Description: Highlights • High-resolution deep-water record for Pliocene western tropical Pacific. • Changes in NADW production at ∼4.6 Ma and ∼2.7 Ma influenced Pacific • These changes controlled a seesaw fluctuation between deep Pacific and Atlantic oceans. • Antarctic ice-sheet/sea-ice expansions influenced deep Pacific • These ice-mass changes resulted in long-term decline during late Pliocene. Abstract Quantifying changes in seawater carbonate chemistry is crucial to deciphering of patterns and drivers of the oceanic carbon cycle and climate change. Here, we present a new deep-water carbonate ion saturation state record for the Pliocene western tropical Pacific, reconstructed from the size-normalized weight of the planktonic foraminifer Trilobatus sacculifer of IODP Site U1490. A steep decline in deep-water occurred at ∼4.6 Ma synchronous to the enhanced production of North Atlantic Deep Water (NADW) related to the closure of the Panamanian Gateway. Subsequently, at the onset of the Northern Hemisphere glaciation at ∼2.7 Ma the weakening of NADW formation resulted in a deep-water peak. The changes in NADW production rate likely controlled a seesaw-like fluctuation in deep-water between the Pacific and Atlantic oceans. During the late Pliocene (∼3.8–2.8 Ma), Antarctic ice-sheet/sea-ice expansions sequestered CO2 in the deep Pacific through ventilation of the deep watermass, leading to a long-term decrease in deep Pacific . We infer that fluctuating NADW production rates at ∼4.6 Ma and ∼2.7 Ma influenced inter-basinal fractionation of deep-ocean carbon between the Atlantic and Pacific, and that deep Pacific carbon storage linked to expansions of Antarctic ice sheet/sea ice contributed to the lowering of atmospheric pCO2 and global cooling during the late Pliocene.

Description: We take two typical Northeast Asia bimodal volcanoes as examples to explain the general features of Cenozoic bimodal ocean island basalt (OIB)-type volcanism in Northeast Asia. We present mineralogical, petrological, geochemical, isotopic, and full-waveform seismic tomographic evidence for the existence of two-layer magma chambers of Late Cenozoic volcanic activity beneath Ulleung Island and Mt. Changbai (Paektu). Ulleung Island volcanic rocks, which are composed of alkaline basalt, phonotephrite, trachyte, and phonolite, belong to the alkaline magma series and display enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs), slight depletion of heavy rare earth elements (HREEs), enriched 87Sr/86Sr (0.70475–0.70507) and 143Nd/144Nd (0.51250–0.51255) isotopic values, and enriched 207Pb/204Pb (15.544–15.626) and 208Pb/204Pb (38.750–38.954) values, similar to the geochemistry of OIB. Ulleung Island felsic volcanic rocks are characterized by significant negative Ba, Sr, P, Eu, and Ti anomalies (δEu = 0.14–0.35) and positive Pb anomalies, slightly higher 87Sr/86Sr isotopic ratios relative to those of mafic volcanic rocks, although the mafic and felsic samples have similar Sr, Nd, and Pb isotope compositions without significant differences. Ulleung Island and Mt. Changbai volcanic activities are likely related to the involvement of subduction-related compositions, but parts of the Mt. Changbai samples have been contaminated by crustal components to a certain extent. Mafic volcanic rocks of Ulleung Island are segregated from a deeper mantle source within a pressure range of 10.1–21.2 kbar compared with felsic volcanic rocks, which exhibit fractional crystallization of clinopyxene, spinel, plagioclase, and olivine. To explain this, a two-layer magma chamber beneath Ulleung Island with depths of 30–40 and 60–80 km is proposed, which is supported by mineral crystallization pressure and a three-dimensional full-waveform seismic tomography model. We also suggest that similar magma eruption processes and a two-layer magma chamber with depths of ~10 and 40–60 km also exist beneath Mt. Changbai. Taking the typical Cenozoic bimodal samples from Ulleung Island and Mt. Changbai as examples, we argue that two-layer magma chambers exist beneath Cenozoic bimodal OIB-type volcanic activities in Northeast Asia.

Description: Highlights • Accurate age model during Pliocene for site U1490 established • Co-variant nutricline depth and productivity in WPWP throughout Pliocene • Deeper nutricline and lower productivity during 4.8–3.5 Ma linked to CAS closure • Nutricline shoaling during 3.5–3.0 Ma due to restriction of Indonesian Seaway Abstract The tropical Pacific played an important role in modulating global climate change during the Pliocene. Studies of tropical Pacific sea surface temperatures covering the period from the Pliocene onwards indicate that changes in the thermal mean state over the tropical Pacific can significantly influence global climate feedbacks and connect the high- and low-latitude climates. Tropical productivity fluctuations are a significant mechanism with respect to the operation of the global carbon cycle. Yet, temporal changes in primary productivity are not well constrained in the western Pacific warm pool (WPWP), where the ocean–climate system is not dominated by upwelling systems. Furthermore, the role of nutricline dynamics in forcing productivity over tectonic timescales remains uncertain. Here we use relatively high-resolution foraminiferal carbon isotope records combined with Ba/Ti ratios obtained from International Ocean Discovery Program (IODP) Site U1490 in the WPWP to reconstruct nutricline depth and paleoproductivity over the period 5.1–2.6 Ma. Our records imply that nutricline and productivity variations were closely coupled over tectonic timescales, implying that the dynamics of the nutricline play a significant role in regulating productivity in the WPWP. The deeper nutricline and lower productivity during 4.8–3.5 Ma might have been fostered by the closure of the Central American Seaway through the thickening of the mixed layer in the WPWP. We relate the overall shallower nutricline and increased productivity during 3.5–3.0 Ma to the restriction of the Indonesian Seaway via the enhanced influence and upwelling of high-latitude southern-source waters.