in the latest iteration of the geologic timescale. Furthermore, it provides independent evidence that the relatively large (several 10 000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity constitute a real feature of the Oligocene-Miocene climate system and carbon cycle. The age constraints from Site U1334 thus indicate that the delayed responses of the Oligocene-Miocene climate-cryosphere system and (marine) carbon cycle resulted from highly nonlinear feedbacks to astronomical forcing. [ABSTRACT FROM AUTHOR]

Phosphorus (P) concentrations in sediments are frequently used to reconstruct past environmental conditions in freshwater and marine systems, with high values thought to be indicative of a high biological productivity. Recent studies suggest that the post-depositional formation of vivianite, an iron(II)-phosphate mineral, might significantly alter trends in P with sediment depth. To assess its importance, we investigate a sediment record from the Bornholm Basin that was retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013, consisting of lake sediments overlain by brackish-marine deposits. Combining bulk sediment geochemistry with microanalysis using scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption spectroscopy (XAS), we demonstrate that vivianite-type minerals rich in manganese and magnesium are present in the lake deposits just below the transition to the brackish-marine sediments (at 11.5 to 12m sediment depth). In this depth interval, phosphate that diffuses down from the organic-rich, brackish-marine sediments meets porewaters rich in dissolved iron in the lake sediments, resulting in the precipitation of iron(II) phosphate. Results from a reactive transport model suggest that the peak in iron(II) phosphate originally occurred at the lake-marine transition (9 to 10 m) and moved downwards due to changes in the depth of a sulfidization front. However, its current position relative to the lake-marine transition is stable as the vivianite-type minerals and active sulfidization fronts have been spatially separated over time. Experiments in which vivianite was subjected to sulfidic conditions demonstrate that incorporation of manganese or magnesium in vivianite does not affect its susceptibility to sulfide-induced dissolution. Our work highlights that post-depositional formation of iron(II) phosphates such as vivianite has the potential to strongly alter sedimentary P records particularly in systems that are subject to environmental perturbation, such as a change in primary productivity, which can be associated with a lake-marine transition. [ABSTRACT FROM AUTHOR]

Salinity variations in restricted basins like the Baltic Sea can alter their vulnerability to hypoxia (i.e., bottom water oxygen concentrations <2 mg/l) and can affect the burial of phosphorus (P), a key nutrient for marine organisms. We combine porewater and solid-phase geochemistry, micro-analysis of sieved sediments (including XRD and synchrotron-based XAS), and foraminiferal δO and δC analyses to reconstruct the bottom water salinity, redox conditions, and P burial in the Ångermanälven estuary, Bothnian Sea. Our sediment records were retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013. We demonstrate that bottom waters in the Ångermanälven estuary became anoxic upon the intrusion of seawater in the early Holocene, like in the central Bothnian Sea. The subsequent refreshening and reoxygenation, which was caused by gradual isostatic uplift, promoted P burial in the sediment in the form of Mn-rich vivianite. Vivianite authigenesis in the surface sediments of the more isolated part of the estuary ultimately ceased, likely due to continued refreshening and an associated decline in productivity and P supply to the sediment. The observed shifts in environmental conditions also created conditions for post-depositional formation of authigenic vivianite, and possibly apatite formation, at ∼8 m composite depth. These salinity-related changes in redox conditions and P burial are highly relevant in light of current climate change. The results specifically highlight that increased freshwater input linked to global warming may enhance coastal P retention, thereby contributing to oligotrophication in both coastal and adjacent open waters. [ABSTRACT FROM AUTHOR]

IODP Expedition 357 utilized seabed drills for the first time in the history of the ocean drilling program, with the aim of collecting intact sequences of shallow mantle core from the Atlantis Massif to examine serpentinization processes and the deep biosphere. This novel drilling approach required the development of a new remote seafloor system for delivering synthetic tracers during drilling to assess for possible sample contamination. Here, we describe this new tracer delivery system, assess the performance of the system during the expedition, provide an overview of the quality of the core samples collected for deep biosphere investigations based on tracer concentrations, and make recommendations for future applications of the system. [ABSTRACT FROM AUTHOR]

Dinoflagellate cysts (dinocysts) are commonly used to reconstruct past environmental conditions at the sea surface, such as primary production, temperature and salinity. Abundances of selected dinocyst taxa are used in qualitative indices, whereas the modern analogue technique (MAT) is used for quantitative reconstructions. Qualitative indices use process-based knowledge of present-day relations between the environmental variables and the distribution of dinocysts, whereas the MAT is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions. Here we explore the potential of both approaches to reconstruct sea surface temperature (SST), production (SSP), salinity (SSS) and seasonality during the last 22 thousand years along the West Iberian Margin (WIM), at Integrated Ocean Drilling Program (IODP) Site U1385. We compare results to published paleoclimatic reconstructions. Our SST and SSS reconstructions provide the first continuous dinocyst MAT-based SST and SSS records for this area and time interval. Qualitative and quantitative dinocyst-based SST estimates from the WIM are similar and resemble previous SST estimates from dinocysts, alkenones and foraminifers from nearby sites. The surface temperature trends and millennial-scale variations largely match those from the Greenland ice core records. Quantitative MAT-based SST estimates show increased seasonality in the glacial stage resulting from strong winter cooling. Dinocyst MAT-based salinity decreases concomitantly with cooling during the Younger Dryas and Heinrich Stadial 1 (HS1), likely related to the melting of icebergs that reached the region during HS1. Our qualitative and quantitative SSP estimates show higher values in the glacial stage compared to the Holocene, which is consistent with published records and supports the usefulness of both approaches. Small differences between SST tracer records may be explained by the limited number of modern analogues from warm ocean regions in the dinocyst reference dataset for MAT, the small number of dinocysts used in the qualitative estimates, the possible effect of a parameter other than temperature that might amplify noise, and/or seasonal biases of the tracer species. In any case, the advantage of the qualitative approach is to allow reconstructions in non-analogue situations. Regression of the qualitative index versus present-day SST also allows for a quantitative reconstruction, although over a limited range of SSTs (especially towards the lower end) and with quite some uncertainty, but produces reasonable values beyond the upper limit of the MAT. The MAT reconstructs more reliable SSTs, with a much smaller error of prediction, but only up to present-day WIM values, because it is based on the assumption that past assemblages have modern counterparts that correspond to similar sea-surface conditions, which is not always valid. The advantages of the MAT approach include its quantitative nature and insights into seasonality. Hence both approaches are complementary. At Site U1385, MAT can be used for reconstructions in the colder periods (YD, HS1 and glacial stage), with a small error of prediction and the quantified index can be used to estimate SST beyond the limit of the MAT (Holocene and B-A). [ABSTRACT FROM AUTHOR]

We present high-resolution analyses of clay mineral assemblages combined with analysis of Sr–Nd–Pb isotopic compositions of the <2 μm silicate fraction of sediments from Integrated Ocean Drilling Program (IODP) Site U1430 in the southern Sea of Japan, in order to trace the sources of clay minerals and reconstruct proxy records of past changes in Asian eolian input to the basin since 15 Ma. The clay mineral assemblages at IODP Site U1430 mainly consist of smectite (∼51%) and illite (∼36%), with minor kaolinite (∼7%) and chlorite (∼6%). Provenance analysis suggests that the fine-grained sediment at the study site is a two end-member mixture of eolian dust from Central Asia and fluvial input from the Japanese islands. The Central Asian end member supplied illite-rich and high 87 Sr/ 86 Sr and low ε Nd(0) eolian dust to the study site by wind, while the Japanese end member, characterized by young volcanic rocks, contributed smectite-rich, low 87 Sr/ 86 Sr and high ε Nd(0) weathering products via rivers. The ratio of illite/smectite and ε Nd(0) values of clay-sized silicate sediments at Site U1430 were used as proxies for tracing the changing strength of central Asian eolian input to the Sea of Japan, and thus reconstruct the aridification history of its source region. Our study presents for the first time a continuous, high-resolution record that highlights the four-step drying of Central Asia that occurred at ∼11.8 Ma, 8 Ma, 3.5 Ma and 1.2 Ma. Considered the nature and timing of major climatic and tectonic events in Asia, we conclude that the strengthened aridification of Central Asia starting at ∼11.8 Ma was possibly driven by the combined effect of Tibetan surface uplift and global cooling, whereas the rapid drying at ∼8 Ma was caused primarily by the uplift of the northern Tibetan Plateau. In contrast, global cooling, overwhelming the influence of Tibetan Plateau uplift, has become the primary control on Central Asia aridification since ∼3.5 Ma. [ABSTRACT FROM AUTHOR]

During the Integrated Ocean Drilling Program (IODP) Expedition 331, five sites were drilled into the Iheya North Knoll hydrothermal system in the Okinawa Trough (OT) — a back-arc basin characterized by thick terrigenous sediment. Following up on the previous study by Shao et al. (2015), we present new mineralogical, geochemical, and Sr-Nd isotope data to investigate the origin of the hydrothermal sediments and characterize the hydrothermal system. The substrate at the Iheya North Knoll is dominated by pumiceous sediment and other volcanoclastic materials interbedded with hemipelagic (terrigenous and biogenous) sediments. Impermeable layers separate the hydrothermal sediments into distinct units with depth that are characterized by various assemblages of alteration materials, including polymetallic sulfides, sulfates, chlorite- and kaolinite-rich sediments. The rare earth elements (REEs) and Nd isotope data suggest that the chlorite-rich and kaolinite-rich layers primarily resulted from the alteration of pumiceous materials in different chemical and physical conditions. Kaolinite-rich sediment likely reflects low pH and low Mg concentration fluids, while chlorite-rich sediment formed from fluids with high pH and increased Mg contents, likely at higher temperatures. The Sr isotopic compositions of subsurface anhydrite reflect high seawater/hydrothermal fluid ratios in the mid-OT hydrothermal area. Compared with chlorite-rich sediments from other sediment-covered or felsic-hosted hydrothermal systems, the chlorite-rich sediments in the mid-OT are characterized by lower concentrations of Al and Fe but much higher Y, Zr, Hf, Th and REEs, indicative of the distinct nature of the precursor rocks in this region. [ABSTRACT FROM AUTHOR]

The presence and high abundances of the benthic foraminiferal group “elevated epifauna” has been proposed as indicator of the existence of Mediterranean Outflow Water (MOW) in the Gulf of Cadiz. Here we intend to use this potential proxy to reconstruct MOW in the early Pliocene at the Integrated Ocean Drilling Program (IODP) Hole U1387C. Cibicides lobatulus , Planulina ariminensis and Cibicides refulgens were found at this site, but high abundances of C. lobatulus and C. refulgens coincide with increases of shelf taxa and grain size, related to episodes of downslope transport. This issue calls into question the applicability of these species as MOW proxies. The present study therefore reassesses the role of these three elevated epifaunal species by means of stable isotope analyses (δ 18 O, δ 13 C) by contrasting their isotopic signature with that of shelf dwellers and deep-water taxa from Pliocene and Recent sediments from the Gulf of Cadiz and the western Iberian margin. Since foraminiferal calcite does not always precipitate in equilibrium with seawater, substantial efforts have been taken in order to determine species-specific offset values and to correct the isotopic signature for vital effects. Our corrected results demonstrate that C. lobatulus and C. refulgens are isotopically similar to the shelf dwellers in the Pliocene data-set, eliminating them as MOW indicators. Recent samples from the Gulf of Cadiz and the western Portugal shelf corroborate the wide bathymetric range of C. lobatulus from the shelf to the slope. Our results thus warrant for caution when considering C. lobatulus and C. refulgens as indicators of bottom current strength in unstable slope settings, particularly when co-occurring with allochthonous shelf dwellers. In contrast, P. ariminensis shows a signature close to deep-water taxa, corroborating its reliability as indicator of MOW. [ABSTRACT FROM AUTHOR]

The vertical profiles of chloride ion (Cl − ) concentration and oxygen and hydrogen isotopic ratios in pore fluids of basin-fill sediments in the southern Kumano Basin were examined. A model has been proposed to explain those profiles in conjunction with published data by invoking diffusion and advection of freshwater from methane hydrate dissolution. The model requires a low initial Cl − concentration in the old accretionary prism below the basin before the basin began to fill with sediments. It also requires little or no methane hydrate formation in the old accretionary prism. Given these requirements, an upward fluid advection rate of 1 × 10 −12 m/s has been estimated which is very low compared to other accretionary prisms. Our data suggests that the tectonic compaction of the basin-filling sediments and fault activity under the basin sediments have not been that active recently in the Kumano Basin. [ABSTRACT FROM AUTHOR]

The discovery of slow earthquakes has revolutionized the field of earthquake seismology. Defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults. We report on a family of recurring slow-slip events (SSEs) on the plate interface immediately seaward of repeated historical moment magnitude (Mw) 8 earthquake rupture areas offshore of Japan. The SSEs continue for days to several weeks, include both spontaneous and triggered slip, recur every 8 to 15 months, and are accompanied by swarms of low-frequency tremors. We can explain the SSEs with 1 to 4 centimeters of slip along the megathrust, centered 25 to 35 kilometers (km) from the trench (4 to 10 km depth). The SSEs accommodate 30 to 55% of the plate motion, indicating frequent release of accumulated strain near the trench. [ABSTRACT FROM AUTHOR]

Integrated Ocean Drilling Program (IODP) Expedition 303 to the North Atlantic provided 16 records of the Matuyama–Brunhes polarity transition (MBT), based on u-channel and discrete samples, from holes drilled at three sites (Sites U1304, U1305 and U1306) that have mean Brunhes sedimentation rates of 16–18 cm/kyr. The MBT occurs during the transition from marine isotope stage (MIS) 19c to MIS 18e, with mid-point at ∼773 ka, and a transition duration of ∼8 kyr. Combining the new MBT records, including one new record for the top Jaramillo, with previously published North Atlantic MBT records (ODP Sites 983, 984 and 1063) yields a total of more than 20 high-sedimentation-rate polarity transition records. The MBT yields a repetitive pattern of transitional field states as virtual geomagnetic poles (VGPs) move from high southern latitudes to loop over the Pacific, group in NE Asia, and transit into the mid-latitude South Atlantic before reaching high latitudes in the Northern Hemisphere. The VGPs for the top Jaramillo transition feature a loop over the Pacific, then a NE Asia group before transit over the Indian Ocean to high southerly latitudes. The North Atlantic MBT records described here contrast with longitudinally-constrained VGP paths for the MBT, indicating that relatively low sedimentation rate (∼4 cm/kyr) records of the MBT are heavily smoothed by the remanence acquisition process and do not adequately represent the MBT field. The VGPs at the MBT and top Jaramillo, as measured in the North Atlantic, have similarities with excursion (Iceland Basin) VGP paths, and were apparently guided by maxima in downward vertical flux similar to those seen in the modern non-dipole (ND) field, implying longevity in ND features through time. [ABSTRACT FROM AUTHOR]

For the first time during an Integrated Ocean Drilling Program (IODP) Expedition (Exp. 339, Mediterranean Outflow) water samples for living coccolithophore distributions and mudline samples for coccoliths, benthic foraminifera, and geochemical analyses in the underlying surface sediments were collected. In total, 14 water samples (from 5 to 20 m water depth) and 7 mudline samples were gathered at the drill sites. Coccolithophore distributions show spatial variations in species diversity. In particular, assemblages that characterize the Western Iberian Margin differ from those in the Gulf of Cadiz, indicative of oceanographic and environmental controls on the community in the upper ocean (0–20 m depth). Comparison of the living assemblages to those in surface sediments shows differences in the presence of some species, suggesting the influence of post deposition sedimentary processes. Other factors such as the season of sampling and the limited sampling depth may also have a role in the differences recorded. Benthic foraminiferal assemblages seem to be primarily determined by source, quantity and quality of available food. Sites in the Gulf of Cadiz are bathed by Mediterranean Outflow Water (MOW) and characterized by a considerable amount of advected food particles. Elevated epibenthic foraminifera exploit this niche, while arborescent epifaunal and infaunal taxa thrive on food particles falling out of MOW. The combined data suggest different flow speeds and settling of MOW suspension load in the Gulf of Cadiz. In contrast, assemblages from the Western Iberian Margin located farthest from or outside of MOW are determined by local export productivity and mirror trophic conditions in the surface waters. Both assemblages reveal variation in the composition at intermediate and deep water depths along the southern and western Iberian Margins with distance from the Strait of Gibraltar. [ABSTRACT FROM AUTHOR]

We investigate changes in benthic foraminiferal assemblages and estimate bottom water temperatures (BWT), based on Mg/Ca ratios of Oridorsalis umbonatus , over three selected intervals of major climate change during the late early to middle Miocene at Integrated Ocean Drilling Program (IODP) Sites U1337 (4463 m water depth) and U1338 (4200 m water depth), eastern equatorial Pacific Ocean. The targeted intervals are: (1) the onset of the Miocene Climatic Optimum (MCO; at ~ 16.9 Ma) and associated carbon cycle perturbation (Site U1337); (2) the episode of peak warmth within the MCO centered at 15.6 Ma (Site U1338); (3) the major cooling step at ~ 13.8 Ma related to east Antarctic ice-sheet expansion (Site U1338). Assemblages from these three intervals are mainly composed of cosmopolitan, long ranging (e.g., Paleogene to recent), lower bathyal to abyssal species, including calcareous elongated forms that became extinct during the middle Pleistocene. The onset of the MCO and interval of peak warmth had little impact on benthic foraminiferal accumulation rates (BFAR), abundances and assemblage composition. A transient BWT warming of 2.6 °C at the onset of the interval of peak warmth concurred with a benthic stable oxygen isotope (δ 18 O) decrease of 1‰, suggesting that the δ 18 O decrease was largely controlled by BWT changes. A substantial increase in BFAR and in the abundances of Epistominella exigua and epifaunal taxa after ~ 13.83 Ma coincides with increased opal accumulation rates, reflecting enhanced and seasonally pulsed organic carbon (C org ) flux to the seafloor during the global cooling step. During this interval, BWT decrease by 1.7 °C concurrent with a 1.0‰ increase in the stable oxygen isotope composition of seawater (δ 18 O sw ). Comparable trends at Ocean Drilling Program (ODP) Site 1146 in the South China Sea, with a 2.2 °C cooling and 0.9‰ increase in δ 18 O sw at ~ 13.8 Ma, further support that the benthic δ 18 O increase during the major cooling step was largely controlled by ice volume changes. [ABSTRACT FROM AUTHOR]

Modern seafloor hydrothermal systems provide important insights into the formation and discovery of ancient volcanic-hosted massive sulfide (VHMS) deposits. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 drilled five sites in the Iheya North hydrothermal field in the middle Okinawa Trough back-arc basin, Japan. Hydrothermal alteration and sulfide mineralization is hosted in a geologically complex, mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying a dacitic to rhyolitic volcanic substrate. At site C0016, located adjacent to the foot of the actively venting North Big Chimney massive sulfide mound, massive sphalerite-(pyrite-chalcopyrite ± galena)-rich sulfides were intersected (to 30.2% Zn, 12.3% Pb, 2.68% Cu, 33.1 ppm Ag and 0.07 ppm Au) that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan. Sulfide mineralization shows clear evidence of formation through a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Volcanic rocks beneath massive sulfides exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration reminiscent of VHMS proximal footwall alteration associated with Kuroko-type deposits, characterized by increasing MgO, Fe/Zn and Cu/Zn with depth. Recovered felsic footwall rocks are of FII to FIII affinity with well-developed negative Eu anomalies, consistent with VHMS-hosting felsic rocks in Phanerozoic ensialic arc/back-arc settings worldwide. Site C0013, ∼100 m east of North Big Chimney, represents a likely location of recent high temperature discharge, preserved as surficial coarse-grained sulfidic sediments (43.2% Zn, 4.4% Pb, 5.4% Cu, 42 ppm Ag and 0.02 ppm Au) containing high concentrations of As, Cd, Mo, Sb, and W. Near surface hydrothermal alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, indicative of acidic hydrothermal fluids. Alteration grades to Mg-chlorite dominated assemblages at depths of >5 mbsf (metres below sea floor). Late coarse-grained anhydrite veining overprints earlier alteration and is interpreted to have precipitated from down welling seawater as hydrothermal activity waned. At site C0014, ∼350 m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30 mbsf. Recovered lithologies from distal, recharge site C0017 are unaltered, with low MgO, Fe 2 O 3 and base metal concentrations. Mineralization and alteration assemblages are consistent with the Iheya North system representing a modern analogue for Kuroko-type VHMS mineralization. Fluid flow is focussed laterally along pumiceous volcaniclastic strata (compartmentalized between impermeable hemipelagic sediments), and vertically along faults. The abundance of Fe-poor sphalerite and Mg-rich chlorite (clinochlore/penninite) is consistent with the lower Fe budget, temperature and higher oxidation state of felsic volcanic-hosted hydrothermal systems worldwide compared to Mid Ocean Ridge black smoker systems. [ABSTRACT FROM AUTHOR]

Water properties change with confinement within nanofilms trapped between natural charged clay particles. We investigated nanofilm characteristics through high-stress laboratory compression tests in combination with analyses of expelled pore fluids. We utilized sediments obtained from deep drilling of the Nankai subduction zone at Site C0002 of the Integrated Ocean Drilling Program (IODP). We show that below 1–2 km, there should be widespread ultrafiltration of migrating fluids. Experiments to > ∼ 100 MPa normal compression collapse pores below a few ion monofilm thicknesses. A reduction towards a single condensing/dehydrating ion monofilm occurs as stresses rise >100–200 MPa and clay separations are reduced to <10–20 Å. Thus, porosity in high mineral surface area systems only consists of double and single monofilms at depths below a few km leaving little room for either bulk water or the deep biosphere. The resulting semipermeable properties result in variable segregation of ions and charged isotopes and water during active flow. The ultrafiltration and ion dehydration processes are coupled in that both require the partial immobilization of ions between the charged clay surfaces. The general effect is to increase salinities in residual pore fluids at depth and freshen fluids expelled during consolidation. Cessation of nanofilm collapse to a near constant ∼17 Å below 2 km depth at Nankai supports the contention for the onset of substantial geopressuring on the deeper seismogenic fault. The properties of monofilm water, thus, have considerable implications for the deep water properties of subduction zones generating major tremor and Mw 8+ earthquakes. Indeed, the combined effects of advective flow, ultrafiltration, diffusion, and diagenesis could provide a unifying explanation for the origins of overpressuring and pore water geochemical signals observed in many natural systems. [ABSTRACT FROM AUTHOR]

Site U1396 was piston cored as a part of Integrated Ocean Drilling Project Expedition 340 to establish a long record for Lesser Antilles volcanism. A ~150 m sediment succession was recovered from three holes on a bathymetric high ~33 km southwest of Montserrat. Aseries of shipboard and newly-generated chronostratigraphic tools (biostratigraphy, magnetostratigraphy, astrochronology, and stable isotope chemostratigraphy) were employed to generate an integrated age model. Two possible chronostratigraphic interpretations for the Brunhes chron are presented, with hypotheses to explain the discrepancies seen between this study and Wall-Palmer et al. (2014). The recentWade et al. (2011) planktic foraminiferal biostratigraphic calibration is tested, revealing good agreement between primary datums observed at Site U1396 and calibrated ages, but significant mismatches for some secondary datums. Sedimentation rates are calculated, both including and excluding the contribution of discrete volcanic sediment layers within the succession. Rates are found to be 'pulsed' or highly variable within the Pliocene interval, declining through the 1.5-2.4 Ma interval, and then lower through the Pleistocene. Different explanations for the trends in the sedimentation rates are discussed, including orbitally-forced biogenic production spikes, elevated contributions of cryptotephra (dispersed ash), and changes in bottom water sources and flow rates with increased winnowing in the area of Site U1396 into the Pleistocene. [ABSTRACT FROM AUTHOR]