ALBERT

Description: Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth's orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ18O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition.

Description: Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from 〈10 to ~10**4 cells cm**-3. Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

Description: The North Atlantic Current (NAC) transports warm salty water to high northern latitudes, with important repercussions for ocean circulation and global climate. A southward displacement of the NAC and Subarctic Front, which separate subpolar and subtropical water masses, is widely suggested for the last glacial maximum (LGM) and may have acted as a positive feedback in glacial expansion at this time. However, the role of the NAC during the intensification of northern hemisphere glaciation (iNHG) ~3.5 to 2.5 Ma, is less clear. Here, we present new records from IODP Site U1313 (41°N) spanning ~2.8-2.4 Ma to trace the influence of Subarctic Front waters above this mid-latitude site. We reconstruct surface and permanent pycnocline temperatures and seawater δ18O using paired Mg/Ca-δ18O measurements on the planktic foraminifers Globigerinoides ruber and Globorotalia crassaformis, and determine abundances of the subpolar foraminifer Neogloboquadrina atlantica. We find that the first significant glacial incursions of Subarctic Front surface waters above Site U1313 did not occur until ~2.6 Ma. At no time during our study interval was (sub)surface reorganisation in the mid-latitude North Atlantic analogous to the LGM. Our findings suggest that LGM-like processes sensu stricto cannot be invoked to explain interglacial-glacial cycle amplification during iNHG. They also imply that increased glacial productivity at Site U1313 during iNHG was not only driven by southward deflections of the Subarctic Front. We suggest nutrient injection from cold-core eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the mid-latitude North Atlantic from 2.7 Ma.

Description: The 2011 Tohoku-Oki earthquake demonstrated that the shallowest reaches of plate boundary subduction megathrusts can host substantial coseismic slip that generates large and destructive tsunamis, contrary to the common assumption that the frictional properties of unconsolidated clay-rich sediments at depths less than View the MathML source should inhibit rupture. We report on laboratory shearing experiments at low sliding velocities (View the MathML source) using borehole samples recovered during IODP Expedition 343 (JFAST), spanning the plate-boundary décollement within the region of large coseismic slip during the Tohoku earthquake. We show that at sub-seismic slip rates the fault is weak (sliding friction µs=0.2-0.26), in contrast to the much stronger wall rocks (µs〉~0.5). The fault is weak due to elevated smectite clay content and is frictionally similar to a pelagic clay layer of similar composition. The higher cohesion of intact wall rock samples coupled with their higher amorphous silica content suggests that the wall rock is stronger due to diagenetic cementation and low clay content. Our measurements also show that the strongly developed in-situ fabric in the fault zone does not contribute to its frictional weakness, but does lead to a near-cohesionless fault zone, which may facilitate rupture propagation by reducing shear strength and surface energy at the tip of the rupture front. We suggest that the shallow rupture and large coseismic slip during the 2011 Tohoku earthquake was facilitated by a weak and cohesionless fault combined with strong wall rocks that drive localized deformation within a narrow zone.

Description: Four gabbroic and four highly serpentinised peridotite samples were acquired during the IODP expeditions 304-305 at the Central Dome and expedition 357 at the Southern Wall of the Atlantis Massif, respectively. Physical properties of the rock samples, including ultra-sonic P- and S-wave velocities and attenuations, electrical resistivity and permeability, were measured under increasing and decreasing pressure conditions (up to 50 MPa, ~ 2 km depth) using the experimental rig of the rock physics laboratory of National Oceanography Centre, Southampton, UK. The density and porosity of the samples were estimated using wet/dry weight difference of the rocks.

Description: Integrated Ocean Drilling Program Expedition 313 recovered siliciclastic sediments from three holes cored through a series of Miocene clinoforms offshore New Jersey. The clinoform sequence that lies between seismic reflectors m5.2 and m4.1 has been dated as mid-Miocene within an interval of major climatic change and displays interesting sedimentological and petrophysical features. However, the depth ties between surfaces in the recovered succession and seismic reflectors, correlation across sites, and depositional environments are not all well defined in this interval. Additionally, features observed in the two more proximal boreholes are absent from the most distal borehole. This report presents X-ray fluorescence (XRF) measurements from scanning the split surface of archive sediment cores and from individual core samples from Holes M0027A, M0028A, and M0029A. Major trends are identified and described, aided by statistical analyses (correlation coefficient matrix plots and principal component analyses). Si/Al and Zr/Rb ratios and, to a lesser extent, Th correspond with changes in the ratio of clay minerals to quartz. In the most proximal Hole M0027A, an alternating sequence of dark and light bands in an extended sequence of clays is characterized by distinctive high and variable magnetic susceptibility and equivalently variable Fe/S ratios. A similar sequence is observed in Hole M0028A, with both sequences located above the inferred m4.1 seismic sequence boundary. Redox elements in this interval are highly variable and suggest the influence of postdepositional processes. In Hole M0029A, despite an expanded sequence, similar characteristics are absent from the clay sequences, which are also geochemically more homogeneous. The analyzed geochemical compositions are compared with sedimentological observations and petrophysical analyses before discussing in their wider context.

Description: Earth's climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma_405_1 to Ma_405_7) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4 per mil) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a ~1 Myr period in the late Maastrichtian (67.8-66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change.

Description: We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked d18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic d18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene ('41-kyr world') when boundary conditions differed significantly from those of the late Pleistocene ('100-kyr world'). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic d18O surpassed ~ 3.3?3.5?. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.

Description: Listed are edited, spliced, and in situ corrected data vs. various depth scales, the shipboard age scale and two-way-traveltime (TWT). The shipboard age model for Site U1475 was derived from time estimates based on a combination of major planktonic foraminifer, calcareous nanno-plankton, diatom, and paleomagnetic datums. K (wt.%) is derived from measurements of natural gamma radiation (NGR) according to De Vleeschouwer, D., Dunlea, A. G., Auer, G., Anderson, C. H., Brumsack, H., de Loach, A., et al. (2017). Quantifying K, U, and Th contents of marine sediments using shipboard natural gamma radiation spectra measured on DVJOIDESResolution. Geochemistry, Geophysics, Geosystems, 18(3), 1053-1064, doi:10.1002/2016GC006715. Description of the depth scales: The CSF-A scale (here DEPTH, sediment/rock) is specific to each hole of a site and combines the drilling depth below seafloor of the core top depth and the curated depth within a core after retrieval. The CSF-A depth scale is equivalent to the meters below seafloor (mbsf) scale known from, e.g., the Ocean Drilling Program (ODP). For the construction of the most representative single continuous sedimentary section, intervals from multiple holes need to be spliced together. This requires a common, composite depth scale (CCSF, formerly known as mcd) for a given IODP Site which is based on the correlation of coeval, laterally continuous features seen in the physical properties in all drilled holes (which will generally occur at different depths on the CSF-A depth scales for each hole). Once such correlative features (tie-points) were identified at Site U1475 the depth of individual cores was offset relative to CSF-A in that hole, resulting in the Composite Curated depth below Sea Floor (CCSF-A) depth scale (here Depth composite) for each hole. By combining selected intervals from Holes U1475B, C, E and F between the previously established tie points a complete stratigraphic section (splice) was constructed. The designated depth scale of the splice is the CCSF-D scale. CCSF-D applies only to intervals included in the splice and intervals not included in the primary splice retain the CCSF-A scale. The CCSF-A scale does not result in alignment of all coeval features because of the differing effects of coring-induced stretching and squeezing among cores, as well as sedimentological differences between holes. For our study it was desirable to map into the splice those intervals not included in the splice itself. We accomplished this by simultaneously comparing color reflectance (b*) and NGR for all holes with subsequent identification of correlative tie points at the highest possible resolution and linear adjustments of depths between ties. This adjusted depth is designated as the CCSF-C depth scale (here Depth composite revised), and to the extent that the correlations are accurate, the CCSF-C and CCSF-D scales are equivalent. CCSF-C and -D typically exceed the in situ depth (core depth below sea floor CSF-A) by ~10%. The growth rate of the CCSF-D depth scale, relative to CSF-A is on average 9.5% for all holes. Thus to correct for the depth offset a linear compression - Depth (m CCSF-B) = Depth (m CCSF-C)/1.095 - was applied to the entire depth so that the compressed core length was equal to the interval cored. The CCSF-B scale (here Depth composite corrected) hence indicates the in situ depth in meters below the seafloor (mbsf).

Description: The Contourite Depositional Systems (CDS) in the Gulf of Cádiz and on the West Iberian margin preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. These CDS have been recently drilled in several places during the IODP Expedition 339. These drill sites now offer a new window to the internal Pliocene and Quaternary architecture of the CDS. In this study, we use downhole and core Gamma Ray (GR) data acquired from 5 sites drilled in the CDS along the middle slope and 1 site drilled in the deeper setting of the lower slope, out of the MOW path. The GR data primarily tracks the clay content in the sediment and is the expression of sediment supply and, for sites drilled in the CDS, of the bottom current processes. Both appear astronomically controlled as shown by spectral analysis performed on the GR data. Results also reveal that the GR log patterns correlate well across the sites over the last 1.4 My. Several GR horizons corresponding to drops in GR values were identified, most of which fit with coarse-grained deposits observed in cores and interpreted as contourite beds. The GR horizons are interpreted as isochronous horizons, providing a regional scale chronostratigraphic framework for the CDS depositional records with an accuracy of ~ 20 ky. We further assess the spatial and temporal variability of the CDS hiatuses at the regional scale.