Description: Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).

Description: The Line Islands Ridge (LIR), located south of the Hawaiian Islands between 7°N and 1°S, is one of the few large central Pacific regions shallower than the regional carbonate compensation depth. Thick sequences of carbonate sediments have accumulated around the LIR despite it being located in the sediment-starved central tropical Pacific. The LIR is an important source of carbonates to the surrounding region and deposition around the LIR has expanded the equatorial Pacific carbonate sediment tongue by about 5% of its total area. Furthermore, sediments on the ridge are potentially important paleoceanographic archives. A recent survey at the crest of the LIR finds evidence for high current activity, significant erosion, but overall net sediment deposition. Currents are strong enough to form sediment waves and lee drifts in the Palmyra Basin, at the northern terminus of the LIR. Sediments along the LIR are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems. As channels migrate, pelagic sediments fill in the abandoned channel arms. Despite significant sediment losses from the top of the ridge, 1.3 km of sediment has accumulated in the upper Palmyra Basin over basement formed 68 to 85 million years ago (Ma). Late Neogene erosion may be more extensive than earlier erosion cycles, in response to reduced sediment production as the Palmyra Basin exited the high productivity equatorial latitudes. Sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment, but can be found with proper survey.

Description: Geochemical analyses of trace elements in the ocean water column have suggested that pelagic clay‐rich sediments are a major source of various elements to bottom‐waters. However, corresponding high‐quality measurements of trace element concentrations in porewaters of pelagic clay‐rich sediments are scarce, making it difficult to evaluate the contributions from benthic processes to global oceanic cycles of trace elements. To bridge this gap, we analyzed porewater and bulk sediment concentrations of vanadium, chromium, cobalt, nickel, copper, arsenic, molybdenum, barium and uranium, as well as concentrations of the major oxidants nitrate, manganese, iron, and sulfate in the top 30 cm of cores collected along a transect from Hawaii to Alaska. The data show large increases in porewater concentrations of vanadium, manganese, cobalt, nickel, copper, and arsenic within the top cm of the sediment, consistent with the release of these elements from remineralized organic matter. The sediments are a sink for sulfate, uranium, and molybdenum, even though conditions within the sampled top 30 cm remain aerobic. Porewater chromium concentrations generally increase with depth due to release from sediment particles. Extrapolated to the global aerial extent of pelagic clay sediment, the benthic fluxes in mol yr −1 are Ba 3.9 ± 3.6 × 10 9 , Mn 3.4 ± 3.5 × 10 8 , Co 2.6 ± 1.3 × 10 7 , Ni 9.6 ± 8.6 × 10 8 , Cu 4.6 ± 2.4 × 10 9 , Cr 1.7 ± 1.1 × 10 8 , As 6.1 ± 7.0 × 10 8 , V 6.0 ± 2.5 × 10 9 . With the exception of vanadium, calculated fluxes across the sediment–water interface are consistent with the variability in bottom‐water concentrations and ocean residence time of the studied elements.

Description: We examine the paleoceanographic record over the last ∼400 kyr derived from major, trace, and rare earth elements in bulk sediment from two sites in the East China Sea drilled during Integrated Ocean Drilling Program Expedition 346. We use multivariate statistical partitioning techniques (Q‐mode factor analysis, multiple linear regression) to identify and quantify five crustal source components (Upper Continental Crust (UCC), Luochuan Loess, Xiashu Loess, Southern Japanese Islands, Kyushu Volcanics), and model their mass accumulation rates (MARs). UCC (35–79% of terrigenous contribution) and Luochuan Loess (16–55% contribution) are the most abundant end‐members through time, while Xiashu Loess, Southern Japanese Islands, and Kyushu Volcanics (1–22% contribution) are the lowest in abundance when present. Cycles in UCC and Luochuan Loess MARs may indicate continental and loess‐like material transported by major rivers into the Okinawa Trough. Increases in sea level and grain size proxy (e.g., SiO2/Al2O3) are coincident with increased flux of Southern Japanese Islands, indicating localized sediment supply from Japan. Increases in total terrigenous MAR precede minimum relative sea levels by several thousand years and may indicate remobilization of continental shelf material. Changes in the relative contribution of these end‐members are decoupled from total MAR, indicating compositional changes in the sediment are distinct from accumulation rate changes but may be linked to variations in sea level, riverine and eolian fluxes, and shelf‐bypass processes over glacial‐interglacials, complicating accurate monsoon reconstructions from fluvial dominated sediment.

Description: We reconstruct the provenance of aluminosilicate sediment deposited in Ulleung Basin, Japan Sea, over the last 12 Ma at Site U1430 drilled during Integrated Ocean Drilling Program Expedition 346. Using multivariate partitioning techniques (Q-mode factor analysis, multiple linear regressions) applied to the major, trace and rare earth element composition of the bulk sediment, we identify and quantify four aluminosilicate components (Taklimakan, Gobi, Chinese Loess and Korean Peninsula), and model their mass accumulation rates. Each of these end-members, or materials from these regions, were present in the top-performing models in all tests. Material from the Taklimakan Desert (50–60 % of aluminosilicate contribution) is the most abundant end-member through time, while Chinese Loess and Gobi Desert components increase in contribution and flux in the Plio-Pleistocene. A Korean Peninsula component is lowest in abundance when present, and its occurrence reflects the opening of the Tsushima Strait at c. 3 Ma. Variation in dust source regions appears to track step-wise Asian aridification influenced by Cenozoic global cooling and periods of uplift of the Tibetan Plateau. During early stages of the evolution of the East Asian Monsoon, the Taklimakan Desert was the major source of dust to the Pacific. Continued uplift of the Tibetan Plateau may have influenced the increase in aeolian supply from the Gobi Desert and Chinese Loess Plateau into the Pleistocene. Consistent with existing records from the Pacific Ocean, these observations of aeolian fluxes provide more detail and specificity regarding the evolution of different Asian source regions through the latest Cenozoic.

Description: Seven different labs XRF scanned the same seven marine sediment sections. Additionally, four labs XRF scanned pellets that had known compositions determined by ICP-ES and ICP-MS. These datasets contain the XRF scanning results of the seven sediment section and four pellets. The seven 1.5 m core sections of marine sediment core used in this study were drilled during Integrated Ocean Drilling Program (IODP) Expedition 346 at Site U1424 in the Japan Basin (40°11.39'N, 138°13.90'E, 2808 m water depth) and Site U1425 on the Yamato Rise (39°29.43' N, 134°26.55' E, 1909 m water depth). The sections selected (Hole U1424C Sections 1H4, 2H5, 3H5 and Hole U1425C Sections 2H3, 2H4, and 2H6, and 3H6) cover a range of sediment compositions. U-channels extracted continuous marine sediment approximately 1 cm thick from the center of each split core section. One lab scanned sections from different holes at the same sites (U1424A, U1425B, and U1425D) that were stratigraphically aligned with the sections listed above. Over the course of four years (2014 to 2017), the set of seven u-channels was shipped around the world to seven labs with XRF scanners including, in no particular order, the Kochi Core Center at Kochi University (Japan), IODP Core Repository at Texas A&M University (U.S.A.), Nanjing Normal University (China), Rosenstiel School of Marine and Atmospheric Science at the University of Miami (U.S.A.), ETH Zurich (Switzerland), Woods Hole Oceanographic Institution (U.S.A.), and the Royal Netherlands Institute of Sea Research (The Netherlands). We intentionally do not identify which lab generated which scans, as many of the variables (e.g., X-ray tube aging, detector aging, and/or dehydration of the core material) could affect any instrument at various times or be exacerbated during the transit between labs. Instead, we label the XRF scans #1-#7 in the order in which they were scanned. The lead investigators overseeing the XRF scanning in these labs were shipboard participants on IODP Expedition 346 and are among the authors of this paper. The only instructions to each lab were "to XRF scan the seven sediment sections at 1mm or 2mm resolution using the approach and elements typical for paleoceanographic research performed in your lab." To emulate variations in the XRF results that have been previously published, these simple guidelines were intentionally broad and general to determine the degree of intercomparability between the labs amongst all the different settings and nuances of XRF scanning. The labs used various types and different generations of XRF scanning instruments (4 Avaatech Core Scanners, 2 ITRAX Core Scanners, and 1 Geotek Core Scanning Logger) with different X-ray sources (Rhodium, Molybdenum). Three of the labs scanned the cores at two or three excitation energies (e.g., 10 kV, 30 kV, and 50 kV). Each lab reported a different suite of elements, but all included Ca, Fe, K, Mn, Si, Sr, Ti, and Zr. Six labs also reported Al, Br, Cr, Cu, Ni, Pb, Rb, S, and Zn and five labs reported and Ba, Cl, Ga, Mo, V, and Y. In addition to the seven core sediment sections, we freeze-dried and powdered four discrete samples that were pressed into disc-shaped pellets about 2 cm in diameter from nearby Core MD01-2407 on the Oki Ridge (37°04'N, 134°42'E, 932m water depth). The four samples have a similar matrix to the seven sediment sections scanned in this study. The four samples from Core MD01-2407 covered a range of sediment types (calcareous, siliceous, light-, and dark-colored; Kido et al., 2007) that span the dynamic range of at least Fe and Ca element cps scanned for this study. A set of four pellets was sent to four of the seven labs (1 ITRAX and 3 Avaatech) involved in the study to be scanned using the same instrument parameters they used on the sediment sections. Three labs used the same instrument and parameters used for the sediment section, but the fourth lab replaced the X-ray tube in between scanning the pellets and sediment sections. The major and trace element concentrations of the pellets were also analyzed by inductively coupled plasma (ICP)-optical emission spectrometry (OES) and ICP-mass spectrometry (MS) in the Analytical Geochemistry Facilities at Boston University, Boston, MA, USA. The ICP analyses had ~2% precision and a standard reference material analyzed as an unknown alongside the samples was accurate within precision.

Description: Inorganic analyses of major, trace, and rare earth element concentrations for 30 bulk sediment samples at Site U1445 and additional samples from other sites in the Bay of Bengal for reference. Bulk sediment samples were freeze-dried and hand-powdered in an agate mortar and pestle prior to flux fusion for analyses of major elements with ICP-ES and an acid cocktail digestions for analyses of trace and rare earth elements on ICP-MS (Dunlea et al., 2015, doi:10.1002/2015PA002829). Analyses of 57 bulk sediment samples from Site U1445 for bulk calcium carbonate, total organic carbon, total carbon, total acidified nitrogen, carbon isotopes of the total organic carbon, and the designation of visually lighter versus darker samples at similar depths. Hydrogen isotopes and carbon isotope analyses of leaf wax fatty acids extracted from 57 samples at Site U1445. Measurements from fatty acid chainlengths C26, C28, and C30 are reported with their standard deviation. The correction for C3-C4 physiological differences in the hydrogen isotopes of C30 fatty acids is reported, estimating C3 vegetation as having a δ13C of -35.4 ‰ and C4 vegetation as -21.4‰.

Description: During International Ocean Discovery Program (IODP) expeditions, shipboardgenerated data provide the first insights into the cored sequences. The natural gamma radiation (NGR) of the recovered material, for example, is routinely measured on the ocean drilling research vessel DV JOIDES Resolution. At present, only total NGR counts are readily available as shipboard data, although full NGR spectra (counts as a function of gamma-ray energy level) are produced and archived. These spectra contain unexploited information, as one can estimate the sedimentary contents of potassium (K), thorium (Th), and uranium (U) from the characteristic gamma-ray energies of isotopes in the 40K, 232Th, and 238U radioactive decay series. Dunlea et al. [2013] quantified K, Th and U contents in sediment from the South Pacific Gyre by integrating counts over specific energy levels of the NGR spectrum. However, the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons. Here, we present a new MATLAB algorithm for the quantification of NGR spectra that is transparent and accessible to future NGR users. We demonstrate the algorithm's performance by comparing its results to shore-based inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-emission spectrometry (ICP-ES), and quantitative wavelength-dispersive X-ray fluorescence (XRF) analyses. Samples for these comparisons come from eleven sites (U1341, U1343, U1366-U1369, U1414, U1428- U1430, U1463) cored in two oceans during five expeditions. In short, our algorithm rapidly produces detailed high-quality information on sediment properties during IODP expeditions at no extra cost.