Data report: Pleistocene planktonic foraminiferal oxygen and carbon stable isotope records and their use to improve the age model of Hole U1436C cores recovered east of the Aogashima Volcano

International Ocean Discovery Program (IODP) Expedition 350 cored Site U1436 at intermediate water depth (1776 meters below sea level) in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano, Aogashima. Site U1436 lies 1.5 km west of Ocean Drilling Program Site 792 (Leg 126). Site U1436 (proposed Site IBM-4), conceived as a 150 m deep geotechnical test hole for future deep drilling (5500 meters below seafloor) with the D/V Chikyu, provides a rich record of Pleistocene volcanism. Isotopic stratigraphy data reported here extend the timescale and improve the precision of the shipboard-determined biostratigraphy to enhance further investigations on the nature, origin, and rhythm of the volcanic eruptions recorded at this site. The δ18O and δ13C values in selected samples containing planktonic foraminifers (Neogloboquadrina dutertrei) were measured over the 70 m long record from Hole U1436C. Isotopic ratios were determined for 167 samples and are examined in conjunction with nannofossil and planktonic foraminifer datums obtained during Expedition 350. These data allow fairly good identification of all marine isotope stages over the last 1 My. The results from this data report provide a refined age scale that will enhance the scientific appeal of this site to volcanologists and sedimentologists and increase the potential impact of their interpretations in later research stages. Hole U1436C was cored near the Kuroshio Current in the North Pacific Ocean realm, where any new paleoceanographic and paleoclimatologic data would be valuable. Furthermore, the refined stratigraphic framework from this study also clearly shows that the original goals of Expedition 350 can easily be expanded beyond that of the study of the evolution of the Earth’s crust toward new targets focused on Earth surface processes. Introduction During International Ocean Discovery Program (IODP) Expedition 350 on board the R/V JOIDES Resolution, two sites were cored at intermediate water depth in the western Pacific Ocean (Philippine Sea). The main focus of the expedition was IODP Site U1437, at which rear-arc evolution over the last 10 My will be studied using the sedimentary record of changing volcanism through time recovered from an interval extending to 1800 meters below seafloor (mbsf). In contrast, IODP Site U1436 was initially thought of as an ancillary target because it was intended as a short (150 m) geotechnical hole to prepare for potential future drilling at proposed Site IBM-4 using the D/V Chikyu, which has the capacity to drill to the arc middle crust target at 5500 mbsf. Nonetheless, Site U1436 yielded a potentially continuous record of Late Pleistocene fore-arc sediments influenced by arc-front explosive volcanism. This site, therefore, provides an opportunity to investigate in a rather proximal location (i.e., near the volcanic island of Aogashima) (Figure F1) the detailed history and evolution of Late Pleistocene volcanism within the Izu arc. This additional goal became particularly appealing once drilling had to be stopped at Site U1437 and a contingency plan was put in place. Indeed, this change meant that Site U1436 could be cored through more than one hole to improve the quality of the entire section (i.e., with fewer intervals lost to coring disturbance) as well as more particularly in an interval containing a conspicuously thick black glassy mafic ash layer. The preliminary age for this layer, based on the age model constructed for Hole U1436A, was estimated to be about 0.75 Ma. Core recovery at Site U1436 was excellent, particularly in Hole U1436C, with 100% recovery for the 70 m cored. The samples used in this study were taken exclusively from Hole U1436C because of the limited time available for samM.J. Vautravers et al. Data report: Pleistocene planktonic foraminiferal isotope records pling, which was conducted after Expedition 350 during the transit at the start of IODP Expedition 351, because of the absence of a composite section, and because Hole U1436C was mostly cored using the half-length advanced piston corer (HLAPC) and is consequently much less disturbed than cores from Hole U1436A. A quick assessment of the samples prior to picking revealed low abundances and discontinuous downcore occurrences of benthic foraminiferal species commonly used for stable isotope studies (e.g., Cibicides or Uvigerina). Therefore, one planktonic foraminifer species was chosen instead. At such a subtropical site (~32°N; Figure F1) and in the vicinity of the Kuroshio Current, the thermoclinedwelling species Neogloboquadrina dutertrei (see inset image in Figure F2 for illustration) has the best likelihood to be both well preserved and abundant enough in one single, narrow size fraction throughout the whole section to be able to provide a continuous isotope record for the site over the Upper Pleistocene. It is well established that oxygen isotopes in marine calcite, in particular in foraminifer tests, provide an excellent record of glacial–interglacial cycles. They capture the water δ18O composition through a composite recording of the effects of local water temperature changes (Emiliani, 1955) and global changes in ocean δ18O composition, which varies through time as a consequence of changing ice volume (Shackleton, 1967). Within the limitation imposed by the need for continuous recording (i.e., no missing cycles), the regular and cyclic pattern shown by δ18O and its global nature makes it now a classic (i.e., used routinely for ~50 y) and straightforward tool for stratigraphic correlation and nonabsolute dating. This is particularly true for the Neogene (i.e., the last 23.5 My) (Gradstein et al., 2012), over which δ18O provides a highly accurate record. We visually correlated our oxygen isotope record from Hole U1436C to a stacked δ18O benthic record, the so-called LR04 (Figure F3B), which has a resolution of ~1 ky and was developed from the compilation of the benthic δ18O data from 57 marine sites by Lisiecki and Raymo (2005). This allowed us to transfer our newly obtained stable isotope record from its depth scale to an age scale and establish a more detailed and precise stratigraphy than that obtained via biostratigraphy only (see the Expedition 350 methods chapter [Tamura et al., 2015a]). Figure F1. Location of Expedition 350 Hole U1436C and Ocean Drilling Program (ODP) Leg 126 Sites 792, 786, and 787. Site U1436 lies 60 km east of Aogashima, an arc-front mafic volcano that forms a small and inhabited island. Figure was slightly modified from the Expedition 350 summary chapter (Tamura et al., 2015b).