Description: We present geochemical data collected from volcanic ash-bearing sediments on the upper slope of the northern Hikurangi margin during the RV SONNE SO247 expedition in 2016. Gravity coring and seafloor drilling with the MARUM-MeBo200 allowed for collection of sediments down to 105 meters below seafloor (mbsf). Release of dissolved Sr2+with isotopic composition enriched in 86Sr (87Sr/86Sr minimum = 0.708461 at 83.5 mbsf) is indicative of ash alteration. This reaction releases other cations in the 30-70 mbsf depth interval as reflected by maxima in pore-water Ca2+and Ba2+concentrations. In addition, we posit that Fe(III) in volcanogenic glass serves as an electron acceptor for methane oxidation, a reaction that releases Fe2+measured in the pore fluids to a maximum concentration of 184 μM. Several lines of evidence support our proposed coupling of ash alteration with Fe-mediated anaerobic oxidation of methane (Fe-AOM) beneath the sulfate-methane transition (SMT), which lies at ∼7 mbsf at this site. In the ∼30-70 mbsf interval, we observe a concurrent increase in Fe2+and a depletion of CH4with a well-defined decrease in δ13C-CH4values indicative of microbial fractionation of carbon. The negative excursions in δ13C values of both DIC and CH4are similar to that observed by sulfate-driven AOM at low SO2−4concentrations, and can only be explained by the microbially-mediated carbon isotope equilibration between CH4and DIC. Mass balance considerations reveal that the iron cycled through the coupled ash alteration and AOM reactions is consumed as authigenic Fe-bearing minerals. This iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals, as estimated from sequential extraction analyses. Using a numerical modeling approach we estimate the rate of Fe-AOM to be on the order of 0.4μmol cm−2yr−1, which accounts for ∼12% of total CH4removal in the sediments. Although not without uncertainties, the results presented reveal that Fe-AOM in ash-bearing sediments is significantly lower than the sulfate-driven CH4consumption, which at this site is 3.0μmol cm−2yr−1. We highlight that Fe(III) in ash can potentially serve as an electron acceptor for methane oxidation in sulfate-depleted settings. This is relevant to our understanding of C-Fe cycling in the methanic zone that typically underlies the SMT and could be important in supporting the deep biosphere.

Description: We present the first tephroanalysis based on geochemical fingerprinting of volcanic glass shards from eastern Apulian shelf sediments in the Gulf of Taranto (Italy). High sedimentation rates in the gulf are ideal for high-resolution paleoclimate studies, which rely on accurate age models. Cryptotephrostratigraphy is a novel tool for the age assessment of marine sediment cores in the absence of discrete tephra layers. High-resolution quantitative analysis of glass shard abundance in the uppermost 45 cm of a gravity core identified two cryptotephras. Microprobe analysis of glass shards supported by an accelerator mass spectrometry 14C-based age model identified the pronounced primary cryptotephra at 36 cm bsf (below sea floor) as the felsic AD 776 Monte Pilato Eruption on the island of Lipari, whereas the thinner, mafic tephra layer at 1.5 cm bsf is associated with the AD 1944 eruption of Somma-Vesuvius. Identifying these tephra layers provides an additional, 14C-independent, stratigraphic framework for further paleoclimatic studies allowing us to link Mediterranean climate and hydrology to orbital variation and large-scale atmospheric processes. Our results underline the importance of qualitative tephrostratigraphy in a highly geodynamic region, where solely quantitative approaches have demonstrated to bear a high potential for false correlations between tephra layers and eruptions.

Description: Highlights • Evaluation of environmental variability induced by Heinrich Stadials (HS5a-HS1) in continental northern Neotropical region. • Multiproxy evidence reveals mild temperature decreases and drastic fluctuations in precipitation during HSs. • Ultrastructure of HSs suggests individual environmental response of each Stadial making them contrasting from each other. • Most drastic climate changes induced by HSs exerted positive effects on diversity of aquatic communities. Abstract We reconstruct environmental conditions of the period 53-14 kyr BP in the continental northern Neotropical region. We evaluate in detail the magnitude of climatic fluctuations and their effects on aquatic communities during six Heinrich Stadials (HS1-HS5a), using sediments from Lake Petén Itzá, Guatemala, and a multiproxy approach. In Lake Petén Itzá typical Heinrich Stadials (HSs) are recorded in sediments as alternations of gypsum and clay, and abrupt changes in magnetic susceptibility, CaCO3 and biological compositions. This suggests that HSs were periods of hydrological unbalance, characterized by dry spells, punctuating the predominant humid conditions characterizing the period 53-14 kyr BP. The ultrastructure of HSs allows us to identify four different types of climatic conditions associated to HSs: 1) prevailing dry conditions but changing to humid (HS5, HS3); 2) predominantly humid conditions but changing to arid (HS2); 3) fluctuating humid-dry-humid (HS4, HS1); and 4) arid with high lake water conductivity (HS5a). The continuous presence of tropical ostracode species during HSs suggests that lake water temperatures were not drastically lowered. Ostracode-based transfer functions indicate that during HSs, epilimnetic water temperatures decreased by 1–3 °C compared to mean modern temperatures. Lake solute composition and conductivity were strongly affected by HSs. During HS5a and HS1 we estimate conductivity values 〉 800 μS cm−1. Diversity indices show significant differences (F5,70 = 3.74, p = 0.004) of ostracode species composition among HSs. Highest diversities occurred during HS5a, HS4 and HS1, which display greater climatic alterations than the other HSs. Fluctuating climates seem to have exerted positive effects on diversity of aquatic communities by producing an increase in habitat heterogeneity.

Description: Highlights • Sediment accumulation rates in Nicobar Fan abruptly increase 9.5 Ma. • Increased sediment flux to eastern Indian Ocean and restructuring of sediment routing. • Nicobar Fan holds significant record of Indian Ocean sedimentation in late Neogene. • Shillong Plateau and Indo–Burmese wedge uplift drive sediment south in late Miocene. A holistic view of the Bengal–Nicobar Fan system requires sampling the full sedimentary section of the Nicobar Fan, which was achieved for the first time by International Ocean Discovery Program (IODP) Expedition 362 west of North Sumatra. We identified a distinct rise in sediment accumulation rate (SAR) beginning ∼9.5 Ma and reaching 250–350 m/Myr in the 9.5–2 Ma interval, which equal or far exceed rates on the Bengal Fan at similar latitudes. This marked rise in SAR and a constant Himalayan-derived provenance necessitates a major restructuring of sediment routing in the Bengal–Nicobar submarine fan. This coincides with the inversion of the Eastern Himalayan Shillong Plateau and encroachment of the west-propagating Indo–Burmese wedge, which reduced continental accommodation space and increased sediment supply directly to the fan. Our results challenge a commonly held view that changes in sediment flux seen in the Bengal–Nicobar submarine fan were caused by discrete tectonic or climatic events acting on the Himalayan–Tibetan Plateau. Instead, an interplay of tectonic and climatic processes caused the fan system to develop by punctuated changes rather than gradual progradation.

Description: The subduction-related volcanic front in Nicaragua consists of the Tertiary “Coyol” member in the eastern highlands and the Quaternary to recent volcanic arc within the Nicaraguan depression. Although the Holocene to recent explosive volcanism has been studied extensively no detailed work has been done on the products of explosive volcanism from Quaternary volcanic complexes comprising also the Malpaisillo and Monte Galán Calderas, the focus of this study. The 11 km-wide Malpaisillo Caldera and ~3.5 km-wide Monte Galán Caldera, located ~50 km northwest of Managua, are surrounded by tens of meters of rhyolitic tephras. These pyroclastic flow and fall deposits extend proximally at least 11 km to the southeast and 23 km to the southwest, with observed depositional thicknesses of 〉16 m for a single ignimbrite unit (or 〉25 m for the entire section). Distal deposits are found as far as 350 km offshore in the Pacific. At least twelve highly explosive large-volume eruptive phases with corresponding tephra deposits (LPT = La Paz Centro Tephra, PPT = Punta de Plancha Tephra, LCbT = Lower Chibola Tephra, GT = Guacucal Tephra, UCbT = Upper Chibola Tephra, FeT = La Fuente Tephra, ST = Sabanettas Tephra, MgT = Miralago Tephra, ToT = Tolapa Tephra, LMT, MMT, UMT = Lower, Middle, and Upper Maderas Negras Tephras) are distinguished based on geochemical correlations and similar depositional characteristics. Radiometric 40Ar/39Ar ages indicate that most activity related to the large Malpaisillo Caldera occurred between ~570 and ~420 ka. The large Pleistocene Malpaisillo and Monte Galán Calderas are characterized by a long-lived history and, if evolved, a distinctly alkaline (K2O = 2.3–3.8 wt%; Na2O = 4.0–4.9 wt%) geochemical signature compared to the other Nicaraguan tephra deposits. As a result, the previously defined Malpaisillo Formation has been considerably extended and revised. Our findings contribute to fill a considerable gap in the long-term eruptive history of Nicaraguan volcanoes, with prominent implications for volcanic hazard evaluation for Nicaragua.

Description: Handheld energy dispersive portable X-ray spectrometers (pXRF) are generally designed and used for qualitative survey applications. We developed shipboard quantitative analysis protocols for pXRF and employed the instrument to make over 2000 individual abundance measurements for a selection of major and trace elements on over 1200 m of recovered core during the eight weeks of the International Ocean Discovery Program (IODP) Expedition 352 to the Izu-Bonin forearc. pXRF analytical performance, accuracy and precision were found to be the same on powdered rock samples and on freshly cut rock surfaces, and sample results were similar within error to measurements made via shipboard ICP-OES analysis save at low abundance levels for a few elements. Instrument performance was optimal for elements between Z = 19 and Z = 40, and the system yielded reproducible data for K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Rb, Sr, and Zr on both powdered samples and rock surfaces. Working curves developed via pXRF measurement of a suite of geologic standard reference materials and well-characterized lavas permitted accurate quantitative measurements for many of the examined elements on both sample powders and rock surfaces. Although pXRF has been sporadically employed on previous cruises, Expedition 352 is the first time a detailed, high-density chemostratigraphy of recovered core samples was collected using pXRF measurements of rock core surfaces. These high-resolution data allowed the recognition of chemically distinct eruptive units in near real-time. The rapid identification of geochemical trends vastly improved our selection of samples for shipboard and shore-based analysis, permitted a more comprehensive interpretation of our Expedition results, and provided key decision-making information for drilling operations.

Description: Highlights • Individual evolution of temporal and spatial co-existing magma suites • Determination of pre-eruptive magma chamber conditions of the Cão Grande Formation magma chambers • Cão Grande Formation phonolite magmas typically reach H2O-saturation prior to the eruption. Abstract The Cão Grande Formation (CGF) on the western plateau of Santo Antão is a sequence of four phonolitic tephras (Canudo Tephra, Cão Grande I Tephra, Cão Grande II Tephra and Furninha Tephra) produced by highly explosive eruptions that alternatingly originated from a basanitic - phonolitic and a nephelinitic - phonolitic magmatic system. Detailed stratigraphy and petrological investigations of each unit are used to demonstrate the unusual situation that two distinct highly evolved magmas differentiated contemporaneously in separate magmatic systems. Chemical thermobarometry suggests that both magmatic systems not only temporally co-existed, but also that their magma chambers resided close to each other at 7 to 16 km depth, beneath the western plateau of Santo Antão. However, the distinct melt and magma compositions indicate that both systems evolved independently. The only interaction between both magmatic systems was an injection of magma from the nephelinitic - phonolitic magmatic system into the Cão Grande II Tephra (CG II) phonolitic reservoir, which is associated to the basanitic - phonolitic magmatic system. Compositional zonations in the tephra deposits indicate that the eruptions of the CGF tapped stratified magma reservoirs that mainly resulted from crystal accumulation generating downward increasing magma density. However, the CG II tephras also show a significant gradient in melt (glass) compositions. Magmas of the Canudo Tephra (CT) and the Cão Grande I Tephra (CG I) were H2O-saturated and their eruptions were probably triggered by fluid overpressure in the magma chamber. On the other hand, the CG II magma was H2O-undersaturated; we therefore assume that the injection of the hot nephelinitic - phonolitic magma system-type melt/magma triggered the eruption. The zoned deposit of the Furninha Tephra (FT) indicates mafic magma replenishment into a phonolitic reservoir directly prior to the eruption, thus providing a probable triggering mechanism. The new magma chamber models and thermobarometric results for the four CGF units provide constraints for hazard assessments, because similar events may occur in the future considering the longevity of the CGF magma systems.

Description: Remotely Operated Vehicles (ROVs) have proven to be highly effective in recovering well localized samples and observations from the seafloor. In the course of ROV deployments, however, huge amounts of video and photographic data are gathered which present tremendous potential for data mining. We present a new workflow based on industrial software to derive fundamental field geology information such as quantitative stratigraphy and tectonic structures from ROV-based photo and video material. We demonstrate proof of principle tests for this workflow on video data collected during dives with the ROV Kiel6000 on a new hot spot volcanic field that was recently identified southwest of the island of Santo Antão in the Cape Verdes. Our workflow allows us to derive three-dimensional models of outcrops facilitating quantitative measurements of joint orientation, bedding structure, grain size comparison and photo mosaicking within a georeferenced framework. The compiled data facilitate volcanological and tectonic interpretations from hand specimen to outcrop scales based on the quantified optical data. The demonstrated procedure is readily replicable and opens up possibilities for post-cruise “virtual fieldwork” on the seafloor.

Description: During IODP NanTroSEIZE Expedition 322, four packages of tuffaceous sandstones (TST 1, 2, 3a, 3b) were recovered within a moderately lithified and bioturbated silty claystone succession in the Late Miocene (〉 7.6 to ~ 9.1 Ma) upper part of the middle Shikoku Basin deposits. To assess the emplacement processes of the tuffaceous sandstones we investigate modal and geochemical compositions of 24 thin sections that reveal systematic vertical changes within each bed. TST 1, 2 and 3b are single beds whereas TST 3a is composed of at least two beds suggesting several rapidly succeeding sedimentation events. The beds are density-graded such that low-density pyroclasts including pumice lapilli are enriched at the top whereas dense lithic components and minerals are enriched at the bottom. The volcanic glass particles (pumice and shards) that are the dominant modal constituents of each sandstone bed have homogeneous geochemical compositions in each bed. Moreover, TST 1, 2, and 3a glass compositions overlap completely but TST 3b glass has a different composition, as is analogously observed for the mineral compositions. This unique multistage approach of sedimentological and geochemical methods facilitated the detailed investigation of distal volcano-derived, probably tsunamogenic, turbidites in order to contribute to the distinction between primary and secondary induced mass flows. We interpret that all tuffaceous sandstones were emplaced by turbidity currents that were formed during major explosive volcanic eruptions. However, while TST 1, 2, and 3a turbidity currents formed by the entry into the ocean of voluminous pyroclastic flows erupted at a volcano on mainland Japan, TST 3b was emplaced by a turbidity current formed by a shallow submarine or subaerial volcanic eruption at the Izu–Bonin arc where it collided with Japan. These results regarding distal turbidites encourage the revisiting of older marine deposits in the scope of hazard evaluation through past events, especially in regions near to volcanic sources.

Description: Atmospheric deposition of volcanic ash has recently been recognized as an important nutrient source into the surface ocean. Mount Etna (Italy), one of the world's most active volcanoes, is located in the oligotrophic Mediterranean Sea (MedSea). Despite the active volcanism on Mount Etna, the biogeochemical impacts of volcanic ash fallouts on the marine primary productivity (MPP) remain largely unknown. Here we present the results of seawater nutrient release experiments with volcanic ash samples from Mount Etna that have been collected during different eruptive episodes between 2001 and 2007. Our results show that volcanic ash from Mount Etna releases significant amounts of fixed-N (35-855 nmol/g), P (7-970 nmol/g), Si (3-2060 nmol/g), Fe (10-130 nmol/g) and Zn (〈21 nmol/g). We further estimated an example representative of ash-fall from Etna based on the case-study focusing on 4-5 November 2002 activity, by using the general relation between the thicknesses of the ash deposits and the ash depositional areas. Etna explosive eruptions can transport volcanic ash as far as 800 km, with ash emissions exceeding the particle flux during dust storm events (of 10 g/m(2) input) as far as 400 km downwind from the volcano. Our results emphasize that Etna ash can provide a significant supply of nutrients, which can favor the MPP in the central MedSea