ALBERT

Description: We revisited the stratigraphy at Deep Sea Drilling Project (DSDP) Site 296, which has promise as a reference sequence for the mid-latitude western North Pacific. We constructed the biostratigraphy (calcareous nannofossils, planktic foraminifera, and radiolaria) and chemostratigraphy (strontium isotope ratios, and stable oxygen and carbon isotope ratios) to reveal continuous sedimentation at Site 296 through the past 20 million years (Myr). The biostratigraphy of calcareous nannofossils comprised 27 biohorizons from biozones NN2 to NN21 (early Miocene to Pleistocene), which are consistent with the biohorizons of planktic foraminifera and radiolaria. The uninterrupted sedimentation throughout the past 20 Myr was further supported by strontium isotope stratigraphy aligned to nannofossil datums and by correlation of stable isotope data from benthic foraminifera with an isotopic compilation from the Pacific Ocean. The refined age–depth model showed low sedimentation rates (〈2 cm/kyr) through most of the Miocene and higher sedimentation rates (2–4 cm/kyr) during the Plio–Pleistocene, and potentially identified the “biogenic bloom” event from the late Miocene to early Pliocene. The continuity of sedimentation through the middle Miocene contrasts with the shipboard biostratigraphy, which inferred a hiatus (erosion or non-deposition) during the middle Miocene. Thus, the revised stratigraphy at Site 296 provides a key to correlation with other deep-sea sites in the North Pacific. Our revised age–depth model provides a framework for future studies of important climatic events during the Miocene, including the Miocene Climatic Optimum, the middle Miocene Climatic Transition, and the late Miocene global cooling under the influence of the past Kuroshio Current.

Description: This study presents a new set of paired d18Osw and salinity data (n = 83) from a large region of the western Pacific (mainly the western south Pacific) collected during the 2014–2015 El Niño period. We determined regional salinity–d18Osw relationships for three ocean regions (40º–20ºN, 20ºN–30ºS, and 30º–66ºS) and found that all three regions exhibited highly linear relationships between d18Osw and salinity. The 40º–20ºN and 20ºN–30ºS regions had relatively low slopes (0.33 and 0.37 ‰ psu-1, respectively), while the 30º–66ºS region had a relatively high slope (0.54 ‰ psu-1). Each regional regression was statistically different from those of the GEOSECS (1973–1974 La Niña) data, indicating that inter-annual ENSO variability has an impact on salinity–d18Osw relationships over a wide area of the western Pacific.